The initial driver is using a small PIC 12F675 and and an IR detector to give me pulse timing information from the solenoid. I went the IR sensor route rather than a mechanical switch so there was no rubbing parts that could wear as acrylic is rather soft. To get a good timing signal aluminum foil is placed on one side of the flywheel to give a good reflection back to the IR emitter receiver pair on the PCB.
The flywheel has an acrylic boss which hold in a 9mm ball race, this is secured with 5 M2 screws which keep it centered and true. One of the M2 screws is longer than the others to allow for a connection to the con-rod with attaches to the solenoid.
First fire up video
After the success of these tests I redesigned the acrylic, PCB and solenoid mounts into a much more stable model. There are now two pieces of acrylic with feet for stability and I moved the fast/slow buttons to the rear of the PCB so they are easily accessible from the back of the motor. A PP9 battery also fits between the two motor sides and powers the motor for a couple of hours at low speeds.
The finished kit, mounted on a wooden plinth (just for looks)