To the guy who has the noisy drive keep building it up and don't worry just yet. Mine has really taken some punishment and been taken fully apart and reassembled twice now and done thousands of km. The first time it did chew a bearing up that cost less than a tenner to replace, the second time it was noisy as hell so I suspected the worst. I took it fully apart and found absolutely nothing wrong. I cleaned it and refilled it totally with grease and it was good as new.
A lot of noise seems to come from the bit the sprocket attaches to. It scrapes on the casing especially when dirt gets in there. Don't be afraid to liberally apply wd40 or similar to the area and see if it fixes anything. I have flooded mine with the stuff in the past trying to flush things out. I actually apply the liquid chain lube I have which is a thin oil to the area now when I do the chain which helps keep things quiet, also a lot of noise comes from the chain itself striking the front sprocket when it gets dirty.
If you need any advise then pm me as I have been running one of these daily on a road bike for over a year, maybe two years now, I forget. You need to get a bigger front sprocket so you can use normal size rears because they wear out too fast and and jump teeth on the smallest ones. That's if you want to go fast that is. 13t lasts about two months, don't even bother trying 12s IMO. I need a bigger front myself as I just keep throwing new rear freewheels on for about £6 each. I have gone through about 4 now. When I say 'last' what I mean is takes maximum leg power plus max motor without slippage. I ride em hard til they slip then ride slower to get maybe 4/5 months use out of them until they start to slip with motor plus light pedalling. Then I swap them as its annoying to ride otherwise. My front cog is severely shark tooth worn now but it won't slip as its so large, however its the right time to get a bigger one and stop this slippage problem being so frequent. IMO if you have a 250w 36v one like mine aim to gear it to 45kph no load speed with the smallest rear cog of minimum 15t and it will probably last a long time.
MY PROBLEM... So I had the bike up on the stand in the garage and tried everything to make it do the problem... Chain off on all speeds, chain on trying to slow the rear wheel to simulate riding, vibrated the hell out of the bike, wiggled all connections, wiggled battery, got brutal on it and just went nuts trying everything I could... Nothing! So I think ,
'Hey maybe its working'? So I jump on and go off for a ride. Its NOT working right at all! Immediately its juddery under load, then the battery goes from 3 bars to zero and power stops, display is on though, shows code 06, then power is back, battery indicator seems erratic. Its doing it on throttle and pas. I am 99% certain its the battery. I believe as soon as the motor kicks in or to be more exact a second or two after, the battery voltage is plummeting due to motor demand.
The weird thing is I thought if I put less load on motor, i.e. low gear, I thought I could 'diagnose' a bad battery by keeping the demand low thus voltage high and avoid lvc conditions but I can't! It does it with the throttle fixed on the lowest setting on low speed exactly as much as if I have the throttle flat out on high speed. I suspect the batt has a major issue now.
I will ghetto rig a voltmeter and go for a ride tomorrow and know for sure. I believe 30v is lvc. I actually think its more than a voltage issue with the batt because it shows 39.5v off the bike but I bet when you begin to demand amps the thing goes screwy.
So good news seems to be that the actual motor unit and install seems okay, (of course it is... I built it really well

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Also I should add the battery still works okay on my other hub drive brushed motor planetary geared bike, no cutting out or weird antics, just reduced range as I arrive at work with 2 lights out of 4 when it used to be 3 in winter and 4 lights in summer. My theory here is that the actual motor on that bike must be the size of a matchbox, much smaller than the bafang. Maybe draws less? My battery must be nearly 5 years old and done thousands of miles, maybe 7000, also been half discharged and recharged probably 1200 times by now.