Since the one-way clutch in my Bafang BPM2 is frequently locking up (again), it’s time for a new motor. The Bafang served me well for >6,000km since its last repair (>10,000km in total) but regularly running a bit shy of 1kW at 35mph on my daily commute is obviously just a bit too much for that little oil cooled hub to take.
I’m still a bit undecided what kind of motor to choose next. A geared hub motor again (Bafang BPM, Mac/Puma), a direct drive hub (9Continent, Crystalyte HT/HS) or maybe Lightning Rods mid drive kit directly driving a chain ring at the rear wheel (via disc brake adapter).
A ‘normal’ mid drive kit (like the 750W Bafang BBS 02) isn’t on my list. I think the strain on chain drive and derailleur is a bit too much and I like to keep human power train and electric power train separated. Changing 4m of chain and 9-speed cassette on a regular basis isn’t something to look forward to either.
If getting a second Bafang BPM, or a slightly bigger Mac, I most likely have to swap and repair my hub motors every 5-6 month (4-5,000km). A new one-way clutch cost just 50 bucks, but that procedure will get annoying very soon.
An air-cooled 9Continent direct drive hub at 72V and 35-40A might be just the ticket. The ebike simulator predicts torque and top speed similar to my current setup. It’s the cheapest hub motor option and at 5.5kg weights only 2kg more than the Bafang BPM.
The bigger Crystalyte HT3525 hub probably has more headroom for thermal abuse, but at 7.5kg weights 2kg more than the 9C and twice as much as the BPM. The just as heavy but faster Crystalyte HS3540 is an other option, but I seriously doubt that enabling me to go above 45mph with my Sprint is a very sensible idea…
Since after nearly 21,000km I have to swap all chain drive components of the Sprint as well (new chain and chain rings, 9-speed freewheel, new derailleur, short 155mm cranks) I think I’ll get a cheap 9Continent 2807 hub for now, drill some holes in the side plates for air cooling and see how it goes.
In the mean time I will follow the developement of Lightning Rods mid drive kit. Maybe a modified version will be a more affordable, albeit less powerful, alternative to Matt Shumakers V4 drive system.
On the other hand, just using a cheap 100 bucks ‘Big Block’ rickshaw motor with a simple one stage chain drive might be an interesting option too (albeit a bit crude looking)…
…four days after this posting and one day after inquiring about a MXUS direct drive hub (9Continent clone) from elfKW.at in Austria, the gears in my BPM2 gave up on my way home. I haven’t opened the BPM2 yet but judging by the rumbling noise probably some teeth broke off the planetary gears. For now the smaller hod rodded SWXH is back on duty till the 9C arrives.