Possible Rad Project, What Do I Need!?!

Question

Comments made by my parents suggest i'm getting a rad for my birthday june 14(celebrating sooner) So I want to have a plan in place for what ill need to make the rad. Diagram of possible rad

CardboardHacker · Answer

Add: micro servo and ping sensor where cup holder is Camera as nose in the head

CardboardHacker · Answer

Still don't know what ill need.

Im thinking ill extend the neck to add pan and tilt abilities.

So what i'm thinking is: Head- 2 normal/ 2 micro servos(micro or normal?), camera

Arms- 2 normal/2 micro servos(Micro or normal?)

What should I do with the gun? How could I control it?

And should I add micro servos to the shoulders to make it possible for it to grab things?

Dylan.

irobot58 · Answer

Its always difficult planning what size servo's to install on a particular linkage....most people I ...suspect...install a higher torque servo to err on the size of strength. I suppose the engineering way is to measure or calculate the required torque using a spring scale! the rest of your questions are the creative ideas color, personality ,actions noises etc...enjoy

CardboardHacker · Answer

Thanks. to bad I don't have a spring scale!

Rich · Answer

After my wasted time, effort and money on Melvin I always go high torque to cover it. But, they require external power to avoid browning out the EZ-B, and if you aren't using a 6V supply you need to add in regulators.

Micro servos have very little torque, if gravity is going against them then you may struggle.

You could use a tip transistor switch for the launcher in the chest and connect it to the original motor, I'm not sure how it works but there isn't a lot to it. If you remove it there will be a big hole left to fill, the same goes for the cup holder and battery connection.

The waist will definitely need the highest torque servo you can find, with the arms attached as standard there will be a lot of force on the waist, gravity will try to pull it all down and lifting anything may pose a problem.

CardboardHacker · Answer

Ok so...

Rich · Answer

The arms don't move up and down, they open/close. From the looks of it, changing that is a fair amount of cutting and bonding.

CardboardHacker · Answer

could you post a picture rich?

Rich · Answer

Sorry I don't have one and my arms are in pieces (not my arms but the robots arms, my arms are fine)

CardboardHacker · Answer

Ha ha ha.

CardboardHacker · Answer

so final plan:

jstarne1 · Answer

@techno pro , I would just use the stock motor on the arms opening band closing. They do their job well. You could use a H bridge or a couple switching transistors and diodes to control them. As far as a battery go with the 7.2 v 2s lipo. Technically you want 6 volt for servos but if you buy high torque most are compatible with 7 volts. Take in mind analog servos like Power HD 1501mg do not make a buzzing racket where digital ones makes a buzz under a load. Its mostly a preference both will do the job for you. Digital are said to be more accurate but when you get down to real world testing you wonder if that's true sometimes.

jstarne1 · Answer

Est cost for basic equipment- -Lynx motion pan bracket B $9.99 -EZ robot kit has your standard servos , ultrasonic, camera and ezb all together in one package $169.99 -Hbridge for the tracks - $15 -Lipo 2s battery pack 7.2 volts -under $20 -Darlington switching transistors , 4 x diodes and 2x 1k ohm resistors ( to control your arms) -around $20 -2 x pololu.com power HD 1501mg 240 oz in servos $19.99 each nOTE: I would have one servo on each side of your waist one servo will be reversed in ARC and they work together. Because they are analog they want be constantly buzzing to hold the waist up. One servo at 240 oz might be fine for you if you want to do only one but it wouldn't have much "lifting power". -Maybe 25 servo ext cables , they are cheap but you need them for connections from servos and motors to EZB. .50 each Standoffs- x8 ( mount ezb and h bridge) - $6 Best total of the basics - $291 All you need after this is super glue, hot glue, dremel/rotary tool, assorted drill bits , soldering iron, solder assorted LEDs, PC speaker...

