Help finding a solution to Bafang gear stripping

[Miles]

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...

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.

[dazzassj6]

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.

[voicecoils]

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.

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.

[Kurt]

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.

[dazzassj6]

voicecoils

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

[HornetB]

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

[Mathurin]

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.

[voicecoils]

voicecoils

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

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.

[Miles]

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.

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

[voicecoils]

.

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.

[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