The 250W Bafang CST geared hub motor in the Milan gave-up a bit prematurely. Well it didn’t actually give-up completely, but the freewheel clutch of the internal planetary gear seized-up after being in use for close to 3,500km.
To my amazement, the Nylon planetary gears of the Bafang CST still looked quiet pristine, though. I tried a small 250W Bafang SWXH in the Milan, but its smaller planetary gears shredded after a mere 1,800km. It most likely didn’t get enough cooling inside the wheel well of the velomobile. Hence, I went with the bigger CST and its sturdier planetary gears.
The seized clutch is no big deal, since a spare part cost €39 and its an easy job to swap. While the seized clutch was undeniably inconvenient (but not unexpected), I wanted to change the mounted, slow, Marathon GT 365 tires anyway and had a spare clutch from the old CST already at hand.
This is a picture of my old Bafang CST:
My guess, the clutch isn’t lubricated well enough to deal with regularly freewheeling at high speed in a velomobile. In the past, I’ve set-up a Bafang CST for oil lubrication, to prevent a seized-up freewheel clutch, but didn’t want to mess with oil inside the shell of a velomobile this time. Lets see how long it takes till the next clutch seizes-up. Maybe I’ll have to use oil lubrication after all, or just go for a much sturdier direct drive hub motor*.
This is a picture of a Bafang CST freewheel clutch without side cover:
Anyway, I was expecting some longevity problems if a stock geared hub motor is pressed into service in a fast velomobile and ordered two 250W Bafang CST from the start. It allows me to change the hub motors quickly and gives me time to order spare parts if needed.
It also allowed me to lace one hub motor in a 559 (26″) rim, while the other is laced in a 584 (650b/27,5″) rim. Unfortunately, in recent years most tire manufacturers jumped on the 27,5″ bandwagon and discontinued some rather good tires in 26″ size. New tires (like the Schwalbe G-One line, or the GP 5000) are almost exclusively offered in 700c and 650b. Good, fast, narrow to medium wide 26″ tires are getting kind of scarce.
The 26″ wheel is my designated “winter wheel” usually shod with some wide touring tire (Big Ben, Marathon GT 365) or potentially a studded Marathon Winter if the streets get icy. Fortunately, snow and ice didn’t happened around here, yet.
The Bafang CST in the 584/650b wheel can be shod with a quick tire (G-One Allround, G-One Speed, or the fast Conti GP 5000 come to mind) for longer tours. I’ve used a cheap G-One Allround 35-584 Performance past Summer and was quite pleased with the tire. It offered pretty good grip, even in rain, but the tread was all but gone after 1,900km, though. Its currently used in the velomobile and even without thread, the grip is still pretty good. I’ve already got a new G-One Allround Evo in 40-584 size as replacement.
The Bafang CST got the spare clutch installed, the 50-559 Marathon GT 365 swapped for a 50-559 Big Ben and is ready to go back into the Milan. A new spare clutch arrived as well.
*the Phaserunner motor controller can be programmed to permanently drive a direct drive hub motor with 10-15W to compensate for the unavoidable cogging effect. If set to regenerative braking, the gain in harvested power more than make-up for the small power drain of this setting. I’ve already got a Grin Tech edition MXUS 300xRC at hand if needed, but couldn’t decide about the rim size yet.
Update 4. February
Well, that motor swap didn’t work out too swimmingly. After just 430km (2,300km total run time) the freewheel clutch in the second Bafang CST starts to seize-up as well. Guess tomorrow I’ll squirt 15ml ATF into the motor and see if this cures the clutch behavior.
Why only 15ml ATF? Well, if the motor rests, the oil level is high enough to submerge 8-10 teeth of the ring gear (I checked!), but too low to reach the coil of the stator.
When the motor runs, the planetary gears will transport the oil to the sun gear, where its squeezed to the sides and wet the little recess at the center of the clutch body. Capillary forces should do the rest to distribute the oil between the clutch body and the riveted side covers to the clutch rollers inside.