Robot Arm Designs

Question

Anyone interested in creating a team to brain storm ideas and designs for robot arms for large or small robots. Perhaps collectively we could come up with a universal design that many of us could use. We each could provide input, drawings and/or services.

Rex

bret.tallent · Answer

I like it. I have a design for my small B9 where each arm will use 4 servos but only 3 ports on the EZ-B. I think it will give me a very similar movement to the real B9 and have the claws too. Bret

rgordon · Answer

Thanks for responding Bret. Do you have any drawings or pictures yet? I am going to get together all my pictures and drawings that I was working on for Magnus and post them soon.

JT · Answer

I also like this idea, @rgordon. I struggle with mechanical designs and implementation. I'm software, by profession, not hardware! eyeroll A universal design would be great! What I'd be looking for in an arm design is something that's simple electrically and mechanically, but reasonably strong. Maybe strong enough to pick up a deck of playing cards or your favorite carbonated beverage? For example, a DIY linear actuator using a screw thread, a nut, and a motor/360 servo seems like a strong/effective implementation to me. But what do I know?

kkeast · Answer

I would be interested in this too! A few weeks ago the family and I went to Wolf Lodge and there was a robot arm ice cream machine that made you a sundae with your favorite toppings! Now the whole family wants one, including me! Anyway, I would love to work on a design like this..that would be reasonably priced as well. v/r Kevin

rgordon · Answer

I think we all have enough combined talents to achieve something useful. I may need lots of help when it comes to programming. I am using a DIY linear actuator design for T.E.C.H. Although I think it could be simplified a little more by using a small cordless screwdriver which already has the gears built in. It all depends on the size arm you need for your bot.

bret.tallent · Answer

I'll try to make up some drawings and get them uploaded. My idea for my B9 hack is two servos tied together to make a bending motion so I can get 90 degrees in either direction. Then one servo to operate his claw, and a final servo to twist the entire arm. As B9 doesn't have shoulders it actually makes it a little easier. I will work on some drawings this week.

rgordon · Answer

Super....I am working on drawings for the arm I am building for T.E.C.H. I guess you would call him a medium sized robot? test...test  just wanted to see if I could post a decent looking drawing. If you don't have it already, a good free drawing program is emachineshop It's a free download. I just use it for drawing. Their prices are too high for actually machining the parts. The reason I like using it is because it so easy to draw parts to scale and print them out as actual size. It has lots of cool things you can do to make drawing easier. Keep in mind it is mainly used for drawing individual parts and not say for instance a complete drawing of your robot. 100 times easier than learning Auto-Cad. After I create the drawing I use software called Print Key 2000 to take a snapshot of my screen then it lets me save it as a .jpg file so I can upload it here.

bret.tallent · Answer

Okay, I'm a little more old school so here are some drawings:  This is the whole unit that would protrude from the front of B9 - I am using 2" PVC coupling as the arm sockets.  Mounting some plastic disks to aluminum flat bar and then the whole thing spins preely inside the PVC. I can use a servo to rotate the whole assembly. Then off that are two more pieces of flat bar attached to two servos for bending motion. The two are tied together off one port (with a Y extension) so work in unison. It is important to make sure they are going the same way so they move the same direction.  Then I have a claw mounted on the end disk and use a scissors motion to open and close with my micro servo. As you rotate the whole arm, the claw will rotate too. I am using a rubber air supply line from a filter mask as a covering because of it's flexibility with minimal resistance. What do you think?

edison2 · Answer

What do you think??? (I did it... but is in spanish.. ahha sorry )

DJ Sures · Answer

If you came up with a version that could be cut on a laser cutter, I could get them done for you Google's sketch-up software is free and pretty awesome i hear

rgordon · Answer

Bret, I like your design. Hey the majority of my drawings are hand drawn. What are the lengths of the aluminum bars? So the plastic disks turn freely within the PVC and provide support? Correct? How are you mounting the servos to the aluminum? Have you tested the operation yet?

bret.tallent · Answer

Yeah, the plastic disks are 1/16" smaller than the ID of the PVC so they turn very freely. They provide the support for the arm. As I am doing a small B9, the length of my arms is only about 7 inches so my bars are not that long. The one coming out of the PVC is 4 inches long and the other two pieces are 2 inches each. I am just going to use epoxy and zip ties to attach the servo bodys to the bars, then an aluminum servo horn and screws to attach the shaft. I am going to use all metal gear servos. I have not tested operation yet, got sidelined with my motorcontroller issues, but hope to get back to the arms soon.

sfoy · Answer

What a wonderful idea!!! I want to do some sort of arm. There's been a few posts etc about them I was given this link for a hand. Here is the buster post to see it in action. I wasn't sure how to make it smaller but still usable. So I decided to hack a robosapien for his arms.

rgordon · Answer

@edison2- Have you started to build this arm yet? Do you have pictures?

rgordon · Answer

@DJ Sures - I have heard of Google's sketch-up but have not tried it yet. Will have to look into it... That's a cool offer about the laser cutter. Have you had pieces / parts cut for your robots? Are the prices reasonable?

rgordon · Answer

@sfoy - How's Minion coming along? That's a cool idea to use robosapien arms. Can the hands actually move and grip things? Do the elbows have servos? Rex

sfoy · Answer

@Rex .... Hahahahaha could you imagine minion with robosapien arms. I'd have to name him Arnold (Schwarzenegger) Minion is done besides missing hands. I can't seem to find something light enough to work. (The limitations in his design does not motivate me to work on him) so I am moving on to my next robot. So the robosapien arms are not for the minion. He would not look ridiculous. This one is gonna be a Frankenstein bot. But I have high hopes for him.

Steve_C · Answer

@sfoy That would make minion your IGOR when you make a frankinbot.

rgordon · Answer

@ kkeast Did you take pictures of the ice cream robot arm? Or can you sketch it?

rgordon · Answer

Robot Arm Calculator is designed to help you determine the lifting capability of your robot arm. robot_arm_calculator

sfoy · Answer

Thanks for sharing the arm calculator. That's very interesting. Samantha

sfoy · Answer

Design files 3d printed hand

Troy · Answer

That hand looks amazing! Is the arm calculator accurate? It seems like the calculations are pretty high.

rgordon · Answer

I have not tried using the arm calculator yet. I will look into it as soon as I can.

