20mm axle fork, front hub adapter

[whereswally606]

so both my dh ebikes have 200mm travel stantions with 20mm axles. boxxer ones.

and I have wondered for a while about the viability of creating an insert which would allow the use of a hub motor on the front forks which normally take a 20mm axle.

I saw Justin's hub motor that can do this and this is my poor (with lathe) mans alternative if indeed it can work.



The idea is that you try your best to get the axle through with the wiggle room that the 20mm give you on the fork, you may need to cut one of the axles short and/or spread the forks(I don't really approve of this) and that should allow the hub maybe to go into the fork loosely. then from the outside of the forks push on the inserts each side over the axle and through the 20mm hole. the hex is to provide extra flats for a stronger torque arm to grip.

I am thinking flat tyres would be a pain to I would use those linear inner tubes where you can take them off without removing the wheel.

Still I fancy giving this idea ago but don't have the time so figured Id put it out in the wild for others to maybe run with.

 

[ferret]

You can't make the 10mm double D "slot" in a lathe or a mill. That shape can be broached or EDMed.

Avner.

 

[whereswally606]

my other idea was laser cut a stack of them like washers and have two bolts to align them and secure to a torque arm.

but cant see why this inner couldn't be done on a cnc.

 

[E-geezer]

The sharp inner corners.

You could print them, cast them and turn them down on a lathe if you could work out the shrinkage.

 

[whereswally606]

ok this is my second iteration which I think could be cheaply laser cut and normal threaded bolts to align it all. Opinions?

obviously if a hub motor can be slipped into the dropouts its all a non starter but if it can then we have a nice way of using 20 mm dropouts with front hub motors.

 

[MadRhino]

A Boxxer lower is Magnesium and pretty thin. It is good for what it is meant for, but not to take the torque of a motor. No matter how good you do it, it is running after catastrophic failure. I have seen this, and you don't want a fork breaking under you, seeing your motor flying backward just before you scratch the pavement with your teeth. Then, even if you succeed and ride it very low power to keep it from breaking, it will not have any of its suspension qualities anymore. I am using Boxxer WC forks for a decade and I love them, but I would never fit a motor to one.

I don't recommend a motor on front suspension because it rides like sh*t, but: If you really want to fit a motor to a suspension fork, do it on an old heavy fork with thick Alu lowers or a robust, even heavier inverted fork.

 

[\/ampa]

There seems to be a market hole.
Some designs here https://endless-sphere.com/forums/viewtopic.php?f=2&t=80360
With the right material produced should work for a few KW.

 

[Drunkskunk]

I think your last idea has some merit. Maybe. If you can get the fit tight enough.
However, I agree with MadRhino. this is a bad idea on a Boxxer. Old, thick aluminum forks might hold up. Marzocchi Monster for example, but a modern fork would snap with the added torque and weight. I think you would be blowing out valves and seals on most forks with the added weight of most motors, too. That's far more unsprung weight than they were designed for.

Maybe this would work for a Q75 or Q85. I think anything bigger is going to be trouble.

 

[whereswally606]

Thanks DrunkenSkunk && Vampa,

I was only thinking q85 or rather its disc brake enabled sibling. The idea I had was to balance out the weight and power for an overall awd bike.

It one of those ideas where I just want to try it and didn't know if anyone else had and hadn't shared or had and I hadn't heard about it or most unlikely was actually a good idea that I came up with. The fourth possibility is that its a terrible plan which will see me toothless, and drinking soup until I get some dentures fitted. I will in time maybe try this but I have many other distractions.