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Originally Posted by artdutra04
Thus, by having more motors in a drivetrain, they will increase the odds that the motors will be able to overcome the maximum static friction with the ground and start spinning their wheels, thus lowering their ability to push other robots.
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Doesn't that depend on whether the driver is blindly giving it full throttle (spinning the wheels), or modulating the output in proportion to what the robot is doing? (Or better; the cRIO is handling this for him.) And in the case where a robot is geared rather high, and therefore is using a high power setting to push as hard as it can, by having more motors, the load will be distributed among them. Although the output force is limited by traction, with more motors, each will each be operating at a more desirable point on the efficiency curve; that gives the robot more endurance.
So there's a trade: is the added complexity, weight and opportunity cost (in terms of not having those motors on another mechanism) worth it? In drivetrain-heavy games where robots are operating at high power most of the time, my sense is that this is often a good decision.
Quote:
Originally Posted by artdutra04
Now even if they can overcome the traction limitations, they still have to deal with the relatively small field size. How likely is it that robots will have the room to accelerate to speeds beyond the top speeds of 15-16 ft/sec already seen on many FRC robots? Why do you think teams don't currently use three or four speed gearboxes that can theoretically take their robot to 20, 25, or 30 ft/sec? It's because the field is small enough such that gearing for that speed would never be useful.
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Though I don't know how often this figures into teams' design decisions, I'd say that the current state of the art with FRC transmissions is such that none can shift fast enough to make more than two speeds really valuable. Though that's far from an absolute rule, I haven't seen any 3+ transmissions that can shift fast enough to make the unpowered time between shifts worth it for accelerating a robot. Even many two speeds are (counterintuitively) sacrificing acceleration for endurance (because the ratios in each gear mean less total power consumption, due to motors operating at more efficient points).
For example, a servo-shifted Super Shifter with default configuration, mounted in place of the Toughboxes on a 2010 kitbot probably should just stay in high gear most of the time: there's no point waiting a half-second for the shift to happen.
So, returning to the constraint of limited field size, and recalling the previous discussion about motors, I'd say the most practical way to achieve really high speed (in the current FRC game) is lots of motors and a high gear ratio.