R2D2 · Answer

It seems a great discussion topic! I have some ideas to share, and always with the subtitle "low cost". When you have some spare time publishes some drawings of my ideas, I have a feeling that this issue will be long and educational for all.

rgordon · Answer

Sorry I have been away so long. Been very busy lately. Can't seem to find time for me tired . I still want to pursue this topic. I would like to get several arm designs done of different sizes and capabilities so members could have drawings to work from or a kit to build. Take some of the design headache out of their builds. Maybe if we work together we could come up with designs for several of the most popular robots so they have stronger more articulated arms and grippers.

sfoy · Answer

There have been a few added. Depending on design here's more: vehicle arm mechanical arm hand

rgordon · Answer

@sfoy-Thanks for the links. Every bit of info helps More questions for everyone interested: 1. What do you want do with the robot arm? Purpose? 2. Is it just for looks? 3. Will it just be for gesturing or does it need to be able to physically lift or move something other than its own weight? 4. How many degrees of freedom does it need? 5. What type of gripper, claw, hand etc. does it need? 6. Will it use all servos or all DC motors or a combination of them? 7. What type of material does it need to be made from? Some folks will need specially designed arms due to the type of robot toy they are modifying. It would be neat if we had a set of step by step plans for a particular robot toy. Some may just need a good generic type of arm to use on their homemade bot. Some with large bots need very large and strong arms where weight becomes a factor. If someone has good ideas for homemade claws, hands, elbows, shoulders etc. let's put them out on the table and see what we can do with them. I think this will help spark everyone's imagination. If we get some good designs going we may can get parts laser cut or done with a CNC machine.

R2D2 · Answer

I love this theme, which I think if we categorize the different types of arms starting from the number of degrees of freedom (axles or joints) without the degrees of freedom for the clamp or hand, for example: Arm: 4 degrees of freedom (type b) + clip * 4 degrees of freedom indicates the axles * (type b) indicates that you can make different combinations with 4 axles and the type b corresponds to a combination of these axes (I'll tackle poersonalmente to publish pictures with all or nearly all combinations of axle shafts from 1 to 6 axes and all its variations: A, B, C, D, E, etc. The more degrees of freedom there are more combinations or types. * And clip indicates the type of key employee could also be hand vacuum, electromagnet, etc.. This is a drawing of an arm of: 4 degrees of freedom (type A) + clip  This way someone can say: I am building a 3-axis arm (type a) + clip, look in the catalog of arms and you know which are the axes or degrees of freedom and where they are, you'll know if the doll has rotation or is fixed, or if the shoulder in front and back ranges, etc. .. If it seems a good idea to begin to make the catalog with pictures, plus every new idea or design not listed arm will include it in the catalog with a new letter.:)

sfoy · Answer

I think this is something that everyone will have to work out. I personally want a humanoid style hand and arm. It doesn't have to lift massive amounts of weight but it needs to be functioning. I want it to be able to pick something up, like a ball for example but gentle enough where it could pick up a flower. I also want it to look somewhat decent. Our goals are still function arms that are reasonably priced/to build? I think mainly we're gonna have to gather tons of ideas, then as someone is going to build it. They should document and post. If there's a specific toy then great but I think we'll mainly end up with a collection of arm styles and each of us will have to figure out how to implement into our project. I wish I had the time/money to just build all of them to see which ones work best.

R2D2 · Answer

A humanoid type arm is just what I want to pair my robot RSP, or rather two arms, and also I have the same goal as you sfoy that can lift light, a light object held by the robot hand is a burden large shoulder on the shaft due to the lever, so it is a challenge to an arm to handle heavy loads, especially if our goal is low cost. The idea of the catalog is only a part, as you say mate rgordon other aspects such as materials, if used servos or motors or a combination of both, etc. .. I think this applies to anyone who wants to build an arm from scratch, find a toy robot arm to change it is cheaper but I have not seen any humanoid. Personally I prefer to think that the arm is going to do, then how to get that with cheap materials and that I can work them and especially the choice of servos or motors apply to each axis servo arm because there is not strong enough, other just having the force but soon broken by overloading and proper that can last a long time and are usually more expensive. If your target is a humanoid robot arm with hand me know if you want to have full mobility similar to a human, or just need the humanoid with several degrees of freedom: shoulder, elbow and wrist. If you want to lift an empty glass or want to play with a glass liquid to another without spilling a lot of wine in the attempt, in which case you need more axles rotation of the hand or forearm. I have some ideas for a simple humanoid arm, using a 6-turn servo shoulder (delicate point effort) coupled to a much bigger gear, so the 6 laps you turn the servo = 2160 degrees become half rev = 180 degrees and also multiply the force of the servo. I think I've spent a little writing I hope will pardon my excess free time today, hehe.

rgordon · Answer

More links for study ROBOT STATICS ROBOT ARM TUTORIAL

Troy · Answer

Using that formula I may definitely need bigger shoulder servos. Using the formula with round figures for the shoulder servo: Moment = can_weight * arm_length + arm_weight * 1/2 * arm_length 5oz * 20in + 32oz * 1/2 * 20 100oz-in + 320oz-in total torque required for a light 2lb arm lifting a 5oz object is 420oz-in. sick Now the elbow requires much less. Less than a third of the shoulder. 5oz * 10in + 16oz * 1/2 * 10 50oz-in + 80oz-in Obviously I didnt subtract the elbow's servo weight but.... the elbow needs only 130oz-in Thank you for the link!

rgordon · Answer

Thanks everyone for the input. I think arms are the coolest part of a robot design If you type in robot arm on Google and search under images you can get tons of ideas on different types of designs just by looking at the pictures. What I would like to do is pick ...say...4 of the most popular robot toys that people like to hack and come up with step by step plans or a kit to utilize for arms and give them a choice of different types of hands, claws, grippers, etc. Also maybe a generic type of arm that people could use on homemade robots. My ultimate dream though would be to come up with a good heavy duty arm for large robots like the full size B9.

rgordon · Answer

@Glickclik---How's Pinhead coming along? I really like the head. Gives him personality Reminds me of the robot from the cartoon movie "The Iron Giant." Did you say you were going to try servos for the arms? Have you done any tests yet?

