jk1,
While I've not disassembled the entire unit yet, the secondary cover is hiding metallic alloy outer ring gear and of all things decent lithium grease in there too.
To get the whole thing apart requires a traditional 4 pawl freewheel removal tool but the hole (the through hole) needs to be large enough in diameter to fit over the tapered axle shaft to reach the 4 square pawls. This needs to be used on the non motor side to remove the retaining nut holding the axle in place.
Once that part is removed, a set of allen wrenches will complete the dissassembly.
I've come up with some rated specs at 48.13v and it looks like most efficiency is at 82.6% with 37.1 N.m. or 27.36 ft lbs torque and 10.37 A for 413w output power. The maximum power spec is: 638w @ 48.13 (minus voltage drop), 16.88 A draw, loaded RPM of 88.6 and torque of 68.7 N.m. / 50.60 ft lbs torque.
What surprised me of this design (and no I have yet to install it, taking a ride to the bike shop today to see if they can provide me the spawl wrench or freewheel removal tool to open the bafang BPM drive.
Now depending on headwinds, level of ground, etc - my math shows normal 48t -> 11 final ratio providing up to 22.598 MPH on a 20" bike
In comparison on a 26" bike the theoretical limit would be: 29.3774 mph
So without limiting of speed (actively) this setup seems just mildly enemic as 638w is not enough to get above 25 on a 26" without some real input from the rider.
My thoughts on this are 2 fold - the mount system should be able to shed heat due to it's mounting method I think this motor could be power increased by about 50% minimum safely - my plan stage #1 is to open the drive, plum in a few more wires (out really) so that my new drive has both the Bafang standard DC connection but also 3 Phase Output at minimum 12G and the hall sensor loom.
While I have it open on the bench I will spec the controller internally, still working to get the flashing software / parameter designer from Bafang so I can program the cutouts in this onboard controller but....
If I can increase current by 1/3 maximum and nominal it would produce 638w at 16.88 A and 48.13v by adding a shunt and increase the maximum to perhaps 22.45A as main battery maximum current for a total at 48v of 1082.925 watts and 68.15 ft lbs of torque.
Final step would be to increase the voltage... presuming that I can retain the 82% efficiency rate claimed, going from 48.13 to 55.5 (15S) nominal then we can recalculate top speeds too: 55.5 * 22.45 = 1245.975 watts * .82 = 1021w useable power and the need to dissipate 1245.975 - 1021 = 224 watts of heat power.
In stock configuration at max power output the losses are on the order of 114w, with the upgraded voltage and current the total increases to 224 watts of heat produced.
Then I realized if the controller is built in (it is) then we can eliminate some weight removing it and if we remove it some of the thermal losses will be dissipated externally to an external controller... this is just theory now - anyone with ideas on the proper tool to remove the crank shaft or on suggestions for modifying this unit.
The other benefit to going to 55.5v would be higher top speed: 55.5 * 2.3297 = 106.0247 RPM @ crank (I think) instead of the 88 RPM at crank maximum - this translates on the above 20 and 26" to be respectively: 27 and 35 mph respectively.
Please weigh in on this at your convenience
-Mike