We have tons of electrical engineers but are there any mechanical engineers here?
Getadirtbike's design was a CLOSED shape!!knoxie wrote:Hi
The axle will still turn inside the nut though thats the problem, no matter how tight you make it, I have seen this on the Pumas, they will bend 4mm stainless steel no problem, most steel rear dropouts do not need torque arms, I would only bother with them on aluminium frames or manganese forks, there are a number of ways you can make a simple torque arm, my Puma is putting out 1.2KW on the rear of my steel bike, I had been using a torque arm but removed it recently as it was clear that it was not being put under any stress, the dropouts seem fine after a few weeks.
The team hybrid torque arm was pretty simple just a spanner shaped 3mm flat piece of stainless steel with an axle shaped hole in 1 end, someone also posted a nice simple version recently which was basically an open ended spanner shape that sat over the top of the axle and bolted to the rack carrying holes on the rear dropout, however this was on a steel frame and probably didnt need one anyway, Steve Heads little dirt monkeys were throwing out some amazing levels of torque in those 12 inch wheels and he never fitted a torque arm and never had any problems.
IMHO e-bike suppliers should sell them with the kits in a better to have one and not need it kind of idea.
But the evidence suggests the axle nut is the main factor when determining if the axle spins in the dropout or not.Drunkskunk wrote:your idea just won't work. there is no path for the force of the axle to be placed on your torque arm if it doesn't grip on the flats. the clamping force of the nuts is only about 30 pounds. more than that and you strip the threads on the axle stud, and that doesn't translate to 30 pounds of shear force against the arm. that depends solely on the friction between the torque arm, the dropout, and the nut, but it will be less than the clamping force.
But none of that matters since the axle isn't putting the rotational force directly on the arm, all you'll get is 10 pounds of resistance against one nut, causing it to loosen, the other won't tighten, since its at a 3:1 disadvantage.
That's not the kind of force they'd be subjected to here. Also 0.02 mm is like paper. I think you mean 0.2 mm at the very least, but even that sounds too thin. Anyway, the way I'll be using them, the force would be parallel to the direction of the screw, but my torque arm is 10" long and the hose clamp goes on the very end, so due to leverage its job will be easy. I can also use multiple hose clamps if I deem it necessary.As for hose clamps, .02 MM of stainless steel isn't going to hold a torque arm if 4 mm of steel dropout won't. I remove old hoseclamps off my car by sticking a screwdriver under them and twisting. They pop right apart so easy its not worth taking the time to unscrew them.
But again, the evidence, as I see it, suggests the shearing friction inhibits the torque more than a steel [open-bottomed] dropout.The only way to make a torque arm work is if the rotational force of the axle is directly inhibited by something that can withstand more than the maximum shaft torque the motor can produce.
That's actually a good test for a throwaway bike frame. It shouldn't damage the motor, just the torque arm and dropout if they're inadequate.Most of these motors can produce 75-100 foot pounds of torque under ideal conditions. thats the same as if you took a 6 inch wrench, put it on the axle, and stood on the end of it.
As I understand it, when the axle spins, it rips out the wires, shorting the halls and blowing the FETs & whatnot in the controller.CGameProgrammer wrote: It shouldn't damage the motor, just the torque arm and dropout if they're inadequate...
I think he means the "stand on the end of a six-inch wrench" thing. Really puts the torque of these things in perspective, though.TylerDurden wrote:As I understand it, when the axle spins, it rips out the wires, shorting the halls and blowing the FETs & whatnot in the controller.CGameProgrammer wrote: It shouldn't damage the motor, just the torque arm and dropout if they're inadequate...
Exactly. The wires would be unplugged, but the axle can't even rotate more than 45 degrees or so before your foot slides off the wrench.Link wrote:I think he means the "stand on the end of a six-inch wrench" thing. Really puts the torque of these things in perspective, though.
And if you keep the wires free while doing that, they shouldn't get pulled on.
It's a gas. It will never come close to the torque of an electric. However, that engine is operating at a much higher RPM, so you get more horsepower.CGameProgrammer wrote:Is there any proof of the 75-100 lb-ft claim? My 650cc motorcycle makes a peak 45 lb-ft of torque.
I was being lazy. I just stuck the thing in a 24" rim and used that. It gives the exact same number, since the wheel is one foot away from the axle.CGameProgrammer wrote:OK. It says 66 lb-ft of torque with a 5303, 66V, 35A, and 86 lb-ft with 99V 40A. It's important to note that the "lbs" measurement on that simulator is *not* the same as lb-ft; you have to use N-m (Newton-meters) and then convert to lb-ft. Multiply the N-m by 0.7376.
Of course those figures assume I use maximum throttle from a stop, which I never do. But it would be good planning for the worst-case scenario...