Troy · Answer

Unfortunately Im still waiting for the pan/tilt mount. After reading this Im going to have to invest in high dollar servos too. I finally gave in and gutted the brain out and I ordered cheap S3003 servos to harvest the control boards. I tested it using the one I had for the neck and it worked fine. I hooked the board to the existing motor and potentiometer in the neck and it worked great. Even made a script for random movement personality (ie random interval, random speed, random position). He seemed alive just with THAT. I cant wait to get the other servos in. I also took apart the eyes and test fit the MinM RGB led board and they fit too! They have little light scripts that can run in them too and you can make a few just by sending an I2C string. I probably wont do much with that though.

rgordon · Answer

@sfoy---Yeah keeping the cost down is a priority. Thank everyone who is participating All input and ideas are welcome.

kkeast · Answer

@bret, Sorry, been busy and away form the forum. I am kicking myself now for not getting a picture of the ice cream robot arm.....but i hit paydirt with youtube!.....I love this arm!

Troy · Answer

I checked that MinM led link when I posted. I saw that it didnt list the EZ-B as a product requirement list but it has the arduino there! NO WAY! They even sell EZ-B. A quick email to them and it was fixed right away. We got your back DJ!!

rgordon · Answer

@kkeast- Thanks for finding the video. That's really neat. All input is helpful.

rgordon · Answer

@Glickclik Was it difficult to get the boards out of the S3003 servos? Could you give us a run down on how you did this and a wiring schematic showing how it all hooks up? Rex

Troy · Answer

Ok I will try. Oh! In fact I will do one better. Here is a good instruction from a website and it is exactly what I did to remove the servo board: 1. "For the Futaba S3003 servo there are five connections that must be desoldered before the existing control board can removed. These connections include three small pads that attach to the potentiometer and two larger pads that attach to the motor. The use of a desoldering braid or wick is typically the best way to desolder the connections. Servos vary in how their control boards can be removed. For instance, some control boards will be attached to the motor and potentiometer using wires. In such cases, the control board can be partially removed away from the case and the wires clipped or desoldered where they attach to the board. Other servos, such as the Futaba S3003, will require that certain pads be desoldered before the control board can be removed." A solder sucker will work as well as the braid. Whatever you feel works best for you. 2. Next all you need to do is solder your new (low amp) motor where the previous one was soldered. 3. Then solder the new potentiometer where the other was attached. 4. Leave the control cable attached as it will not need any modification. NOTE: If your motor is running in reverse of what you want it to, you may either invert it in EZ-B control or just desolder the motor and reverse the attachment to it. The only reason I did it was because mechanically it was the best option to re-animate Pinhead. --Troy

rgordon · Answer

Here is my first try at a generic robot arm design. EDIT Update the drawing listed here has been updated on a later post.See below. Arm.zip The drawing is a pdf file. I am open to all suggestions, ideas, criticisms, and comments from everyone. Thanks, Rex

rgordon · Answer

Just scored a 1998 Toymax RAD ROBOT 1.0 + Rechargeable Battery on Ebay for $18.00 Cool Beans!

ndavid79 · Answer

@rgordon Cool arm! But its not as simple as just using a Y-cable in that design, in both instances the twin servos need to turn in opposite directions.

Troy · Answer

wow only $18?

TMesserschmidt · Answer

I'm doing life-size robots. I"m interested. --Thomas

rgordon · Answer

@ndavid79 Dough! My bad. Wasn't thinking. Well I guess I'll have to separate them and use extra ports. Bummer. Do you think the double servo setup for extra torque will work if I do this? Or should I maybe settle on using one servo with better torque? Maybe that would be better and also save on weight and port usage. Here is the corrected drawing without the Y-harness Arm.zip Thanks, Rex

R2D2 · Answer

I like that design rgordon! to save ez-b ports connect couples with a "Y" cable, but first we must reverse the rotation of a servo in each pair and investing the wires of the motor and servo potentiometer. I have also read any comments that two servos acting on the same axis produces a struggle between the two sevos to reach an exact position, perhaps some good quality servos might be appropriate.

rgordon · Answer

I had wondered about that. See I'm learning all kinds of good stuff from this post. I had better just try to come up with a new plan to only use one servo for each joint. It's just frustrating because so much torque is needed just to lift the weight of the arm itself. I may have to resort to using DC gear-motors and doing it like Glickclik said.

rgordon · Answer

Oh well, I was outbid on Ebay for a RAD Robot 2.0 in good working condition with remote and battery charger. I didn't check on it at the last minute. Someone else got it for $51.00 stress It looked like it was in great shape. tired

ndavid79 · Answer

@rgordon, I have a RAD 2.0 in great condition I'd be willing to part with, email me at nlkdavid AT pinnacle175 DOT com if your interested.

Troy · Answer

@rgordon Remember the board will only take the current draw the original servo took! idk actual figure but im guessing 1-2 amps. My bot's head only had tiny servo sized motors to power. You are better off with single high torque servo.

Danger! · Answer

Rgordon, I am working on a design for arms in my B9. They will be very heavy duty, but not too, too expensive. They might be suitable for something the size of Magnus. I think that I mentioned before that I bought a case of surplus windshield wiper motors. They will be the muscle. I plan on having one joint just beyond the torso with a universal joint that will allow motion in all directions. Two motors will power that from inside the torso, using cables. Beyond that, he will have about an 18 inch "forearm" with a wrist that only bends up and down. That will be moved by a push/pull cable, again, originating in the torso. I am doing it this way to keep the weight of the motors within his center of gravity, and to reduce weight on the arms. I will need small motors in his wrists to rotate them. As far as keeping track of the motion, I will be installing something like this at the origin of each cable. I am taking some vacation in a few weeks, and hope to get started on that phase. I will send some pictures when I make a little progress.

rgordon · Answer

Hi Danger! Sounds great. I am looking forward to seeing it! I have struggled for some time to come up with arms for Magnus. They always ended up being to heavy. The elbow gear motor would droop whenever there was no power going to it. The shoulder motors are no problem. Got them surplus. They were used to unfurl camper awnings. They have each have 400 in-lbs of torque. Made my own chain and sprocket drives for the shoulder joints. The wrist and claw I think will not be to much of a problem. It has always been the elbow that eludes me. I thought by using a worm gear motor it would work but it still has issues with torque and droop.:( Another thing I have never been sure of is, how do you remove the B9 torso to work on the Central Support Structure? Will you have to remove the arms each time you do this? For my bots torso I used a clothes dryer drum and made custom arm sockets. I came up with a quick disconnect to remove the arms so I could lift the torso up and off of the robot. I will get pictures for you to look at tomorrow. You mentioned cables. Are you going to use some method similar to the way power seat motors work? Or how about small linear actuators? I look forward to your reply.

