RonnieBrowen2106
100 W
I know that my 48v 1000w motor needs torque arms, but does a 500w geared motor need one? I am relatively new to electric bikes.
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.
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.
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.
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.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.
spinningmagnets said:(and two is always better).
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"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.