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Motor Restrictions
Perhaps this has been asked multiple times, but as I just started helping out my old high school's FRC team this year as a mentor I've come up with a bit of a question. Our team is looking at a very simple solution to a problem, but we're potentially being hamstrung by the infamous motor legality issue. We're looking at an actuator with an included motor that would be exactly what we need, but due to the rules we may not be able to use it and might have to essentially build our own actuator, which only adds time and complexity to our already fairly new team.
All that said, my basic question is what is the purpose behind limiting what motors teams can use? They are already limited by the overall price restriction ($400 max), power draw (PDB has 40 amp max on a single channel), and voltage (12V limit for motors), which effectively limits high power motors fairly effectively. I can understand limiting the number of higher power motors as is currently done with CIMs, but this rule could be rewritten to state "only X number of motors over Y watts" or something like that.
Restricting small motors is what seems so odd. I've taken apart a printer and found several small motors that could be useful for things, but can't use them because they aren't automotive (per 2015 rules at least). I can use a large number of powerful automotive motors all over the robot, but not one smaller, less powerful one just because it hasn't been used in an automotive application? Similarly, if I want to tailor motor selection based on rpm and torque I'm limited to trying to find a gearbox that will interface with one of the approved motors as opposed to just sourcing a motor that does what I want to start with. Along those lines, a lot of the approved motors don't have output shafts that are easy to deal with. Trying to use a tiny 1/8" round output shaft to drive anything larger is difficult. I almost need to grind a flat onto the shaft to make it D shaped so I have anything I can key into.
I understand that this late in the game I don't expect the motor rules to magically change and get more open, but I'd like to encourage those who write the rules to consider loosening the restrictions for future years. Instead of our team determining how to mount and use the components we want, we're spending time trying to figure out if they're legal to begin with or could be made legal. We're hesitant to buy anything with our limited budget since there's a chance we could get turned away at tech. Instead of letting the kids branch out and try new options, they're stuck reading the rules to see if they can use any of their ideas. That's not what FIRST is about. FIRST is about letting kids turn their imaginations into real physical form. Instead of part number limitations I'd encourage the rule writers to limit motors by output or other specs, similar to what is done with solenoids (max watts, limited stroke, etc.). Maybe have an RPM and torque cap for motors at 12V and 40A, or some curve that relates the two (ex. a 200 rpm motor can have more torque than a 10,000 rpm motor, some kind of inverse relationship between the two). Admittedly, testing and verification of the motors would be the next challenge, but perhaps this could be solved by requiring teams to have a data sheet for each motor they use submitted at the time of tech.
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