Coyote DIY Torque-arm, open source 2600W DD hub

[spinningmagnets]

I recommend that copies of this clamping torque-arm be made from mild steel, aluminum was used to make the prototyping easy.


Here is the current version. If was doing this over, I would make them 8-1/4 inches long (instead of 6 inches shown) and use two U-bolts instead of one. That size would fit in the smallest post office "if it fits, it ships" box, roughly $10 to anywhere in the USA.

edit, I stumbled across an interesting fact. I've swapped the first version of these plates onto my fat bike, so I can test a DD hubmotor. When dry fitting everything together, I suddenly realized I could move the entire plate to the rear just a little, and that would tension the chain enough that I wouldn't need a tensioner, if using a 14T single-speed freewheel.

your derailleurs might be longer or shorter than mine, so your chains will be shorter or longer than mine. That being said, these plates have a 10mm wide slot for the axle, and the length of the slot is 1.6 inches (42mm).

The distance from the center of the bolt hole (the bolt which goes into the stock frames' drop out) to the front edge of the slot is 1-3/4 inches (55mm). If you want to try to make these, I recommend mocking up one of them out of 1/4-inch thick plywood, which is cheap, fast, and easy to cut.

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Original thread starts here:

Its only a matter of time before mid-drives take over the off-road market, but...for a street hot rod ebike? large direct drive (DD) hubs remain popular. The big hold up is torque arms, and the wide variety of frames out there. Some frames have the desirable broad and flat drop-outs, which allow a lot of options. Here are 6 pages of Torque Arm ideas: https://endless-sphere.com/forums/viewtopic.php?f=2&t=26444

A while back, an Australian ES member used laser-cutting and water-jetting to make a 3-level torque-arm for a specific popular off-road frame. The three levels were welded together to create a desirable clamping element (here's the link, thanks, Sam https://endless-sphere.com/forums/viewtopic.php?t=33767). It worked, but the more levels/layers you use, the more expensive it would be.

https://www.electricbike.com/cadcam-the-diy-builders-best-friend/

It would work great if you could just use slightly thicker metal and use just one layer. If you simply use very thick steel, no clamping element is needed (like Doc's beefy TAs), but...there must be a way to have a single layer of thinner steel (or possibly even aluminum, with a clamping element).

I think I found something, and I need everyones help to find a purchase source, and alternates. Imagine this as a thin single-layer steel water-jetted part:

and then add these:

http://www.mksinst.com/product/product.aspx?ProductID=333

 

[e-beach]

Hummm....giving this one a good think....as my next bike will need a one piece, one-off machined TA because nothing else around here will fit, Doc's or otherwise.....Quoted as $200 USA locally to make.......subscribed.

Edit: As a potential alternative design, I am up to something like this..........sorry it is a bit sloppy at the moment.......



I am of the opinion that for a universal Torque arm is hard to do in only 1 piece, but maybe in 2 pieces plus 3 bolts....maybe a bit of welding once set for the specific dropout.

 

[spinningmagnets]

There is no perfect TA design for all bike frames. But...there MUST be a way to have one design that covers a fairly wide variety of common frames, right? In my mind, the issue remaining is how the end customer would attach the TA to the bikes stock drop-outs. I want to explore ideas for builders who don't have a welder, or don't want to pay for a shop to weld. Anyone willing to do some custom work at all will have a drill and hacksaw, and...since the best possible version of what I am envisioning would still require some work by the end-user (to attach the TA to the bike), it is not unreasonable for this to be directed at someone who would be expected to have a drill and hacksaw, and know how to use them.

I have bought the torque-arms from Grin Tech, I like them, and I will use them again in the future. I can't emphasize enough how wonderful they are. They are a very strong type of stainless steel, and are stronger than they might look, since competing TAs have a similar thickness of metal (but, are made from soft junk steel). If they will fit on a frame you want to use, you will not save any money or effort by copying designs pondered in this thread, just get the Grin Tech TA.

Personally, I would rather drill thick aluminum than thin steel. Steel is the perfect metal for a TA due to the need for them to be reasonably thin, so the axle-nut can screw on with an adequate number of threads. However, drilling steel remains a PITA and wears out bits in a way that aluminum doesn't. If this is made from aluminum, the end user can easily drill and bolt the blank end to any one of hundreds of different frames. I'm wondering about how to use aluminum for a "universal" TA, and still have it strong enough? The answer may be to add a clamping element to the outer tips.

I went to my local supplier, and asked for the stronger 7000-series aluminum, but they don't stock it. I bought 4" X 6" 6061-T6 in 3/8-inch thick plate. I don't want to sound like I think this is going to be a great design, but don't post any ideas here if you don't want people to copy it and maybe even sell them. Anybody who wants can copy this, and even sell them, I don't care. I just want something to be available...

First step is a "no weld" clamp. An idea I want to experiment with uses a "cable clamp", two threaded hexagonal "couplers" (found near all-threaded rod in hardware stores), and two common bolts. Swap all the parts around and it can make a no-weld clamp. If you get 5/16-inch clamps, couplers, and bolts...the gap between the couplers is 1/4-inch, which is what I wanted to start with if they had 7000-series aluminum...

