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Belgium
Asked — Edited

New Grippers Who Can Really Grip Something

i found these grippers,where you can actully grip something whithout,
burning the servo when stalling.they work on 5 volt up to 12 volt.


grippers


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Synthiam
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PRO
Synthiam
#1  
Those tiny plastic cheap servos will burn out in less than 2 seconds holding an object. The description says it can hold a ping pong ball, which will still damage them. Those blue plastic cheap servos are found in many Chinese ripoff products.

The only way to protect a servo from being damaged is to not force it to move further than physical limitations. This is because that's how a servo works, but using all its force to move into the desired position. Find out how a servo works here: http://www.ez-robot.com/Tutorials/Lesson/48?courseId=6

Dampening/cushioning the gripper with foam is a partial solution to aid gripping. The most reliable solution is to adjust your gripper position based on the object that it is gripping, as specified in the tutorial learn section.

Take your human hand, for example. You do not attempt to close it with all your ability every time you hold an object. If you did, you would be the hulk and squish everything.

So the same common sense logic must be applied to Robotics. You cannot program a gripper servo to move to its furthest close position every time it attempts to hold something.
PRO
Belgium
#2  
maybe replace the servo with one mini from here and use foam.

thanks for the link and warning.
#3  
This gripper clearly doesn't have this, but it is possible to design a gripper with a clutch so the servo keeps spinning but the clutch slips when it squeezes too tightly on an object. I have a cheap robot arm that uses just hobby motors and switches to operate and all of the joints and the grippers are clutched. I don't like the overall design of the grippers but if I ever manage to get a 3d printer I will use some elements of the design to make something better.

That being said, as DJ pointed out, that advertisement is simply a lie.

Alan
PRO
Synthiam
#4  
You can use a clutch - i have seen magnetic ones. However, you lose positioning.
Singapore
#5  
Is there such a thing as servo's with force feedback? i.e. A way to detect resistance in the gripping action and prevent an attempt to move the server further once the resistance reaches a prescribed level?

I know there are all sorts of pressure sensors available separately, so I'm betting it's been found that simple resistance to the servo motor is inadequate, but I'd be interested to know why. Is it that you have to apply a large force before obtaining the resistance, thereby only knowing after the effect that you've squished the object already?
PRO
Synthiam
#7  
@Aceboss you can get into dynamixel servos with a dramatic increase in cost - but they do exist. The feedback mechanism requires you to program the expected values - and if you make a mistake with a dynamixel servo, the mistake cost is 2 or 3 times
#8  
If you add a feedback line to the potemeter, you can monitor if the servo movement stopped and set it to that position or one less. That's the only other way.
Singapore
#9  
yikes I looked at the price of those dynamixel servo's, and all I can say is... Thanks again EZ-robot for making robotics fun AND affordable!
PRO
USA
#10  
Another option might be to use a pressure sensor or a lever switch. This is what I'm still looking to do for CY. The idea is to have the object being gripped press against a sensor which sends a signal back to the EZB and the software would then tell the gripper servo to stop moving.
#11  
@RoboHappy ... Unless you "release" the servo there is no easy way to stop it, A pressure or lever switch may tell you contact was made, but how do you tell a servo to stop where it is unless you release it? You could write a script that "steps" a servo one position at a time in a loop but that would be kind of crude IMHO...
#12  

Quote:


Unless you "release" the servo there is no easy way to stop it, A pressure or lever switch may tell you contact was made, but how do you tell a servo to stop where it is unless you release it? You could write a script that "steps" a servo one position at a time in a loop but that would be kind of crude IMHO...


I actually have scripts that do just that for my Roli claws (although I don't currently have feedback, the script just executes as long as I have a key or joystick button depressed. Putting some kind of pressure feedback is the next step). Works pretty well, although if I recall I am stepping 2 or 3 steps when closing and 5 when opening.

If I remember I can post the scripts when I get home, or just look for Myroli-MKii project on the cloud. The claw controls are in the script manager.

Alan
PRO
USA
#13  
I wish that this was not discontinued. may have been interesting to mess with


Link

Aaron
PRO
USA
#16  
Yes exactly. A script that would either release or stop. Even stepping it is a good idea. When I get the time, I do plan on revisiting this plan because I also want to add a small IR sensor to detech when an object is within the claws of the gripper. I did something like this some years ago with dc geared motors so hope to see what a servo will do too.
PRO
USA
#18  
That's cool ! I actually remember seeing that some time ago, while looking for ideas.
My idea stems from the recent book, "the robot you always wanted" by John B.
in his design(where my CY comes from) he uses the EZB grippers, Pololu IR sensers and a limit switch for each hand. Even an additional webcam to visually see the objects being placed or picked up, all arm servos and sensors connected to a Meastro 24 usb servo driver. He even designed his own interface thats very V3 like with bluetooth and uses his Robotbasic for sw. Seems to work pretty well too.
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