My GNG setup bit the dust back in July and I have been wanting to go off-roading again so I am building another off-roader.
For this build I am going to blow about $500.
Bafang BPM from evassemble.com $122
"Force" brand 48t crank from ebay.com $12
donor bicycle from thrift store to chop tail off of and put motor in dropouts $5
muffler clamps to attach donor bicycle dropouts to bicycle $10
velo-solo gear from ebay.com $25
Gravity FSX from bikesdirect.com $329
My trusty Lyen 12 fet sensorless.
Misty Glamour Fun bicycle riders best look away now!
My original plan of having the dropouts like this fell through
and I ended up building them like this because the dropouts were blocking the chain. This is just a girl's bicyle dropout welded to a muffler clamp base; nothing too special
I built the battery bay out of roof flashing bent into a square.
Update 11/23: Bike was working great until the rear derailer came apart. I was just cruising along down a smooth road and heard a big kerchunk. I hit the brakes and watched a gear from the rear derailer roll past. Not sure what happened, it appears that it just wanted to come apart for some reason.
Update 1/16/14: Got her going again, still not sure why the old derailer decided to come apart, but new derailer is holding fine.
Update 2/12: I have been experimenting with a rear rack for the batteries setup and I think I am liking this better than batteries up front; the front suspension doesn't mash in as hard on the jumps. I think batteries up front was ok for my GNG kit because the motor is so light, but the extra weight of my hub setup makes this less viable.
Update 5/19: I decided that now that I have a Mobius it would be neat to do a video on my new setup for the off-roader V2. I put the batteries behind the seat instead of up front, and reduced down to 10ah instead of my usual 20ah. I am glad to report that I still am able to get my standard couple of hours of riding in with just 10 aH on board. The lighter weight yields improved maneuverability and all around a better ride and it's nice that it makes it easier to pop wheelies and trials bike bounce your way over stuff but unfortunately it makes it pop wheelies when you are climbing steep grades too. My tack welds on my battery mount (unsurprisingly) didn't last after much riding and broke on me. Fortunately I was able to bungee cord everything back together and get a good ride in.
I am also pleased to report that mid-hub has been a better setup for me than chain modded GNG kit. GNG was better than hub because of it's lighter weight and because it took less effort to just strap the sucker to my bike than having to fabricate a mid hub mount but worse than mid-hub in almost every other way. Both systems have an issue where if you run too much power down them, the chain skips on the sprocket and grinds so you are limited to only about 1500ish watts (input) or so. My biggest gripe with GNG was the noise levels; in an attempt to avoid confrontation I would find myself staying off throttle when around hikers and other trail users, certainly I could just blast by but it was noisy enough it was hard to do that without feeling like a total dick. Mid-hub allows a much appreciated access to all 24 gears opposed to GNG's configuration that only allows only 8 of your gears to be used. Perhaps it was just my build, but I had a tougher time of keeping the reduction chains on the GNG from de-railing typically leading to a bit of cussing every now and then opposed to mid-drive which has had no de-railing issues at all. The wider range of speeds, the reduced noise, and the increased reliability make me believe a mid-hub is a superior system to rc drives and GNG style setups at the expense of weight and ease of initial setup.