help to setup Bafang BPM and arm torque on aluminum fork

[casainho]

Hello.

I am looking for help on how to setup my Bafang BPM 500W motor and the arm torque on my aluminum fork. I bought all the components from BMSBattery (minus the bicycle).

I wasn't aware of torque arms and the first time I setup this Bafang BPM 500W motor on my aluminum fork, I had the accident, the dropouts broke. Now I need help on the setup. Thank in in advance.

Before receiving the arms torque from BMSBattery, I were preparing the fork dropouts and the washers. On the disk brake side I don't get room to a torque arm, to say the true, there is even not enough axle for the nut:





And on the other side, I get about 8mm free of axle. Note that since I have space, I am using one of the strong (4mm thick) "C" washers that BMSBattery sent with the motor:




And today I received the BMSBattery arms torque made of stainless steel:






On this side I have enough room for using 2 arms torque. I want to weld them on the local of the screw so they can't rotate on that "joint". Since the wheel will be moving forward, the torque will try to move the axle backwards and so I think this position will be the best since arm torque will be pushing the fork. Maybe I can weld also some bigger piece of metal in the end of arm torque to spread the point of contact/force against the aluminum fork.




And here a picture showing the other side of Bafang BPM 500W motor and not enough axle to hold the torque arm and the nut...


Please give me ideas, your opinion on what would you do on this situation were I have this material: the nuts, washers, arm torque and aluminum fork.

Thank you.

[dogman]

Hmm quite a dilemma on the side with the short threads. My inclination in that case would be to start grinding away at the torque arm for that side. get it to fit on the fork nicely without a washer, then you might get enough threads on to the nut. Very likely, you will also have to shave some fork material too.

[casainho]

Hmm quite a dilemma on the side with the short threads. My inclination in that case would be to start grinding away at the torque arm for that side. get it to fit on the fork nicely without a washer, then you might get enough threads on to the nut. Very likely, you will also have to shave some fork material too.

dogman, thank you for your help.

I put that torque arm on the inner side of the fork in exchange of the washer. Looks Like I will need to grind a bit the torque arm anyway.

Do you think I should weld (I will need to pay for professional service to solder the stainless steel parts) the torque arm joints on the screw? Do you have any suggestion, were I can make the system more safe?

[Wurly]

I used the C washers to make torque plates. It is possible to weld them if you have access to Tig. If you see my build thread below it will show you how i did this for my rear mounted BPM. To make torque plates for the front is going to be difficult but not impossible. Could you remove some of the aluminium to allow the torque arm to 'seat' on the C washer and get it welded to the torque arm? That would give you enough thread to safely secure the axle nut.
C washers are steel which should weld ok to stainless...like i said, get it Tig welded.
You have a real problem if you want to use the heavy slotted part of the BMS torque arms.