robotmaker · Answer

GLICKCLICK looking at this post about using servo for ams and your formula is off if you go to servo city it tell you that oz-in ,like as 200 oz per one inch lift if a 12 inch arm you divide by 12 = 16.6 oz lift if like on the omnibot you have more then 24 inches so you have 6.3 oz lift you need to understand what the term meens OZ-IN second there is servo's are rated at stall torque (smoke) so it about 75% rating of the servo torque we test motors witch are close to servo's with a feedback and gear box,and the test come out almost the same we put weights on a long bar attached to a motor and see how it lifts it,it has up to 36 inches long ,also has a scope ,amp meter ,volt meter,high precision torque tester and calibrated power supply,electronics all my design,engineering lab had machinst design and built it we dont use servo's but the test is still the same check my post on using servo's for projects has long info on selecting servo's

Troy · Answer

Robotmaker, first, I fully understand what the term OZ-IN.... "MEENZ". I got the formula from Society of Robots article. It's not mine. Second, I understand that this is the stall weight. So the rated OZ-IN will have to be higher or the weight lifted lower for it to work. As you saw in the post I was only using thumbnail picture to show that in order to lift the smallest weight at a robots arm length you will need a very high torque servo. Lastly, in your "tutorial" you neglected any mention of the weight of the arm as well. If I am in error, I will gladly admit it.

robotmaker · Answer

total weight depends on the torque of the servo,you need to add weight of the total length of the arm plus servo's you are using plus weight of the item you want to lift and how high you want it to lift plus another more then 25 % for over weight,and the servo has to be rated at 75% of the rated torque and the article by society of robots is for basic arms with motors NOT SERVO'S its a little different then using servo's

Troy · Answer

So in the beginning you just repeated what I said. The weight of the arm includes the servos and the max payload. Why reword it to sound like you made that up? The reason you add all that up and compute using 1/2 of the arm length is due to the center of balance, but even that is a thumbnail figure of where it might be. Its possible to design one where the center of ballance is 3/4 of the total length. If that were the case, then you need to rework your figures. The best way is to take the COMPLETE arm with the max payload you want to carry attached to the gripper and balance it on the back of a chair. Of course your robots elbow needs to be straight as well. Now measure that balance point to the pivot point. From there on the math is simple. If you want to make lifting easier you could add weight on the other side of the pivot point and will help. The greater the weight and the greater the distance from the pivot point (other side) the more it brings the center of balance to the pivot point thereby reducing the torque required. Most of our toy robots dont have room for that though. - "and how high you want to lift", this statement is in error. Gravity is not going to vary. The numbers are rated at horizontal from pivot point. It is actually easier to raise the closer you get to verticle. Test it on your expensive machines. - Adding 25% I can see just to be sure it breaks the stall point. "Servo rated at 75% of rated torque" is just increasing your margin of error with no basis on why. You could do one or the other. I havent done the math on which gives the greater margin of error but lets keep things simple for people. Remember there are a lot of people just starting out. - Lastly, the article is about physics of torque. Not about any special device. It can be gas, electric or heck even nuclear machine. The physics remain the same.

robotmaker · Answer

only thing difference is that you ,that when building a arm you need to add the ounce per inch for servo,s on motors you dont need that ,society of robots article is about the physics of torque (yes you are right about that ) there is a very simple test to check to see how much a servo will lift take any servo attach 1 inch arm to it and a piece of string add a weight and see how much it will lift shound have a ampmeter inline with the power supply for stall current then try a 2 inch arm same weight you will see it half and so on. so if using a 400 oz servo and the arm is 24 inches long ,stall torque is 16.6 oz the above test can comfirm this ALSO when you start building a hand design using servo's also start at the hand part and what max weight you want to pick up ,like all like the (beer fetching robot) so the grip area is first,then rotate ,need to add up all design weights ,like beer ,servos's that was picked for the right torque,plus all parts,then get total weight of the first arm part for elbow lift and see what torque is needed ,need to measure from beer can to center point of the servo motor in elbow, example 14 inches total then times total weight of that arm part,that will tell how much torque for that part then same for elbow servo the society of robots is fairly close to it ,but need to add total length of complete arm and divide by the torque of the servo,that will tell how much it can lift

Troy · Answer

"when building an arm you need to add the once per inch" Where would you add them? "on motors you don't need that". Are you saying that motors don't produce torque? I disagree. The servo already has a rating that shows how much it will lift from the center of balance of the total weight of the arm to the pivot point of the servo. It is divided down to ounce per inch. So yes, as the other formula has been trying to show, divide your sum total weight of the arm and payload by the distance of the "center of BALANCE" of that arm to the pivot point of the servo. total of arm weight=400 center of balance=24 inches from servo stall torque=16.6 Imagine an imaginary arm that has NO weight. This servo will stall at 400 ounces from one inch. Now imagine that arm weighs 400 ounces but it is TWO inches in length. Its center of balance is still at the ONE inch mark and will stall at the SAME number. Now imagine an arm that is FOUR inches in length but most of its weight is near the servo making is center of balance at the one inch mark. The servo will still stall at 400 ounces EVEN THOUGH ITS FOUR INCHES LONG. Again this is stall torque rating given my the manufacturer. If you don't get the same results as described by them you may have a fake servo from china. There are been many reports to this effect and also in false mAh ratings on rechargeable batteries. As Robotmaker says, figure in a margin of error. If you don't you may be disappointed after you made a hefty investment. I hope that its more clear now that center of balance plays a part in arm design.

robotmaker · Answer

motors do produce torque ,but dont have a gear box like a servo ,so its not the same ask servocity techs they will tell you much more on selecting a servo for a arm design try the test it works and proves the point,buy not trying a lot of rework so you lose much money arm designs are the hardest to design,took me awhile with many tests and losing some money and rework building arm,still i used part of the society of robot article and understanding OZ-INCH and running a lot of tests you need about 2000 oz servo to lift a beer with added weight ,plastics,gears, and all other parts if using a 400 oz servo it will lift a about a pound,check some og the robot arm designs the sell using a 400 oz servo max lift on a arm is under a pound beer weights about a pound for small can,bigger can 1.5 lb about and glass much more,so you need at least 4 lbs lift my design at shoulder is 2000 servo (special) and 400 oz servo at elbow and 133 oz at wrist rotate ,it can lift little over 10 lbs big reason to use a higher torque servo is use half the current and stay under stall torque ,stall torque on mine is near 19 lbs lift so with lifting a beer it use much less current oin each servo main thing i look at in designing robots is using low current sensors,servo's ,motors and hardware even the led on the ezb ad ups too ,since it inside and not needed for anything,so use less weight on a extra battery or a short run time

TMesserschmidt · Answer

Is that 2000 at the elbow or 2000 at the shoulder?

