I electrified a Bike Friday NWT (folding 20" wheel bike) with a Bafang G311 Fast Wind kit and a 52 V em3ev battery. I used what I thought were conservative settings (20 mph speed limit and 36 Nm torque limit). But after 4 months and 500 miles it failed: loose magnets and one was rusty (thanks @amberwolf for helping me diagnose!). See attachment, rust on the magnet at 12 o'clock. This is very surprising for two reasons:
1) Grin says they use an adhesive that should not fail, at least not at the temperatures that the Baserunner allows before thermal limiting (110-130 C)
2) No clue where the rust came from. No water visible when I opened the motor. I rode ~50 miles on some slushy and salty roads back in winter. Have fenders. Storage is under cover but outdoors.
Major challenge to diagnosing is that I didn't really monitor motor temps before magnets came loose. All I know is that baserunner came with a 130 C thermal limit. Here is simulator output from a hill I climb regularly:
This is on a 30 C day with 20 kg in saddle bags (i.e. worst case scenario for me). Not bad right? It ends at my destination so motor cools off after. Whole trip is 6 min so its over 100 C for just 2 minutes. This is with 100 W of human power and it's totally possible that I got heavy on the throttle and lazy on the legs (that's a solvable problem though! will get a torque sensor, see below).
So now I have two options: A) get the G311 fixed under warranty for free or B) upgrade. My question is am I asking for trouble sticking with it?
Reasons to stick with the G311:
TL;DR: was the G311 failure was a fluke? Or are these motors doomed in hilly conditions? What is a safe thermal limit for them to last a long time? What could have caused that rust? Am I crazy to try again?
1) Grin says they use an adhesive that should not fail, at least not at the temperatures that the Baserunner allows before thermal limiting (110-130 C)
2) No clue where the rust came from. No water visible when I opened the motor. I rode ~50 miles on some slushy and salty roads back in winter. Have fenders. Storage is under cover but outdoors.
Major challenge to diagnosing is that I didn't really monitor motor temps before magnets came loose. All I know is that baserunner came with a 130 C thermal limit. Here is simulator output from a hill I climb regularly:
This is on a 30 C day with 20 kg in saddle bags (i.e. worst case scenario for me). Not bad right? It ends at my destination so motor cools off after. Whole trip is 6 min so its over 100 C for just 2 minutes. This is with 100 W of human power and it's totally possible that I got heavy on the throttle and lazy on the legs (that's a solvable problem though! will get a torque sensor, see below).
So now I have two options: A) get the G311 fixed under warranty for free or B) upgrade. My question is am I asking for trouble sticking with it?
Reasons to stick with the G311:
- Free
- Maybe first one had defective adhesive and I'll be fine just running as I was
- Maybe I ran it too hard and could manage to keep the temps 10-20C lower by adding a torque sensor, pedaling a little harder up hills, lowering the thermal limit and just keeping an eye on things, I think I do this with little effect on my travel times.
- Get down to the bottom of this, in the name of science! I feel they shouldn't be selling this motor with those claims about the adhesive and those thermal limits if it's not reliable?
- It's the lightest option
- 3/8" axle allowed me to use a gravity-based anti-theft lock nut (Abus nutfix or Kryptonite wheelnutz). Believe it or not this is huge for me. If I can't do this I'll probably go with a rear hub so I can lock it with the frame (folding bike has no top tube so only place to lock frame is rear triangle)
- The performance was ample while it worked, I have little desire to go more than 20 mph, and happy to go less than that up hills and make up for it on the way down; I've been riding with no motor again for 2 weeks and it's fun! I like exercise, I am not expecting a motorcycle
- Higher likelihood of reliability (but how much higher, that's what I'm trying to figure), especially if I go with the ezee
- Potential to go significantly faster if I ever want to
- Trade my Z9 baserunner for an L10, which seems like it might be handy for a future project
TL;DR: was the G311 failure was a fluke? Or are these motors doomed in hilly conditions? What is a safe thermal limit for them to last a long time? What could have caused that rust? Am I crazy to try again?
