Universal torque arm

[Dumsterdave]

Im looking for a torque arm for my new kit, but there are so many and they are all a bit different. Honestly, I dont even know what the purpose of a torque arm is. I take it that it will keep my wheel from coming off, but i don't know how. I have a 1000w rear hub

Thanks

 

[mark5]

What make and model bike will you use? Is your frame, more importantly are your dropouts, aluminum or steel?

Read up on how torque arms work: Grin Technologies on Torque Arms.

 

[spinningmagnets]

When the motor is applying torque to spin forwards, the axle is trying to spin backwards. If you are using more than 250W, the hub axle will eventually twist out of the slots in the frame, called "drop-outs".

The more power you apply, the faster they spin-out, while breaking the frame or forks. This is not theory, it is well-established. Take a quick look at the pics in this post:

https://endless-sphere.com/forums/viewtopic.php?f=2&t=26444&start=75#p628023

 

[Ykick]

Simple yet important item that can often be fabricated with modest shop tools.

Nothing wrong with purchased ones either but if cost/time is important, 'really not hard to fabricate. And some frames will just need a custom TA (torque arm) regardless.

I suggest learn how to upload photos (640x480, less than 120kB) of your bike and components. You’ll probably receive much more specific advice for your eBike project.

 

[dogman dan]

The Grin universal torque arm is a real good one. One should be sufficient for your particular setup.

If your bike has steel rear dropouts, particularly the semi horizontal type common on the less expensive bikes, you may not really need a TA.

You do need one, if you have the shallower, vertical type dropouts.

What a TA does, is keep the axle from rotating in the frame. As the motor pulls you forward, the axle is trying just as hard to rotate the opposite direction. so a lot of force is trying to rip that axle out of the frame.

Making your own is not very hard, using simple tools like a hacksaw, drill, and a small round or flat file.

This might be a good place to put up some pics of what I did last summer. I wanted a good universal torque arm, but copying Grins with hand tools is a bit hard. I tried very hard, for several months, to come up with an independent design, not copying Grins.

In the process of evolving to something that would truly fit every bike, I ended up with a nice, easy to hand make design. Alas, when done, I found I had still copied the essence of the grin TA. That was the idea of having the hole tilted about 30 degrees to the angle of the arm. This tilt was the key to having the TA fit both vertical and horizontal dropouts.


Here is what I came up with, for a universal TA. It combines with the second piece of a typical two piece front torque arm.

 

[friendly1uk]

For a person to push a car, their shoes must grip the floor well, because as hard as the car is pushed, their feet must also. The motor is no different. It needs something to push off from. It's stationary object is the dropout which it tries to twist round in with the same force that is turning the wheel.

The two piece kit shown above is never going on one of my bikes. The way it's utilised there may work without the long bit, as the short bit is hitting the frame. It's as good a fit as I have seen. Normally the expectation is that the long bit being clamped to the frame will stop it moving. A pipe clip holding a hard rounded surface to softer rounded surface to resist a transverse force. Many of these you see have twisted. Correctly orientated they work, but generally they are used wrongly. Lets pretend the frame above offered no interference. The turning force would be trying to straighten the two pieces inline with each other. To come inline the pivot point between them need move 20mm upwards. This action would move the hose clamp around 5mm outwards. The clamp must resist moving sideways when the motor has a 4 fold leverage advantage. Even a 250w geared hub could put 100lbs on that skinny stainless band and there is no meaningful stiction to overcome. The frame might be alloy. It is just horrible imo. Frankenstein stuff not a marketable solution. The smaller piece is often useful though. I see two alternatives here straight away. The pivot bolt could be used to hold washers on the other side, that butt up to the frame to stop movement, so the long bit was not needed. Another idea would be to point the short bit the other way, putting a bolt in the mud guard location to stop it turning. Or drill through the short bit and pop a bolt through it to rest a bit lower on the edge of the mudguard eye. This would also form a hook, so you have a wheel retainer should the nut come loose.

Avoid using that pipe clip as the sole anchor when the force is trying to slide it along. It's only real use used that way is assisting a thin front fork dropout that won't hold 250w safely

 

[friendly1uk]

I had a similar kit. Discarded the long arm and bolted the short bit directly to my large dropouts. Alternately I could of span it and drilled for a mudguard fastening. Recently I have noticed some of these other one's that seem prime for chopping and drilling to pick up on local bolt holes.

http://www.ebay.co.uk/itm/Torque-Arm-Drehmomentstutze-12-14mm-for-Electric-bikes-e-bikes-Pedelecs-/262431332139?var=&hash=item3d1a20572b:m:mVvJh0e85EwHj3DRjMkygWw