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.