TMesserschmidt · Answer

To lighten the weight of an arm, one could use "tendons" that attach to motors in the torso. I never tried it, but heard it could work.

robotmaker · Answer

2000 oz at the shoulder,and springs or tendons does help fairly easy to build 2000 oz servo ,at the shoulder it takes the most load, like it says at society of robots article (witch is very good) other arms you need is about 1/3 less on servo torque can buy a 2000 oz servo but at $800 to $1000 each will be posting my hand claw design of my omnibot as soon as the parts come in (2 days) and then build it holding a beer i also bought a plastic hand to look like a real hand to add latter,but it uses plastics parts ,so looking at machining them out of aluminum ,fingers are the hardest to make and control

sfoy · Answer

Look at these rubber bans & compressed air Thomas this one uses tendons and motors... tendons & motors Different type of arm but interesting. how robot arm works

Danger! · Answer

Rgordon, To answer your questions from 6/27... My arms are only going to have two flexible joints in each. The part that I think of as a shoulder will only slide in and out, extending just past the arm socket. There will be a wrist beyond that. I figure that when Bob May wore the original costume; he would have not gotten his shoulders out into the arms anyway. The two joints should be able to more than replicate any moves that the original robot had. I made a rough CG model. I do not have a cad program to put in all of the details, but this should give you an idea. Where the red and blue cables meet the motors, there will actually be a section of bicycle chain that fits over a sprocket on the shaft. Of course, by the time they get to the pulleys, it will be plastic coated cable. The green piece will be a universal joint. Unlike the picture, it will be attached to both sections. I already have a few small ones, but the ones that fit into a ratchet and socket set would work. As the red and blue cables move, they will pull the forearm in any direction. I intend to put the sliding potentiometers on the flat board under the cables and attaching them somehow to keep track of their positions. The cable to bend the wrist will be similar to a brake cable for a bicycle, but heavier duty. I didn't show the other end, but it will be a simple lever on the end of the motor. My picture shows the whole inside to look like wood. I did that just for clarity. The flat board will probably be MDF. The shaft to the universal joint will likely be aluminum. (It does not necessarily have to be round either). The forearm will be PVC. The wrist will have to be fabricated. I will need a motor to rotate the wrists. I may use actuators to open and close the claws, or I might use bicycle cables there as well. In my case, and probably with Magnus too, the whole mechanism will have to slide in and out. I will attach it to drawer slides between the arm sockets and the back of the torso. Just picture the flat piece moving right out to the arm socket with everything else sticking out into the rubber arm bellows. To answer your last question, I do not think that I will have a central support system. The arms will be built right into the torso. The electronics will be built into a unit that can slide in and out of the top. I am sorry for such a long post. Perhaps there are ideas here that others can use. I also have to add that I have not tried any of this yet. It may be a miserable failure. In a few weeks, I have some time off and I will be trying it out.

Danger! · Answer

Incidentally, sfoy, I found the links that you have been sharing fascinating. The goal of my bumbling B9 is just to animate him in some crude fashion. I do love to study real robotics however. Perhaps some day I will be able to work on something more sophisticated.

robotmaker · Answer

i guess the motors you are using are car window motors,they do draw a lot and lot of current i bought for them ,2 to have on hand for spares or other robot design and 2 for for my hand design for a very big robot,waiting to get a lathe to build the arm and hand with fingers fngers with be the hardest to control,in my design i have 3 itx computers ,one for navigation ,one for sensors and servo,s other for the main brain and software,body and wheel base done as head design did some tests at work and from the tests using a torque tester and weight looks to handle and lift 25 lb or more

Danger! · Answer

robotmaker The motors are actually windshield wiper motors. I've never scientifically tested the torque on them, but they have a lot of guts. If you ever had the wipers come on while trying to clean the snow off the windshield you'll know what I mean. My arms will be geared down much slower than wipers move as well. They do draw a lot of power. Because of the size of my robot, I am putting in two deep cycle marine batteries in him. I have 900 amps of cold cranking power. That ought to keep him going for a while. Besides, he probably won't be moving his arms much. Maybe an occasional handshake, or wave. I do not foresee him taking up tennis, or anything like that.

robotmaker · Answer

wow one very very heavy robot,marine batteries are the worst for robots,mostly acid and corrosion seen many of them use in robots and go bad alot gel cells are rated #1 for robot designs, i guess you are using wheel chair motors for the base thats what i am using in my big robot design,work out the current to be very low with all sensors,boards plus window power lift motors on arns and other current servo's and design is so well lasts over 4 hours on 35 amp gel battery that does weigh to much,and still handle a over extra 130 lb load and windowshield wiper motors dont have alot of torque as you think,but do have more then most servo's i think 700 oz i saw somewhere online they only moving a wiper blade back and forth,not like a window power motor that has to lift a heavy glass window

TMesserschmidt · Answer

wiper motors don't just go back and forth. They go around the same as a window motor.

