How To Calc Torque w/Rack


#1

Hi All - I’m helping a team with calculating torque of their mechanisms. While levers, gear ratios etc are easy enough I’m clueless on calculating the ‘lifting torque’ of their vertical rack.

We are using V2 rack with a 12T gear - can I simple use the (mean) diameter of the gear (teeth) to estimate torque?


#2

I think that is correct, the lever in effect here is just the radius of the 12t pinion.


#3

The calculation for torque is (number of motors*14.76)/radius of gear 12t gears are about 0.5 inch radius.


#4

Thanks! 14.76 being in/lb of stock motor correct?

Seeing the mechanism is lifting (vertically) an arm would we simply take the over-all weight of the assy or consider the moment of arm when it’s horizontal? (confusing myself here)


#5

Yes it is. With stock gearing.

If it’s lifting vertically then I would just use the total weight it is lifting. Also remember to factor in friction (Quite high with linear slide lifts) and also remember 14.76 lb/in is the maximum stall torque of each motor. Repeatedly stressing the motor(s) that much will cause them to cut out.


#6

Yes, if you want the motor to be lifting at any decent speed, I would presume the motor can output no more than about 6 to 8 inch-pounds. Stalling a motor (in other words, the motor is powered but not moving) will over heat it unless you keep its RobotC value at no more than about 10-20 (a value that varies from motor to motor). You can sometimes assist a motor or spread out its load somewhat with rubber bands but don’t allow it to stall for more than a few seconds.


#7

Thanks all for Good advice!