Bafang G310 geared hub - 11:1 reduction ratio!!!

[TDB]

About 20k now. 250eW. The important parts are 30A max phase amps, minimum 4-6kph (I played a bit) start speed so it isn't pulling from a stop, 60-65C normal operating temperature, thermal roll back starts at 80C and I recognise it as an assist motor (not a prime mover) and put in at least as much as the motor puts out.
Up to 40kg push trailer with 20" wheel and total mass 120-130kg.

 

[Jil]

Interesting, thank you :thumb:

 

[hias9]

Max safe phase amps depends on your winding. I would say 32A is fine for a 10T, 40A for a 8T, 45T for a 7T, 27A for a 12T and 25A for a 13T.
I had a gear failure (while motor case was not even warm and stator at 90 degrees Celsius) at 30A on a 13T.

 

[hias9]

What do you think is this sound?
https://files.fm/f/edwtrp9wp

 

[Mahe]

I recently swapped the Bafang G020.500 out, replacing it with a G310. I'm VERY pleased with the motor. I gives me plenty of power for the type of riding I do, and it's so quiet.

Hi ! May I ask why you swapped? I just received a G020.500 kit, and it is pretty small in size and weight... Is it so noisy? (as mentioned by https://endless-sphere.com/forums/viewtopic.php?f=3&t=110859&p=1624919&hilit=g020+500#p1624839) I have yet to get it running, that's why I ask (display won't turn on, for some reason). I am just surprised that it is the most commonly found bafang rear hub motor for 500W on aliexpress, but has relatively few reviews (and the bafang website lists G020.250 and G040.500, but no G020.500, not very reassuring for sure)

 

[lightrush]

Max safe phase amps depends on your winding. I would say 32A is fine for a 10T, 40A for a 8T, 45T for a 7T, 27A for a 12T and 25A for a 13T.
I had a gear failure (while motor case was not even warm and stator at 90 degrees Celsius) at 30A on a 13T.

Nylon loses strength pretty quickly with temperature:



So at 70C at the gears you have "half the strength" of the gear teeth than at 50C. At 90C there's almost nothing left. I don't know how the stator temperature correlates with the gears but I'd assume something like 20C delta. So when it gets to 80C+ I dial back the PAS if it's too high.

 

[hias9]

The 90 degrees celsius were at the stator which is where the majority ot the heat is created.
The case was not even warm when that happened.
30A on a 13T: gear failure at only 90 degrees celsius at the stator after about 200 miles.
25A on a 13T: already worked fine for 3000 miles with stator temperature up to 120 degrees celsius.

 

[amberwolf]

Lower current (all other conditions the same) creates less torque, which can mean less stress on softer gears.

Another cause of tooth failure of gears is shock loads, so using "soft start" or throttle ramping, rather than "instant start" or sudden throttle application, will lessen the stress on them.

 

[Tirica]

Here's what they look like installed behind the planet gears, it's pretty slick since they fit inside a recess in the gear casting and don't add any width to to the gear assembly.
View attachment 253261



It is tight, and there isn't the same amount of space for a thrust beraing washer like there is on the other half of the gear. Assuming though that the ball bearings inside the gears bottom out against a lip, then you could in principle replace the 3 bearings here with angular contact bearings that have the same geometry but are designed to take a thrust load as well.

View attachment 253260

That would be the neatest solution. Then you should just need to add a small thrust bearing on the end of the helical sun gear to take the thrust loading on the rotor. I've taken apart another small geared motor with helical gears which had one of these on it:

View attachment 253262

So that's definitely doable too. Unfortunately Bafang isn't a company that is game for upgrade requests or small mods like this unless you are talking orders in the 5K-10K volumes at least, so until then any regen ona G310/G311 motor would have to be a DIY affair.

I do have lots of random miscellaneous G310/311 motor parts around if someone wanted to carry the torch and try this out!

Hi Justin, Do you think it is necessary for the rotor to have a thrust bearing as well? In other words, would it not be sufficient if only the gears have thrust bearings? The rotor originally does not have a thrust bearing and is supporting the same axial forces as the gears.

