Gearing That Cannot Overcome Static Friction

[KenWittlief]

we dont know what the game will be this year, but high speed may not be what you need.

Remember a few years back, teams pulling two mobile goal platforms around with one robot - geared down to speeds like 6 inches per second, and lifting the goals in the air to get extra traction? Maybe thats what they are thinking - several gears to get very low speeds with super pushing power, and everything in between up to a normal 10 or 12 F/S?

Making a transmission that shifts quickly is part of the challenge.

One other thing Ive noticed - Ive yet to see a FIRST transmission that has a clutch, like a car does. Im sure they didnt have torque converters either, so how they get away with shifting under power, with no clutch, is beyond me!

I can do it with my car, by matching the engine rpms while I upshift - but that has taken years of practice to accomplish without mashing the gears.

[Andrew Blair]

Originally Posted by KenWittlief

we dont know what the game will be this year, but high speed may not be what you need.

Remember a few years back, teams pulling two mobile goal platforms around with one robot - geared down to speeds like 6 inches per second, and lifting the goals in the air to get extra traction? Maybe thats what they are thinking - several gears to get very low speeds with super pushing power, and everything in between up to a normal 10 or 12 F/S?

Making a transmission that shifts quickly is part of the challenge.

One other thing Ive noticed - Ive yet to see a FIRST transmission that has a clutch, like a car does. Im sure they didnt have torque converters either, so how they get away with shifting under power, with no clutch, is beyond me!

I can do it with my car, by matching the engine rpms while I upshift - but that has taken years of practice to accomplish without mashing the gears.

Actually Ken, CIA had a clutched transmission a few years back. There was a double sided rubber disk that acted as a clutch, and it engaged one of two transmission stages. It was very smooth. No grindy noises at all.

As far as 40 ft/sec goes, I would say it could only realistically be used on a field like this past years: flat and open. But it would be wild to watch.

As far as keeping it out of neutral, perhaps a sacrifice to a finer tooth gear? you could more easily aquire .25" wide gears, and 222's ball shifter could be used effectively. especially if it was activated by a motor & lead screw, or other fast actuator. Perhaps you could even use helical? With respect to gearboxes we've had in the past, even though they were built badly, with awful tolerances and extreme loads, Boston Gear 1/4", I think 24 or 28 DP helical's stood up wonderfully.

An 1/8" or 3/16" ball could travel 1/4" quite quickly, and if you put some sort of lateral spring allowance into the shifter, the balls would *pop* between gears.

[Dick Linn]

Originally Posted by KenWittlief

... HP is a function of torque and RPM -Im not sure off the top of my head where the max HP point is on the curve...

Max power is right at half the maximum RPM on these DC motors. Power is Torque x RPM. In the attached picture, power is "inside the box" if you will. At any other point on the chart, the resulting box will be rectangular and thus have less area (less power). Maximum efficiency is at somewhat higher RPM. Ideally, you want to have the motor working at somewhere between 20% to 50% of maximum torque to keep the motor happy.

[Ken, are you still using globe motors soaked in liquid hydrogen? ]