Can a 1000W hub motor damage a steel frame if ridden harshly (not powerfully)

[5w30]

Hi
I'm not sure if this is the right section to post in as there seems to be overlap between general/technical so i'm sorry if this is the wrong section.
I am planning to upgrade my bike to a cheap ebay hub motor to save myself some headaches however though the motor is stocked by local sellers torque arms are cheaper from china and may take longer, so can I ride temporarily on a steel or cromoly frame with a 1000W rear hub motor without any torque arms and will a wrench and some hose clamps make a difference (I have no means to make a torque plate of satisfactory quality) or should I not bother? My riding conditions are as follows:

• Hot Australian weather

• Primarily off-road

• A hilly area with most hills less than 500 metres long and max grade for most is about 1 in 10, though there are some very short 1 in 5 inclines

• looking to cruise at about 30kmh on level terrain with light pedaling

• Some short stretches of harsh unpaved terrain with dirt and rocks that I like to ride very roughly up and down

• Occasionally will haul heavy loads or burnouts

• 52V 30-40A

The torque arm I am looking to get is something like this https://www.ebay.com.au/itm/1-2Set-E-Bike-Electric-Bicycle-Universal-Torque-Arm-For-Front-Or-Rear-Use-14mm/302909331194

My question is will these kinds of conditions cause dropout or motor failure without a heavy-duty torque plate setup or if I do something stupid accidentally like stall the motor and cause extreme torque to act on the dropouts? Would the dropouts be unsuitable for hub motors if I spread them (e.g. 130 -> 135) and in that case is it better to go with a front hub?

Also if I am getting a 350W front hub motor then do I need a torque arm for that if I'm riding with the conditions above, and what if I increase the voltage to 48 or 52V with 20-30A. It looks like the 250W/350W motors look the same so I wonder if it's just the controller that's different in these kits or would the 350W version be able to handle higher wattages better somehow?

p.s for some reason front hub bikes seem to be the most common type down here, at least from my observation, despite the lack of stealth...
thanks

 

[neptronix]

You need a pair of good torque arms at the power you're looking to push. Otherwise the dropouts will spread and the frame will become a paperweight at 2000w. Especially if you use regen w/o torque arms.

Front motors kinda suck, and you'll find that they really suck offroad. Think about it - ~75% of your weight is on the rear tire, and the front wheel thus has 25% of traction. The higher the power, the more likely your front wheel will slip. Front fork dropouts are also not very strong because of the small amount of weight they have to deal with, and many members here have had front suspension fork failures. A steel front fork tends to be sturdy enough to handle a front motor, but do you really wanna run an unsuspended fork offroad?

Front motors are slightly easier to install, and they work OK at lower power levels. It's probably why all the prebuilt bikes in your area use them.

 

[999zip999]

What parts do you have now ? Motor , batter ect. ?

 

[5w30]

http://dillengerelectricbikes.com.au/spares/electric-bike-kit-spares/torque-arms/arc-torque-arm-by-arc.html

Would these be good enough (they still mount by hose clamps) at the rear and are they worth the price difference over cheap ebay ones? at this moment im thinking one of those small silver motors may be a better idea... just dont have the money for any mid drive system though i'm considering them for hypothetical future builds. I digress...

 

[neptronix]

Water hose clamps are not good at handling torque at all.
You want to bolt to the frame one way or another. You want less than 1mm of motion in the whole assembly, ideally.

The best maker of torque arms is still ebikes.ca. I've tried almost everyone else's, and the 4 other kinds i've tried all had loose dropout slots, or looseness in the hardware, which means it can't really act as a torque arm at high power levels whatsoever.

 

[amberwolf]

torque arms are cheaper from china and may take longer,

They're also potentially crappier (depending on the source and design of your local shop's stuff). If they have slop in their holes/slots that let your axle wiggle, it can be as bad as not having one at all.

Like this one:

Wrenches and clamps can work. I've used them on both CrazyBike2 and SB Cruiser with higher power levels than yours, with mixed results. Broke a wrench on CB2, bent one (the box end spread open) on a low-power geared hub on DayGlo Avenger, and broke a number of hose clamps on various bikes.

Clamps only really work if you can use a wrench that lines up with your fork or frame so you can clamp it directly to the tube.

This wasn't good enough; the wrench eventually broke:

If the wrench is not in a straight line with the tube, you have to make a plate or something that bolts to the wrench securely, and then clamps or bolts to the frame/fork tube. Otherwise, the rocking action that occurs between acceleration and regen will just move the wrench too, and it wont' help keep your axle solidly mounted.

This didn't work, and allowed it to wiggle, and then a wrench actually came off the axle entirely because the clamp let the wrench slide along the tube:

Similar thing happened here:

When it eventually wiggles far enough, it'll be cutting into the frame's dropouts, and either break them or just round them out and then the next acceleration or regen will spin the axle and rip out the wires or damage them in various other ways, whcih can blow up your controller (and force you to open up the motor to rewire it, and possibly replace the hall sensors that cna get damaged by the shorting of phase voltages to hall wires).

Sometimes it breaks the axle instead.

If you want lots of DIY ideas, as well as seeing what is commercially available, look up the Torque Arm Picture Thread, and look up
torque arm*
in forum posts and/or thread titles. Lots of stuff to help there.

 

[5w30]

So it is demonstrated that torque arms are necessary. If I make my own, I'll probably go with a clamping design since I don't have any precision manufacturing facilities available to me, like this https://endless-sphere.com/forums/viewtopic.php?t=32140#p465932

I will also settle for lower power motors and I get more range that way as well.

 

[Chalo]

Water hose clamps are not good at handling torque at all.

While that's true as a rule of thumb, torque is a force times a radius. If you increase the radius, you don't need as much force to have the same torque.

 

[neptronix]

Oh man, that's overkill on that tiny motor.. but i understand going that far on a carbon frame .

But look at the torque arm he's looking to use to quantify my statement..

1) fairly short arm
2) some degree of movement is going to be present in the angle adjuster bit.
3) some degree of movement will be present in the bit that connects the third piece of this torque arm.
4) water hose clamps will have some movement no matter what, especially if you have regen.

The three things that can move a little will turn into one assembly that moves a lot.

We're talking about 2000w here, so this is where a little movement can become a big problem. Especially if you have regen.

 

[neptronix]

So it is demonstrated that torque arms are necessary. If I make my own, I'll probably go with a clamping design since I don't have any precision manufacturing facilities available to me

Look at how i used ebikes.ca torque arms on my super hiryuu build in my sig for some hints on how to make precision machined bits fit nearly anything
That setup held 8000w of power and regen so strong, you'd have to clench your ass cheeks around the seat to stay on when it hit! sturdy enough!

I usually started with ebikes.ca torque arms, and then use a drill, angle grinder, and/or file to get the last bits that hook to the frame machined.

I always have a set of various types of ebikes.ca torque arms in my nuts 'n bolts pile, cuz you never know what you are really going to need for that piece of the equation. The hardware store has the rest of what you need

 

[amberwolf]

While that's true as a rule of thumb, torque is a force times a radius. If you increase the radius, you don't need as much force to have the same torque.

But you do have to have something for them to clamp down that, like the above-pictured mount, will prevent the arm from having any movement in either direction once the clamps are tightened.

Otherwise you end up with the failure I showed above with the short stub arm, which had nothing but the hose clamp to keep it from moving, which it couldn't completley do, and which eventually fatigues the clamp and breaks it.