Help finding a solution to Bafang gear stripping

[EDIT] I'm hoping this thread will be of interest to current or future Bafang owners or anyone with ideas on how to solve the "peanut butter" problem. Anyone interested in my bike specifically, click my signature link and feel free to post on my build thread, Cheers guys!

[EDIT 2] For a list of people who have stripped their nylon gears, click HERE. A few people have been looking at stronger gear replacement options but no widely available drop-in replacement has been found or manufactured and made available.

I've managed to strip out two sets of Bafang's nylon gears (3 per set) in two short rides. I had the EV grin, but it was brief. The first set lasted 3min, the second lasted 15min and 6km. I was much more wary of my current the second time and kept it under 18A at ~70V. I also tried to roll the throttle on slow and smooth.

Ended up with peanut butter gears:


Replacing them is quite a pain. It's a big help that Knuckles offers them, and kindly posted me two sets to Australia But at $10/gear it makes petrol look cheap at the rate I'm burning through them. Others may find themselves in a similar situation, I hope we can find a solution together

Any ideas on the causes (voltage|speed or current|thrust)?

Any ideas of a stronger replacement, either a composite material or metal?

I think with metal, the motor might need to be decently sealed and lubricated to keep the metal on metal meshing happy.

More details on my experience here:
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=4925&p=105938#p105935

Gear details:

28 teeth

Outer diameter (gear tip to gear tip):
37.35mm, 1.465"

Hub diameter (root of gear to root of gear)
32mm, 1.260"

Gear width
9.85mm ,0.388"

Bore of freewheel
8.04mm, 0.316"

http://98.131.176.65/endless-sphere/GEDC0799.JPG
http://98.131.176.65/endless-sphere/GEDC0800.JPG
http://98.131.176.65/endless-sphere/GEDC0801.JPG

Sh*t Happens at 72V

Knuckles said:

Sh*t Happens

Click to expand...

I think a better (engineering) approach should be:
sh*t happens, for a reason, therefore determine the cause and find a solution.

I feel your pain.

But Bafang is only rated at 48V.



ps ... I'll post the CA wiring for the Infineon.

I went for 72v based on your 72v, 30A, 26" wheel setup and experience. I'm not blaming you, I want to find a solution. If the weak link is closed, 72v 30A reliably may become an option.

I can't run 48v with two 36V packs. I also can't run 36v because the old ecrazyman 72v craps out below 40v, I'm told.

A possibility?

Word!

I DEMAND ALLOY GEARS FOM CHINA!

F-N-A!

email your local Chinese Consulate

Knuckles said:

Word!

I DEMAND ALLOY GEARS FOM CHINA!

F-N-A!

email your local Chinese Consulate

Click to expand...

Motor from China is fine. I've emailed keywin asking for more spare nylon gears, BUT

metal gears from Japan or Germany, even US of A sounds better to me :wink:

How were you riding at the times it busted. was it like up a 70 degree mountain no pedaling or just cruising?

mickk said:

How were you riding at the times it busted. was it like up a 70 degree mountain no pedaling or just cruising?

Click to expand...

I posted above, the link to my build page where I described the first fateful outing :

"Eased the throttle on to full throttle going down a gentle hill and
kept the throttle wide open as I hit the bottom and started heading up
a gentle hill again. The grinding started as I was heading up hill.
Max reported speed was only 22.3 mph so nothing crazy! Was definitely
not using the brakes and throttle at the same time either."

voicecoils said:

Click to expand...

"Aluminium anodised before gear cutting" :lol:

Miles said:

voicecoils said:

"Aluminium anodised before gear cutting" :lol:

Click to expand...

Click to expand...

I would think aluminium would be quite soft as a small gear material. Cart racers use a hardened steel pinion and an aluminium anodised and hobbed sprocket on the wheel. The load is spread over a much larger area for the rear sprocket however.

What are you getting at miles? Spell it out, I'm not a mechanical engineer, but I am trying to source a solution to this. I'm sitting on nearly $1k of batteries I can't use w/o a motor

What would be the point of creating a protective coating on the gears and then machining it off?

If you want to use aluminium gears they will need to be hard-anodised or treated with the Keronite process. The surface created by both these treatments is porous and can be impregnated/sealed with PTFE.

It might also be worth investigating the possibility of reinforced plastic gears - the new BMC motors seem to be using them.

Miles said:

What would be the point of creating a protective coating on the gears and then machining it off?

If you want to use aluminium gears they will need to be hard-anodised or treated with the Keronite process. The surface created by both these treatments is porous and can be impregnated/sealed with PTFE.

It might also be worth investigating the possibility of reinforced plastic gears - the new BMC motors seem to be using them.

Click to expand...

Got it. What would reinforced plastic mean?

One thing I thought of was having the gear pattern laser cut out of thin steel , shaving down the thickness of the nylon gears and putting the steel cut outs as inserts on either side...

Hi voicecoils,

What were you doing when they stripped? Was it large throttle opening at low speed- that's the situation that generates most torque from the motor?

The answer might be a controller that limits motor current rather than battery current. The problem is that most controllers check the battery current and at low speeds it is still possible to put large current into the motor. Running at higher battery voltage makes this more likely.

Nick

voicecoils said:

Got it. What would reinforced plastic mean?

One thing I thought of was having the gear pattern laser cut out of thin steel , shaving down the thickness of the nylon gears and putting the steel cut outs as inserts on either side...

Click to expand...

Reinforced with fibres: glass, carbon, kevlar etc.

Simply replacing one of the nylon gears with a steel one might be the simplest solution - this is what Heinzmann does.

hey voicecoil i have the exact same problem as you.

You know how i overvolted my greenewheels with the bafang motor on it. Well the 2nd day i used it it started to stuff up liek urs.

I emailed keywin for spare gears, he asks for the model no and i dont know what it is. What model number is urs? and how do u find out?????

I overvolted mine to 60v, the reason why the gears strip is because the higher the voltage, the more heat it has. Especially if ur motor is rated for 200w or so, the bigger then watts the less heat you are going to get. Which means it will limit your distance if you dont want to damage your motor by overheating it.

The other reason why they dont use metal is because of thermo expansion, they dont want the gears to expand under heat.

If you use it at what its rated, the plastic gears will never strip and motor wont even be warm at all.

dazzassj6 said:

hey voicecoil i have the exact same problem as you.

You know how i overvolted my greenewheels with the bafang motor on it. Well the 2nd day i used it it started to stuff up liek urs.

I emailed keywin for spare gears, he asks for the model no and i dont know what it is. What model number is urs? and how do u find out?????

I overvolted mine to 60v, the reason why the gears strip is because the higher the voltage, the more heat it has. Especially if ur motor is rated for 200w or so, the bigger then watts the less heat you are going to get. Which means it will limit your distance if you dont want to damage your motor by overheating it.

The other reason why they dont use metal is because of thermo expansion, they dont want the gears to expand under heat.

If you use it at what its rated, the plastic gears will never strip and motor wont even be warm at all.

Click to expand...

Do you have a number etched into the side? I think that is the serial or production number. Mine is model QSWXB. Yours is a rear motor so a different model. Can you measure the drop-out width of the motor? Is it 138mm or 155mm?

I don't think heat was a big issue for me, the motor barely got warm. The high RPM would increase chance of slipping potentially and if that combines with a spurt of acceleration from a decent speed I'm not surprised that they just strip straight out.

The thing is, I liked the Bafang at around ~1200W At 2kW it should carry decent speed up hills and scoot off from stops nicely.

I don't know if I agree with your last point. I think if you were using it at 36v 10a and tried to let the motor do all the work up a steep hill you'd have the same problem. I could be wrong though.

I am just thinking this may not be the way you want to tackle it but how about the idea of buying a gear less hub motor just to get you out on the bike? perhaps one of the 48v 1000w $250 jobs on ebay at 72 volts you would have the power to get you up hills.

You don't have to give up on your geared hub but this option gives you time to come up with a solution in a more relaxed manner while you enjoy the ev grin .It wouldn't be a wast of money because you could sell the hub later.You never know you might like it .

As for your peanut butter gears you have exceeded there mechanical load rating unless you back down significantly on your power output the same is going to happen again. Remember when ford used a plastic gear on there distributor on there falcons it wasn't to successfully .I am sure there is a hi tech solution/material but this usually = expensive or difficult to find.

I run two geared motors that have steel on steel for the gears and yes it's a little noisy but you wont brake it no matter what you do with the throttle or what wattage you feed it. As far as wear on the gears with only little bit of grease as a lubricant I cant see any visible wear on mine. So noise is the only down side.

You could relate it to racing car gearboxes that runs straight cut gears instead of helical gears they make more noise but you wont brake them.
Kurt.

voicecoils

whats the drop out width of the motor? whats that?

Sorry to hear of your motor problems Voicecoils. Man, that sucks. I've been watching your build with great excitement too.

It's no consolation to you but FWIW you are making me feel a whole lot better for holding back on buying one of these motors now. Several weeks ago I was just about ready to drop nearly $400 into a rear bafang, custom 24" wide rim, wheel build and black spokes plus shipping. It was going to be around $380 for the wheel alone, no controllers, no batteries. I was planning on running it at either 56v Milwaukee or possibly 72v Bosch depending on the battery I bought, either way both were going to be run off a 30 amp controller. How glad I am that I didn't do that. If I'd spent that much money, time and effort and then blown out two sets of gears in such short succession, indicating that it's simply not going to work, I'd be violently ill I think and probably throw the whole ebike idea thing out and sell to recoup costs. My bike was going to be heavy too, hence the idea of the geared motor so quite likely even worse than your position.

Lets hope yours is an isolated case but over volting these motors is quickly starting to sound like a bad idea. 48v max would be a bit disappointing after planning and building for 72v. I ended up getting an entire wilderness BL36 kit, new but unused for $180 shipped (arrives on Thursday) so I am now able to test this ebike thing before sinking big $$ into it. All going well and if I find the wilderness kit satisfactory I will still make plans to build a better performer but I might have to rethink the bafang idea.

I wish you the best of luck in what must be an incredibly disappointing outcome. Hope you can find a solution.
Cheers, HB

Pretty sure gear cutters could find a solution, here's 3 around Sydney:
http://maps.google.com/maps?hl=en&q=Gear+Cutting+Sydney&oe=UTF-8&um=1&ie=UTF-8&sa=N&tab=wl&oi=property_suggestions&resnum=0&ct=property-revision&cd=1
Bet quite a few ES members will be willing to buy gears from you if you work something out.

dazzassj6 said:

voicecoils

whats the drop out width of the motor? whats that?

Click to expand...

It's basically the inside width of the frame where the motor sits. So the drop out width of the motor (or any bicycle hub) is the width that corresponds to it just fitting in a frame.

voicecoils said:

It's basically the inside width of the frame where the motor sits. So the drop out width of the motor (or any bicycle hub) is the width that corresponds to it just fitting in a frame.

Click to expand...

It's commonly referred to as "Over-Locknut-Dimension" or "O.L.D.".

Kurt said:

.

Click to expand...

That's not a bad idea about the temporary hub motor. I don't see those motors on ebay, do you have a link?

I think I'll concentrate on wiring and my battery box for the moment. I have a second front wheel, so I can still use the bike without any electrics.