Aluminium Torque Arm ? Have you made your own ?

While looking for a bike I would like to convert to electric , ( use my electric hub motor 500-1000 watt )
I am finding many different Full Suspension Types of Rear Triangles,

For instance, Specialized Endruo/FSR / Camber , that have a pivot on the Chain Stay, near the Dropout/Axle

If you have a Specialized Full Suspension Bike how did you do / attach a torque arm ?

Then there are the the Single Pivot Bikes like Santa Cruz, Extralite , etc.

Since I do not have my own machine shop, I am thinking about getting a flat plate of Aluminium and just making my own torque arm that would fit perfectly
for what ever rear system I get.

Have you made your own, or know someone who has done this successfully ?

Make one with a combination of Steel, and Fiberglass ? or Aluminium and Fiberglass ?

My 500w bike is alloy framed and has no torque arms. There are some tests here somewhere done by justin the site owner. He puts various motors in to front forks looking for the limit. It is higher than most imagine. If my 5mm thick alloy frame can hold 500w then adding 5mm alloy torque arms of similar hardness would surely hold 1000w. Especially if your 1000w is direct drive, not geared like my 500w. For example, my 500w bpm has more torque than a 1000w dd ebay motor. So neither need torque arms unless I were to use regen.

Alloy is a poor choice though. I wouldn't waste my time. Bright mild steel is just about as easy to work with and can be heat hardened.

10mm flats on a 12mm round axle? Did yo know a 10mm spanner also has an r6 curve at the back. The $1 shop might be all you need.

Edit: I'm looking for someone to make me some. I don't fancy ages with hand tools. I need someone with the right stuff to drop the hole though the large end of an egg shaped plate. Just the hole is all I need really. I can make the eggs. I need about 10 of them.

My Motor is a geared hub motor, sold as a high torque motor as well, so to be safe I will use some kind of torque arm,

Aluminium is not as hard as steel, but it is workable with my simple tools , Hack Saw/File/Grinder/Dremmel .

I don't know where to get plates of steel to work with, small pieces of Aluminium Plates are abundant in the trash bins of machine shops .

Steel is also pretty easy to find. If you have "bulk trash day" or similar, where people toss out big items, you can look for old computer or desk chairs that have a large L bracket between the seat and the back. This will usually be thick (3-5mm or more) steel, and not so hard a steel that it can't be cut with hacksaws and drills and dremels and such. But it is much more resistant to axle spinout with the narrow flats that most axles have, than most of the aluminum you might find as scrap.

I'm using a piece of such a chair right now as part of my steering on CrazyBike2, which takes a fair load wihtout issue. (the older thin steel I'd used bent an awful lot, and kept cracking, until I welded on it quite a bit, hardening it wiht repeated welding/cooling cycles as well as thickening it).

I plan to use more of the same chair brace for some clamping dropouts at some point, and/or some torque arms for a front motor.

I've also used old thick rear BMX dropouts in place of my regular thin rear dropouts, and they are presently doing good work on CB2. If you find ones with a large enough flat area, you might be able to cut them off the BMX frame in a way tha tleaves enough tubing on them to then cut and modify so it'd be able to clamp to your bike's frame as additonal thickness to the dropouts already there. (similar to what I did, though I welded them on).


Sometimes you can also find thick steel on the legs of those same chairs, underneath the plastic or wood coverings.

Justin did a lot of torque arm testing which is documented here on ES, and he found that aluminum wasn't strong enough to take the force from the flats of the motor axle (in a reasonable thickness). Even steel had to be fairly thick, many torque arms at the time were too thin and they just cut the axle at high torque. Of course it depends on the torque you actually use.

I calculated that aluminum was adequate for the second part of the torque arm (the torque strut) which is much lower stress since it is much farther away from the center of rotation, and have had no problems with the several I have made in 1/2 x 1/8" 6061-T6.

But the part that holds the axle is too close to the center of rotation and the leverage is too great so if the motor is strong it will endanger the aluminum.

I use the steel part from Justin's (ebikes.ca) torque arms and then make a custom strut with 6061-T6 for my mountain bike and recumbent. The CroBorg has no torque arms, it has a CroMoly dropout that is rated to handle the CroMotor's torque IF the axle is fully in the bottom of the slot.

