Quote:
Originally Posted by 2829ron
We built our arm with the CIM and toughbox and were having problems getting it past about vertical.
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Let's say 90 degrees per second is the approximate arm speed you'd like at full motor voltage (speeds faster than this can be difficult to control, slower speeds may make you uncompetitive)
Let's say you've got the equivalent of 5 pounds at 6 feet from the pivot, or 30 foot-pounds of torque.
From these two numbers you can calculate the required mechanical power in watts:
90 degrees per second = 15 rpm
(15 rpm)*(30 ft-lb)/7.043 = 63.9 watts
Now using the motor curves, or
this simple calculator, you can find that the CIM motor speed which generates 63.9 watts at 12 volts input is 5045 rpm. Since 5045 is 95% of the CIM's free speed, it should run cool at this operating point.
Take the ratio of the motor rpm to the arm rpm to get the required gear ratio:
5045/15 = 336:1 gear ratio.
If you use a gear ratio much less than this, you will either get an arm which moves so fast that it is uncontrollable, or you will have to operate the motor far outside its design point which can cause overheating. The CIM is can tolerate a lot of abuse but it is not immune to burn-out.