[Mike Betts]

Originally Posted by Charlie675

Our team has an arm driven by two cim motors. The motors are obviously strong enough because the arm can fly up in a fraction of a second (no one dead yet!). but we need to hold the arm in a constant position to score. when the motors are set to a value that holds them in a specific place, they work for a few seconds and then the arm suddenly drops. I assume this is because the motors aren't meant to apply torque without moving but I don't know. what should we do? would pulsing the motors help? if so why and what is the best curve to give the speed controllers?
Thanks for the help. our whole design is based on this working!

Charlie,

Let's look at this from a control-ability standpoint. In order to achieve precise arm positioning for the human driver, you want a rotational speed of about 45 degrees per second. This gives you a gear ratio of about 350:1 at the peak power point.

At that gear ratio, you get over 600 ft*lbf of torque at the shoulder and at the peak power point. Neglecting the weight of the arm, you could lift about 125 lbs at a distance of 5 feet!

In my opinion, you are trying to hang a picture with a sledge hammer.

Regards,

Mike