Help finding a solution to Bafang gear stripping

[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.

[voicecoils]

Ok, sounds good fetcher.

Shock loading is a worry. I'd rather wear the gears planetary gears then bust the freewheel if something has to give.

With a cad drawing of the gear, a mold could be laser cut out and stacked to give the desired thickness. I could pour molten solder into a mold but that's about all I've got the in-house ability to melt

I think if some one more mechanically minded then I and with shop access, had a hack at this problem a few workable solutions could come out pretty fast.

{EDIT EDIT} I just realised I've been saying "sun gear" when what I meant to say was "ring gear". My terminology in previous posts is therefore incorrect. Sorry to anyone for the confusion. A bit of a "doh" moment, now that its dawned upon me.

[Knuckles]

SSAY1_25-28.dwg

SSAY1_25-28.dwg

(11.39 KiB) Downloaded 77 times

I just plotted the dwg to scale at it appears to be a dead on match.
This gear is (of course) discontinued! Go figure!
http://www.khkgears.co.jp/en/khk_produc ... lition.pdf

I also assume the inner bore of the bearing is exactly 8mm.

SSAY1.25-28.jpg

(133.29 KiB) Downloaded 35 times

SSAY.pdf

(313.77 KiB) Downloaded 71 times

This may have potential ...
This is located very close to me ... http://www.qtcgears.com/

I may have to pay them a visit!

[TPA]

Hi,

I am a machinist. I work in a fully equipped machine shop. We might be able to work out a little barter if you are interested.

There is a good chance I can make that gear, unfortunately only small quantities though.

My proposal:

1. you need gears (aluminum, stainless, chromoly...), I might be able to make them.

2. I need a hub motor...you sell them.

If you sent me a single new gear and the mating bearing, I would make you a set of three gears out of the material of your choice identical to the one you sent me. I send the set to you and you test it out. If it works, I make you about 10 sets in exchange for a complete wheel kit. I would offer you any plans and drawings, but I'm not likely to make any. If the gears do not work, then you do not have to send me the kit.

This should save you a considerable amount of money, and helps me out at the same time.

The might part of it depends on the possible need of special tools and how expensive they might be.

I can't make large quantities at one time because it is not my shop.

[dnmun]

'sun gear' is the correct term. a ring gear is a hypoid bevel gear where angular rotation is turned 90 degrees as in the rear axle diferential. teeth are on the outside of the flywheel ring gear. sun gear is the classic term for the gear when used for overdrive in a tranny.

it would be interesting to see if the new composite gears for the BMC are the same size. maybe there is some way to convince bafang to manufacture with the composite gears from the start.

EDIT: thanks miles, i stand corrected. so the other uses of ring gear are just by similar position?

ps: with respect to whether it is possible that bafang would use composite gears, i suspect they also are already economically developed enuff to start using planned obsolesence in the motor, and every dead motor to them is just a possible new sale. if it were possible to find the manufacturer of the composite gears for BMC, they might consider developing a replacement composite gear for the bafang. was it mark at team hybrid who originally started the push towards steel gears for the puma? that may be the way to go too since it got BMC to actually change their manufacturing process. chalk another one up to our fav silent member.

[Miles]

Sun gear is the one in the centre.

Planet gears are arranged around it on the planet carrier.

Ring gear is the outermost one, with teeth facing inwards to engage with the planets.

[fechter]

'
it would be interesting to see if the new composite gears for the BMC are the same size. maybe there is some way to convince bafang to manufacture with the composite gears from the start.

Not likely the BMC gears will fit. I have a set of metal gears for a Puma, which I believe are the same size as the BMC. They are quite a bit larger in diameter.

[TPA]

A gear made out of aluminum or brass would meet the load requirements and not damage steel components in the hub because brass and alum. is softer.

If nylon can make it as far as it has been described here, then non anodized 6011-t6 can handle it with no problem. It would wear over time because it is softer than steel, but still last a while.

[voicecoils]

A gear made out of aluminum or brass would meet the load requirements and not damage steel components in the hub because brass and alum. is softer.

If nylon can make it as far as it has been described here, then non anodized 6011-t6 can handle it with no problem. It would wear over time because it is softer than steel, but still last a while.

Awesome TPA I was hoping someone on this forum would have the skills in-house.

Brass sounds good. If no one state side can send you a gear, I'll send you one of mine from Sydney, Australia.

Hopefully a more local offer offer will come through.

[voicecoils]

appropriate bearings:
http://www.vxb.com/page/bearings/PROD/SkateboardBearings/sk8zz
http://www.vxb.com/page/bearings/PROD/Scooter/608ZZ10




608ZZ Dimensions:8mm x22mm x7mm
Quantity 10 Bearings 608ZZ
$4.95

[johnrobholmes]

Ok, Ok, I spent an hour today sourcing gears. Found a match that would just need boring, and found a company that makes spur gear stock.

Want to measure the width of the gear for me? 10mm work fine? Are we positive it is 20* pressure angle?

[Knuckles]

Metal gear installed and ready for testing.

Heavy_Metal.jpg (24.13 KiB) Viewed 1065 times

http://98.131.176.65/endless-sphere/GEDC0828.JPG
http://98.131.176.65/endless-sphere/GEDC0827.JPG
http://98.131.176.65/endless-sphere/GEDC0826.JPG
http://98.131.176.65/endless-sphere/Metal_Gears.jpg

Knuckles

[dnmun]

before you grease it why not paint the faces with prussian blue and see where the wear faces are on the gears? excellent find!

[snowranger]

The 826.jpg shows the steel gear barely engaging the ring gear. Is it just the photo?

[Knuckles]

Gravity. When I rotated the assembly the nylon did the same.

Original_Gears.jpg (47.64 KiB) Viewed 1042 times

And of course no racer bearing on the "non-available" gear.

I got the last two in stock at the local "Gear Store"

WTF!

But the gear dude said he can get more as "special order"
He was blown away about e bikes ... never heard of them ...

But only torture testing will tell ...

[lawsonuw]

Nice!

No bearing but it should work just fine for a while. Hadn't heard of KHK before, added them to my list of stock gear companies.

Marty

[johnrobholmes]

So the metal gear will be riding direct on the planet gear post?

[Knuckles]

So the metal gear will be riding direct on the planet gear post?

YUP!

[voicecoils]

:D Metal gear installed and ready for testing.

Heavy_Metal.jpg

http://71.18.69.167/endless-sphere/GEDC0828.JPG
Knuckles

Well done! Can the metal gear spin freely on the post? Obviously a bearing would be better but... you might still be able to test it.

Can you pop the metal gear on top of the nylon one and comment on whether the tooth profile / pressure angles are identical? What are the specs from the shop?

[Knuckles]

It's tight but spins free as birdie! But of course this is really just a test of M 1.25 28 teeth gears.
(Dead on Identical VC! Dead on!)

I showed the peanut butter to "Mr. Gear Dude" (Brian) and I know these guys can make anything.
Very cool shop. Making gears likes SOB's they were! NY cost I would think (of course) for custom gears.
This shop is located very close to me ... http://www.qtcgears.com/
The "discontinued" KHK gear is made in Japan btw.
Part Number KSSAY1.25-28

Makes me feel great hope for 'lil' Bafang.

72V 30A off road time!

[zibbby]

What about if the gear is made of BRONZE?
The bronze is self lubricated and would work great with steel and my be little quiter then steel. It may also not need bearing.