Having accumulated bits and pieces over the years, I can usually "jury rig" something without "fab'ing" for motors under 1200 Watts.
I use these on the vertical drop-outs;

http://www.electric-bikekit.com/freewheels-torque-arm/short-torque-arms-1-pair/

I use a pair on each side and attach them with parts of the standard 2-piece torque arm.s
On the brk side I secure with a brk. mount bolt.
On the other side, I use the long arm and clamp to the swing arm.

Aluminum is a creep metal, it will not hold up to the high stresses of such a small axle. Steel is going to be an only option unless you have a source of titanium or beryllium copper. Beryllium copper dust is very dangerous to human heath. It's going to cost more in the long run to experiment w/ aluminum.

Aluminum is so weak, it will NEVER penetrate structural steel at subsonic speed (STP@SL). This is how we know, no planes were involved in the great Carpetbagger's HOAX, which occurred on Moby's 36th birthday.

Solution, learn how to grade steel hardness using a file. Consider alt means of working steel, the easiest may be a hydraulic punch press but the die set may be a problem. If this is not what you want to hear, research metal properties to get a better comprehension.

Good luck

Looks like I will , now, be looking for some small pieces of flat ... Steel .

Thank You all,

Just found a hard tail MTB, that will be the first build for my MAC 6 T , I did not find a good quality full suspension MTB at a cheep price.not even used ones, in my size and/or with a strong unified rear triangle ,
but I found a 8 speed MTB with 27.5 inch ( 650b ) wheels, that was on sale this weekend, I have been wanting to test out a 27.5 bike other than just a parking lot test ride. it should arrive in just over a week, There are some street tires available in 650b size, and one rim maker that has a 27.5 / 36 hole rim, that I can buy for the wheel build.

motomech said:

Having accumulated bits and pieces over the years, I can usually "jury rig" something without "fab'ing" for motors under 1200 Watts.
I use these on the vertical drop-outs;

http://www.electric-bikekit.com/freewheels-torque-arm/short-torque-arms-1-pair/

I use a pair on each side and attach them with parts of the standard 2-piece torque arm.s
On the brk side I secure with a brk. mount bolt.
On the other side, I use the long arm and clamp to the swing arm.

Click to expand...

I got half way through checkout with them, but I don't want a two piece design. I want them, just how they are, but with only the axle hole, not the bolt slot. Though if the axle hole was rotated 10 degree's it would be better still. As flipping it over could move it 10 degree's one way or the other. In my quest to find an existing 5mm threaded accessory hole. One I can drill a proper hole in the torque arm for myself

I quit the payment as they stuck £6.22 postage on, way after the paypal page had said £6.22 for the goods.

I laser cut them for lots of mods. Which specialized? Im about to do a Demo 8.

Use the brake pickup points. Or some wedges to stop rotation.
Do a search for dp420 epoxy on this forum.

It's fairly easy to cut a custom torque arm from 1/8-1/4 thick from mild steel. You can buy bar stock in any hardware store fairly cheap.

A drill, a small flat or triangle file, and a hacksaw would do the job. A small grinder would make shaping the outside edges easier. Drill rows of 1/8 inch holes to remove most of the material, then the tiny bumps left are fairly easy to file away with a new sharp file.

I sort of wish an ebike shop would sell blanks with a 14mm x 9.5 mm slot. Why 9.5mm? So you can file away the last .5mm yourself for a super tight fit.

The two piece stainless steel units with offset hole from ebikes.ca work fine (and can be flipped over for flexibility), I just don't care for the sliding slotted strut they come with, so I make my own aluminum struts that are drilled and tapped at the right length. It makes a very compact and easy to make combo. See either my eBikeE thread in my signature for one example.

A blank would be nice, but make it 9.9mm stainless, it is a lot of work to file good steel. No need to be that far off.

It is possible do make adequate torque pates with alu, but they need to be through axle, very precise and thick. Best is to do them with steel plate, or Ti if you are obsessed with light weight.

I really enjoy the ideas of ingenuity, trying new things in new directions. However, in this case, I might suggest taking the easier route and buying doctorbass torque arms. http://www.endless-sphere.com/forums/viewtopic.php?f=31&t=29129&start=300 It'll be really difficult to make something as good as these.

I am not saying you can't or shouldn't try and make your own torque arms, but these well made excellently designed open mouth(open mouth is an awesome feature when you consider doing something like changing a flat tire on the side of the road) torque arms are likely going to save you a lot of time and energy in various ways.

