dogman wrote:I tend to agree about the steel dropouts. At least for installing without tourqe arms. This first graph is a no tourqe arms test.
Clearly an axle hard enough and a nut that allows tightening to 90 helps. I don't know that it would be good to squeeze alloy that hard either, but I would never run a powerfull motor on alloy drops anyway. The established safe method for installing powerfull motors to alloy frames is a custom made steel tourqe plate, that effectively replaces the alloy rear drop with a steel one.
About the 700 watts, I don't agree. But that is about the limit for running without tourqe arms.
I would say that 700 watts is about the limit you want to put on a bike and sell it, and be liable for though.
lester12483 wrote:Its pretty simple
Your bike must have steel forks
Your ebike then must have a torque arm
Its not safe for a hub motor to be over 700 watts. Way too much torque.
Not necessarily, it just has to be engineered properly. The forks are ally, the reinforcements are STEEL. And the end is closed over the axle - this is important even if I have an axle spinout I will not lose the front wheel.
el_walto wrote:Would you recommended tightening the eZee hub motors to 90Nm? I'm afraid I might strip the threads, or even crush the aluminum dropouts on my bike.
I'm curious as to what is the maximum torque a standard axle/bolt starts to strip at.
dequinox wrote:Perhaps the axles Justin has are of a different alloy than the one's you work with. That might explain the stainless torque arms getting mutilated while the axle was less affected.
justin_le wrote:Will do a thorough description of the test procedure later. Justin
liveforphysics wrote:As far as the puzzle with the clyte axle taking 70nm on one end, and holding 130nm on the other, a smear of moly-lube on the threads can make a very substantial difference in indicated torque vs the tension on the axle.
We throw a special bolt-strain measuring tool with a dial indicator onto the dip in the face of the fastener, and one on the end of the fastener. Seat and zero the gage, then proceed to torque until you've set the optimal stretch indicated by the manufacture. The bolts all have a consistent modulus of elasticity and x-section, so when you set the stretch distance, you know you've accurately set the correct tension on the bolt.
When you try to estimate how hard a bolt is clamping by setting a torque value on a nut, what is really happening is the conversion of a supplied torque through a friction interference of a thread pitch, and the actual loading on the axle is determined by this friction value. This friction value can be surprisingly variable.
For example, when setting rod-bolt torque with premium no expense spared and clean fasteners, running dry clean surfaces and setting torque to 40ft-lbs could mean 0.05" stretch on the bolt (a direct representative of the tension on the fastner, aka all that matters for our needs.) To match the exact same amount of tension on the fastener on a bolt with bit of a moly torque compound on the threads, 0.05" of stretch might occur at only 25ft-lbs measured at the wrench.
dogman wrote:While the two peice tourqe arm clearly is a design to fit more bikes, I have felt from the start that the pivot point with a bolt introduces a possible weakness.
Two bolts would prevent that rotation, but the customer would have to drill at least one of the second holes, once he sets the angle.
At the forces you are testing at though, wouldn't a lot of us be over the handlebars by then? So the current design is most likely fine, with tight nuts.
If if worries somebody, the tourqe arm could be welded once the angle was set I suppose. Then the clamp couldn't slip down the fork.
dogman wrote: Which way would the axle want to spin when throttle is put on? The wheel spins front to back, to roll forward. Does the axle tend then to rotate the opposite direction, back to front?
Do you still intend to do the aluminum dropout experiments?
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