Heavy Duty Torque Arm - Disc mount, clamping optional $35

[dmwahl]

Still have more of these?

You bet. The Paypal link will let you know when they're out of stock, I'll order more before then as they've been selling well.

[dmwahl]

Bump. Have 7 of these available.

[spinningmagnets]

The unit I bought looked fantastic, but since it worked better for a friend, I ended up giving it to him. In the pic below, you can see that there are minor variations in the angle of the 10mm slot for the axle. You might consider possibly making the two holes for the disc brake mounting holes into perpendicular slots, to allow for more frames to fit it. Just a thought...

Part of the reason I bought one without knowing the exact angle, was to record it's angle (for future builds), since I knew if it didn't fit my current frame, I could use it later, or sell it. Based on the sellers customer service and the quality of the product, I would definitely buy again. Well worth the price.

[dmwahl]

You might consider possibly making the two holes for the disc brake mounting holes into perpendicular slots, to allow for more frames to fit it. Just a thought...

Yes, definitely a consideration. I didn't on this one because I made it for a specific frame (my KMX) but it wouldn't be too difficult to do. It's too bad the disc brake standard doesn't define the hole location more completely, but they probably also didn't design it with people like us in mind.

Based on the sellers customer service and the quality of the product, I would definitely buy again. Well worth the price.

Appreciate the compliment

[sonnetg]

Really nice work, but fitting or drilling this torque arm may be a major setback for many.

Would it be possible to epoxy this torque arm onto the frame using TD420 weld epoxy?

[methods]

Why the hell didn't I think of that ?!?

Very nice.

-methods

[dmwahl]

Really nice work, but fitting or drilling this torque arm may be a major setback for many.

Would it be possible to epoxy this torque arm onto the frame using TD420 weld epoxy?

I wouldn't recommend it, it's designed to attach to the disc brake mounts and I didn't even consider epoxy when I designed it. Filing to fit only takes a few minutes anyways. Drbass has one that you can epoxy on if that's the route you'd prefer. Honestly I designed this for my own use with no intent to sell it, but it worked so well for my bike I figured I'd make them available. Drilling a clamp hole is definitely not required, but I figured it would be a nice option to have for those with the tools/skills to do so.

[methods]

Epoxy has a failure mode which is unpredictable, instantaneous, and catastrophic. Its great to aid mechanical fastening but insane to use as a primary in a braking system and likely creates serviceability issues.

Did you perform an analysis to see if the forces applied are similar enough to the forces anticipated with a standard braking application? If so... it should suffice yes? Given that I have had 50mph ebikes with brakes that were zip-tied on... I would certainly give it a whirl.

How come we have not solved this axle issue yet? Seems there should be an elegant solution that dominates. This is the closest I have seen, as rocking is a bugger on drops, and the clamping force should really help.

-methods

[sonnetg]

Really nice work, but fitting or drilling this torque arm may be a major setback for many.

Would it be possible to epoxy this torque arm onto the frame using TD420 weld epoxy?

I wouldn't recommend it, it's designed to attach to the disc brake mounts and I didn't even consider epoxy when I designed it. Filing to fit only takes a few minutes anyways. Drbass has one that you can epoxy on if that's the route you'd prefer. Honestly I designed this for my own use with no intent to sell it, but it worked so well for my bike I figured I'd make them available. Drilling a clamp hole is definitely not required, but I figured it would be a nice option to have for those with the tools/skills to do so.

Thanks for your feedback. Dr. Bass seems to be out of stock, and no updates on the next batch.

I think I will hold off for now, and probably use a grin or some other generic torque arms for now. It would be nice to be able to epoxy or bolt a torque plate to the frame, even if the IS mounts doesn't line up. I dont have much tools, but I should be able to drill a hole with a hand held drill i suppose.

Thank you.

[dmwahl]

Did you perform an analysis to see if the forces applied are similar enough to the forces anticipated with a standard braking application? If so... it should suffice yes? Given that I have had 50mph ebikes with brakes that were zip-tied on... I would certainly give it a whirl.

How come we have not solved this axle issue yet? Seems there should be an elegant solution that dominates. This is the closest I have seen, as rocking is a bugger on drops, and the clamping force should really help.

