Help finding a solution to Bafang gear stripping

[TPA]

my intention is to supply someone with 3 drop in replacements to test for strength and wear. I'm not making any promises, because I'm in school until dec 18th, and time is a premium until then. I've ordered the tooling, but still need to get the aluminum and bearings (I'm assuming shielded is ok looks like whats in the picture). I will try to make many (60?) at one time, but can't promise when they will be ready.

[voicecoils]

my intention is to supply someone with 3 drop in replacements to test for strength and wear. I'm not making any promises, because I'm in school until dec 18th, and time is a premium until then. I've ordered the tooling, but still need to get the aluminum and bearings (I'm assuming shielded is ok looks like whats in the picture). I will try to make many (60?) at one time, but can't promise when they will be ready.

Sounds great. I would be happy to be a guinea pig but wouldn't be able to do any testing till the first week of December. After that I'd be happy to give them a go at progressively higher current and voltage to see how they fare.

I've got 4 spare bearings too that could be pressed in locally if need be.

Cheers!

[Knuckles]

Another thing to look at would be the freewheel assembly that the nylon gears mount to. It may have a limited life as well. Nogwin is nearing 2k miles however, so he's our best torture tester yet IMO. The freewheel assembly cannot be disassembled from what I could see, so a bit hard to check the construction quality.

The freewheel mechanism in the Bafang looks well machined and durable. I have no concern about its durability thus far.

Voicecoils says the bearing is the 608zz. I am considering making some gears out of 6061 aluminum. Can the bearing 608zz be confirmed with absolute certainty? And should they be shielded or sealed? Can anyone say whether it would be a good idea to increase the o.d. of the gear slightly to cut out the slop?

I would stay with the 1.25 module 28-tooth standard for now. With metal it is good to have a little play for thermal expansion.
The existing nylon gear is exactly a 1.25 module 28-tooth gear.

Also any bearing would do fine. It just needs an 8mm bore. It doesn't have to be a 608. But a sealed bearing is always preferred.

Just hearing today that a Chinese gear manufacturer (same as makes the metal gear for the PUMA) will make orders of 500 metal gears for the Bafang.
However, I would encourage a smaller startup batch and more testing first.

[johnrobholmes]

Shielded bearings have lower rolling resistance as compared to sealed. 608z should be single shield, and 608zz should be double shield.

[Knuckles]

John,

Are you planning to get a dozen or so metal "test" gears for the Bafang any time soon?

[johnrobholmes]

I have access to either 10ft of gears or none right now. I have not gotten the gearblanks cut yet.

I am working harder to get the motors built with consistent phase and hall wires so that we can predict how to hook em up. I already had a customer burn one up. Otherwise I have been very pleased with the construction. I may even see if I can get the inner workings of the motor separate for a divorced driveline system.

[docnjoj]

So when can I get my Bafang back on the road? I need 2 Nylon and 1 steel combo, at least at first! To whom do I send money to? And how much? Sorry to be so insistant, but I kinda like the motor!
otherDoc

[Knuckles]

John in CR may be the best bet for a batch gears with bearings. Three metal gears will also work btw.

Maybe I need to work out some "trade" with John (controllers for gears perhaps?).

Then I can distribute the gears out to folks.

[docnjoj]

Noise level with three metal gears will probably be too high for my sensitive ears!
otherDoc

[Knuckles]

I'll test all metal gears (3) for noise myself. John in CR could do the same.

[docnjoj]

I'll pay money for the winning combo! Still have a little bit left!
otherDoc

[docnjoj]

One would think that Bafang would have more than a passing interest in all this activity. The Chinese dont overvolt like we do, but they sure overload their bikes as true means of transport and commerce. I'll bet their gears also fail from heavy loads!
otherDoc

[johnrobholmes]

But the motor can only provide so much power on 36v. I have beat the snot out of mine on 36v with zero issues. Even my 16" build on 72v does well, but I baby the throttle to ensure I don't fly off the back.


Except for this issue I still really like the Bafang motors.

[docnjoj]

Quite true, JohnRob. But they dont use little teeny wheels either. They have those 26-28 cart wheels on their bikes! Remember the 155 mm dropout clearance for the rear ones?
otherDoc

[John in CR]

I only have the one metal gear, which is now installed. I'm finishing my Konion packs and wiring today, so I should finally be on the road with my 2wd tomorrow. I agree with Doc, Bafang needs to be resolving this issue. In the meantime, don't count on me as a source for gears any time soon. I only have the one Bafang, and I want to give the alignment some thorough testing before buying into the "Bafang solution". Plus I've got a dozen different motors and kits in route, which should start arriving later this week, so my plate is full. I have to come up with a drivetrain and then build a bike that is efficient through the wind carrying 4-5kwh of batts for my coast-to-coast on a single charge ride. The Bafang may be part of that if the large motors I'm getting prove inadequately efficient on the flats, and the 1 steel geared Bafang holds up to my abuse.

Assuming it does hold up, I'll order 100 Bafangs as a low cost solution for the hilly terrain down here, so I'd need gears too, but the earliest would be January.

John

[docnjoj]

Thanks for your efforts, JohninCR! I do appreciate the road testing, and at least we will see if the rest of the motor holds up!
otherDoc

[John in CR]

I just opened mine back up to double check the wiring before mounting it on the bike. I've reharnessed a hubbie before, and everything is so tight and compact in the Bafang that there's no way I want to rewire this one. I'll be adding some kind of extra protection where the wires exit the axle to help ensure everything inward from a few inches out can't get damaged.