CardboardHacker · Answer

I can see buying a second Hbridge for the arms. would save me a bit of $. Not sure on what to do for the body tilt. This is the servo you think I should use for body tilt? A little expensive for my blood! www.pololu.com/catalog/product/1057 I was looking at getting a jumper cable set. is it worth it? Could you tell me how much the shipping for pan/tilt bracket would be on lynxmotion to southwestern ontario? What would be the best bang for my buck battery type(with a charger)? Think 8.4v is a set voltage for this project.

jstarne1 · Answer

Really? The 19.99 high torque servo is too pricy? Lol that's a very low cost. The eZ robot store has a high torque servo that's is about 130 oz in torque I believe for 13 dollars. Go to hobby king.com and look at turnigy 2S batteries

CardboardHacker · Answer

how many servos do I need for the body tilt? just one of those power HD 1501mg 240 oz servos? the pan and tilt bracket is good quality?

jstarne1 · Answer

Yes I'm using three of those brackets. I don't recommend anything I haven't used with success. One 1501mg servo has 15 pounds of torque. Its probably 3 times stronger than the original gearbox.

CardboardHacker · Answer

so one or 2 of those analog servos for the body tilt? could I get away with 1? And you say that lipo batteries are good for this?

jstarne1 · Answer

Yes you can use just one for body tilt. Just replace the current gearbox with it. I just have a symmetrical obsession , one servo will be enough to hold your body upright and do "some" lifting. The standard servos should be fine for your neck because the head doesn't way but a few ounces and so does the EZ-Cam. Lipo batteries are seriously the best kind of battery and are worth the money. They aren't but a few dollars more than a quality/ new sealed lead acid battery now.

CardboardHacker · Answer

Ive always put my trust in ni-mh batteries. ill look into the lipo's. How hard do you think it would be to make a mounting bracket for the head turn/horizontal servo in the head? Could you use 2 heavy duty servos from the shop in the body tilt?

jstarne1 · Answer

No really need for a bracket , there's already and insert there you can cut a hole the shape of a servo out and hot glue or screw the head to. So if you only want side to side movement you don't need a tilt bracket.

CardboardHacker · Answer

would I need 2 of the heavy duty servos in the shop for body tilt? I want to try to keep all the things I need together to save on shipping.

jstarne1 · Answer

If you go with the ones in eZ robot store then yes two of them. I can show you how to modify them to move in sync as one servo. Together two should have a combined strength of around 260 oz in at 6 volts

CardboardHacker · Answer

ok. what I was thinking for powering the robot is: 8.4V ni-mh battery. I think its 10000 mah. will this be enough to power 2 hBridges, and the ez-b? the heavy duty servos will be powered with the battery pack that comes with the ez-b.

jstarne1 · Answer

I'm telling ya lithium polymer (lipo) is the way to go , great in price and performance. They can handle the current demands without voltage sag that causes ezb to disconnect. Large capacity battery 5000mah https://hobbyking.com/hobbyking/store/__9172__Turnigy_5000mAh_2S_20C_Lipo_Pack.html

CardboardHacker · Answer

Ok. They will be able to power 2 hbridges and the ez-b? Thanks for all the help by the way.

Rich · Answer

I use a 5000mAh in Melvin and it copes very well, and lasts a long time. I will be using the same in Jarvis. There will be no problem powering 2 hbridges and the EZ-B (provided you don't throw on 4 extremely large big motors).

CardboardHacker · Answer

ill just be using the motors in the arms and the tracks on the motor controllers. how long do those 5000mah lipo's last?

Rich · Answer

5 amps for 1 hour, 1 amp for 5 hours, 500mA for 10 hours. It depends on what's running. Add up the current draw of each thing on the robot, convert to amps if it's in mA (just multiply by 1000 for anyone who doesn't know that) and divide 5 by that number and that's how many hours it'll run on full load. If it isn't moving all the time then it can be greatly reduced as the motors are no doubt the biggest current draw.

CardboardHacker · Answer

the arms will only be used every so often. theres one power saving area.

