Regenerative braking

[flecc]

The presence (or not) of a freewheel applies equally to geared and direct drive hub motors.

I've never known of a DD motor with a freewheel, freewheels are te norm in most internally geared hub motors in the e-bike field.
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[Sylvester]

I've never known of a DD motor with a freewheel, freewheels are te norm in most internally geared hub motors in the e-bike field.
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How do DD motors manage without a freewheel?

 

[flecc]

They just turn all the time, even when no power is delivered, That's how they regenerate, they couldn't if they had a freewheel.
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[jhruk]

I'm thinking of a system with an electrically-operated friction brake working in parallel with the motor/generator. A control unit would take the brake demand signal (ie, load on the brake lever) and share it between the two retardation systems, favouring the motor/generator as much as possible. A lot easier said than done, I know, but it's basically how current F1 cars work.

But isn't that like most e-bike regen brakes work now, but without the complication of the electrically operated friction brake? I can't recall which bikes have them but they have a normal brake lever with an electrical switch, as fitted to many e-bikes. A light pull switches on the regenerative braking, which is quite low due to the limitations of the lithium battery mentioned above, while further pulling initiates the conventional mechanical brakes. When the battery is full there'd be no regen braking so you just pull the mechanical brake a bit harder.

 

[Sylvester]

They just turn all the time, even when no power is delivered, That's how they regenerate, they couldn't if they had a freewheel.
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I meant why do you need a freewheel on a geared motor but not on a DD? Actually, answering my own question, maybe the drag of the high-revving geared motor would be more significant on the overrun (measured at the wheel) than that of a DD motor. Which would make a DD motor more efficient for regen braking than a non-freewheel geared motor.

 

[Sylvester]

But isn't that like most e-bike regen brakes work now, but without the complication of the electrically operated friction brake? I can't recall which bikes have them but they have a normal brake lever with an electrical switch, as fitted to many e-bikes. A light pull switches on the regenerative braking, which is quite low due to the limitations of the lithium battery mentioned above, while further pulling initiates the conventional mechanical brakes. When the battery is full there'd be no regen braking so you just pull the mechanical brake a bit harder.

The pull required on the brakes would depend on the state of the battery, so would be inconsistent and therefore unsafe. I think one needs a constant relationship between brake effort and retardation.

 

[flecc]

I meant why do you need a freewheel on a geared motor but not on a DD?

The motor speed is geared down about 6 to 1 to drive the wheel. Without a freewheel, pedalling unpowered would mean up gearing the pedal effort 1 to 6 to spin the motor fast, creating excessive drag and making pedalling alone difficult.

There's also drag on DDs of course, but not as severe as that latter case.
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[Sylvester]

The motor speed is geared down about 6 to 1 to drive the wheel. Without a freewheel, pedalling unpowered would mean up gearing the pedal effort 1 to 6 to spin the motor fast, creating excessive drag and making pedalling alone difficult.

There's also drag on DDs of course, but not as severe as that latter case.
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Yes, that makes sense.