What happens to freegen when teeth get stripped?

[taiwwa]

It appears to me that freegen systems will result in more wear on the teeth of the hub and so over time they might be stripped. What happens?

 

[lnanek]

You mean regenerative braking with a direct drive hub motor? Why would the teeth of the hub wear at all? As far as the chain is concerned, it's just freewheeling the same as if you coasted down a hill without your feet and chain moving?

Less wear actually, since the motor is acting as a generator and the wheel is tough to turn, so the wheel turns less than if you weren't engaged in regenerative breaking and just coasted down full speed.

Saving mechanical wear is the biggest benefit of regenerative breaking since it replaces wearing out your mechanical brake pads. The amount of battery capacity it returns is barely anything. If you get 5% more range, you'd be lucky.

Freegen is something different. That's using a disk brake to slow the planetary carrier of a geared hub motor. The savings on mechanical wear aren't as great, but it gives you a way to get regenerative braking with a geared hub motor instead of a direct drive one without welding the clutch. Chain and cassette/freewheel teeth still aren't involved, though, since they can just sit unmoving and freewheel/freehub while you do it.

 

[justin_le]

It appears to me that freegen systems will result in more wear on the teeth of the hub and so over time they might be stripped. What happens?

If the gears strip then you would indeed loose the braking capability of the motor, just like you would loose forward propulsion, and you'd have to use the other brakes on the bike to come to a stop. That puts a higher onus for specifying the gear material and gear design in a freegen motor to be overengineered sufficiently that this scenario isn't likely. Loosing propulsion is annoying but not a big safety risk, while loosing a brake can be dangerous if the rider isn't swift at switching to the other lever.

I'm not sure why there would be an expectation of more wear on the teeth though. During normal use only one side of the teeth is rubbing, while during regen it would be the back side of those teeth which are otherwise not it any high pressure contact.

Our own experience with gear failures of hub motors is that the (typically) nylon gears don't fail as a result of predicable wear. Lots of people have 40,000+ km and 10-15 years of use on their original geared motors from the late 2000's with not a single issue, while in cases where gears did strip it it was often in the first months or year of use. Excessive power at high motor tempertures is definitely a problem but the evidence suggest most stripped gears are the result of material defects or poor overall tolerance control, and not general wear.