I do like the idea of an easily removable drive. The bolted joint give me pause though, we pull on the chain pretty hard. What about the half of the mounting plate that would still be on the bike? I'd like it not to be there enough to pull the BB to remove the whole thing, but what do you guys think? Are there enough times you'd like to be able to unbolt the motor, even if it left mounting hardware on the frame?
Update on new design: These are entirely new parts, a complete redesign. In the pics is the housing for a 3220- this will be available to anybody with a 3220 or 3210 (the upgrade path). New units will have the stator bonded directly to the housing/heat sink.
This is machined from solid, it starts out life as a 3.6kg piece of billet and becomes our sub 400g drive unit housing. This contains all but the last 10mm of the 3220 (where the end cap screws stick out the sides and the phase wires exit). The o-rings in the second pic retain 10mL of heat transfer fluid (water) to make up for not clamping the heat sink to the source. The cavity holds about 13mL so there is room for the water to slosh a bit; it's filled through a tapped hole in the side.
The gearbox is sealed from the motor at the motor shaft and sealed flathead screws. The outside of the gearbox is sealed against the output shaft with a commercially available rotary rubber seal by SKF. Another o-ring rides in a groove around the output cover, sealing the outer diameter.
We'll still thread on left handed freewheels, they seem to be working fine. The motor chain is moving to the outer position, the derailleur chainring should be in a better position now for more frames. The 6kW kit uses a 16t motor freewheel to a 24t sprocket at the BB, 3kW will use the same gearbox with probably a 14/32 chain reduction.
Changes to the internals of the gearbox as well. We're using an even larger output bearing to accommodate a more advantageous positioning of the output pins. The eccentricity has been increased to move the tooth contact we're concerned with to the root of the teeth. A machined ring gear is used instead of pins- it's 30% lighter and requires less volume since the pins would need parts to secure them. The cuts remove weight and allow lube to circulate and lower pressures at high RPM. The eccentric gears and ring gear are machined from 4140 chromoly steel. The shape of the cycloidal profile has been chosen for strength, contact angle and lube retention. Machining tolerances have been optimized, this is the first copy of the production ready unit made using the production setups.
Testing and such to follow asap, things should speed up now that the design and setups are about finished. Still need to assemble the test equipment (big ass fan) and torture both oil and grease filled units. I like oil, but we'll see. There's not enough inside the gearbox to be able to drain it effectively, but maybe a regular rinsing with fresh oil could do the same.
-dave