torque arm designs

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bowlofsalad   1 MW

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torque arm designs

Post by bowlofsalad » Apr 16 2013 7:16pm

Hello,

I am not entirely sure why some ebikers only use one torque arm while others use two. Another thing I wonder about is why some torque arms are closed and some are open? To make sure what I mean by closed, the bottom of the torque arm is blocked, the hole for the axle is like an island. I imagine it is stronger for the torque arm to be closed, but it would also be substantially harder to install on the side with wires.
Is it really worth it to have the torque arm closed?

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friendly1uk   10 MW

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Re: torque arm designs

Post by friendly1uk » Apr 16 2013 7:34pm

Closed would stop the otherwise forked design from splaying. I can't say I'm keen though. Better to make it of something stronger if possible. How about open with a pinch bolt though? best of both worlds.

Have you seen the long picture thread? Well worth a read if you have not
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bowlofsalad   1 MW

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Re: torque arm designs

Post by bowlofsalad » Apr 16 2013 8:50pm

friendly1uk wrote:Closed would stop the otherwise forked design from splaying. I can't say I'm keen though. Better to make it of something stronger if possible. How about open with a pinch bolt though? best of both worlds.

Have you seen the long picture thread? Well worth a read if you have not
Which picture thread?

How does an open with a pinch bolt work? I am struggling to understand.

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bowlofsalad   1 MW

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Re: torque arm designs

Post by bowlofsalad » Apr 16 2013 10:43pm

I almost made a new thread about torque arms, but I realized I just made one of a similar topic. I guess I'll just pile in the subject, hah. I recently purchased a used bike from some one online. Upon receiving the bike I discover the chainstay has a fair amount of metal gouged from it, likely from the chain itself. I've seen enough pictures of destroyed dropouts to scare me into over doing torque arms.
However, I was thinking that I'd add the torque arm concept in to extend to the end of the chainstay opposite of the dropout. I am scared that the chainstay might twist and break under excess weight, torque or something like that. Does this sound excessive or pointless? The damage to the chainstay isn't immense, but I doubt the pictures do it justice.
The frame is made out of chromoly.

I have one torque arm, ebike.ca's torque arm rev 3 which I may just use on one side.

http://postimg.org/gallery/11b76e70/0f6e8502/ Pictures.

I think I now understand what a pinch bolt torque arm is. However, the design or concept seems pointless and broken. All I see in pinch bolt design is an open torque arm that is very thick, this can be achieved without the bolts. Nuts and bolts can shake loose and fail, making them a worthless torque arm and a real danger in my mind. The nuts and bolts shaking loose can be countered in a number of ways well enough (nord, glue, weld, etc) but that just adds to the cost and complexity and it begs the question, why not just use thicker material and use an open and typically designed torque arm?

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biohazardman   100 kW

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Re: torque arm designs

Post by biohazardman » Apr 16 2013 11:37pm

You can see the extremes in e-bike building here on the forum. Some very low power others with motorcycle like power. The more power you have the stronger your torque arms need to be. Thicker units made of hardened metal and or units with pinch bolts and solid arms are stronger if they fit well. Thicker open units made with good quality materials can be very strong as well. Most of us don't need the kind of strength two arms will bring and a single arm will do just fine. I tried to do one on both sides but by the time I would have finished one side would have been so weakened by my modification to get it to fit it would not have done much. Ebikes.ca sells a nice unit, although they were not available when I bought mine, as do several others here. I can hit 2K watts now and then and a single well fitting arm managed for near 9K miles now as well as help support my kickstand. Second pic is of my first bike and first torque arm it is suitable for my 500-2K+ watt application. These are both closed arms and therefor can be made of thinner material and still be strong enough.



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dogman dan   100 GW

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Re: torque arm designs

Post by dogman dan » Apr 17 2013 8:54am

I have to agree, attaching a torque arm to a damaged chain stay is asking for trouble. Nearly as much trouble as attaching a motor to a bike with frame damage. :wink:

I'd have to say, if the damaged stay has a lot more than a few scratches on it it's not for making into an ebike.

In general, for typical ebike motors that are not hot rods, a great deal of the torque resistance is from the pressure of the nut on the axle. This is why getting your washers, and perhaps even inner washers fitted right becomes crucial. Then when bolted up right, the torque arm is more of a back up.

Increase the power, add regen, or ride hard off road pounding the bike, and then you need to rely on the torque arm for primary restraint. You have too much for nut pressure, or are doing things that like to loosen a nut. At that point, you simply cannot overdo your torque arms.

Open design torque arms need to be very thick to resist prying open. Closed designs do better with less metal. Closed is a pita to put on the wire side, you have to remove the plug housings so you can thread the wires through the holes. Chances are, you may need to do that anyway, to get your spacer washers right, if you don't wish to dish the wheel.

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Re: torque arm designs

Post by friendly1uk » Apr 17 2013 10:13am

bowlofsalad wrote:
friendly1uk wrote:Closed would stop the otherwise forked design from splaying. I can't say I'm keen though. Better to make it of something stronger if possible. How about open with a pinch bolt though? best of both worlds.

Have you seen the long picture thread? Well worth a read if you have not
Which picture thread?

How does an open with a pinch bolt work? I am struggling to understand.
http://endless-sphere.com/forums/viewto ... =2&t=26444
bmsbattery sent me broken and incorrect stuff, and won't even talk to me about it.

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bowlofsalad   1 MW

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Re: torque arm designs

Post by bowlofsalad » Apr 17 2013 7:22pm

I am not entirely sure what the right order of washers are. I did buy some nord washers from 'shinyballs' on this forum, but beyond that, I wouldn't what the correct order of washer type items would be.

