[Kevin Sevcik]

To bring a little more "training" to the discussion... you just have to look at the maximum power of your motors to determine the absolute fastest you can get a robot up.

Power = Work / Time
Work = Force * Distance
so
Power = Force * Distance / Time
or
Power = Force * Speeeeeeeed

The CIM motors max out at 343W = 252 lbf*ft/s

So the fastest an optimally geared CIM will lift a bot is about 1.5 ft/s. Or you lift in about a second.

Mind, this assume you're instantly at the max power point, no friction losses, spherical chickens, the works. But, lifting your robot 20" in, say, 5 seconds is easily doable if you gear it right. The gearing it right being key. Max power occurs at 1/2 stall torque. But I'd really aim for 1/4 - 1/3 stall torque for your full load, for safety and losses and all that.