The 1/4-inch 7000 I wanted to start with is equivalent to 6mm, and the 3/8-inch 6061 I have now is 9mm thick

 

[e-beach]

My front fork 1000w hub setup uses 2 of these. One per side...I have a high degree of confidence in them. Consider throwing these into the mix. One hole for the axle, your plate, one big bolt plus epoxy could make for a very solid unit.

 

[Lurkin]

Ihe big hold up is torque arms, and the variety of frames out there. Some frames have the desirable broad and flat drop-outs, which allow a lot of options.

The real question is - at what torque (and rough corresponding power rating) does Grin's generic torque arm become ineffective? They do not require welding and are not expensive given their relative safety/strength.

 

[spinningmagnets]

I certainly recommend them if they fit the frame you want to use, and using two of them should work quite well. This thread is about providing half-finished blanks that would be as "easy as possible" for the end user to adapt to an odd frame that might not accept the Grin TAs.

The question I want to answer is: If I make two 9mm thick aluminum clamping TA's, will they survive from me hammering it with 52V X 50A = 2600W?...and if the answer is yes, will ONE of them still hold? (I see damaged phase wires in my future). As a side note, I also want to lower the axle slot one inch because I am putting a 24-inch wheel in a 26-inch frame. I will also likely extend the wheelbase two inches.

I'm not even worried about the disc brake caliper mount or the derailleur mount...yet. First I have to determine the material and the minimum thickness that will reliably work before I want to put any time or effort into something more complex

 

[Lurkin]

Good, we are on the same page. I faced this recently where I was consider decent power on a bike frame and didn't want to use a two/three piece torque arm.

The most practical, strongest method would be to start with a really thick flat plate, cut to fit exactly. If thick enough, drill and pinch bolt. This removes the need for multiple levels. My problem was lacking the tools to:

- design it well/nice enough for someone else to cnc it (suggested programs?)
- cut out the shape (I was going to engage someone else to cut it out on cnc. Recommendations on the best method to do this?)
- fix to frame (Which epoxy is best?)
- drill out pinch bolt nicely? (had given up already at this point. Not sure on bolt sizing to be effective)

The other issue I found with this method is: what if you want to revert it to a regular bike and sell it? welding/epoxy to frame is likely to damage the frame on it's removal?

But if you must make it out of readily available parts...

 

[teslanv]

This is a topic I am very interested in pursuing.
I have developed custom torque arms for a couple cheap Mongoose Fat bike frames, and they seem to sell OK, but would love to come up with a semi-universal/user customizable option.
Anything that can be laser cut from Stainless or Aluminum plate would be easy and cheap to produce in sufficient quantities.
The other route is to start with the most popular frames and design custom torque arms for those bikes specifically. Cheap BSO frames like the Genesis V2100 frame and the Mongoose Dolomite come to mind. Any more expensive "Donor" frames are now being replaced with Flux/Vector/EBB frames which typically have clamping drop-outs.

 

[spinningmagnets]

Here is an example of a single-plate TA that has a clamping element. This is what I have seen on many steel and aluminum swingarm builds, but of course it requires a welder/brazing/etc. If a "bolt on" TA is made for sale, and there is a sufficient customer base, this type of welding could be used to produce a sleeker and more professional-looking clamp (I'm only referring to welding the clamping bolt onto the TA, not the weld that attaches the TA to the frame).

However, the type of "no weld" clamp I have shown is less than $10 per TA, and can be assembled by anyone locally, so no shipping would need to be added to the cost. Pic is from puchwudi's Puch/QS moped.

 

[Samd]

Credit has to go to Kiwi for the famous Giant DH drops at the top of the page. Who is from NZ not surprisingly.

I've been approaching this differently with an attempt to put together a few different designs as there hasn't been a solution for 1 size fits all for me in the past.

That said I'm happy to get anything quoted at cost price for sending out from oz.

Mind you in the age of Waterjet and laser if you can use a cad package you're gonna have a good time.

 

[Samd]

Hey lurkin the answer is quarter inch. Or 6mm. About 4 years ago from memory we all sent dozens of forks and torque arms to Justin for destructive testing. That's how his v4 was developed.

That said I generally use 8mm per side as it costs little extra.

 

[cwah]

Can it be done with thicker mild steel? If yes, what size?

 

[tomjasz]

Can it be done with thicker mild steel? If yes, what size?

Why use something prone to corrosion?

