Torque Arm question

[SweetTrade324]

I have a 2000w motor with a 72v battery on the way. The kit comes with a basic torque arm but I’ve heard people having issues with such cheap torque arms. I am thinking of getting the Grin v4 but it’s 45$. Is it worth the investment? The motor has 60n.m. Of torque.

 

[Tom@WashDC]

I would think its worth the investment. If you spin-out the rear drop out your screwed. Don't go cheap on that. Go over-engineered for sure.

 

[indianajo]

I sawed drilled & filed my torque arm out of a bed frame rail. 4" long, 1" wide, 1/8" thick. The oblong hole is two 5/16" holes connected and squared off by a file. Took about 2 hours.
The Mac12t had beaucoup torque. Several mac motors for sale on ebay with the wires twisted off.

 

[AHicks]

Seems like Grin is pretty proud of that torque arm....

I judge them for their ability to hold the axle snug, so it can't turn.

I'm not so sure a set of these wouldn't serve that purpose well enough -
https://www.amazon.com/TIKSCIENCE-Universal-Conversion-Electric-Bicycle/dp/B07S28NY52/ref=sr_1_3?crid=1GJ47TI999BTM&keywords=torque+arm+ebike&qid=1664327565&qu=eyJxc2MiOiIzLjIxIiwicXNhIjoiMy4xMCIsInFzcCI6IjIuOTQifQ==&sprefix=torque+arm,aps,250&sr=8-3

 

[Tom@WashDC]

I have a 2000w motor with a 72v battery on the way. The kit comes with a basic torque arm but I’ve heard people having issues with such cheap torque arms. I am thinking of getting the Grin v4 but it’s 45$. Is it worth the investment? The mirror has 60n.m. Of torque.

What is the peak amperage of your controller, and what is the peak amperage of your battery BMS?

 

[rich c]

$45 vs the cost of a frame is really cheap insurance.

 

[indianajo]

I'm not so sure a set of these wouldn't serve that purpose well enough -
https://www.amazon.com

Ha! SS Hose clamps on that amazon toy. Pretty wimpy for a 2000 w motor w/ a 72 volt battery. My clamp is 22 ga steel 1" wide held by #10 machine screws & elastic stop nut. Steel is cut from a box fan frame.

 

[harryS]

Justin at Grin did the science fabbing up torque arms and seeing how much torque could be applied by his motors before they ripped the nuts off. He can ask $45 if he wants. Certainly, his arms have been copied by a lot of shops in China.
.
I've made most of mine. I got two that came with motor kits, but I avoid the hose clamps. I'll make a short arm to fasten the arm to a caliper boss, or I'll make a one piece torque plate like this,

 

[SweetTrade324]

What is the peak amperage of your controller, and what is the peak amperage of your battery BMS?

45a controller 60a battery

 

[AHicks]

Ha! SS Hose clamps on that amazon toy. Pretty wimpy for a 2000 w motor w/ a 72 volt battery. My clamp is 22 ga steel 1" wide held by #10 machine screws & elastic stop nut. Steel is cut from a box fan frame.

I would only use the part that slides over the axle. From there it only takes a minute to fabricate a bracket that's bolted solidly to whatever is available.

 

[Tom@WashDC]

45a controller 60a battery

Yes, go with the an overengineered torque arm. With that much potential power applied to the rear motor, I surmise your drop outs could wear out over time with a poorly designed torque arm.