Steve_C · Answer

@robotmaker What you say about marine batteries can all happen. You need to put them in a plastic box keep a eye on the acid levels. Dont run them to flat charge them with a proper charger and they can last for years. the two i use on my boat for the bow thruster have lasted two years so far , with no sign of giving up just yet. The bowthruster draws far more current than my robot will . they are big and heavy and gel cells are better for bots but far more expensive. PS Expensive AH for AH.

robotmaker · Answer

i get them very cheap,mainly used on outside,fumes is a very big problem besides the weight i have to see any robot in the world use marine batteries,acid is very deadly as they also have a corrosion problem too

rgordon · Answer

This is one of my favorite robots that I have found online. Has a really neat arm.

robotmaker · Answer

thats dave shinsel robot,i built one of his designs to try it out

rgordon · Answer

@robotmaker Did you build a copy of Loki? I am trying to get in contact with his creator. I am very interested in the chat bot he is using. Do you know what it is?

robotmaker · Answer

i made the SEEKER design ,called SEEKER 2 using part of LOKI part SEEKER

rgordon · Answer

I am very interested in his arm design. The servos are strong. But, very expensive. RX64 Servo

robotmaker · Answer

no didnt use chatbot

DJ Sures · Answer

Loki looks pre-scripted. The video skips a lot per take to get it right I think

robotmaker · Answer

all software and hardware on main website

rgordon · Answer

I also got that impression...but was hoping....anyway... DJ any updates on Synthia? There I go again... getting off topic of my own thread

bret.tallent · Answer

Back to topic, I am working on my arms for B9 and the design may be good for small bots. I'll post images/videos after I get the kinks worked out.

rgordon · Answer

Thanks for sewing the thread back into the topic If I don't get to many more"honey do" lists when I get home, I'll do my best to take pictures of my shoulder setup for Magnus. The claws I think I can create OK. The elbow is the problem.

rgordon · Answer

Here are some pictures of the shoulder drive mechanism and arm socket for Magnus. Please pardon the dust. Paint job is still far in the future

Arm Socket that I installed into the clothes dryer drum.

Shoulder Drive Mechanism: Support structure is two 1/8" thick steel plates and a 2" x 2" steel tube pedestal. Chain drive with two pillow block bearings. 1" hollow steel tube passes through the bearings. #25 chain and associated sprockets. 12V 400 in.lb. torque motor.

Picture of the two interior decks for all my electronics and both shoulder drives.

The actual arm is a separate entity. It will mount to this disk and tube. This tube was turned down on a lathe so that it slides smoothly into the 1" tube and serves as a wire-way to the arm as well. It will have a pin (not shown in picture) that will lock it into the shoulder disc so that the arm will rotate with the shoulder. That way when I need to remove the torso all I have to do is unplug the cable harness, pull a lock pin and off pops his arm.

bret.tallent · Answer

Holy crap that is beefy - you want Magnus to be able to lift an engine block? lol

sfoy · Answer

Bret... I was thinking the same thing. Oh my. He's going to be huge....

robotmaker · Answer

and weigh about a ton

rgordon · Answer

Close to 280 pounds already. But, the wheelchair motors, running at 24V, have great torque. The base section weighs 183 pounds. I sat on it and drove myself around (which was very fun BTW) I weigh 180 pounds and it had no problem pulling me around. Using two Victor 883 variable speed drives which can handle 60A each. Cost a lot though. $150 each. @bret.tallent - now you see why I am having trouble finding a good motor for the elbow LOL. Thanks for all the kind comments

bret.tallent · Answer

I think you should look at using a linear actuator for the elbow.

robotmaker · Answer

AT ALMOST 300 LB unless you have a truck,when i build robots i make the low weight for one very big reason,so charging for many hours i have a robot using wheelchair motors and has enougth power to move me around plus the robot too doest use very large batteries and last 8 hours till next charge,i work the motors and electronics and sensors to use very little current,also has a on-board computer,next part is my hand design,since i did much testing and was able to use a torque tester from work,if you have the right equipment can design and build the best arm ,i work the design out to use very low current ,but still have more torque then needed about 20 lb to 30 lb lift,but can handle alot more,but current goes way up just like on saving on sensors since on all the time,all ultrasonic sensors draw 30 ma about,i am using ones at 2 ma and at 8 of them at 30 ma,is a lot of current

Danger! · Answer

With all due respect, Rgordon, I think you went a little overkill on the shoulder. Did you happen to watch the movie "Real Steel" before you designed it?  (Only joking about that). But in all seriousness, you probably should consider going much lighter when it comes to the arm itself. Not only will the motors and joints be a problem, but if you have too much weight in front of him, combined with the ability to lift a huge amount of weight, he could easily try to pick something up and pull himself over. For my arms, I am will be using PVC pipe. I'll put a " inside a 2" and fill the gap with expanding polyurethane foam. That will be plenty strong enough for what I need, but light. I have some universal joints from a car steering mechanism for the actual joints, but many things would work. As I said in an earlier post, I have some heavy "push/ pull" cables, like the ones that steer an outboard motor on a boat. They will bend the arms but leave the weight of the motors inside the torso. You might consider something like that.

rgordon · Answer

Yeah.....got a little carried away....got tired of not having enough torque for the shoulders...................but it's so much fun! Muhahahahha! @robotmaker -not to worried about power, I have two maintenance free 34 Ahr wheelchair batteries. If it's good enough for a wheelchair, it's good enough for Magnus. Magnus will strictly be just a show robot. Totally remote controlled as far as movement goes. Does not need to run for very long periods of time. I do want to be able to steer and drive him when he is out of my line of sight and he will definitely need to have sensors to help with not bumping into things or running someone over. I will always have an assistant nearby to help keep an eye on things. Drop dead feature if he gets out of R/C range. Of course the EZ-B will allow me to automate certain features and make him appear more lifelike. See Project Magnus  thread for details about Magnus. Hopefully, I can use Magnus to make a little money on the side (for buying more robots and parts:D) . I know there are places in California and Florida that rent out robots and an operator for a day for places like shopping malls, car dealerships, office parties, etc. for whopping amounts of money. @bret.tallent -I am experimenting with a linear actuator to see if it will fit inside the arm bellows. I am thinking of making the elbow the same way as is used on a Backhoe . I do think this is the only way I will get it to work. Also worried about his arms appearing too long...wouldn't look right. @Danger! - I share your concerns. All ideas are helpful. I think using PVC pipe is the way to go. I really like your idea about the expanding foam. Weight is definitely a problem so I am extremely interested in your idea about using the push/pull cables. I could easily route one through the hollow rod on my shoulder joint and use it for claw "open/close". Also, I may be able to use a cable like is used on a weed eater (that turns the cutting head) for wrist rotation. The problem is, whenever I need to work on the stuff inside the torso, I need to be able to remove the arms. I can do it now just by disconnecting a cable connector and pull a lock pin and his arm slides right off. So it might be tricky trying to figure out how to disconnect/reconnect the push/pull cables easily and quickly. Any ideas? And BTW I really like the Real Steel movie!