The reason for using a file to determine hardness, is to find the metals allotropic stage: http://en.wikipedia.org/wiki/Allotropy
Iron and Titanium have this property, it's hardness will give an indication of how well it can stand up to the high torque forces. Beryllium copper would have to be shaped, then heat treated to harden. Heat treatable (tool) steels can be obtained in small quantities, like a flat bar. It will be soft enough to "cut" (ie drill bits, metal saw, file), then take the finished pieces to be heat treated. The real trick is proper annealing, to prevent cracking. Never leave sharp corners on a piece to be heat treated, it invites cracks in the heat treating process, always use fillets and radii.
Most any type of structural steel will do the job and not require heat treating, but working it will be more difficult as it is at a high hardness. Cut the shape w/ a torch, from an I-beam. Gauge steel, anything that is formed to shape (ie car body panel, propane tank), is going to be less suitable due to it's chemistry, not it's thickness.

I have. Over 10 kw. No problem yet.

Axles are generally soft steel, so anything stronger is not needed and will just cut the axle, and no benefit is gained from hardened torque arm.

Aluminum can work but must be 2-3x thicker (as the example above), and the axle must have corresponding flats to engage to take advantage of the area.

@ Samd

I was going to get a Specialized Enduro FSR , / Enduro FSR Pro, however the two that were candidates were too large ( to high a stand over height )
or too much $$$$ for me. The Down Hill bikes like the Demo 8 and others like the Giant Glory/Reign, are way up there in price , even used, right now where I am living. Look at craigslist.org SF Bay Area region, Calfiornia.
So After looking for a Used, Full Suspension bike, ie: Specialized Enduro or Giant Anthem/Trance or Intense Tracer , for nearly 2 months , and only finding ones that were too much $, and or too large size , I finally just bough a hard tail bike this weekend, 27.5 inch ( 650b) . because it was affordable, $ 200 off , and has a 8 speed drivetrain, so I do not have to change anything there, just put on a 8 speed freewheel on the hub motor and a washer for a spacer on the freewheel side to make it fit, ( the MAC geared 500-1000 watt hub motor wants you to use 7 speed freewheel , I tried a 9 speed freewheel and it would need 4mm + of spacers on the derailleur side to make it fit into the rear chainstay/seatstay . So for my first build I decided yesterday to just make things easier this first time and go with a 8 speed / hard tail bike.

I am interested on what the torque of a hub motor does to a suspension system like the Specialized, which has a pivot on the chain stay , near the drop out .
Anyone ?


vvv Quote below from Samd vvv

laser cut them for lots of mods. Which specialized? Im about to do a Demo 8.

Use the brake pickup points. Or some wedges to stop rotation.
Do a search for dp420 epoxy on this forum.
IMG_20141027_182321.jpg
http://ballaratebikes.com/

ImageImageImage
"Knowledge is knowing that a tomato is a fruit. Wisdom is knowing that a 165mm rear shock can't deliver 220mm of rear swingarm travel." - Oprah Winfrey.
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Samd
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Re choosing your bike, have a look at this thread. http://endless-sphere.com/forums/viewtopic.php?f=3&t=50084

And this one http://endless-sphere.com/forums/viewtopic.php?f=2&t=26444

The bottom line is, if you have some flat area around that slot, you can just buy a cheap torque arm, cut off the leg, or remove the second piece, and bolt it right on. Bam, done in 10 min.

Or, they will also be perfect for some other solutions, such as Dr Bass arms.

I like that alloy can give a little, allowing an axle to seat better. If there is no give at all, then unless assembled very carefully, one side of the axle is going to be held more than the other, leading to twisting. I see the occasional systems here that I imagine cause undue stress just being clamped up.

My alloy frame is fine. I'm using just one torque washer, not arm. Nuts are not particularly tight or anything silly. It's all just happy. If one bit did move, it would just be until another bit took up the slack and shared the work. Only malleable materials can do this. Forming nice seats the axle fits like a glove.

Just make sure with alloy dropouts that you seat it good and tighten the nuts (and have appropriate washers/etc). If you don't, well:





I did that with teh bike upside down, just loading it down with a roll of papertowels on the bare rim, but had no nuts on the axle, just sitting in the dropouts.
http://www.endless-sphere.com/forums/viewtopic.php?f=4&t=64279&p=964445#p964426
It's not a monster motor, either--just an X5304 at that time in a 26" wheel, at I think a peak of just under 16A before it broke the dropouts right off. TING. :/