John

[Knuckles]

I have bad news and good news.

Bad News: I pushed the Bafang (w/ metal gear NO BEARING) hard at 72V and 25A. Running great until motor seized. Upon inspection the metal gear (NO BEARING) had seized on the post.

Good News: No damage at all to any of the gears. It was just a lack of proper bearing in the metal gear. Still have the metal gear (pried it off) and the post is still in good shape.

But I will not use it again until I can get a bearing for the metal gear (expensive for me in NY I am sure).

I’ll put the third nylon gear back in and put this motor on another 26” build limited to 36V and maybe 20 amps. But no more than that for me for now until the Bafang can get a proper metal gear w/ bearing. Such a shame too. Bafang has nice performance at 72V.

But at least this test shows me how well a single metal gear “protects” against the destruction of the nylon gears.

btw ... KHK has a Hong Kong Factory ... http://www.yuenfatgears.com/index_e.htm

[Nogwin]

I now have a few hundred more miles on the Bafang since the last update. I think it's around 2200 km and spent this week running at 80V. I am very careful to pedal first and keep the watts under 1000W during a hard start (typical is around 600W), then settle in for around 300-450W continuous.
Managed 34mph yesterday on the flats WOT for 5 miles, and was a blast. I was pedaling pretty good at the time as well.

I'll settle for a more reasonable 66V for now, but 80V sure feels good. I think like all things, the gears will break at some point, but I will still continue to be light on the throttle.

A friend who works at our machine shop at work will press in bearings for me. He said to provide him with the bearing and 1.25 gear. He and I will do this one weekend in the near future. I'm very concerned about the gears and feel like I'm the last one out there with plastic gears. Now I'm pretty worried


Nog

[voicecoils]

most of us don't have metal gear(s) yet.
You're the lucky oddball not getting any gear stripping at high voltage. Your pedaling habbits are the main factor saving you IMO. Does your commute have any hills?

[fechter]

The motor current has more to do with it than voltage. Most controllers will give the motor more current with a higher battery voltage, so I guess there is a connection.

If you ran a 20 amp limit, I bet the gears would never strip.

[voicecoils]

The motor current has more to do with it than voltage. Most controllers will give the motor more current with a higher battery voltage, so I guess there is a connection.

If you ran a 20 amp limit, I bet the gears would never strip.

I stripped my second set of gears at 80v and under 20A, at least I was not seeing any high spikes on the CA from the 28A PIC ecrazyman controller. Maybe the sample rate wasn't fast enough for me to catch it.

I only road a few km's so far at 80v and 9-10A limited on the CA. Haven't stripped them that way but the motor/gears sound very unhappy on starts or hills. The motor sounds best when run out and stabilised at WOT, even with the motor spinning on it's own without the gears, case or wheel attached. When riding at 80v10A I found that I rarely had enough flat long sections of road to get the motor into the WOT sweet spot. The gear sounds on starts or hills did not inspire confidence at this voltage, but maybe I've just become paranoid.

May do more testing at that voltage once I've got a spot for my batteries in the main triangle. Otherwise the handling is not fun with both of them (9.4kg total).

[Tiberius]

I stripped my second set of gears at 80v and under 20A,

If that was 20A at the battery, then it could be much more at the motor. High voltage has the effect of raising the top speed, but it will also allow higher motor currents at low speed. Ironically, going easy on the throttle may not be enough to save you, as the worst damage could happen at partial throttle settings.

Its part of the peculiarity of the way the controller/motor combination works. 80V / 20A in could translate to 20 V / 80 A out to the motor at low speed, partial throttle. And as Richard says, its the (motor) current that sets the torque.

What we really need is a new type of controller, or a new type of limiter.

Nick

[voicecoils]

Its part of the peculiarity of the way the controller/motor combination works. 80V / 20A in could translate to 20 V / 80 A out to the motor at low speed, partial throttle. And as Richard says, its the (motor) current that sets the torque.

Very interesting, thanks for that! My understanding of these things is developing but fairly slowly. I'm used to thinking of just power (and usually in kW and MW) and energy (kWh, MWh, TWh) but with EV's I'm learning that it's necessary to drill down farther.

20V / 80 A when amps = thrust is clearly a danger to the gears. What you've said about partial throttles agrees with my on-road experience. This I suppose is the benefit of gearing, that the motor can spin up faster to the max RPM's for a given voltage faster.

[Kurt]

Its part of the peculiarity of the way the controller/motor combination works. 80V / 20A in could translate to 20 V / 80 A out to the motor at low speed, partial throttle. And as Richard says, its the (motor) current that sets the torque

So in this example your saying that in some low throttle situations the controller will take The 80v with a limited current flow of 20A and cut the voltage output down to 20v but allow a current flow of 80A to the motor.

My understanding was that you use your max torque/Amp flow at start up from a stand still for a fraction of a second though until you have some momentum.Im sure once your moving if you current limit to the controller you can restrict the forces on your gear train.I remember when I setup current limiting through CA the first time I set it at 1A just to test it in my garage this was when I was running a dual geared motors.I think my 2yo daughter could have held the bike back. So the CA was restricting torque.
Kurt.