Robot gripper unscrews itself when reaching fully open state

#1

Hi,

I assembled my robot gripper (the newer version), and not only it is a little buggy (it locks itself very often, meaning it won’t either open or close and will do “clicking” sounds like it’s trying but something’s blocking it), but it also will very often unscrew itself in the middle; both the ring and nut get thrown away and therefore the motor continues spinning continuously.

If I adjust the nut to be very tight, then it becomes buggy (blocks itself randomly), however I’m not sure this is 100% a fault on the gripper (since resetting arduino seems to solve the problem, which leads me to think it’s not hardware related)

I’m applying 9,6V out of 8 AA 1,2 recheargeable batteries. Same result if I apply 12V from a DC adapter.

Finally, this won’t happen when applying 5V, but it is too slow to be an usable speed.

Any clues / suggestions ?

Thanks

#2

Have you tried loosening (just a 1/4 turn or so) all the bolts that hold the gripper together? If you tighten those too much it can add too much friction to the movement. Then when the gripper is all the way closed or all the open, the motor may not be able to move the arms. The “clicking” almost sounds like the drive bolt is slipping on the threads of the 4-way threaded connector arm. When that happens, is the drive bolt (connected to the motor) turning and the 4-way connector arm not moving?

By the way, you’ve got to put the nylon lock nut (and washer and o-ring) on the drive bolt tight enough to stop the motor when the 4-way connector gets to the end of the bolt.

#3