-methods

I did do a FEA analysis on it to find the torque required to spread the dropouts, and while I don't have the results in front of me right now, the forces at the disc brake mount itself were well below the yield strength of the material even at 100Nm of axle torque. Clamping the axle flats helps, but the real resistance to spinout is from the axle nut torque. The torque arm provides a larger surface for friction with the frame. That's why axle nut torque is so important.

I didn't figure out what the forces due to braking would be, but given the brakes can easily lock up the wheel I have little doubt they're greater than what the motor will generate.

[methods]

Awesome! I was hoping you did an analysis.

Clamping the axle flats helps, but the real resistance to spinout is from the axle nut torque.

I categorically disagree with the statement that the axle nuts provide sufficient (or even reasonable) resistance to spinout. Perhaps in a regen-free bike... but add any sort of powerful regen and the rocking back and forth loosens them up almost immediately. Unless the nuts are fixed (like a castle nut, double nut, wire nut) they will back out and fail at the worst possible time, winding up your motor leads and leaving you sad. Toward the end of my ebike adventures I did not even bother with axle nuts but to snug things up a bit.

Too each their own with that lesson

-methods

Edit: And of course I speak only of high torque applications. I am sure that with standard gear you can get away with it.

[dmwahl]

I agree that with sufficient clamping of the axle flats you wouldn't need an axle nut, perhaps I should have clarified my statement a bit more. What I meant is that on most applications (and many of the people on ES are certainly not in the "most" or "usual" categories), the axle nut torque can be sufficient even under regen. I don't think many realize though, just how much torque is required to keep everything in place. Justin did some tests showing the effect of the axle nut torque, and while his tests were obviously very simplified vs a real ebike application with regen, vibration, etc, they still show a strong relationship between nut torque and spinout torque. It's unfortunate that there aren't any good, published engineering studies on the topic, and probably won't ever be if I had to guess.

Code: Select all

Nut Torque	Axle Spinout Torque

hand tight	38.7 N-m
30 N-m		78.3 N-m
60 N-m		83.9 N-m
90 N-m		96.6 N-m

Although there was a pretty significant increase in the spinout torque when going from loose nuts to moderately tight nuts, further tightening, up to 60 and then 90 N-m had only marginal effect at increasing the ability of the dropouts to resist spinout. The first 30 N-m gives a full 40 N-m of extra spinout resistance, but doubling the tightness of the nuts to 60 N-m only increased the spinout torque by 7%.

For the record, I periodically re-torque my axle nuts with a torque wrench to make sure they're tight, and highly recommend that others do the same.

[methods]

Thanks for keeping it data
I appreciate the effort to post numbers that back up your assertions.


Early on (and perhaps still) the axles arriving in the hubs were cut threads instead of rolled threads. These threads would strip very easy. We tried all sorts of stuff like running longer nuts (lug nuts from a Porsche) to try and avoid the stripping but it was basically pointless. The axles were like butter. After stripping we would have to space out the nut with washers.

Perhaps its just legacy data.

thanks,
-methods

[dmwahl]

Thanks for keeping it data

I like data, hence the last line of my signature. All the self-reinforcing "rules of thumb" and "conventional wisdom" are just old wives tales without it. For my day job I design and support life-support equipment, good data there is literally a matter of life and death.

Regarding the axles stripping, I'm definitely nervous about over-torquing the nuts which is why I went on the low end of around 50ft-lb and check it frequently. You may already know this, but for the benefit of others reading I'll give some (oversimplified) background. The load on a bolt/nut combination is largely carried by only a few of the threads and the goal is to create a clamping load. As the torque is increased, the bolt itself (or axle in this case) stretches out. The force applied by the stretching of the bolt is what clamps together whatever is between the two parts. Part of the torque goes to create the clamping load, the other to friction between the threads. This is why lubrication such as anti-seize on the threads can actually improve the clamping load, it increases the percentage of tightening torque that goes to creating the clamping force rather than friction. Obviously you want some friction in the threads, but the way the math works out is generally such that lubrication helps. Any kind of plastic deformation in the nut/bolt will to some degree strengthen it from the work hardening, but also reduces the prevailing torque that helps keep it from loosening. By the time you notice it, the damage is done.

