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Originally Posted by EricH
I don't remember exactly on the PWM front, but I remember hearing something about the Jaguars/Victors using a slightly different PWM than say a servo/ESC. I think it's PWM vs PMM, but can't for the life of me remember exactly which is which.
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You can just call it a Servo in code and be done.
The only thing that is different is the width of the PWM pulse. Servos use a pulse between 0.5 and 2.5ms, Victors use 1ms to 2ms, both have neutral or center at 1.5ms.
In LabVIEW (I assume C/Java are similar), the Motor cluster type includes a definition of each of the pulse positions for scaling, adding additional motor controllers that fit between a Victor and Servo are quite easy.
Quote:
Originally Posted by EricH
Palardy, there's a minor difference between the max power being regulated electrically and in the motors. The electrical max power is driven by the current limits (and subject to the breakers actually tripping when they're supposed to, and as we all know they can handle short overcurrents)--the motor max available power is driven by the motor characteristics. If I can use 20 BaneBots without tripping a breaker, and you can only use 4 CIMs and 2 FPs, but you need 5 BaneBots on top of that that you can't use without the breaker tripping, I have a higher max available power and somehow worked in a way to use more of the electrical max power. Unless, of course, I used very weak BB motors...
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In any case, the mechanical power available is a factor of electrical power and motor efficiency. Any brushed motor significantly larger than a CIM used in a FRC drivetrain will likely trip the breaker - There are many teams who underpower their drivetrains and already trip the 40a breakers.
In addition, the 120a main breaker and battery limit the total available power of the machine. Drawing too much instantaneous current will lower the battery voltage due to battery resistance, and too much sustained current will trip the 120a main breaker. It's also possible to melt the 50a battery connector. I have personally driven a robot to do both in a competition match (although the battery connector was in the off-season).
Also, every motor, speed controller, gearing, and wire is weight. Weight (and often time) is the most precious thing on a FIRST robot.
Quote:
Originally Posted by EricH
Oh, right: How it's necessary that a part be in the KOP. Teams were supposed to go buy a Kinect last year? That was also a new and readily-available technology.  In all seriousness, it's not, but I'm willing to bet that the economics of scale are better for 2000 than for 20. Motor technology is one of those things where it's better to introduce it in the KOP--then teams will have a better collective knowledge on how to handle it, and where to buy it. |
I don't think it's a requirement to put the part in the KOP if it's commonly available. If FIRST were to allow certain types of motors (e.g. all 5xx-sized brushed motors), there would be many places to get them from (e.g. many cordless tools use 550/540 sized motors, you can get them at home depot if you want). The only exception is the control system - Since the FRC control system must be used as is, the base control system should be included (ideally every year).