Claw Trouble

We’ve been having a little trouble with our claw. After opening and closing it a few times, it will burn out and not open or close. I’m sure this isn’t a programming problem, because after a little wait it works again. We’ve tried replacing the motor. It doesn’t feel like the claw needs much power to open and close, and the gears mesh properly. Any ideas to improve the design so it doesn’t do this? It’s a major issue, and we need to get it fixed soon. Thanks! Here are some photos:



Your motor is overheating, thats why it stops and then works later after cooling down.
You could gear the motor down, rather than using it at 1:1 with only 90degree range of motion. Drive your matching 36t gears with a 12t on the motor.
Likely another part of the problem is that you are operating the motor at stall conditions whenever you are holding it closed.
If you have a physical stop instead of a limit switch to keep it from opening too far,
you are probably stalling it at open also.
If you post your code, someone might have a suggestion for you.

Okay, thanks! We’ll try this!

We did realize this, but the elements fall out if pressure isn’t being applied on them.

Do you have another spot for another motor or are you at 10 now?

Is that a 393 or a 269 motor?

Other ideas:
You could put one of those new I2C sensors on the back of this guy to see when velocity in 0 and have your program ramp down the power until it sees it slips (or ramp down to a lower value that is safe from burn out for a good long while yet still holds your elements in place).

On the bottom, get some of the nylon/telfon washers and use a nylock nut to give it some wiggle room on the pivot.

On the top, make sure the white washer is against the metal instead of the shaft collar.

Friction is a bear. Every bit of help you give might make the motor last longer.

Since you are a claw style grabber, you could make the Nightcrawler claw from last year. Two linear slides opening up via one low power motor grabbing a stack. Does not do a wide open grab like yours but it did the trick. (I have much better photos if you want this) (Our kids went from reusing this design to a feeder after seeing 3057 beat eveyone so deftly in January at Haverford)

IMG_8084

On the programming side, you could put a pot on the claw gear axle, and back off the motor power as long as the claw stays closed.

The position for “fully closed” is relatively small, so there are some clever mechanical engineering solutions available also. The difficulty is in refining them to be simple enough to be built, yet capable enough to function well.
Your two clamp sides are linked with gears, (at top, you might try linking with gears at bottom also) so you only need to power one side.
If you powered one side with a rubbery linkage instead of gear, then you could design the linkage so that the “closed” position was slightly over center, so that no motor power would be required to hold it closed.
https://vexforum.com/gallery/files/1/5/6/8/overcentered_clamp.jpg
Dashed lines show open position of clamp and linkage, it will still need a potentiometer to provide feedback for the position of the clamp, or maybe just a physical stop and limit switch at the closed position will work.
Small green circles are the claw gears.
The thin line shows the “overcenter” position of the closed claw.
The solid and dashed box is the link between the driving gear and the claw.
The larger green circle is the driving gear, which likely needs to be driven by a small gear on a motor, but maybe not.
The thin dotted large black circle is centered on the left clamp gear center, and shows the travel path of the linkage pivot that is on the clamp.
This linkage is a type of 4-bar.

just add another button that closes claw at like 1/5 power to hold it in but now stall motor

are you holding your button down when you have the claw closed? This will continuously run the motors and make them stall.

Like some posters have already said, you will definitely stall your motors if you operate your claw incorrectly. Although you have to apply pressure to an object in the closed position to keep it in the claw while lifting your arm, you definitely do not need full motor power to accomplish this.

If you have your claw operation on the buttons of your joystick, you can try to program in holding the claw closed at 20% of max power after releasing the button that closes the claw. If you have your claw operation on the sticks of your joysticks, you can hold the stick at non-max range so that the claw is only provided with a small amount of the max power of the motor to hold the object.

Thanks to everyone who helped! We’ve fixed the problem and only applied a small amount of power after the claw has closed, and we also now have a 3:1 gear ratio on the claw. The claw doesn’t burn out, and it keeps the elements in. Thanks again! :smiley:

Thanks for following up with a “solution worked” thread cap post.