Next up was to try it with the wider 14mm axle. I only got 2 tests of this in, one with the nuts hand tight and the other with the nut tightened to 60 N-m.
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Nut Torque Axle Spinout Torque
hand tight 49.5 N-m
60 N-m 79.9 N-m
The spinout torque with 14mm axle and loose nuts was 20% higher than for the 12mm axle, OK. But interestingly, with the nuts tightened all the way up, there was NO DIFFERENCE in the spinout torque with the 14mm axle over the 12mm. This at first surprised me, but then made a bit of sense. Ultimately, it takes a certain amount of torque to bend one of the dropout arms and cause the dropouts to appear 'spread out'. It doesn't matter so much whether this torque is applied over a 12mm axle flat surface, or a 14mm, or hell even a 20mm axle. It would start to bend with roughly the same applied torque regardless.
So in the case of open ended dropouts, where the failure mode is spreading as opposed to metal smearing, we can mostly conclude that the larger axles don't really offer any improvement in resistance to spinout.
Next up was to see just what the effect of having a torque arm was with the system. Most of the torque arms we'd seen
were cut from 1/8" steel, so that's what we went with at first in our own design.
When we had the torque arm in place for 12mm axle tests, the 'loose nuts' spinout torque increased from 38 N-m to 48 N-m. With the axle nut tightened up to 60 N-m, the spinout torque increased from 84 N-m with no torque plate to 110 N-m when the torque plate was installed. So it was an improvement, but much less than I had been expecting. The 12mm axle was able to smear the metal around in the 1/8" torque plate without too much difficulty.
Unfortunately, we ran out of spare axles before being able to do more experiments along these lines. (I didn't want to reuse any axles, since they get somewhat rounded after each test).
Big Dummy with prototype 26" Grin thru-axle front hub, 40A field oriented controller, and 52V 11Ah Cellman triangle pack
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