Answered: 393 Motors spin when not engaged

VEX V5 Technical Support OFFICIAL Tech Support
1

Not sure if I worded that properly . . .

I have designed a robotic arm. I have a gear system that give me a lot of torque for the elbow joint. However, when the forearm is extended, and no signal is sent to the motor, the forearm just slowly swings down perpendicular to the floor. I can hear it turning the interal gears in the motor.

I engage the motor, and it moves the elbow just as it should, in both directions. But when I take my fingers off the buttons, the arm falls down to the perpendiular positon.

This is with no add’l weight in the gripper. It is only holding the weight of the hand.

is this normal behavior for the 393? It does not occur when I use the 269 motors.

Thanks!

Todd

2

Todd,

It sounds like the weight of your arms pulls down your robot, and makes your motor backdrive itself. Try incorporating a VEX Potentiometer in the robot, that way every time the sensor detects unwanted movement from the arm it will stop it by energizing the motor.
The reason why this doesn’t happen with the smaller motors is because the gears are different in size.