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Why putting BBSHD forward as much as possible?

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    Why putting BBSHD forward as much as possible?

    According to several Bafang installation videos and docs, it is recommended to lock Bafang motor at a forward position as much as possible, not to let it drop by its weight. Is it simply to reduce the chances of potential motor's hitting something on the ground as much as possible? Or, any other reason?

    #2
    The motor tries to rotate forward/up (clockwise viewed from LH side of bike) when under power. It needs to be against the frame to hold it solid under power.
    Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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      #3
      I trimmed the lug on both my BBSHDs to allow them to rotate as far upwards as possible to increase ground clearance, but I had never thought of the matter of motor torque. Then again, I tightened my securing nuts with the factory socket and a 24" breaker bar.....

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        #4
        Originally posted by Lance Tesla View Post
        I trimmed the lug on both my BBSHDs to allow them to rotate as far upwards as possible to increase ground clearance, but I had never thought of the matter of motor torque. Then again, I tightened my securing nuts with the factory socket and a 24" breaker bar.....
        Good call on trimming the lugs. I did the same. It can really help ground clearance.

        As for the torque, as long as your motor is rotated so it is touching the frame, it's still supported - trimmed lugs, or not. But it is good to not have a sharp contact point, or it could dent the frame. I have a rubber patch clamped TIGHTLY in mine to spread the load and protect the frame. Firm enough, and I think a little quieter.

        I just let the motor rotate while I'm tightening the BB nuts, and it gets pre-loaded against the frame nicely.
        Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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          #5
          Originally posted by JPLabs View Post

          Good call on trimming the lugs. I did the same. It can really help ground clearance.

          As for the torque, as long as your motor is rotated so it is touching the frame, it's still supported - trimmed lugs, or not. But it is good to not have a sharp contact point, or it could dent the frame. I have a rubber patch clamped TIGHTLY in mine to spread the load and protect the frame. Firm enough, and I think a little quieter.

          I just let the motor rotate while I'm tightening the BB nuts, and it gets pre-loaded against the frame nicely.
          Rubber patch? Isn't the general recommendation something a little more solid to spread the load as rubber flexes?

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            #6
            Originally posted by Ade View Post

            Rubber patch? Isn't the general recommendation something a little more solid to spread the load as rubber flexes?
            Like I said, pre-loaded hard. Pinched. It evidently has enough preload to resist the torque of the motor. It's on a portion of the motor which I reshaped to match the contour of the frame, with probably 1/2 sq in area. It works OK.

            It's a piece of inner tube, so actually quite stiff when compressed in there.
            Last edited by JPLabs; 05-15-2016, 04:22 PM.
            Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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              #7
              More than one frame has been damaged by a dropping motor slamming into the down tube under torque. Do it right or prepare for a problem. JP is spot on with a small rubber buffer.

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                #8
                Bang bang you be bent.

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                • Sebz
                  Sebz commented
                  Editing a comment
                  Ok.... a cushion will be placed on my bike this week!

                #9
                More examples. No need to be nervous, just set the motor correctly, pay attention and not knock the idea of a rubber bumper pad. All builds are a little different.

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                  #10
                  I also glued the rubber to the motor, so if the motor does ever move, the rubber won't just fall out. Contact cement.

                  Here's what mine looks like. Remember, the motor boss is shaped to match the frame, in my case. The rubber is easy to trim with a razor after it's glued on.



                  Other suggestions I've seen are to use epoxy putty (hard), or Sugru (rubbery), to make a custom filler block when there is not a nice matching shape. Those both harden in place - just pack some in, install the motor with a small gap to the frame to ensure the filler takes has some thickness so it takes the load, and let it cure. Use a release agent like packing tape or wax on the frame to keep from gluing everything together. Same idea, spread the load.

                  I think large, even contact area is more important than a soft material. Spread the load across as much frame as you can. Bike frames are pretty thin. If you aren't going to shape your motor to match the frame, a filler type solution would be ideal.

                  None of this is truly necessary, but will be more robust than the stock setup. An option.
                  Last edited by JPLabs; 05-17-2016, 07:40 PM.
                  Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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                    #11
                    OK this thread convinced me to do something about my protruding lugnut before riding my new frame. I went out and got some Loctite Repair Putty ($5) from Home Depot, cleaned/sprayed the motor/frame with WD-40, and applied a ball of it on there before tightening the motor into place. Seems like a perfect solution!

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                      #12
                      Originally posted by WebEsquire View Post
                      OK this thread convinced me to do something about my protruding lugnut before riding my new frame. I went out and got some Loctite Repair Putty ($5) from Home Depot, cleaned/sprayed the motor/frame with WD-40, and applied a ball of it on there before tightening the motor into place. Seems like a perfect solution!
                      Worked for me. Blob of generic epoxy putty. I sprayed the frame w/ WD40 but not the motor. I figured the epoxy should be stuck to something.

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