Aside from that, I think there is a slight misunderstanding on what I mean. I am saying to use a torque arm to bypass or strengthen the chainstay. Some use torque plates, a torque arm extends beyond the dropouts. I'd use torque arms on both sides, but I'd use a really long torque arm, as long as the chainstay itself, on one of the sides. Think of it as a brace for a broken finger, only the chainstay is far better off than any finger and the brace would be many times stronger than necessary.

I am thinking that with one torque arm on, a torque arm from ebike.ca (rev 3), I'll ride the ebike real slowly with the 3 way switch at it's lowest setting over to this fabricator guy I found online to see what he thinks. I am going to get him to help make a real solid torque arm. I am probably way over killing on all of this, it's not a tremendously strong setup. 48v with a 30 amp controller, em3ev's slowest winding motor.

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friendly1uk   10 MW

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Re: torque arm designs

Post by friendly1uk » Apr 18 2013 4:39am

bowlofsalad wrote: I think I now understand what a pinch bolt torque arm is. However, the design or concept seems pointless and broken. All I see in pinch bolt design is an open torque arm that is very thick, this can be achieved without the bolts. Nuts and bolts can shake loose and fail, making them a worthless torque arm and a real danger in my mind. The nuts and bolts shaking loose can be countered in a number of ways well enough (nord, glue, weld, etc) but that just adds to the cost and complexity and it begs the question, why not just use thicker material and use an open and typically designed torque arm?
If the nuts and bolts fall out, it is then an open one of good proportion. The bolt is not to allow thinner plate to be used.
The bolt makes the forks pinch the axle. Actually closing up the gap. You no longer need wheel nuts, but you will use them. It is belt and braces on well fitting trousers. A drop-out while cycling is almost impossible.

Oh... I just sat down to find I forgot to post this yesterday. Hope it's still relevant
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Re: torque arm designs

Post by chvidgov.bc.ca » Apr 18 2013 5:36am

Both of the torque arms in the first picture are on backwards and will get pushed into the frame! The arms should be on the top side of the stay, tending to travel away from the stay (clockwise in the picture) but being clamped back to the stay to prevent this. This would pull the wheel back in the same direction as it turns if installed correctly.

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dogman dan   100 GW

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Re: torque arm designs

Post by dogman dan » Apr 18 2013 7:10am

There is a reason I double nut my pinch dropout, trusting that even better than a locknut which gets loose if you ever remove it and put it back.

Go watch some of my off road videos and tell me I didn't try like hell to shake the dropout apart. Hell, one ride I had every screw on the hubmotor cover loosen, and the derailur disassembled itself. But my pinch dropout was still fine.

Just gotta be smarter than a bolt. Lots of other options to keep a bolt tight, like safety wires used on aircraft to name just one.

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spinningmagnets   100 GW

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Re: torque arm designs

Post by spinningmagnets » Apr 18 2013 8:08am

5 pages of torque-arm pics:
http://endless-sphere.com/forums/viewto ... =2&t=26444

Bike frames have a wide variety of issues. On some it is hard to fit a torque arm in there. And if the build is a low-power system, nothing wrong with a single torque-arm that is a little thin. Also, just because two different TAs are steel, the quality and strength of different steels vary widely.

I always recommend going overboard on torque arms, and here's why: Imagine it takes a couple years, but your "adequate" TA finally gets slapped around by regen and acceleration so many times that it gets chewed up enough that...the axle spins out and the wires are ripped out by the roots, and your bike comes to a halt.

You drag it back home, and set it aside until Saturday. Then, the day arrives and you take the wheel off and begin disassembling it. Hopefully nothing shorted in a way that permanently damaged the hall sensors or anything else. This time, you're lucky and all you have to do is pull some more wire through the hollow axle to ensure none of the wire in the axle has had its insulation stripped. The wires are color-coded, so you slide-on some heat-shrink insulation and then solder them back together.

You've mounted a wheel that ended up not working before, so this time you test the wheel before mounting. Fortunately, there was no other damage, and the motor works, so you mount it and go for a test ride.

When mounting, you notice the drop-outs have been spread. Frotunately, your frame (like most) has steel drop-outs. If they had been aluminum, they likely would have suddenly snapped off (the biggest reason to not use aluminum forks).

An "overkill" torque-arm solution means you never have to do this, but the main question is, how much power will you be applying to the axle?

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bowlofsalad   1 MW

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Re: torque arm designs

Post by bowlofsalad » Apr 18 2013 11:49am

I don't know exactly how to answer how much torque I'll apply. It's a 48v battery pack with a 30 amp controller, em3ev's slowest winding motor.

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Re: torque arm designs

Post by alfantastic » Apr 20 2013 1:30pm

Sorry to hijack this thread slightly, but could someone point me to the thread where Justin tests torque arms on various dropouts please :oops:

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Re: torque arm designs

Post by spinningmagnets » Apr 20 2013 7:31pm


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bowlofsalad   1 MW

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Re: torque arm designs

Post by bowlofsalad » Apr 20 2013 9:44pm

This torque arm thread on Justin's tests is great stuff. Very interesting.

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bowlofsalad   1 MW

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Re: torque arm designs

Post by bowlofsalad » Apr 21 2013 4:19am

That thread was an interesting read, I am not sure if it yielded concrete knowledge overall on what to use, I feel like torque arms may still be something of a guess, oh well. Keep your nuts real tight (got myself some nord lock) is mostly what I got out of it. I guess what likely would give a deeper knowledge on the subject would require lots more of the same kinds of forks for Justin, but that'd cost money. It's probably tons cheaper for everyone to just go way over kill and call it a day no matter what.

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