- Dec 21, 2007
- Ft Riley, NE Kansas
The actual drive sprocket will be a fixed 24T, I just put the 16T freewheel on to take the pic. Note the derailleur extension, because now, the stock chain is too short. I believe the MAC is the largest motor that will fit on a desirable downhill (DH) frame in this position (the Bafang-BPM is the same diameter, but slightly thinner). DH bikes are fairly strong, and they seem to consistently have the most room in this area behind the front wheel.
A while back, ES member crossbreak posted the idea that it might be possible to take a geared hub (like the popular MAC or Bafang-BPM http://endless-sphere.com/forums/viewtopic.php?f=28&t=51313), and make a modification to the internal parts so that instead of the motor-case spinning, the case would be stationary and the shaft would spin. http://endless-sphere.com/forums/viewtopic.php?f=28&t=45245. His experiments proved that this idea works, and soon there will be several bikes testing this type of system to identify its strengths and its issues.
There are several potential benefits to this, and I found it interesting enough that; I wanted to copy crossbreaks experiment myself, so...I acquired a MAC from green machine, and performed a tear-down and shaft-drive conversion. http://endless-sphere.com/forums/viewtopic.php?f=16&t=51310
waynebergman has already finished his, and he reports good performance. http://endless-sphere.com/forums/viewtopic.php?f=28&t=49467
Here, I have cut out the shape onto a 0.190" / 4.8mm thick aluminum plate with a jigsaw, and I am filing the edge smooth. Although the steel was water-jetted, the extra-thick aluminum caused MANY jigsaw blades to valiantly give their lives to finish the shape. I wanted to start out with a mount that was perhaps too strong, rather than needing to upgrade a mount that was a little too light. I also didn't mind the extra weight of aluminum, because the mount is now part of the heat-sink for the motor. Later, I can add holes (AJ?) in an interesting shape to lighten it if I can find the time.
The BB-mount plate was water-jet cut by Big Blue Saw (0.105" / 2.6mm thick steel http://endless-sphere.com/forums/viewtopic.php?f=11&t=48811), and here I am using it to ensure proper alignment when drilling the chain tension adjustment bolt slots. The bolt slots accept 8mm or 5/16 bolts. Four on each side should be quite strong.
I thought I might first try attaching the side-plate to the 6-hole disc brake mount. I chose this side-plate shape because I imagined that I might want to also attach a cover over the motor in the future. I may cut the future mounting-plate shape smaller if a motor-cover proves to be un-necessary.