Advice to help avoid destroying my geared motor

danielrlee

danielrlee

10 kW
Joined
Mar 29, 2013
Messages
506
Location
Wiltshire, UK
I have had a string of Bafang gear failures in recent weeks (see http://endless-sphere.com/forums/viewtopic.php?t=52478 for details) and I'm starting to think that the manner in which I ride has something to with it.

I own just one bike which I use both as a commuter on potholed London roads and as an off roader on the root heavy singletrack of Epping Forest, so it doesn't exactly see an easy time.

Can anyone offer any advice about when not to be laying down power in order to avoid unnecessary shock loading to the gearset in my motor?

Thanks
 
I think that a more likely explanation to your problem is due to sub-standard replacement gears. Just bcause they look the same, it doesn't mean that they're made of he same as the originals. I'm sure Bafang are now using a special high strength polymer with a lot og glass reinforcement, while as the replacements might be plain Delrin or something similar. My neighbour's been running a 250w SWX with 22 amps for two years now. We don't do any serious off-road, but we use plenty of unsurfaced cycle tracks through the woods etc. Your first set lasted for a fair while, and then the replacements failed almost immediately.

Did you check that your ring gear hasn't cracked?
 
d8veh said:
I think that a more likely explanation to your problem is due to sub-standard replacement gears. Just bcause they look the same, it doesn't mean that they're made of he same as the originals. I'm sure Bafang are now using a special high strength polymer with a lot og glass reinforcement, while as the replacements might be plain Delrin or something similar. My neighbour's been running a 250w SWX with 22 amps for two years now. We don't do any serious off-road, but we use plenty of unsurfaced cycle tracks through the woods etc. Your first set lasted for a fair while, and then the replacements failed almost immediately.

Did you check that your ring gear hasn't cracked?
Click to expand...
You know, that hadn't occurred to me, but it makes perfect sense as an explanation..... especially since I think I've done another gear today and I REALLY nursed the throttle on every road imperfection. I haven't opened the motor up yet, but I'm pretty certain since I'm hearing that familiar clicking sound. When I do, I'll be sure to check the ring gear too.

I bought my replacement gears from greenbikekit.com and I haven't read of any complaints about them before, but maybe I could have got a bad batch.

As it stands, I think there are two possible solutions to resolve this satisfactorily:

1) Source some metal gears and run either 1 metal and 2 nylon, or 3 metal.

2) Replace the geared motor with a direct drive unit.

Having refined my first build over the past year (you might have read my ghEttoBIKE thread on pedelecs.co.uk), I have reached the point where I am totally happy with the performance of my bike. The reliability issue of my geared motor really is the last remaining problem.

I would really rather prefer the first solution to the second. So many on this forum rave about running metal gears, but not a single person has been able to advise on where to source them from. I have spent hours looking on the interweb, but I just cannot find them in the 36-tooth variety.

I'm getting desperate now as I'm about to use my last spare nylon gear, so I'd really would be appreciative if anyone knows of a source of metal ones.
 
Soon as you said off road I started thinking "this guy needs a direct drive motor".

Sounds like you are just too much like me, every ride a small test to destruction.
 
I don't have a geared motor and never worked on one so ignore if this sounds silly.
I'm guessing it's the planetary gears you are talking about, but what is the condition of the motor pinion, and the hub one? Any damage or wear on them would affect the planetary gears, especially under heavy loads.
 
Deep down I already know that a direct drive motor would be probably be better suited for my use, but it would be great if I could find a way to stick with the bafang for its weight/gearing/efficiency/freewheeling advantages.

I have never experienced a direct drive motor, but have read lots about them. If I were to switch to one, all else being equal, what differences would I notice?
 
How hot is your motor getting? It was widely accepted that when the geared motors are hot, the teeth on the planetaries were weaker. I suggest switching to the better gears as you have stated you want...but while you have it open, perhaps install a cheap temp probe? Oil-cooling doesn't sound as if it's too expensive (although somewhat messy when learning).

For off-road and steep uphills I am becoming a "non-hub" fan, but if you want to explore a geared hubs limits...add the upgraded gears, perhaps a steel gear in the mix, a temp probe as long as its apart...and oil-cooling if you are willing to put in a little extra effort.
 
Mac and BMC are better designed for trail use. I prefer the torque of a geared motor. You would need to run a direct drive with more power to get the torque, but will loose out on efficiency. Ideally a midrive setup for trail riding is my preffered option, but the noise can be an issue unless its a hub setup, or well designed belt and brushless motor combination.
 
To get enough torque, you'd need a bigger DD motor, in which case you might as well just get a bigger geared motor. The Bafang BPM and CST motors are immensely strong compared with the SWX type.

A few years ago, everybody was over-volting the SWX motors and stripping the gears, so someone made a batch or two of steel gears. Since then, people have moved on to other motors, and at the same time Bafang has improved the strength of the gears with new materials, so it's not so common to hear of stripped gears now. I think you only chance to get the steel ones is if a member bought some just in case, but never used them. Try starting a thread "wanted Bafang steel gears".

Alternatively, buy another SWX motor, which will last at least as long as your last one, and probably longer because the gears are better. I bought one recently from Aliexpress for £93 including delivery to UK. Ideally you want one the same as what you already have so that you can swap the clutch/gears to save building a wheel.
 
I haven't had a chance to check the gear assembly yet and I won't until Sunday now because I'm currently travelling to Wiltshire for the weekend.

Thanks for the info d8veh. I'll send him a message right away.
 
I would suggest a different motor as well. While my Bafang BPM II had no gear deterioration at all despite running it at 60V and 35A for 3000km in my trike I wouldn't buy it anymore due to its service unfriendly screw-in side cover. (actually I ordered a BPM but got a BPM II from BMSBattery despite several attempts to confirm my order by email). Torque wise the BPM is an other league compared to the little SWXH.

Since its less likely to get glass reinforced Nylon or steel gears gears for the Bafang BPM or CST you might even better be off with a BMC, MAC or Puma geared hub motor.
 
d8veh said:
Try this guy for gears. He might have some:
ecrazyman@gmail.com
Click to expand...

I tried to reach him a couple of month ago when I searched for SWXH steel gears but never got an answer. :cry:
 
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