Best way to increase strength to dropouts on dh frame

[odi]

Converting a mtb downhill frame to electric.

Motor qs205 v3 50h 5t, controller 72450
Battery EVE 40PL 16Ah peak17kW 20s4p

I need to make new dropouts in steel and connected to the rear alu frame, both for fitting the 14mm qs hub, and also for strength.

My question, how it is done the best?

I know it's alot of torque to put on a downhill alu swingarm

 

[lnanek]

Do the drop outs matter? Just put a huge torque arm on both sides and ignore them.

I've been hoping my V4 ones from Grin would break so I can upgrade to V7 with the slot at the end to make changing tires easier:

Torque Arms - Grin Products - Product Info

For every force there is an equal and opposite force, and for every torque there is an equal and opposite torque. Sadly with import hub motors this opposing torque is often born entirely by bicycle dropouts that are not up to the task, allowing the motor axle to spin out. Grin has pioneered the...

ebikes.ca

No luck, though.

 

[odi]

Any pictures on your setup?

 

[lnanek]

Grin torque arm on a Ariel Rider X-Class frame I got for cheap because the drop outs were all torn up from someone running a high power motor in it without torque arms:


Have been running it at 48V 50A without issue since. Geared motor. No regen. Otherwise I'd upgrade to the better version torque arms.

 

[scianiac]

Yeah it kinda depends on the swingarm design but basically you just want some big and thick as you can clamping torque arms and distribute their torque farther along on the arms, both sides of course. On mine I used two plates on either side and those clamp either side of the existing dropouts.

These are on my Giant Glory with leaf at 8kw but they are way overkill and I expect would take a 50H motor easily and may some day get one.

The 3 M6 socket head bolts clamp the two plates onto the dropout (well it's a dropout now after I cut a slot in the through axle). The M8 in the bottom is the clamping bolt which is probably too much. You can see I used up most of the threads so the axle cut doesn't have much left but not worried since it's clamped with a crazy amount of pressure by those plates (that M8 12.9 is right and proper torqued). All parts were cut by send cut send out of stainless.

Check out the torque arm picture thread for more great examples.

 

[odi]

Yeah it kinda depends on the swingarm design but basically you just want some big and thick as you can clamping torque arms and distribute their torque farther along on the arms, both sides of course. On mine I used two plates on either side and those clamp either side of the existing dropouts.

These are on my Giant Glory with leaf at 8kw but they are way overkill and I expect would take a 50H motor easily and may some day get one.
View attachment 367886
The 3 M6 socket head bolts clamp the two plates onto the dropout (well it's a dropout now after I cut a slot in the through axle). The M8 in the bottom is the clamping bolt which is probably too much. You can see I used up most of the threads so the axle cut doesn't have much left but not worried since it's clamped with a crazy amount of pressure by those plates (that M8 12.9 is right and proper torqued). All parts were cut by send cut send out of stainless.

Check out the torque arm picture thread for more great examples.

That looks like a good solution

 

[MxusMick]

I made a DIY Torque arm with a piece of metal, about 6" long, 1" wide, and roughly 3/16 thick. The DD rear axle has flat sides, so I notched the metal to fit the axle, then used hose clamps to attach metal to frame. The metal stick was beat into shape, to the frame as well, not pretty but does the job. But remember flats suck and taking a motor wheel off will happen.