ndavid79 · Answer

Check out Surplus Center's DC Linear Actuators. Many unique kinds, great prices.

rgordon · Answer

@ndavid79- Thanks. Definitely good prices! Good dc gear motor prices too!

robotmaker · Answer

yes they have great prices,bought many motors from them also my full size full detail JOHNNY FIVE i am designing ,i am going to rent him out too hardly any of his type made yet,and SHORT CIRCUIT creator eric allman is comming out with short circuit 3 in 2013

rgordon · Answer

Hey Short Circuit was one of my favorite movies...mainly for the robot. How far along is your Johnny Five project? Is there a web site to view progress?

rgordon · Answer

Thought everyone would get a kick out of seeing a model robot arm I was working on about 20 years ago. I recently ran across the pictures on an old hard drive I was checking.      As you can tell some of the motors and linear actuators have been in my collection for a long time....waiting for a host. The plastic piece I am using for the voice box on Magnus is almost 35 years old! It was part of an old Sunbeam fingernail polishing gizmo my Mom had.

PhG · Answer

Awesome dude ! Continue the good work, it's inspiering me !

bret.tallent · Answer

Nice design

robotmaker · Answer

on the full size JOHNNY FIVE ROBOT just got a few parts in,main drive motors and mattracks,few head parts so far put in $800 ,total cost looks about $4000 to $5000 waiting on the plans from www.input-inc.com to be finished

bret.tallent · Answer

So here is the design for my B9. It is the small 2 foot B9 so I didn't need much for strength.

robotmaker · Answer

oh,i thought it was like a 5 or 6 foot design,looks good so far i am working on a design concept to get rid of the servo noise ,that most servo's have

rgordon · Answer

That really looks great! Nice and smooth. Did you build your own servo tester or buy? I'm still working on ideas on how to incorporate a linear actuator into the arm of Magnus.

bret.tallent · Answer

I bought the servo tester off ebay for 5 bucks.

robotmaker · Answer

check out SERVO BUDDY in the servo magazine or on the internet search,simple circuit just 2 555 timers and few parts ,good for checking servo's

Troy · Answer

I like that Bret. I too thought you had a large scale B9.

rgordon · Answer

Found a 555 circuit. I'm going to build it tonight if I have time. Bret have you tried placing the rubber arms over the servos to make sure they can flex it?

robotmaker · Answer

circuits for me is much much fun to design and build,can buy them but not as much fun as building it your self ,like in baking,witch i was baker for awhile,i would make a cake from scratch then buy one still do much baking at home with the best in baking equipment

rgordon · Answer

All this mechanical stuff is a good challenge for the mind but kind of a drag too...especially the endless sanding....I am learning a lot though. There are so many talented people on this forum! So many good ideas! But, I have my most fun building circuits

robotmaker · Answer

if you or anyone else stuck or need a design on a circuit ,my service is FREE i first use a proto type bread board,fully test it,then build it and then fully test it again same again with building arms,its pretty easy to come up with the design ,but witout fully test it before you put it together ,it saves alot of rework some of us also overkill ,witch meens a very large battery and puts much stress on motors or short run time when i design like most robot companies do it,make it very efficiency,low current sensors and boards ,motors and servo;s running at half the rated power,LDO regulators and light batteries,can almost run a full day or more if designed right

bret.tallent · Answer

Here is my rubber sleeve over the arm. It is hose from a gas mask.

rgordon · Answer

Terrific! Looks great!

robotmaker · Answer

that look good,also there is many sizes and types at mcmaster-carr also thats where i am getting mine ,for my omnibot hand design so many many projects not enough time in the day to work on them but good news i work at home so far dont need to go to china for work for a few months i am going on a trip to clearwater,tampa,and ocala in florida for 2 weeks in end of sept (not for work) so i have a few months on robot building

rgordon · Answer

Here is a link to a servo tester circuit that I found. hvlabs.com

robotmaker · Answer

here is one a little better uses 2 very cheap 555 times and a few parts servo tester it also talks about servo's and how they work servo buddy page 2 servo buddy page 1

rgordon · Answer

@robotmaker I like the one you found better. I will try that one. I have the parts on hand. I'll let you know how it turns out.

bret.tallent · Answer

My B9 arm design in the torso/arm socket.

robotmaker · Answer

its too bad servo's makes much noises,looking at better design with no noises

rgordon · Answer

@bret.tallent That is just so cool! You should make official drawings and come up with a kit to sell for all who are modifying their own B9. What servo torque will be required for the shoulder? How is the claw design coming along?

R2D2 · Answer

Wow man, I like that this thread does not remain forgotten, while others encourage their ideas. My arm robot RSP unfinished, is four degrees of freedom (more humanoid hand that will work with just two servos) The degrees of freedom are: -Shoulder -Elbow -Wrist Wrist-rotation

rgordon · Answer

Very clever arm design R2D2. What servos are you using for shoulder and elbow? Definitely want to see a video of this arm in action!

R2D2 · Answer

Thanks rgordon :the shoulder servo that is not in the picture because I have not yet purchased, will be this: SPG805A-BM The servo that moves the elbow with a steel rod that is mounted on the shoulder to act as a counterweight is this:S8166M The servo that drives the rotation of the wrist or forearm and still not mounted servo is a Futaba S3003 or maybe a s3004 (with bearings) and will work with a gear of 100 teeth servocity, pulling out the potentiometer to the shaft and coupling forearm rotation   The servo wrist moving up and down function with a steel rod acting on the hinge and it is this: TGY1501 I delayed the most of the location of the servos to delay the center of gravity of the lever arm is the minimum. greetings.

bret.tallent · Answer

THanks Rex! I am using an MG995 servo for the rotation. It doesn't really need that much torque but it is what I had lying around. I am currently working on the claws and rubber cover. I will post more video as I progress.

