Slimjim. The dropouts are exactly as shown in the photo I pasted up a page or so back (in fact that's my frame). The width of each dropout is 8.3mm.

 

From my understanding, the forward motion of the wheel will place a downward force on the swingarm - as shown in my diagram below. The area shaded in pink is where the item may be susceptible without reinforcement... ie, if the swingarm was made of (say) nylon, this is where it would bow downwards in response to the motor's driving force. I think the rod (in red) would take the torque strain away from the arm itself.

 

The vertical positioning of the back end of the rod may be determined by where it would avoid coming into contact with the chain.

 

http://i64.tinypic.com/29wq3av.jpg

Edited September 25, 20169 yr by Slopes

I think the rod (in red) would take the torque strain away from the arm itself.

 

The rod will go into compression, so will not support the torque arm. As I said earlier, if you want to use a compression member, it needs to be rigid, like tube or box section.

The rod will go into compression, so will not support the torque arm. As I said earlier, if you want to use a compression member, it needs to be rigid, like tube or box section.

This is what I struggle to understand, d8veh. I can see that if torque was caused by the backward movement of the bike (if the motor was in reverse), the rod would be forced to compress (and thereby bend or bow). But it seems to me, with the forward movement of the bike the anchored rod would be forced to extend (which, of course, it would resist). This is what I try to illustrate with my diagram.

Edited September 25, 20169 yr by Slopes

The wheel is turning the way your pic shows therefore the hub is trying to turn the other way.

The wheel is turning the way your pic shows therefore the hub is trying to turn the other way.

But aren't the hub and the wheel all of a single piece? The centre point of the torque is where the axle tries to spin in correspondence with the rest of the moving wheel (in a clockwise direction according to my diagram), but is prevented from doing so by it being fixed to the static dropout. This places a clockwise - downward - force onto the resisting dropout which spreads up into the arm it is attached to. This creates an 'extending' force on the rod (it tries to stretch out the rod).

The stator (stationary part of the motor attached to the axle) exerts an opposing force to the direction of the wheel rotation. Only the motor casing, which also contains the magnets moves with the wheel.

Better to say the axel is pushing the frame the opposite way.

The arm is being forced counterclockwise.

 

Straight swing arms do work mine is well over 10 years old and still fine.

Agreed with above, if motor is trying to turn wheel clockwise in above pictures, it can only do so by trying to turn the swingarm anti clockwise. Equal and opposite reactions. I'm assuming also that both ends of your hub axle have double flats, which sit into the inverted-U shaped dropouts on both side. This is how the hub transfers the reaction torque into the dropouts, then into the swingarm. I.e. a tension rod or cable would have to be above the swingarm to be in tension, which would be more difficult to achieve a suitable shape of vertical torque arm.

OK - I get it now. Thanks everybody... back to the drawingboard.

It's a lovely frame. Please consider taking the advice given to convert to a crank drive instead of hub motor. It'll make the bike handle more like it was intended to and won't risk ruining the swingarm.

Edited September 25, 20169 yr by danielrlee

Better to say the axel is pushing the frame the opposite way.

The arm is being forced counterclockwise.

 

Straight swing arms do work mine is well over 10 years old and still fine.

D8ve - a straight swingarm would be much easier the build - although it would still have to splay from the narrow pivot and out around the wheel.

Agree with the others, mid motor all the way for this one.