Crazy drivetrain idea

[Tristan Lall]

The rotary actuators from last year were the Bimba PT-017090, which have a torque rating of 10.2 inch pounds at 60 psi. (See here, page 3, for calculations.) By contrast, the CIM motor is rated at 21.8 inch pounds, at stall (or half of that at maximum power).

The trouble is, neither of those represents enough torque to drive the robot. Of course, we trade speed for torque by gearing the CIMs down so that one rotation of the motor causes only a fraction of a rotation of the wheel—but if we do the same to the rotary actuator, its 90° travel will become problematic! That is, 90° at the rotary actuator might easily become less than 10° at the wheels, depending on how much gearing is necessary to multiply the torque so that you output a useful amount. So you have a useful boost in torque over a very small distance. Depending on the speed of this rotation, you'll very likely end up with much less than 3 seconds of boost; probably more like 0.3.

If you wanted to leave the rotary actuator as-is, and not gear it, that might work, but the additional torque would be negligible, compared to what it takes to drive the robot. You would, however, retain the 90° travel.

You also have the added problem of disengaging the rotary actuator before the motors drive it into the hard stops, destroying the rack and/or pinion.

There's one (worthless) bonus to this: you'll have lots of air left in the tanks, because the actuator itself is rather small.

So, in general, I'm with Cory et. al; give a 2- or 3-speed a shot, with four to six motors, if you're absolutely set on building a defensive robot. Theoretically, Blizzard 5 (Woburn's 2004 six-motor, 2-speed robot) would have broken the wheels loose at 22% power in low gear, or 95% power in high gear, while pushing a nearly-immovable object at its limit of traction; this sort of performance should meet your needs. On the other hand, consider not limiting yourselves to defence—maybe the start of the 2006 season would be a better time to decide on a strategy.