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.
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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.
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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:
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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!