 

[mindgames11]

I've been testing one of these for a few months now. The low level of noise that comes from the motor (when loaded - it can be a bit noisy running unloaded) is impressive. On my aluminum framed commuter bike paired with a phaserunner this motor is effectively silent. Any sinewave controller should provide a low noise level experience as well. I can't comment on a basic trap controller.

I did have an experience where I damaged the gears on one of the motors, while I was late, I increased my phase current limit to 70A, and also removed my speed limit (36V battery, 35A battery current limit). Going up a steep (12% grade according to google maps) I blew the gears. I suspect I was sitting at around 80-90C (I had previously hit the thermal limit on my CA of 100C). I was traveling around 12-15km/h when it happened, so ~55-60A phase current.

Luckily, the motor is quite easy to open (without delacing the wheel), and the gear set is not too challenging to replace, provided one makes sure that the gear tooth indicators all line up with the sun gear. Due to the gear ratios of the motor and the double reduction, there's not very many locations where the teeth will perfectly mesh!

Setting my Phaserunner to a 50A phase current limit has had zero problems. It may be interesting to do some experiments to see if there's a significant gear strength reduction at higher temperatures.

Bafang rates this motor at "30Nm", which would translate to approximately 28A of phase current (simulator derived value), so I can see why 70A would have damaged the gears (http://www.bafang-e.com/en/components/component/motor/rm-g01250d.html).

I hope to hear other users feedback as more people get this awesome little motor. It's been the perfect light weight commuter for me! Its only downside is that due to the helical gears, I don't think locking the clutch for regen would be very smart, the gear set has axial bearings *and* thrust bearings to deal with helical side-forces.

I just took a first attempt at installing the replacement gears I got, which appear identical. however, this replacement set has 3x thrust needle roller bearings and a pair of matched washers for each bearing. they fit perfectly inside the bottom (larger helical) gear which has a cut-out for them (interestingly just like the originals, which didn't have these).
attempting not to break the gears I just bought from china for $40, I'm not forcing them at all, but I'm having some trouble getting them to slide onto the small (~1cm diameter) helical sun gear.
If anyone has any pointers, I'd appreciate it. so far, youtube vids just show swapping straight cut gears.

 

[amberwolf]

If the gears are cut differently, they may not be able to fit together.

If they are a tight fit, sometimes cooling the parts on the "inside" of a circle and warming the parts on the outside will give enough clearance to allow installation. That's not a typical thing for gears, but it is for bearings, etc.

 

[mindgames11]

I just took a first attempt at installing the replacement gears I got, which appear identical. however, this replacement set has 3x thrust needle roller bearings and a pair of matched washers for each bearing. they fit perfectly inside the bottom (larger helical) gear which has a cut-out for them (interestingly just like the originals, which didn't have these).
attempting not to break the gears I just bought from china for $40, I'm not forcing them at all, but I'm having some trouble getting them to slide onto the small (~1cm diameter) helical sun gear.
If anyone has any pointers, I'd appreciate it. so far, youtube vids just show swapping straight cut gears.

ahhh I just took another look and realized that while seemingly identical, the new helical gears are cut in the opposite direction as the old ones. so either this project is on hold for a while, or maybe I can flip the sun gear around on its shaft- whether that will work gear-wise or if the shaft permits it is at the moment unknown to me.
irritating.

 

[amberwolf]

Assuming that flipping anything would actually fix the issue (I am not sure it works that way), then you'll have to flip the ring gear, too, then, so it would be easier to flip the planets on their carrier.

 

[Chalo]

ahhh I just took another look and realized that while seemingly identical, the new helical gears are cut in the opposite direction as the old ones. so either this project is on hold for a while, or maybe I can flip the sun gear around on its shaft- whether that will work gear-wise or if the shaft permits it is at the moment unknown to me.
irritating.

Chirality is a bitch. You can't ever make a left hand thread agree with a right hand thread, and the same goes for LH versus RH helical gears.