Bafang SWXH with steel planetary gears: A short summary

A summary after 1700km
The oil lubricated Bafang SWXH is holding up great so far. Since replacing the shredded Nylon planetary gears with steel planetary gears it got noticeably louder under load. While the noise was really annoying at first it settled since the gears worn in but it’s no stealth drive anymore by any means.

Better freewheeling
Pedalling downhill above the max unloaded speed of the hub motor (>45km/h) I can feel a definite speed increase when switching off the motor. While its relatively hard to go above 48km/h with running motor the same effort immediately brings me above 52km/h when the motor is off. The oil probably produces some drag between magnet ring and housing since the magnet ring is spinning fast ‘backwards’ with only a small gap between the two. I never noticed that behaviour with or without oil filling and Nylon planetary gears though.

ATF lubrication and cooling
So far this little heavy-metal-in-oil experiment runs quite successful. Apart from the occasional drop of oil on the freewheel side. It keeps the chain slightly oily as well. Probably 70ml of ATF for the initial oil filling was slightly too much. 60ml would’ve been better.

No hill climber
Since my SWXH is fast wound for a 20″ wheel it’s no great hill climber after relacing it in a 26″ rim. The motor noticeably bogs down by 5-8km/h on slight uphills even with a 35A controller. It would perform better up hill laced in a 24″ rim I guess. We’ll see. My area is fairly flat and hill climbing of no real concern.
For now it stays in a 26″ rim till I find out if I like 26″ front wheels on my Sprint, better go to 24″ front wheels or simply keep the 20″ wheels.

Different battery voltages
While using a 13s (48V) or 14s (52V) LiPo battery most of the time, I recently choose a 12s (44V) LiPo battery for my commute to avoid unnessesary stress to my trike, keep the noise down and the SWXH a bit cooler in warm weather. Top speed is still around 40km/h and average speed dropped slightly from 32km/h to 28km/h. It takes me only 10min longer for my 35km commute home.

Bafang SWXH at 92V
I’m the first to admit that using a small SWXH hub motor to propel a unfaired ICE Sprint FS 26 to 68km/h top speed on the flat isn’t something someone should do regularly.

The steel gears in my Bafang SWXH sang and the tiny motor still pushed quite hard when accelerating from 40km/h to 60km/h. As the Hub Motor and Ebike Simulator predicted with a 22s battery (92V off the charger) and 25A the controller pushed slightly over 2kW into the SWXH to produce around 1.69kW of continious power to reach 68km/h top speed. Sure it got quite hot (80°C maybe?) but made the 12km ride without a hitch.

The only downside on that test run where the constant throttle cut-outs the Lyen 6 FET Mini Monster controller had under 30km/h even with a very light hand on the throttle. It should have worked ‘out of the box’ since the Lyen is rated for up to 100V. I haven’t found time to reprogram and test the Lyen again. Maybe it needs some surgery with a soldering iron to make it behave and to fix the throttle cut-out problem.
For the time being the trusty KU123 12 FET controller is back on duty.

How bad is the noise?
While the SWXH was quite shockingly loud with new steel planetary gears and 35A controller at first, the noise level got bearable after about 300km and acceptable for use in a recumbent at around 1,000km. It still gives quite an audible feedback when accelerating or going up hill. On the other hand the ‘hot rodded’ SWXH is totally silent when coasting or pedalling and relatively quiet when driven under 30km/h.

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One Response to Bafang SWXH with steel planetary gears: A short summary

  1. punjehl crane says:

    Hi, do you know where these steel gears for the swxk can be found? mine has the 38t ones

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