Retaining a QS205 on a bomber frame

[Evwan]

Howdy all, been lurking for a while, but couldnt find the info I was looking for so I figured i'd make an account and ask

I have this bomber frame (Voilamart Stealth Bomber Electric Bicycle Frame Conversion Kit 3000W-5000W EBike | eBay) and a QS205 motor from, NBpower. I have the motor on the frame, but am having some trouble figuring out how to make sure the motor stays on the frame. Some people have suggested that I need to drill a hole in the swing arm and add a motor stay similar to the one in picture 1, while some have shown me videos of them just using a single bolt on each side of the swing arm to sort of clamp it down (picture 2). Picture 3 is my current setup. I'll flip the motor upside down and run the phase wires below the swing arm, but im more worried about retaining it. This bike was originally running a TC4080 when I purchased it second hand, but I quickly blew up that motor trying to go up some steep hills, so I decided to upgrade.

I intend on running a 72v (20s) battery on a controller capable of 250 phase amps/100 battery amps, in case that makes a difference. The motor has 5t windings, so it's a higher torque setup too.

Any input on how the motor should be retained is much appreciated.

 

[Evwan]

Photos didnt upload, oops

 

[amberwolf]

Assuming axle and dropouts are both of similar hardness, and dropout is flat to the axle flats, and dropout has a slit at the forward end to allow it to "pinch" or "clamp" correctly (faces moving more in parallel), then pinch bolt is more secure.

The slotted torque arms don't usually have enough material in them where the flats sit, and have too long a slot, so the axle is able to pry them open, then damage them with the corners of the axles until the axle can spin in them.

You can always go with both, since you have the axle length for it.

If you do use the slotted arms you will want to install the motor using the pinch bolts first.
Then slip the arms over the axle ends so the axle is at the farthest end of the arm's big slot at the back end of the arm, with the small slot as far from the axle as possible at the front of the dropout plate, and use the axle nut to tighten it down.
Then drill a hole just enough smaller diameter as the small slot of the arm is, at the "front" end of the arm, farthest from the axle, so when you tap threads into it it will fit a bolt that perfectly fits the arm's hole, in the dropout plate, so you can bolt the arm in place so it can't rotate at all.
You have to do this after mounting everything in place so the hole will be *exactly* where the front end of small slot in the arm lines up with. This gives the most arm length to resist axle torque.

 

[Evwan]

Assuming axle and dropouts are both of similar hardness, and dropout is flat to the axle flats, and dropout has a slit at the forward end to allow it to "pinch" or "clamp" correctly (faces moving more in parallel), then pinch bolt is more secure.

The slotted torque arms don't usually have enough material in them where the flats sit, and have too long a slot, so the axle is able to pry them open, then damage them with the corners of the axles until the axle can spin in them.

You can always go with both, since you have the axle length for it.

If you do use the slotted arms you will want to install the motor using the pinch bolts first.
Then slip the arms over the axle ends so the axle is at the farthest end of the arm's big slot at the back end of the arm, with the small slot as far from the axle as possible at the front of the dropout plate, and use the axle nut to tighten it down.
Then drill a hole just enough smaller diameter as the small slot of the arm is, at the "front" end of the arm, farthest from the axle, so when you tap threads into it it will fit a bolt that perfectly fits the arm's hole, in the dropout plate, so you can bolt the arm in place so it can't rotate at all.
You have to do this after mounting everything in place so the hole will be *exactly* where the front end of small slot in the arm lines up with. This gives the most arm length to resist axle torque.

Thank you!
After getting back to my bike, I noticed that on one side of the swing arm, the pinch bolt hole was completely screwed up by the first owner. it appears that I'll have to run a pinch bolt on one end of the swing arm, and a slotted torque arm on the other side. I wanna make this bike work, but it's turning out to be a hassle. I gotta start thinking of a plan B in case I cant end up using this frame.