Quote:
Originally Posted by Jared Russell
Steering motors can be loaded in lots of unexpected ways. Trying to turn when your wheel is up against an obstacle or imperfection in the floor...when dynamics shift most of your normal force onto one or two wheels...on slopes...during intermittent bouncing contact with the floor...
Also, the 300-series motors have not been used nearly as often in FRC as the 500- and 700- series motors. There is less (not none, but less) collective community experience in knowing their limits and endurance under FRC loads. Spec sheets seldom tell the whole story (especially when you are talking about a fairly generic trade sized motor from China).
Given the severity of losing a steering motor, my personal inclination would be to accept the 1 lb penalty and look for opportunities to save weight elsewhere.
EDIT: Also, out of curiosity, what method did you use to calculate the load on each motor in a steering application?
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I used the JVN calc "rotary mechanism" tab. To calculate load I used
wheel width * 1/4 bot weight * CoF. In my case that was 0.75*37.5*1.3, or about 36lbs. Then I added a ~1.5x factor of safety and decided on 50lbs as a good estimate for loading.
Based on what I'm seeing here I guess I'll just suck it up and use a 500. Kind of unfortunate, but I'll take what I can get.
EDIT: Whoops, that calculation is wrong. The load on the wheel is equal to 150lbs/4 wheels * 1.3 CoF, or 48lbs. The lever arm is 1/2 the wheel width, or 3/8".