How to hold a load

[Bradleyowens9]

So for a senior project our class is designing and building a R/C bomb disposal robot. From our statics we have found our 10lb load to need a torque of 33ft-lb to lift it. What we need to figure out is how that load will be held after we stop powering the 18v motor attached to the arm when it reaches the proper height. As far as I know, the instant we release the control stick on the R/C the arm will lower because of the 10lb load. Any ideas??  P.S. We are almost done Inventor drawing so this needs to be handled STAT if it will require a mechanical fix. Thank you.

[rbtying]

At first glance, I'd suggest a worm gear setup - it requires no motor power to stay in one place.  You could also implement a position PID controller for the motor, although this will draw lots of power (not necessarily a good thing).

A way you could reduce the force would be to use a constant-force spring to reduce the load (acting in the opposite direction on the arm).  This allows your arm to be, relative to the motor, a tiny fraction of its weight, and easy to keep in position. 

[Cyntrox]

You could apply partial power to the motor, using pulse width modulation (PWM). You would have to work out how much power to apply, though.

[Bradleyowens9]

Thank you both very much. I will ask the others tomorrow. Great ideas!

[TrickyNekro]

I really support the worm gear setup... But keep in mind that feedback will still be needed for position control.

[Soeren]

Hi,

As much as I second (or "thirth"?) a worm drive...
If the joy stick arm is spring loaded and return, so should the arm it controls, no matter the mechanical implementation, so the stick has to be changed a bit.