Hub motor as generator

[itchy]

Hi,

I would like to try out the following project. I would like to use a hub motor as a generator. The power generated should be variable. A kind of electrically adjustable resistance. The idea behind it is that I like to ride my bike with friends who don't ride as much as I do, and I would still like to have a training effect when I ride with them.

Is it possible in principle to use a hub motor as a generator? Does anyone know of an inexpensive model with a thru axle and disk breaks? (would not have to have much power <100W)

Best
Itchy

 

[scianiac]

Quite possible, you just need either a direct drive hub motor or a geared one with a welded clutch and a controller with variable regen. You also either need to start with a dead battery or if you just wanted the resistance you could use some type of resistance based system, possibly just a rectifier and resistor and no controller.

Either way the issue will mostly be about the motor, there are some very small hub motors but most of those are geared so you would have to weld the clutches on them and most direct drive hub motors are rather heavy for what you want I think. And the thru axle and disc brakes leaves you pretty much with just the grin all axle which is direct drive and is light for what it is but still heavy for what you want but maybe there is some other very small thru axle hub motor I'm unaware of.

 

[itchy]

Thanks for all the input. Weight is not that important. Should not be above 10kg. I am more concerned about the price. The grin all axle is around 1k€ which is way to much.

 

[scianiac]

You can certainly use a much cheaper motors, the grin is totally overkill, the issue is if you need it to be thru axle. Honestly it may be easier to get a bike with dropouts and use it for this purpose. You probably should more clearly define your goals with this project both for us and for your own project planning.

 

[neptronix]

You could buy some super heavy tires, it would cost you a lot less money than doing this electrically.
Kenda makes some 2-3lbs tires for ebikes that would do great at increasing the difficulty level for you.

A dynamo hub connected to a load ( incandescent light? heater? your choice ) would also be a cheap way to add drag.
Maybe you could charge a USB battery bank with one so the energy is actually going somewhere useful.

 

[itchy]

Thanks for all the replies. At the moment, I don't want to consider making the ride less joyful for me (e.g. fat tires or cheap bike with dropouts). The hub dynamo is a good idea, but I saw the maximum drag that you can get out of them is 20W (source). This would be ok sometimes, but I want to have at least 100W to be never restricted.

 

[glennb]

Perhaps consider a friction drive, assuming you’re using slick tires.

 

[gromike]

Could you not just run the output of a direct-drive hub motor into a 3 phase resistor?
You'd need an off/on switch, and some way to vary the resistance.

 

[offGridDownUnder]

I know of no motor which works for thru-axles apart from the Grin motor.

You'll need to address that first. You might be able to use a friction drive or a reverse 'stoke-monkey' approach to take the motor out of the picture.

 

[itchy]

A friction drive mounted on the seatpost and connected to the rear wheel might be a solution. Thanks!! I will investigate in this direction. I think the stoke monkey needs a lot of adaptation on the bike.