Rich · Answer

Melvin runs for hours on one charge. In fact, it has been at least a month since I last charged him (a lot of that time he has been off but I have also done a lot with the LCD and script testing, sneezing, sleeping, blinking etc.) However, one thing you need to be aware of is that LiPo batteries do not like undervoltage, i.e. if it drops below 3v per cell the battery wont charge again. It's a good idea to add in a LiPo monitor circuit & script and possibly an auto cutoff.

CardboardHacker · Answer

that's what I don't like about lipo batteries. they require a fair bit of safety.

Rich · Answer

But they are cheap and you will only let one undervolt before you realise what you need to do Charging needs safety but follow the instructions and it's safe, I charge mine unattended because I'm that confident - so confident I risk 135,000 (~$205,000) of house. I do use a fire proof charging bag mind you, I'm not that stupid Go with LiPo, I cannot recommend them enough.

CardboardHacker · Answer

as ive said, I normally put my trust into ni-mh batteries. I cant entirely trust lipo batteries as I feel that just using, then charging, then using, then charging without any extra supplies or work is normal. lipos as you said I need a fire-proof bag, and I can't allow under voltage(what is that by the way) at all. I don't feel that its worth my while to deal with these batteries.(or time bombs, what ever you think.)

Rich · Answer

Under voltage is when you run the battery too long and the voltage drops below around 3v (I think it's .7 or 2.8 actually, I work on 3v to be safe). Basically, when you use a battery the voltage will drop when it's discharging, the lower the voltage the lower the power left in it. So LiPo start off at 4.2v per cell, over their discharge this drops, which is how you can measure the charge left in it. If you use the script and circuit I did the tutorial for you will know when you need to charge, throw in the auto disconnect circuit (I haven't tested it yet but the theory should work and I have seen similar circuits on other forums) and you're safe. Use a decent charger with safety cut offs (most chargers unless you buy very cheap from dodgy places) and charging is safe, I didn't used to use the charging bag, I only use it now because it come free when I bought my last 2 LiPos. It's now part of Melvin so it's no extra hassle. FYI, short out a NiMh battery, +ve to -ve with no load and tell me they are safe - Do not do that really!

jstarne1 · Answer

@techno pro , under voltage means you run the battery till its completely dead. With a lipo its found to be best for long life ( hundreds of charge cycles) to not let them completely go dead before they are charged again. the recommended voltage is 3.7 volts per cell. 4.18-4.2 volts is considered full charge. A lipo requires the same safety and respect you "should" be giving a NiMH battery when charging. So please don't buy a NiMH battery just to ignore the basics in charging / discharging safety.

Rich · Answer

3.7v? I thought it was 2.7v or 5.4v for a 2S...

jstarne1 · Answer

The "2s" designation indicates the amount of cells. 2x 3.7 = 7.2 volt battery base voltage 8.4 charged. 3s is 3x3.7 volts =11.1 volts base voltage and so on..

Rich · Answer

I may have misunderstood. When you said 3.7v is that the lowest voltage to take it to? Before it starts to damage the cells? Because I thought it was around 2.7v when it undervolted. If its 3.7v I need to change my scripts.

jstarne1 · Answer

At 2.7 volts you have already reduced your batteries overall life. The goal is never under 3.7. 3.4 its not the end of the world but also not the healthiest level for your battery. I believe turnigy considers the cells permanantly damaged and should not be used in a aircraft at risk of failure at 2.4-2.6 volts. The lower you go under 3.7 the worse it affects the ability to retain charge. After even one significant under volt scenario you have reduced the mah capacity forever. It has to do with the lithium beginning to form crystals.

jstarne1 · Answer

Hey if you cut it off at 2.7 then at least its above the "permanently damaged and reduced capacity" point

jstarne1 · Answer

There's are tons of arguments about how much each under volt affects the overall life. Here on rcgroups they suggest you have reduced your battery life to 80 percent at 3.5 volts but I don't think they have tests to confirm that. https://www.rcgroups.com/forums/showthread.php?t=190495 I have read of people using them in planes and running them down to 3.1 volts but then they only get around 30 to 40 cycles of life through them which to me sure feels like a significant impact on the longevity of a lipo. @rich it doesn't sound like you have been through more than a cycle or two , just adjust it for 3.7 volts in the future and you will max the possible future life out of them. Happy batteries lol

