BMV V3 1000 Watt Custom Made Torque Tab

[BVH]

I've been tweaking my new E-Commencal Meta for about a week since I got it. I haven't ridden it yet because I want to beef up the electrical conductors and add a handlebar mounted, contactor activiating On/Off/Kill switch. Hopefully, those parts will arrive today. In the mean time, I've been concerned about riding it without a torque arm. Maybe I'm worring for no reason but so be it. With a very large, unusual shaped swing arm leg, I've been thinking about how to come up with a nice-looking bracket to attach a commercially available arm. Then one day, as I was looking at the dropouts, a simple idea hit me. Why not use the aluminum dropout insert bolt hole. The inserts are held in by a chainring type nut and bolt. I was going to figure out a replacement bolt but its a very fine thread and preliminary searches yielded no 8m, 8.5 threads per inch bolts. As I'm staring at the setup, it suddenly hits me....why not just stick a bolt through the center of the chainring bolt? Here's the result.

The thickness of the tab is a full 3/16" so it's a pretty beefy Torque Tab. Can anyone shoot holes in this setup? The only thoughts that crossed my mind are the size of the bolt - 10/24 - is it strong enough and Is there a possibility that the torque will tear out or elongate the factory insert chainring type bolt or swingarm area and finally, should I have another one on the other side? The other side will have the standard tanged washer that allows about 10 to 15 degrees of turn before it contacts the aluminum dropout.

A thought after looking at these pics. What if I drilled the back of the tab and aluminum dropout insert and bolted them together? That would essentially strengthen the "dropout" by closing it.

EDIT: Inserts are Aluminum, not steel. No room to drill. Scratch that idea.

 

[rkosiorek]

looks like you just used a cheap hardware store variety grade-3 threaded screw. that thing is not a bolt. no matter what the bin at the hardware store had on its label.

i'd feel more secure if a harder bolt like a grade-8 was used. you could try to find a 10-32 allen cap screw. likely that would be the strongest screw that size you could easily find.

rick

 

[BVH]

Thanks, Rick. That's easily changed. I just pulled whatever I had in my bolt bin.

 

[jag]

In the mean time, I've been concerned about riding it without a torque arm. Maybe I'm worring for no reason but so be it. With a very large, unusual shaped swing arm leg, I've been thinking about how to come up with a nice-looking bracket to attach a commercially available arm. Then one day, as I was looking at the dropouts, a simple idea hit me. Why not use the aluminum dropout insert bolt hole. The inserts are held in by a chainring type nut and bolt. I was going to figure out a replacement bolt but its a very fine thread and preliminary searches yielded no 8m, 8.5 threads per inch bolts. As I'm staring at the setup, it suddenly hits me....why not just stick a bolt through the center of the chainring bolt? Here's the result.

Very nice and clean solution for a torque arm. Did you make it manually, hand cranking a milling machine by feel? I made a slotted washer for my 9C with a milling bit in a drill press by hand cranking a cross slide vise. Very tedious and the $39 Canadian Tire drill press wasn't really rigid enough to do the milling.

The 9C comes with small torque arms similar to yours. The problem is of course that the hole in the torque arm doesn't typically match where there is a hole on the bike dropout. A handful of vendors sell torque arms, but none seem to be universally adaptible. (The longer ones could be cut and rewelded at a slightly different angle)

Suggestion: How about if a vendor could make a torque arm with the slotted hole for the axle shaft in place (this is the difficutl part to make at home) and a fairly wide and long extension but without a hole in it? Then users could drill the hole exactly where it is needed (and if desired cut or grind off unnecessary tab length and width).

The thickness of the tab is a full 3/16" so it's a pretty beefy Torque Tab. Can anyone shoot holes in this setup? The only thoughts that crossed my mind are the size of the bolt - 10/24 - is it strong enough and Is there a possibility that the torque will tear out or elongate the factory insert chainring type bolt or swingarm area and finally,

In the picture it looks like the c-c distance is about 20mm. Assuming the BMC does 150nm max torque, then the bolt should be selected with a shear stress of 150/0.02 = 7500N or approx 1500lbs. Maybe double that for safety when sizing a bolt. There are tables for particular types and grades of bolts. A knowledgeable person in a hardware store should be able to pick the right type.

should I have another one on the other side? The other side will have the standard tanged washer that allows about 10 to 15 degrees of turn before it contacts the aluminum dropout.

I think it is a good idea to put the same arm on both sides. Otherwise I suspect your torque arm will break first, then put all the load on the single torque washer. Better to have 1/2 load on each side.

 

[BVH]

I milled the slot exactly as you describe, with my drill press and cross vise. However, the machinery and endmill liked cutting vertically (like drilling) much more than horizontally. As you say, drill presses are not made for side loads. I vertically made 1/10 mm cuts. When I get more time, I'll make one for the other side. I've ordered a grade 8 bolt. The axle nuts, as long as they stay tight, help take much of the shear force off the bolt. I think I will double nut each axle nut. Thanks for the comments.