Do 36v 500w geared motors need torque arms?

Wouldn't hurt, even if the need is borderline.

A torque arm is a lot cheaper than replacing the entire frame because the rear dropouts got destroyed. Cheaper than a hospital bill. Maybe not cheaper than redoing your phase wires after being twisted, but if your halls go... then torque arms are cheaper than that :)
 
Whethter you need torquearms or not depends on the torque the motor produces and the strength of your dropouts. If you have aluminum dropouts I would use torquearms, if you have steel you might get away with not using them.

Btw, depending on winding and controller amps, at only 36v a "500w" geared motor will often produce more torque that a "1000w" directdrive at 48v.
 
250W 1 torque arm
500W+ 2 torque arms

UNLESS it's a steel fork then
500W 1 torque arm
1000W+ 2 torque arms

I've seen 500W motors bend out of the dropouts on designed ebikes(wide looks like a gas scooter types), so yeah on a conversion ALWAYS use a torque arm.
 
maanebedotten said:
Whethter you need torquearms or not depends on the torque the motor produces and the strength of your dropouts. If you have aluminum dropouts I would use torquearms, if you have steel you might get away with not using them.

Ya know, i tried pushing 3000w through some pretty damn thick chromoly dropouts once. Ended up spreading the dropouts and putting a dent in the axle. The dropouts were not wide enough, it turns out.
So, steel is not the cure all.

maanebedotten said:
Btw, depending on winding and controller amps, at only 36v a "500w" geared motor will often produce more torque that a "1000w" directdrive at 48v.

Very true. Low end torque also depends on controller tuning. So, better safe than sorry.
 
I've got ~25K miles on my 1000W motor running up to 4000W peak without torque arms and never had a problem. All depends on the dropout material and installation. I don't buy bikes with aluminum dropouts. if you do, better reinforce the dropouts with torque arms/plates. I also don't use torque arms on my other bike with a 3000W motor and 6000W peak.
 
Bad advice. I never died from sticking my finger in electrical sockets. Doesn't make it good advice...
 
Well hey, ~10% of people here who don't run a torque arm on a powerful motor get away with it, even though the other 90% come back with pictures of destroyed dropouts, shredded axle wires, and sometimes even bodily injury. I could probably find you a thousand threads where someone posted pictures of the resulting carnage.

But if you feel lucky and $20-$40 is too much money for ya, then do as you please.
 
Justin did some tests way back in 2009:

Edit: He made dropouts out of 1/8 inch steel for the test.

justin_le said:
As it is, each set of dropout plates and spare axle could only be used for a single test, so I could only do so many experiments.

For a 12mm axle, with no torque arm installed, here's what we got:

Code:
Nut Torque	Axle Spinout Torque

hand tight	38.7 N-m
30 N-m		78.3 N-m
60 N-m		83.9 N-m
90 N-m		96.6 N-m

Although there was a pretty significant increase in the spinout torque when going from loose nuts to moderately tight nuts, further tightening, up to 60 and then 90 N-m had only marginal effect at increasing the ability of the dropouts to resist spinout. The first 30 N-m gives a full 40 N-m of extra spinout resistance, but doubling the tightness of the nuts to 60 N-m only increased the spinout torque by 7%.

This is interesting, because we've certainly had of a few cases where people have tightened their axle nuts so much as to strip the threads, and it would imply that there perhaps isn't a lot to be gained by going so close to this limit. The other interesting thing was to see how these spinout torque values compare to the torque of typical hub motors setups. Your standard 400 series Crystalyte hub/20A controller arrangement has 35-40 N-m of stall torque, which is pretty much exactly where the dropouts failed with hand tightened nuts. And from our own experience, if you forget to tighten the nuts in the 400 series motor there's a mixed chance that it'll spin in the dropouts or not. At 48V 20A, most likely, but 36V 20A, people have gotten away with pretty loose hardware.

When the nuts are tightened to a pretty reasonable amount (30N-m), the spinout torque increases to almost 80 N-m, and that is a healthy margin over the 35-40 N-m stall torque with these setups. But when you then go to say a 48V 35A controller system, and a higher power motor like the Nine Continent, then the stall torque is more typically in the 70-80 N-m range. That's pretty much exactly where the dropouts here gave way, and it matches our experience that these setups were 'right on the edge' of failing.
 
1/8th inch and 12mm axle is a pretty weak connection to start with. I'm amazed it could even handle that much torque.

I have managed to spread some extremely tight custom cut 1/8th inch torque arms on both sides with a 20" magic pie on 4000W though.
The big problem is when you add regen into the mix.

I'd still put a single torque arm on a 500w motor as it's very cheap insurance.
 
Man, I don't know which is goofier. Building kits that out pace the ability to brake or being to cheap to make certain a motor doesn't torque out of the dropouts. I swear I'm surrounded by teenagers. FFS use a meassure of sense. OSHA and the stupid regulations everyone whines about exist for the very reasons we are seeing here. A total lack of common sense. FFS go mow your neighbors lawns and earn another 30 bucks.

The Curmudgeon.
 
tomjasz said:
Man, I don't know which is goofier. Building kits that out pace the ability to brake or being to cheap to make certain a motor doesn't torque out of the dropouts. I swear I'm surrounded by teenagers. FFS use a meassure of sense. OSHA and the stupid regulations everyone whines about exist for the very reasons we are seeing here. A total lack of common sense. FFS go mow your neighbors lawns and earn another 30 bucks.

The Curmudgeon.
That may be common sense to someone who has been building electric bikes for a while, but I am new to this stuff. What I have learned that when in doubt, ask questions. You never assume anything. That is what leads to snapped dropouts and wasted money. Assuming makes an "ass" out of "u" and "me" better to ask then be an arrogant blind fool who thinks he knows all.
 
A torque-arm doesn't wear out, and long after your ebike has died (years from now), you can transfer the TA to a new ebike build...

The kit you are looking at might be labeled as a 500W, but...The controller you are using may be actually applying 1000W to your axles.

Get a torque arm, at least one (and two is always better).
 
Thanks. I bought two recently. I have one on my new bike build and I saved the other one for when I install the geared motor on my daily driver. My controller is a 36v 22 +/- 1A. So about 756 Watts of power to the motor.
 
RonnieBrowen2106 said:
Thanks. I bought two recently. I have one on my new bike build and I saved the other one for when I install the geared motor on my daily driver. My controller is a 36v 22 +/- 1A. So about 756 Watts of power to the motor.
That is why there is a noticeable, but not huge, gap in increased performance on my 48v 1000w bike. I don't know the exact specs of the controller that came with the new kit. It has nothing on it other than a sticker saying "LY-48V 1000W"
 
Also, I hear people say that the bike controllers get hot when used. I have noticed no such thing on either of my bikes, even after a long ride. It is only the battery that gets warm.
 
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