dogman wrote:For that power level, 1/8" could be thick enough....
Kin wrote:How are you making the plates? As in, what sort of equipment do you have access to? I just ask this because you want the torque arms to be really tight. You can design your torque arm to be tightenable, but many people also try to just have very tight torque arm from the get-go and not have to develop a way to tighten the sidewalls.
I ask this question first because steel isn't that easy to cut nicely. I machined my torque arms in Aluminum with a CNC first just to make sure I didn't screw up the G-code*, because it was going to take a lot of effort to cut the stainless steel. Torque arms don't require a lot of material though, and so I just used some scrap. You want to use a steel that's harder than the softer steels, but I don't see why you would need an insanely hard steel (someone else nicely pointed out that the concern with ultra-hard steels might be the axle, often made of softer steel, deforming).
*Honesty's sake: G-code I don't know. The guy at work who runs the CNC machine helped me machine the file I made.
John in CR wrote:Cal,
Whatever you do don't copy Kin and use aluminum, because it's just not the right material. Steel is what you want, and you want to make them the clamping type, so nothing too hard, since you have to drill holes. Any metal shop will have scraps you can use, and then they can help if you need something welded. Scrap yards are another perfect place. My new favorite material for use in my clamping torque dropouts (I make them part of the bike.) is steel from broken leaf springs. It's cheap, but a far better alloy of steel than just mild steel. If you do go that route don't use sections that look deformed where a mounting plate compressed it during years of service, because that area can be work hardened and virtually impossible to drill a hole.
How thick? That depends upon how much axle you have to work with. There's almost no such thing as overkill when it comes to torque arms and dropouts. I've had slot type that were .5" thick mild steel wallow out over time due to the back and forth forces of regen. All of my latest ones are about .75" clamped width on each side of the axle, and my new test motor is probably getting a full 1", because those are high power motors.
It also depends on your motor. Some of the smaller ones have small axles and narrow flats, and those axles are often lower quality steel. Even though they are lower power they still warrant substantial width to help ensure the axle doesn't spin, since there's less contact surface length. Those with thru axle wires also warrant more width, because the wire side axle is inherently weaker and can't be clamped as tightly or you can crush what is essentially a hollow tube.
Build it so you don't ever have to worry about it, and a clamping type gives you piece of mind that axle nuts don't even matter. One of my bikes runs 12kw and has and axle nut only on one side, and it's only there so the threaded axle isn't a sharp protrusion to clip a shin.
dogman wrote:For that power level, 1/8" could be thick enough. But as said above, make em as thicker if you have the length on the axles to do it. The thin torque arms can just end up cutting a groove into the axle threads.
1/4" mild steel strap about 1.5" wide is easy to find, and easy enough to cut with simple tools. Make your hole undersize, and file to fit the last mm.
Kin wrote:For comparison, I used ~8mm plates on my rear mac (1/8 inch is 3.175mm), because that's what would fit. Check what fits, and give yourself a little bit of spare thread room.
Kin wrote:It sounds like, by the others' descriptions, this might be doable with hassle using something as simple as a dremel tool, the right disks, and a file. But going to a metalworking shop might also work.
I don't have experience finding such shops, but I do notice they exist a lot nearby universities, if you're in that kind of populated area. Frankly, i've been told all of California is of sufficient population density that I bet there's cause for a machine shop nearby. You can also see if your local "hackerspace" would have the equipment, if you want to get into this on a more extreme DIY level (there's always another level, it seems). But besides those terms, also look up "rapid prototyping" or just "prototyping" because companies that specialize in one time builds are usually working with small scale companies to fabricate their prototypes. Finally, if you're really having a hard time finding, this could be within the skill-set and tool-set of a good auto mechanic that knows how to do a bit of metalwork. If you know how to talk to people, that could very well be cheaper than a prototyping company.
Another option is an online place. Pololu, Ponoke, and Bigbluesaw.com are places I know that do 2D cutting, which is optimal for what you want. You probably don't need to weld the torque arms, assuming you use Scotch-Weld DP420 (look at Doctorbass's thread).
For all the hassle it will be to have a local shop make the torque arms, is there some reason why you do not want to do something prefabbed like the Grinn's torque arm? I don't know much about your frame, I surmise that might be relevant.
As always, here with excess information. Wait for the other posters to get a concise and useful response :p.
iamsofunny wrote:You can use steel bar stock 1/2" thick and weld three pieces together rather than cutting a slot. You'll have to make some sort of trailer hitch thing anyway and stick welders are pretty cheap.
dnmun wrote:why even try to fabricate them if you don't have tools or workshop? you can buy the torque arms from a number of sources.
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