electricwheels.de wrote: ↑
Apr 03, 2018 5:32 am
...a squashing the cable in the process = back to the drawing board.
For sure, but the drawing board is not a sad face, that's a happy face place to be. This kind of challenge in product development and testing is fun and exciting!
Instead od using rounded teeth, try using trapeziod teeth with a slightly negative angle. The rounded section at the top of each tooth acts as a ramp aiding the downwards movement. A negative angled flat does the opposite, the shaft wants to go towards the closed end.
This is true, but part of our design goal was also that the spline modifications be relatively easy for the hub motor companies (MAC motors, Crystalyte, eZee, MXUS etc.) to do with the same CNC equipment that produces the axles. We thought that a rounded spline like this allow for it to be machined either with live tooling coming in from the end of the axle, or with a ball-end mill on the side of the axle. To do trapezoidal teeth profile could require EDM or custom tooling.
Anyways, none of this would be an issue if the cable exit didn't consume a full 1/3rd or so of the splined arc. In order to prevent the axle from having some freedom to role down into this extra space after the failure of one or two teeth we needed something that would constrain the axle against moving here. One possibility we saw was having a plate that presses against the round portion of the axle shoulder where the diameter is larger and there is no cable exit.
This was fairly easy to do by exending the backing plate of the arm long enough to press up and mate to this part of the axle. Here you can see that plate on a steel prototype.
We also decided to change the testing method slightly. Instead of gradually applying torque on the axle until it failed while logging the torque and angle, we did a pulsing motion. Each pulse of torque was 5 or 10 Nm stronger than the previous pulse, and this way we could see more definitively when the arm had had yielded somewhat and was no longer returning to the same zero point. So now, rather than an angle on the 'X' axis, we have time on the 'X' axis and plots of both the torque (blue) and deflection angle (red).
The results done this way are a lot more revealing. Here it is with a closed loop aluminum torque arm (ie not one that could support the side cable exit)
You can see that we don't have clearcut yielding going on until we've pushed it to 80 Nm, and the failure happens all the way up at 160 Nm. In this case there were multiple teeth that sheared off
We thought that would be a handy benchmark reference for what we could aspire to with a well designed 'U' shaped arm that accommodated the cable exit slot.
And how did it? With an open 'U' shaped arm but with a steel backing plate that pressed against the axle shoulder, the results were actually even better than this:
We didn't get any plastic deformation until exerting more than 120 Nm on the lever. At 160 Nm, we were at 2 degrees of overall yield/deflection, the same as the closed circle test arm, but we were able to go over 190 Nm
before failure. That's with an aluminum
torque arm that's just 3/16" thick! I was pretty impressed. It's quite uncommon for anyone would have an ebike hub motor setup that is pushing 120 Nm of motor torque.that's an amount of phase current that would overheat and burn up most ebike hubs in very short order.
Currently recovering from the Suntrip race on a back to back tandem solar powered row/cycle trike
. 550 watt solar roof, dual Grin All Axle hub motors, dual Phaserunner controllers, 12 LiGo batteries, and a whole wack of gear.
Now back in Vancouver with my Big Dummy Frame (yes This One
, thanks ES!) with Grin all-axle front hub, Phaserunner controller, and 52V 19Ah Cellman triangle pack
My website: http://www.ebikes.ca
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