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    Torque arms

    where can I learn the procedure for installation of torque arms on a rear hub motor?

    #2
    Originally posted by rpeter12 View Post
    where can I learn the procedure for installation of torque arms on a rear hub motor?
    I recommend custom (for your bike!) torque plates. I made a detailed video on this https://www.youtube.com/watch?v=WYg0mWgnPG4.

    1/4" 303 SS will do ya. Your local machine shop can CNC the D-hole (that's the hole that the axle goes through). Have the machine shop do it on an oversize plate, and then you trim it down for your specific bike, telling yourself that you are saving weight as you remove metal.

    It is very important to have the machine shop make the D-hole just a little too small (so that your axle cannot fit through the D-hole until after you file it for a tight fit).

    This makes for an extremely bombproof torque plate!


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    Last edited by commuter ebikes; 07-18-2018, 08:10 PM.

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      #3
      Here are some photos of the ones I made. They all fit on so tightly! Don't make the mistake of riding your bike without torque plates while you are waiting for the machine shop to do their work. I had the system power turned way down, but ! got a power surge and...BAM! This cracked open the dropouts like they were made out of pot metal. That was an expensive mistake. I had to strip the newly made bike, repair the carnage and then wait four months for the powder coater to redo the powder coat. Oh, well, at least I got to pay $200 to powder coat a frame that I had just paid to powder coat a few months earlier.

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      Last edited by commuter ebikes; 07-18-2018, 08:12 PM.

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        #4
        This sounds like a good idea but no Machine shops anywhere near me. Cost prohibitive as well I think.

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          #5
          Originally posted by rpeter12 View Post
          This sounds like a good idea but no Machine shops anywhere near me. Cost prohibitive as well I think.
          Too bad. I would say try to fab it yourself, but any steel up to the task is really hard to drill. Burning and filing works fine, though.

          You can burn into 1/4” plate steel with a large die grinder and a small conical stone (gray, not pink) tip. Filing with a bastard file from there would work.

          if you do use a new drillbits, make sure to use the bits designed for metal with a slow drilling speed and plenty of cutting fluid.

          Doing all of this hard work yourself is free, But if you make the D-hole too big you’ll have to start over.

          You can get 303 stainless from Online Metals.
          Last edited by commuter ebikes; 07-19-2018, 09:52 PM.

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            #6
            Originally posted by commuter ebikes View Post
            You can get 303 stainless from Online Metals.
            There is a BIG difference between 303 and 304. 303 is a "free machining" 300 series stainless, easy to machine but not very strong - not really suitable for a torque arm. 304 is a bear to machine, and is strong. 4130 would also make good torque arms, but requires corrosion protection - paint or zinc plate.

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              #7
              Originally posted by nfmisso View Post

              There is a BIG difference between 303 and 304. 303 is a "free machining" 300 series stainless, easy to machine but not very strong - not really suitable for a torque arm. 304 is a bear to machine, and is strong. 4130 would also make good torque arms, but requires corrosion protection - paint or zinc plate.
              My local machine shop outright refused to do it in 304 SS citing that 304 was too difficult to machine.

              I have ridden thousands of miles on four different ebikes with the 1/4" 303 SS on both sides of the axle with zero problems. I have drawn 105A at 80V and they held up just dandy. I have also jumped off three stairs many times. Don't ask how the rim held up, though.

              I have my regen cranked up all the way, too, and I use regen every time I brake.

              Here are some details if anybody wants to geek out (I did) on 303 vs. 304 SS:

              303: http://asm.matweb.com/search/Specifi...bassnum=mq303h
              304: http://asm.matweb.com/search/Specifi...bassnum=mq304a
              Last edited by commuter ebikes; 07-24-2018, 09:26 PM.

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                #8
                Here is a snip of the links:

                303:
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                304:
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                  #9
                  The 304 information above is for annealed material. As soon as you attempt to machine 304, it work hardens, which why many shops will not touch it. The strength of the work hardened surface is significantly higher, at full hard 140ksi yield for standard 304. http://www.matweb.com/search/DataShe...bd6cffa36c6b56

                  if you are grinding (as opposed to machining), laser cutting, water jet, or EDM (electro discharge machining); full hard materials are no big deal.

