Utility Cycling Technology: Motorized Retro Direct Drive

Two motors and Two gear speed gear box?

A heavy human powered vehicle (HPV) that can drive 450lbs total combined weight up the steep hills in Vancouver will need at least two gears to climb the steep hills with a legal wattage. Read more: cycle tractor.

With 7500 rpm output for maximum momentum efficiency using a high voltage motor, you will need a lot more gear reduction (like 13:1 total) to keep it down to about 11-13mph [17-21kmh] on a 9% to 10% grade but even that would be quite a fast gear with Canadian legal power.

So two motors would be needed. Making the vehicle illegal only when you need to turn on the second motor. But it will still not be able to drive faster than the speed limit if the gears are low enough. About 16mph [26kmh] on flat land.

A retro-direct drive is a fast (high gear) in the forward direction and a slow (low gear) in the reverse.

Making a switch to reverse the motor: (see the middle of page 5): Epicyclic retro-direct 2 speed transmission.

There’s a problem with the design of planetary gears – there is inherent backlash and play between the gears. There can be problems with binding or jamming. It would be better if the prototype was made without planetary gears.

A hypocycloid gear could be a better way of gearing down but without tight fitting gears you can have the same problem. A harmonic drive would be much better if you could design one to do this retro-direct switching.

Some thoughts on two speed transmissions: