Help finding a solution to Bafang gear stripping

[voicecoils]

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.

Thanks for checking in HornetB. I'm chasing two avenues of options now:

* lower voltage or current or both
* metal or composite gear replacements for one or all 3 gears.

I'd like to run it at 72v but if 36v gives me decent speed and very good torque that would be fine for my commuting purposes. I can use a larger chainring and add top speed by peddling. I'm not trying to build a completely demon bike (hopefully my DH Team will be though ), I want a commuting/utility bike that replaces car trips and reduces sweating

[voicecoils]

Pretty sure gear cutters could find a solution, here's 3 around Sydney:
http://maps.google.com/maps?hl=en&q=Gea ... ision&cd=1
Bet quite a few ES members will be willing to buy gears from you if you work something out.

Nice one Mathurin, I've sent off a quote request to one shop. Cheers!

[solarbbq2003]

try one metal gear and two nylon originals, will keep sound down, but might avoid peanut buttering

[lawsonuw]

From your measurements it looks like you have M1.25 gears. If you get a measurement tooth tip to tooth tip and tooth root to root , and a tooth count on the ring gear or pinion I can confirm this. (not old, not made in USA then Metric gears are most likely)

http://www.Sdp-Si.com stocks a lot of standard gears. Looks like three #S10T12M028S1010 would drop right in if the bore is opened up to fit the existing bearings and the hub removed. If Sdp-Si isn't local I'm sure there are equivalent distributors locally. Also, looking in the yellow pages for "industrial distributors" or similar should net a few places to ask at. Don't worry too much about sealing the motor better. Just keeping dust off the grease is most important. If you really want to be nice to the gears get a high pressure grease with molybdenum disulfide to replace the no-name stock grease.

Marty

[voicecoils]

From your measurements it looks like you have M1.25 gears. If you get a measurement tooth tip to tooth tip and tooth root to root , and a tooth count on the ring gear or pinion I can confirm this. (not old, not made in USA then Metric gears are most likely)

http://www.Sdp-Si.com stocks a lot of standard gears. Looks like three #S10T12M028S1010 would drop right in if the bore is opened up to fit the existing bearings and the hub removed. If Sdp-Si isn't local I'm sure there are equivalent distributors locally. Also, looking in the yellow pages for "industrial distributors" or similar should net a few places to ask at. Don't worry too much about sealing the motor better. Just keeping dust off the grease is most important. If you really want to be nice to the gears get a high pressure grease with molybdenum disulfide to replace the no-name stock grease.

Marty

distance between adjacent teeth, not opposite teeth?

tooth tip to tip = 4.35 mm
toot root to root = 3.5 mm

Nice find, the gear you mention has a pitch diameter of 35mm which seems perfect when I size it up to the gear. I understand pitch diameter to mean basically the diameter half way up the teeth on each side. Or the point where two gears would be meshing together.

[lawsonuw]

distance between adjacent teeth, not opposite teeth?

I meant across the diameter of the gear like you measured before. Mainly I want measurements from a gear that's NOT creamy peanut butter.

Nice find, the gear you mention has a pitch diameter of 35mm which seems perfect when I size it up to the gear. I understand pitch diameter to mean basically the diameter half way up the teeth on each side. Or the point where two gears would be meshing together.

Pitch diameter is the is the point where the gears are theoretically meshing together. In most gears it is about halfway between the tooth tip and tooth root. (slightly closer to the tip though) Btw gear module is really simple. An M1.25 gear's pitch diameter increases by 1.25mm for every tooth. I.e. the units are [mm-diameter/tooth] English gears use diametral pitch ("DP") which is similar but not, [tooth/inch-diameter] in this case.

Marty

[Freddyflatfoot]

VC,
Just another thought on the amount of power you are using.
It maybe be unwise to have that on your front wheel. There have been some nasty stories of front forks not being able to handle the torque. Ar you using any extra torque arms?
Personally, if I were trying to power a bike in excess of 1500 watts, I'd want that power at the rear wheel.
Just a thought.............................................

[voicecoils]

I meant across the diameter of the gear like you measured before. Mainly I want measurements from a gear that's NOT creamy peanut butter.

Marty

The measurements were taken from a fresh minty gear

Here they are again:

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"

[John in CR]

Voicecoils,

Thanks for sharing your misery. I have an extra set of gears, so I was going to light mine up at 80V+, so now I'll wait until we have a replacement gear solution or get a 48V 20A controller. If you need participants in a group buy of metal gears just let me know. Also, I'll bring an extra gear over to my machine shop and find out how much they would charge for copies. I wonder if any more durable composite materials are available that come in a machinable form. Could a machinable or castable ceramic work, because I happen to have some impact resistant ceramic that I picked up for use as a piston in a stirling engine.

John

[voicecoils]

Voicecoils,

Thanks for sharing your misery. I have an extra set of gears, so I was going to light mine up at 80V+, so now I'll wait until we have a replacement gear solution or get a 48V 20A controller. If you need participants in a group buy of metal gears just let me know. Also, I'll bring an extra gear over to my machine shop and find out how much they would charge for copies. I wonder if any more durable composite materials are available that come in a machinable form. Could a machinable or castable ceramic work, because I happen to have some impact resistant ceramic that I picked up for use as a piston in a stirling engine.

John

I'm not sure, and nearing the end of my engineering degree I'm not ready to start enough in material science or mech eng !!!

If you can find a solution that would be awesome. A few people are now looking at options. The more the merrier

I think the basic engineering dilemma is this:

The sun gear and pinion are steel. Steel on steel wears fast and requires lubrication. Lubrication requires sealing, and sealing requires close manufacturing tolerances and additional measures to make the casing oil-tight.

An alternative is a non-metal gear. A non-metal gear may not require lubrication which is factor for consideration. The nylon ones supplied have not worked for me. Higher quality nylon or another plastic might do the job. I don't know about ceramic on metal and bad how noise or wear would be.

I would hold off on 80V operation for SURE. I was hoping that my spare gears would last me a long time. I figured if the first set lasts a year, then I'm set for 3 years! Turns out I was set for less then 20min total. I have one set remaining and I don't want to load them in until I either have a new stronger gear replacement, or a low power option for running them.

JRH has not had problems at 40V 40A. Nogwin has not has problems at 66v 35A (and has clocked up 1k miles). See here: viewtopic.php?f=6&t=4925&start=75#p106208

Maybe I have an isolated case? The high voltage seems to be a major factor.

[voicecoils]

More photo evidence...


My sun gears, after degreasing. They look fine to me, not worn. If I run my finger down the grove, they do seem to have a tiny lip or rough spot at the edges, at the face of the sun ring, on either side.


Second Peanuting. This time the gears did not get completly stripped around the whole circumference.

It looks like they locked up in one position.

[lawsonuw]

oh yea, and measurements off of metal gears are better because the root of the gear is usually not cut as deeply. With your numbers and estimating that the pitch diameter is the average of the tooth tip and root diameters I get about M1.238 for your gears. Considering that plastic gears can often have a deeper tooth root to allow for a large radius, I'd call that an 1.25 module gear.

I wouldn't worry too much about sealing up the gears and running them in oil. Just get some good grease and keep the grease clean. Plenty of hub gears for bicycles run un-sealed and packed in grease. An oil bath would quiet things down though.

If you're bent on staying with plastic, Torlon is used for bearing balls on sail boat rigging. Holds up a lot better than nylon or delron. Not sure how well it works for gears, one of it's relatives could be better suited.

Marty

P.S. The sun and ring gears are likely powder metal parts, hence the edge from when they were pressed

[voicecoils]

oh yea, and measurements off of metal gears are better because the root of the gear is usually not cut as deeply. With your numbers and estimating that the pitch diameter is the average of the tooth tip and root diameters I get about M1.238 for your gears. Considering that plastic gears can often have a deeper tooth root to allow for a large radius, I'd call that an 1.25 module gear.

I wouldn't worry too much about sealing up the gears and running them in oil. Just get some good grease and keep the grease clean. Plenty of hub gears for bicycles run un-sealed and packed in grease. An oil bath would quiet things down though.

If you're bent on staying with plastic, Torlon is used for bearing balls on sail boat rigging. Holds up a lot better than nylon or delron. Not sure how well it works for gears, one of it's relatives could be better suited.

Marty

P.S. The sun and ring gears are likely powder metal parts, hence the edge from when they were pressed

Your insights are really helpful on materials and manufacturing process. Much appreciated! I hope a great outcome will result from this discussion and benefit a number of people.

I'm not dead set on anything, metal or non-metal. Any ideas on a good grease to use? My girlfriend's dad has spare graphite based grease he used in Porsche racing that I might be able to pinch a dab of

Here are some more photos of fresh gears, I hope they'll help people with visualising. The backs show more of the bearings, if anyone needs to see that side let me know. The sun gear seems to have sharper tooth angles then the little nylon ones...

[lawsonuw]

I'm not dead set on anything, metal or non-metal. Any ideas on a good grease to use? My girlfriend's dad has spare graphite based grease he used in Porsche racing that I might be able to pinch a dab of

Yea, the graphite grease will work well. Molybdenum disulfide has a bit lower friction than graphite. Should be able to find a tube at the local hardware store, look for molybdenum disulfide on the label, preferably with a stated % content. (my old stuff is 15% molybdenum disulfide which is likely overkill, 5% should be more than plenty)

Ah, the planets have a 6082 ball bearing. "6082" is an ISO, or some such, standard size so it'll be easy to replace.

Sleeping on this a bit, I'm pretty sure heat was a contributing factor in your gear failures. The several-min delay, the mushy final shape of the teeth, combined with the tendency of plastics to get a lot softer as temperature rises. How about running the gears in an ice water bath to keep them cool? Torlon holds up a lot better when things get hot.

Marty

[Miles]

Reference:
http://www.dsm.com/en_US/html/dep/products.htm
http://www.dsm.com/en_US/html/dep/ind_apps_gears.htm
http://www.dsm.com/en_US/downloads/dep/ ... s_2005.pdf

[shinyballs]

Your motor may come defective from the factory. Have you tried contacting the seller for an exchange? The problem may not be visible by the naked eye, and can be only diagnosed using precision tools.

[voicecoils]

Reference:
http://www.dsm.com/en_US/html/dep/products.htm
http://www.dsm.com/en_US/html/dep/ind_apps_gears.htm
http://www.dsm.com/en_US/downloads/dep/ ... s_2005.pdf

According to the calculator here:
http://www.omnexus.com/tc/pa4-6/index.aspx?id=grade

For the pitch diameter (35mm) and the number of teeth (28), any thing over 3 Nm should use
Polymide 46: Stanyl Carbon Fibre reinforced gears. And, I think they won't want to talk to you if your after 3 custom bore gears
30k of them maybe

Interesting links though...

[voicecoils]

Your motor may come defective from the factory. Have you tried contacting the seller for an exchange? The problem may not be visible by the naked eye, and can be only diagnosed using precision tools.

It was used over 36v, therefore warranty is void. The seller Keywin is a nice guy but he's not throwing motors around for free.

However many people will likely be using the motor at 48V or even higher, therefore finding a solution has the potential to benefit a number of us.

[fechter]

There are a bunch of places that sell gears.

Here's one: https://sdp-si.com/eStore/Direct.asp?GroupID=591

How about 303 stainless steel?
https://sdp-si.com/ss/PDF/78001063.PDF

The hub is wrong and would need to be machined out, but that would be easier than making the whole gear. I have no idea if the one above would match exactly, but it looks close.

[voicecoils]

There are a bunch of places that sell gears.

Here's one: https://sdp-si.com/eStore/Direct.asp?GroupID=591

How about 303 stainless steel?
https://sdp-si.com/ss/PDF/78001063.PDF

The hub is wrong and would need to be machined out, but that would be easier than making the whole gear. I have no idea if the one above would match exactly, but it looks close.

That's the one linked earlier in this post. It looks perfect fit wise, but yes it would have to be bored out to fit the a bearing. The current bearings could possibly be re-used, but really any bearing with the inner bore of the correct size could be used.

Something I wonder about though, would the stainless be TOO strong? WIth gear to gear contact, something's got to give, ie gears will wear. With the current nylon gears, they will wear before the pinion and sun gear.

A stainless set of 3 gears could wear out the pinion and sun gear quickly, possibly. This could be something to think about...

[Knuckles]

This is an excellent thread. I have silently wanted metal gears for the Bafang motor for a while now.

I run my rear Bafang at 72V and the top speed of the bike is 30 MPH.
I also use a Direct Drive front motor and the feel of the 2x2 e bike is fantastic.
(Although 2 motors really didn’t increase my top speed that much).

The Bafang motor itself is very powerful for a 3 kg motor.
It is not an issue of heat for me now. But gear failure occurred from “shock”.

I was coasting at maybe 15 MPH and then I ramped up the throttle and BAM … peanut butter gears.

When coasting the rotor inside the Bafang stops spinning and the freewheel bearing is active. By ramping up the throttle the rotor rapidly started spinning (rotationally accelerated) under a no-load condition. When it catches up to the hub speed (ring gear speed) the gear assembly was shocked (like hitting a brick wall) when it engaged the hub.

The gear assembly (freewheel bearing) stops spinning when the rotor is “engaging” the ring gear. I suspect that the sudden “shock” of going from a no-load condition to a full-load condition was enough to shear the plastic teeth of the planet gears.

I suspect this can also happen at lower voltages like 48V.

The solution when coasting then accelerating is to be gentle on the throttle until the rotor is fully engaged.

Ideally at least one metal gear is the best way to go. The Bafang Company has so far not been willing to accommodate this request. And they won’t provide the gear shop drawings either.

Btw … Mark at TH in UK also obtained metal gears for his PUMA PMGR motors for folks whom like hard riding (like me and other in this thread).

I do look forward to obtaining metal gears for the Bafang motors.

[voicecoils]

This is an excellent thread. I have silently wanted metal gears for the Bafang motor for a while now.



*

Knuckles, the gear you have proposed only has 5 teeth. Furthermore, it is much too small.

At least 3 people are looking at metal solutions now, not including myself:
johnrobholmes
John_in_CR
getadirtbike

Discussions of non-metal gears which are stronger or have better heat resistance are being thought about as well.

Get ahold of an 28 tooth M1.25 gear and give us the results

p.s. Keywin will not supply metal gears, I do not think he has the power to do so even if he could. Maybe you know better?

[Knuckles]

Knuckles, the gear you have proposed only has 5 teeth. Furthermore, it is much too small.

I haven't proposed any specific gear model. I have yet to find one "off the shelf".

I did check with local gear shops moths ago. They want $500 to analyze the gear.
And even more money to fabricate it from scratch.

Shame. That lil motor packs a lot a power.
Would be nice to have gears that can handle it.

[voicecoils]

Knuckles, the gear you have proposed only has 5 teeth. Furthermore, it is much too small.

I haven't proposed any specific gear model. I have yet to find one "off the shelf".

I did check with local gear shops moths ago. They want $500 to analyze the gear.
And even more money to fabricate it from scratch.

Shame. That lil motor packs a lot a power.
Would be nice to have gears that can handle it.

Just a joke on the * you had in the post, before you finished writing it. neva mind...

No need to have a gear shop "analyze" it. The gear has been found, it is a standard metric M1.25. It's 28 tooth with a pitch diameter of 35mm exact.

The sealed bearing is the same as can be found in any skateboard shop. I just checked with a skateboard wheel bearing which were used in the pivots of an old full suspension MTB I had. My skateboard wheel bearing says ABEC-1 PT 608ZZ. The bafang bearing says: GM BEM 608Z. Both have the exact same outer diameter and inner bore. ~0.83" and ~0.316" respectively.

[fechter]

Something I wonder about though, would the stainless be TOO strong? WIth gear to gear contact, something's got to give, ie gears will wear. With the current nylon gears, they will wear before the pinion and sun gear.

A stainless set of 3 gears could wear out the pinion and sun gear quickly, possibly. This could be something to think about...

I don't think you have to worry much about that. I suspect the stainless would be softer than the sun gear and would take most of the wear. Wear should be minimal with decent grease. The metal to metal gear contact in the Heinzmann motors has proven to be long wearing.

Using one metal and two nylon gears may be a good comprimise also.

The shock loading that Knuckles is describing will still be an issue. Too bad the controller doesn't do something to prevent that...
If the gears are super strong, the next weak point might be the freewheel mechanism.
You can get similar shock loading if the wheel loses traction while accelerating and regains traction suddenly, like going over a curb with the throttle on.

One crazy idea I had is you might be able to use a new nylon gear to make a mold out of plaster or something and use it to cast your own metal gears. I'm not sure if there is a casting mold material that will give you a smooth enough surface finish. Brass or bronze would be easier than steel. You may also be able to create your own composite gears using this method.