Hello Charles, PRA (Popular Rotorcraft Association} has open source projects for educational purposed.
For Pre-rotators we have 1 soft start circuit using a car starter that can also be a 48-volt high-speed pre-rotator in our library. Members-only pages but will post here if you wish as we changed the new modern PRA to a tax-deductible, non-profit, charity that supports our community whether you support us or not. We still have valuable member benefits and are adding more all the time.
We also have just finished a new two-speed transmission pre-rotator using a cheap car starter with San Diego University senior students. PRA chapter 31 is testing.
See this link to learn more....
https://www.rotaryforum.com/threads...t-is-done-and-ready-for-more-testing.1144536/
This year we have 5 projects with S.D.S.U., S.D.U, and UCLA has reached out but they are 1.5 hours from San Diego. They would have to come to us for testing.
One of those projects is another prerotator you might want to wait for and S.D.U. will be continuing to improve our first prerotator project this next year.
Projects
1) State of the art high-speed (at least 220 RRM with 30' blades) lightweight prerotator using a brushless motor, lithium batteries, and controller. With all things lightweight and powerful it will be expensive.
2) G'force impact fuel-cut-off-switch.
3) Test-stand to test pre-rotators, drive systems, and different manufacturers rotor-blades with data-logger.
4) Lightweight stop and drop landing gear with anti-tip-over (self-leveling on impact).
5) Jump-take-off system to retrofit the fleet. Adapt a helicopter rotor head add electric drive system for jump-take-off capability.
Now I have 3 colleges fighting over PRA projects. But PRA can only pay for the parts for one project at a time. May ask for donations to run all 5 at all 3 colleges is the only way we could let them all try at the same time.