robotmaker · Answer

i am using higher torque servo (my design) for my arms on my omnibot 2000 project inside the arms will have aluminium,it best stuff to use for robots,easy to machine and add boards or servos and to remove them,and soon setting up a special MIG WELDER to weld aluminium,needs a high output MIG welder,plus a special mig welder feeder gun made for aluminium with gas input,and argon gas for shielding gas,also on order is a metal lathe and mill machine work out my design to lift over 50 lbs ,more like the bionic arm in 6 million dollar man movie project is called 6 million dollar omnibot lot of times i make my own servo's its pretty easy all you need is the futaba s3003 servo and remove the board and pot and motor ,and add your own motor and gear box and add the pot for feedback,now on the h-bridge on s3003 board it rated at 1 amp,so 2 in parallel gives you 2 amps or remove it and add your own h-bridge for gear box kinda easy to work it out,just need specs on motor you are using,speed and torque and torgue you want out ,then gear ratio is kinda easy if like example you need a 4 to 1 ratio, and want to use the smallest pinion gear for the motor like 9 teeth output gear would be 36 teeth,reason for a small pinion gear is that the output gear is small to fit inside your design or get a little harder like in servo are made with a few gear ratio's, now with a 4-1 ratio speed will be 4 times less and torque 4 times more

R2D2 · Answer

rgordon and soon will modify robot hand with aluminum and two servos like this:

robotmaker · Answer

i have a hand like that as a template for my aluminium hand design,one main reason a lathe and mill machine is very needed plastic hands makes a great template

rgordon · Answer

Thanks to you all for keeping this thread alive. Just wish I had more time to work on my bots. Seems as though there are always so many things that need to be done after I get home from work. And even when I find a little time, I'm just to tired to get motivated. Guess I should feel blessed that I have a good job. Life has a funny way of putting a damper on your dreams. Just makes it seem hopeless sometimes. tired Watching you guys develop your robots gives me and others lots of inspiration. Your designs are outstanding! @R2D2 Those look like a great find on servos. Very good looking arm. @robotmaker Do the gear motors behave and control/maintain position as well as as servo does when you set it up this way? Would love to see videos and pictures. @bret That robot is coming along nicely. Can't wait to see him in action. More videos

robotmaker · Answer

rgordon they are made the same as servo's,if you take apart a servo you will see a gear box,dc motor and control board and feedback pot,so you are making the same design,but with higher torque motors feedback is very important the pot must be on the last gear the best servo board easy to modify and there is a schematic on it is FUTUBA S3003 plus very cheap from CHINA on ebay about $4 each or less

Cobra71 · Answer

Did you know this one from Festo, it's pneumatic, but very impressive. I thinkl it could be made of servo driven steel ropes too.  Marc

rgordon · Answer

@Cobra71 Yeah I have seen that one and I really like it. I have thought about trying something like this using miniature linear actuators and the steel cables used on lawn mowers (the ones that position the choke or throttle).

Antron007 · Answer

I think Spiderman used to fight that guy all of the time. It's good to see DocOc got an honest job.

Cobra71 · Answer

@rgordon Now I have seen your avatar....your maximillian always have added a pair of festo arms....I've not seen this before. I think four steel cables for the Arm, driven bei two servos should make up/down/left/right, but I think you need the same again for the wrist and one servo for the Hand. So we need at least five Servos for one arm, but it seems to be an interesting experiment. EDIT: I read the complete thread now, I think strong RC-Servos are really expensive. In my opinion the better way is to use a servo elektronik and a strong motor with (planet)gearbox and pot. I looked for "servoelektronik" on google and found a two channel servo elektronik that can handle motors with 10A. You can get the electronic for 6V, 12V or 24V, but it seems that is fixed and have to be ordered with the needed voltage. It's a german site, but I think there would be others in the web: 5. Servocontroller Here is another electronic, called "Thor15 Servo" that can handle up to 12V/18A. Thor15 Servo Here's a diy schematic for a one channel servo electronic for 24V/15A with MosFet's: ServoController 24V/15A Marc

TMesserschmidt · Answer

I'm Printing up the InMoov robot since I got my 3d printer working again. Stay away from solidoodle. It has been nothing but trouble for me since it arrived, and suport is bad at best. Also, if it breaks the first week, like mine did, they don't have any obligation to fix it.  --Thomas

Toymaker · Answer

Here is an AIMEC:EZ1 arm with 5 DOF just before the wiring loom has been added. We had to develop our own shoulder servo which has a massive 200 kg.cm torque.

Steve S · Answer

Toymaker, I am sure looking forward to the changes. Thank you Tony - EZ1 robot maker and D J Sures, EZ robot creator. Steve S

irobot58 · Answer

Sheesh ! A guy goes away for a few days to build a robot and finds dozens of new posts! gotta love it..anyways, here are a few pics of my robots's arm and hand..( for @Sfoy! ) who wants something more "human like"..Thanks to ALL for really geat posts! I am using home made custom gears for three reasons... they're cheap(wood), customized to fit my robot arms and they fit into my Steampunk theme! Of course by adding gears one can increase torque.   recycled bike cable go back to the forarm servo platform  rivots can be used for more then just rivoting metal together   the right arm layout with 4 degrees of movement...servos not installed yet. All servos are "gear" assisted for esthetics and torque..the wooden hand took about 2 days to complete. Its nice to have the "hand model" in sight the left arm will have a claw pulled together by a single servo. All supplies on "hand" therefor zero cost (@rgordon)..but...time is a huge factor

Steve S · Answer

irobot58, Your work is extremely impressive. I have always liked the look and movement of a cable type tension hand. I wish there was an easy way to apply enough torque to operate and modify a toy tension hand for my Captain Ann Droid. Looking forward to your progress. Keep up the great work. Steve S

sfoy · Answer

Thomas I'd love to know how that goes... irobot wow that arm is pretty impressive.

Dave Schulpius · Answer

irobot58, cool arm and kinda creepy. I love it! Now, just don't try to do what Howard did on Big Bang Theory and end up in the Emergency Room! eek

sfoy · Answer

Oh I love the Big Bang Theory....

bret.tallent · Answer

ouch!

irobot58 · Answer

I saw that Episode of Big Bang and LMAO! The total arm will be heavy but plan on either a DC motor for the shoulder and or bungees for tendon assist.

irobot58 · Answer

This thread is very informative about servos and math torque but I think a very direct way of knowing what kinda servo with how much torque , can be done by simply measuring the actual torque with a spring guage! They're easy to build using a spring ( and if you dont have a reference scale for calibration you can always take it to the supermarket and use their scale|) or bungee cord! Cheap fishing scales are usable as well and most of us probably have those in the garage behind the net! ..... Add in all the known payload..ie A can of Moosehead Beer(micro brewery) or the glass of wine for the Ladies.! Its the old ..which came first, the chicken or the egg(egg actually) ...build the arm or buy the servo first

rgordon

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