Just to fill in some gaps here and there:
1) Our design didn't use the balls in the shaft to create a ball bearing like assembly when the gears were not engaged.
2) Though simple in concept, these transmissions take a while to build for the first time (get prototyping!!!!).
3) Spring load your shifting device!!!! One thing I've seen with the designs is that everyone uses air or some sort of device to engage gears.....Air is good, but at the same time air along with a spring load is less harsh and more accurate at engaging the gears and will tend to solve SOME of the syncro. grindage. The spring load allows for error in shifting with no damage to your machine.
Happy Shifting!
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"Engineering is making the impossible happen"
"We are here to create, not merely survive" - unknown fortune cookie
"If you don't push the envelope you're just spinning your wheels"