Rich · Answer

Undervolt batteries will not charge, at least not on any decent charger, they will error and refuse to try. Just checked it on google and a bunch of RC forums and 2.7v is the absolute minimum, most claim 3v so even the cheaper LiPos don't undervolt. Retail protection circuits hard cut off at 3.0v and soft cut off at 3.3v. Everything I found suggests a low level cut off at 3.3-3.4v Where did you get the 3.7v from since everything I just read (and remember reading when I was making the LiPo monitor script) seems to say otherwise (3.3v to give that wriggle room before damaging the cells). In case it's not apparent, I'm not arguing it It's just I have provided people with scripts etc. for shutting off or warning on LiPos and since it's other people's batteries I want to make sure it's all OK. I'm not worried about my battery, I have only charged it once and then I don't think it was even that low. What I don't want is to have a lot of angry people coming on because of a script I provided

CardboardHacker · Answer

how can I tell that a lipo battery is going to undervolt and how can I prevent it the cheapest way?

Rich · Answer

Use the lipo circuit and monitor I did a tutorial on (it's linked to in an earlier post here). It's a very cheap and simple circuit, one cell connects directly to one ADC port the other goes through a voltage divider (3 resistors), with a diode for over voltage protection on the ADC port (optional, but recommended). Then a script runs and checks the voltage every x ms, the discharge rate isn't too bad so every 500ms or even 1s would be fine. If it's getting low it tells you, it can shut down things or even disconnect the EZ-B from the PC. It doesn't shut off the battery though so you will need to disconnect or charge it relatively quickly depending on min voltage level set. Or, you can get balance port monitors that plug in to the balance port, report the voltage and buzz when low. They are cheap and stand alone, but don't shut the battery off. Or try the auto shutoff circuit I posted, but I haven't had chance to test it yet. This one will shut off power to everything on low voltage but does draw current itself so eventually will undervolt the battery (would take a fair amount of time, like hours or maybe even days). Melvin uses the monitor circuit and reports the voltage on the LCD in a similar way to the battery icon on a phone. The only time I undervolted a battery was when I forgot to disconnect it and didn't touch it for weeks.

jstarne1 · Answer

Rich built a circuit and can show you how to monitor it on your ezb. He's very talented with script. @Rich, I use to be into rc cars and planes. I've always stayed with the 3.7 volt rating from the factories but lots of individual hobbiest like to push the equipment as far as they can before something noticeably bad happens. 3.7 is what I have stayed with and worked very well to maximize battery life. I use to work for horizon hobbies and we tested all kinds of stuff , even melted just about every lipo bag too. To be safe I would have the script stop at 3.7 volt. Thats my suggestion. I realize that others claim various voltages but for me its safe over sorry lol.

Rich · Answer

That's good enough for me I'm not 100% sure what I put in the script anyway, I know it's a variable at the start so the user can set it themselves if they want to risk going lower but it's always good to have good values as defaults. Edit: Just checked, it's set at 3.7v for low and 3.5v critical anyway which should be OK depending on the current draw of the robot and circumstance.

CardboardHacker · Answer

now for me to do all that, slim. I barely understood half of what I just read. Yes lipo batteries are awesome for life, but the care you have to take with them is to far out of what I think of as my standard. I would love to use lipo batteries but I just dont have the patience and/or understanding to work with them. @jstarne, Ni-mh batteries you can drain completely, and charge from anywhere in its power level. On another note, what is the next best battery?

Robot Doc · Answer

I thought that NiMH batteries should not be discharged lower than 1 volt. When a group of cell are wired in series and one cell drops below 1 volt it may not recover and charge with the proper polarity. In other words the cell becomes reversed. A good second choice would be Sealed Lead Acid (SLA) batteries.

CardboardHacker · Answer

I don't know robot_Doc. I put my trust in ni-mh batteries anyways. Here are the Final plans for the rad.

CardboardHacker

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