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                  #10
                  I appreciate the thought of having the torque arms as hard as possible. But my thoughts are what would you have get worn or damaged? Your torque arm(s)... or your axle? I just made mine out of simple easy to get and work with mild steel. Took my time to get a great fit. And preloaded them in opposite rotational torque directions having adequate torque on the nuts with jam nut back-up. Bullet proof so far.

                  Fabrication of my torque arms link, Post #16...
                  See my completed Magic Pie V5 rear hub motor E-Bike build HERE.

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                    #11
                    Originally posted by Tommycat View Post
                    I appreciate the thought of having the torque arms as hard as possible. But my thoughts are what would you have get worn or damaged? Your torque arm(s)... or your axle? I just made mine out of simple easy to get and work with mild steel. Took my time to get a great fit. And preloaded them in opposite rotational torque directions having adequate torque on the nuts with jam nut back-up. Bullet proof so far.

                    Fabrication of my torque arms link, Post #16...
                    For me, the main idea is to keep the axle in place for the purposes of (1) not breaking down on the road, and (2) protecting the frame. I think if you make the torque arm strong and tight fitting enough, it will keep the axle from rotating which will not damage either the torque arm (or torque plate), frame or axle. I really like the axle cross section to fit crazy tight in the torque plate (or torque arm).

                    I think the weak link in my torque plates is the nuts and bolts mounting the torque plate to the frame. I bought Grade 12.9 bolts, but they are only M5. I have two M5 bolts on one side and one M6 + two M5 bolts one the other side.

                    One of the benefits of replacing a worn tire or punctured tube is the opportunity to check for wear on all of the parts.

                    Another huge benefit of (most) torque arms and plates is that they are an additional means of keeping the wheel on the bike! One could make chromoly dropouts that are 3/8" thick, but you would still be completely depending on the axle nuts to keep the wheel on the bike. Axle nuts loosen, especially with regenerative braking. If both axle nuts are loose and the bike has an upward motion, the wheel could break free. When I was a kid, I had a MTB front wheel come off when I was in the air--that was a bad crash in the dirt.
                    Last edited by commuter ebikes; 07-27-2018, 08:41 PM.

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                      #12
                      If a machine shop refuses to work with 304 they don't know what they are doing. Move on and find a different shop. 17-4 PH is a good SS to work with but will need to be hardened. It's actually easier to work with AFTER it's hardened. It's an air hardening process which means it doesn't need to be quenched when you risk warping and cracking. Cook it at 900 degrees for an hour and let it air cool and its hard through and through. I'm sure you can find a local shop with an oven or pottery place with a regulated kiln. As someone else in the thread said you need to be aggressive with your drilling or it will work harden making your job nearly impossible by hand. If you have a drill press don't be afraid to push. Push the drill for a few seconds and then back out and lubricate. I recently drilled 72 3/8 holes 2" deep in 17-4 with a high speed steel drill bit that came out still reasonably sharp. Be aggressive and peck at it. The rest can be done with an angle grinder and a file (for the 'hole').
                      Life's journey is not to arrive at the grave in a well preserved body, but to slide in sideways screaming "Holy shit! What a ride!"

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                        #13
                        Im no rocket scientist, and had to go over to a friends house to use his tools, but I slapped these torque arms together in maybe an hour total time out of a piece of scrap steel. They work. Theyre probably overbuilt but i dont give a sht. I welded them to my frame because i didnt have any pipe straps laying around. Do or die out here man.

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                          #14
                          I have my torque plates off to replace a bent rim. Here are pictures after 1818 miles. This had been my "abuse" bike (thus the bent rim), but no more of that nonsense.

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                            #15
                            Now I remember that I replaced the aluminum derailleur hanger with a steel derailleur hanger because that is 3.92mm of material in contact with the rotating force of the axle flats. Here are pictures of the frame that the torque plate was tasked to protect. Unfortunately, I applied a coat of touch up paint so the wear points have been masked.

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