I want to put a hub motor on an old dirtjumper and generally just mess around local spots. I am more focused on getting up hills and having some zip, rather than holding a solid top speed for miles.
How much can this little 3.55kg 52v 500W geared hub motor from leaf take? Can I run a 72v battery, controller and statoraid to get a little more juice?
Geared hubs are limited by a few things:
--clutch, if they are internally freewheeling (most are). Shock loads are bad for them, and torque exceeding their design limits can slip it or just plain break it. You can lock the clutch by welding it, but then you have a higher drag on the wheel when unpowered.
--plastic of the gears (warm them up and it softens, then shears them off. Shock loads can break them too. You can use metal planetary gears instead (if you can find them or make them) but they will wear the axle (sun) gear and the shell (ring) gear faster, and will be a lot noisier.
--they are multiple thermal layers, so things like statoraid only help for a momentary instantaneous peak power--the heat will be pulled out of the stator into the magnets and rotor, but then it has another airgap and the external motor shell to get thru. Oil cooling might help, but it's messy and will almost certainly be able to get out thru the axle bearings, so you'll have to add some way to top it off.
But a geared hub will have (for the same size motor, controller, and battery) greater torque at lower wheel speeds than a DD hub because it will spin faster (same reason a middrive can usually be smaller for same power). A DD hub will need higher current to do that, so the battery and controller have to be better (which usually means bigger).
If you go to the ebikes.ca motor simulator, you can play around with different systems under your specific riding conditions and see what it will take to do what you want, power-wise, without melting the motor, etc.
Should I just pony up and get the 4kg hub motor from GRIN?
Which specific motor are you looking at?
The GMAC (grin geared hub that can do 1000w easily enough, and peaks of double that, IIRC) might work, but I'll warn you now that it is VERY noisy in smaller wheels. At lower motor RPMs its' not so bad, but you get that thing up to 250-300RPM+ under load and it's like a kitchen blender. The one I have in a 20" wheel on the SB Cruiser trike is great for it's power vs size, but damn it's more than annoyingly loud even at just 15mph, and 20mph that I cruise at is...well, I took it off the trike yesterday to put a silent DD hub back on there. :/ (not just because of the noise, but that's a big reason).
I like the idea of having the bike drivetrain separate from the motor, but want the lightest rear hub I can get away with. I am planning on building into a 24" rim.
To truly have the pedal drivetrain separate from the motor, you'd have to use FWD for the motor. Otherwise they both go thru the same wheel. FWD is probably not the best choice for hills and loose-dirt terrain; there's conditions that can cause loss of control due to loss of traction.
RWD means your pedal forces are going to go thru the motor shell, and not all of them are very strong--people have broken the cassette or freewheel threads right out of the cover. It's less of a problem with cassettes that have an outer axle bearing, but still happens. I had a Fusin geared hub's cassette bearings just plain disintegrate and grind up the insides of the freehub, and they weren't even being loaded. (should be pics in the review thread, if you're curious).
www.leafbike.com