All this is to say that axle nut torque can absolutely be important, but due to other factors as you've pointed out may not always be the best way to restrain the axle relative to the frame (ie prevent spinout). It's unfortunate that you can get a motor capable of such high torque that's built with an axle that can't handle it. A lot of the higher power motors seem to do a good job handling the power from, say, a thermal or electrical perspective but then go and use the same small axle as a 500W motor to maintain compatibility with a standard bike frame. I'd rather have them all use a bigger axle with stronger (roll formed) threads and force the user to take extra measures to securely mount it, but that's not what the market pressure has encouraged.

[methods]

You may already know this, but for the benefit of others reading I'll give some (oversimplified) background. The load on a bolt/nut combination is largely carried by only a few of the threads...

That's what we are here for dmwahl, please always feel free to explain in detail to me (or anyone else) the particulars of anything we are working on. If some random guy on the street in China reads into the minutia and it results in higher quality products - WIN.

thanks,
-methods

[migueralliart]

I've been abusing the $hit out of my design but they're filed to fit and close ended. I have heard that clamping is even stronger so I don't see how anybody could have any issues with these arms.

Its always good to see more options to fit different needs.

[methods]

My next torque arm will be clamping

-methods

[dmwahl]

Bump. 4 remaining.

[wannesd]

will these work for the M16 axle of the mxus v3?

[dmwahl]

will these work for the M16 axle of the mxus v3?

I don't know, but if you print out the pdf on the first page you can check.

[wannesd]

will these work for the M16 axle of the mxus v3?

I don't know, but if you print out the pdf on the first page you can check.

Haven't got the motor yet, still another month to go.

[wannesd]

I'd like to buy 2 of these.
Could you drill the clamping holes for M6? I will do the threading myself.

Shipping to Belgium.

Thanks,
Wannes

Made from 3/8" (9.5mm) stainless steel and designed to bolt on to a standard IS disc brake mount. Can be used with or without an installed disc brake. No need to modify your frame, remove paint, epoxy, etc. Bolts on in a few minutes. I designed it for my KMX trike frame, but it should fit many other frames with an IS disc mount. Print the PDF below to verify your own frame will fit.

Features
- Standard IS disc mount geometry
- 3/8" (9.5mm) Stainless Steel
- 9.90mm wide opening, file to fit your specific axle for a precise fit
- Includes flats specifically sized to drill and tap hole for a 30mm M6 bolt (you will need to drill/tap yourself, it it NOT included).
- No sharp corners to reduce stress concentrations and weak points

Use this PDF to verify fit prior to purchasing. It needs to be printed actual size, not scaled or sized to fit which is often the default setting.
Profile PDF - PRINT ACTUAL SIZE, NOT SCALED

File to 3D print the part to test out fit below. I made the file 3mm thick instead of 9.5mm (3/8") so it prints faster and uses less material, but the profile is identical. Note that many 3D printers don't have great resolution, so sometimes holes and internal cuts like this part can be a tight fit when made of plastic but a better fit when properly cut out of metal.

torque-arm-stl.zip

Shipping
Price includes USPS shipping in the US. If you are not in the US, please PM me and I can figure out shipping for your country and send you an invoice via Paypal. I will not do things like mark it as gift, sample, etc to avoid you paying customs or other country specific fees. Countries I've already calculated shipping for are listed below.

Prices outside US
Canada - $40
United Kingdom - $45

To purchase via Paypal, go here.
Price is $35 which includes US shipping. You'll need an address set up in Paypal, which allows me to automatically print a shipping label and expedites the process significantly. For non-US orders, pm me with your Paypal email address and I'll send you a request or give you my paypal email address.

They are in stock and ready to ship.

Design thread here

I will support this as well as I can, but can't answer questions like "Will this fit frame _____?" or similar build specific questions. I've included a PDF to verify fit, and if anyone would like I can also post a .stl file to 3d print the design as well.

[dmwahl]

I'd like to buy 2 of these.
Could you drill the clamping holes for M6? I will do the threading myself.

Shipping to Belgium.

Thanks,
Wannes

I'm not set up to do the drilling right now, but if you PM me your address I'll get a shipping quote.

[wannesd]

PM sent.

[dmwahl]

Just got another batch of these, plenty in stock now.