 

[cwah]

It's easier to cut with simple tool like an angle grinder. And for corrosion I just need to put some paint on it

 

[tomjasz]

It's easier to cut with simple tool like an angle grinder. And for corrosion I just need to put some paint on it

I get your point I made one early this year for a 1000W DD Mxus. Before I bought the Grin v4. The paint didn't hold where the shaft contacted and it corroded quite quickly. I'm just fussy. It got me by until I could buy something more costly. But is was far from my ideal. YMMV

 

[cwah]

so stainless torque arm are the way to go?

btw drbass torque arm are made of steel that rust a lot. Mine are completely rusted but still work fine

 

[spinningmagnets]

The MXUS 205/28 V2 I have (from Kinaye Motorsports) has an extra long axle, but many hubs do not. Making the TA very thick might make it harder to get full thread engagement with the lugnut, once the thickness of the TA is added to the stock drop outs. That being said, I have a feeling the 9mm aluminum with clamps will work OK.

 

[Obiwan007]

Hey spin! Leave it to you to start ANOTHER super useful thread. I have given TAs considerable thought too over the years and certainly like the idea of the weight savings and easy workability of aluminum. However I have always been a bit leary of the greater ductility of the material. I DID use aluminum on my first builds custom TAs but went really thick out of fear. It only has to fail once for really bad things to happen; things the typical user would find hard to repair. One thought I had that I have seen used in other applications is to bush, or face the contact surfaces with stronger stuff like stainless. It can give you the best of both worlds. If you were to face the two sides of the axel slot with inserts of a facing material in a shape that mechanically fastens it in place when the clamping forces (axel nut and pinch bolt) are torqued down, then you accomplish a couple of things. First, the slot is far more durable to the high stress of the corner intersection of the axel flats and the rounded threaded part. Rotationally, I would think these corner points impart tremendous force in a small contact patch that seems like aluminum would not stand up to over the long haul or if the axel nut loosened a bit. Second, the more rigid and tougher material of the facing would spread the loads over a larger cross section of the aluminum. Third, the addition of stainless inserts would add little to the overall weight and nothing to the width of the TA. I see no reason that these inserts and their subsequent insert gaps in the aluminum couldn't be easily designed into the water-jet cut-out. It would add to the initial cost somewhat since the base TA would be a three-part "system" but if someone is ordering the parts cut in reasonably high numbers; it seems like the cost could be made reasonable. I think these inserts cloud reside in a rectangular cut out in the aluminum and then be securely held in place by being sandwiched between the drop-out and the outer axel nut for side-to-side security. And firmly held in place front-to-back by the pinch bolts...my $.02.

 

[spinningmagnets]

Adding an inlay of steel right where the axle sits is a brilliant addition, and could be considered a higher power edition? I've even been considering a version where the front half is 3/8 inch aluminum (9mm), and the back half is clamping steel plate.

 

[tomjasz]

Preferred grade of aluminum? Sam? Ron?

 

[teslanv]

Preferred grade of aluminum? Sam? Ron?

7000 series.

 

[tomjasz]

Preferred grade of aluminum? Sam? Ron?

7000 series.

If I reading correctly that narrows it down to 154. "154 materials in the category 7000 Series Aluminum Alloy."

http://www.matweb.com/Search/MaterialGroupSearch.aspx?GroupID=207

 

[spinningmagnets]

If you have the budget for it, 7075-T6, if it is available. Strength and hardness is equal to mild steel.

http://www.onlinemetals.com/productguides/aluminumguide.cfm
(This supplier is great for product and service, but expensive. 9mm-3/8-inch is called 0.375 in their catalog.
A 3/8-inch thick 6061-T6 plate, 12 X 12-inches is $49, (plus tax and shipping)
A 1/4-inch thick 7075-T6 plate, 12 X 12-inches is $48, (plus T&S)

6061__7075
45____83 ____tensile psi
40____73 ____yield psi
95____150____Brinell hardness
860___887____Rockwell hardness

7075 is difficult to weld, but 6061 is designed to be very easy to get a good weld, which is one of the reasons that it is so common.
I would rather have two thin torque-plates instead of one thick one, so if it fits your budget, always take the higher grade (which would then allow you to use thinner plate), whether steel or aluminum.

 

[spinningmagnets]

Ladies and gentlemen, I present...the "Coyote" torque plate. (Or "Dingo" torque plate if you are in Oz)

The 3/8-inch all-thread rod was $2 for a foot, the two 3/8-inch cable clamps (which provided the "saddles") were $1 each, and the 6061-T6 plates (4-inches by 6-inches) were $5 each from my local supplier. Shape was formed by drill, hacksaw, and file. Steel chainstay protector is a 3/4-inch pipe 3-inches long, sliced lengthwise. U-bolt was $1.50, and the bolt in the drop-out is 5/8-inch X 1-1/2-inch long.

Parts in this pic were $14-ish (for two of them, obviously $28), plus an hour of back-shed work...If I was making these to sell, I would order them water-jetted (a little more expensive), but If I only needed just one more pair, I'd use a jigsaw with a Bosch metal-cutting blade, which I have had lots of success with.

View attachment 2

 

[cwah]

AMAZING JOB!!

It seems that it will not only give you a torque arm for your bike but also give you access to larger motors (> 150mm wide) from the construction.

Probably the only question is about the little U Bolt holding all the motor power on the frame, maybe a slightly longer plate and double U bolt so that not all force are on a small area? Love it anyway, I may copy your work