Ok. Let's take the questions one at a time.

The weight depends on a number of factors. The smaller engines require only one gear cluster and a smaller battery. The starter for my Robin 24.5cc weighs about 24 ounces with a 6 cell 1300SCR battery pack on board. This goes up about 4 ounces for the G38 and Q42. They need a 8-10 cell pack to spin them. My G62 system weighs about 32 ounces. It has two gear clusters and requires a 10 cell 1800SCR pack and an electronic ignition. I can't spin the G62 fast enough with the stock Mag.

The torrington clutch bearing is a one way clutch bearing. It locks onto the shaft in one direction and spins free in the other. Remember. Just like a spring starter on your G38 or Q42. After the engine starts you disconnect the switch and the engine shaft turns freely inside the torrington clutch bearing. That's why you have to have a rear shaft. Got to have something for the bearing to grab.

The plate is 3/16" 2024 T3 Aluminum drilled precisely so the gears will work properly. I have templates for all the known production rear shaft engines and the Robin and Toro. I must admit that I had a machinist friend machine some hardened shafts for the Robin. All of the gears are Boston brand and available from any bearing/gear supplier. The Torrington Clutch bearing also comes from the same supplier. Mine came from Allied Bearing here in Muskogee, Oklahoma. They make a number of different sizes for industry to fit you application. I do some light machining and brazing to make up the assembly. Again, everything is in CADD and must fit precisely. I started this design years ago and did everything on a drawing board. CADD makes it much easier and things fit and work.

The hub is a stock hub from a Zenoah G23/26. Horizon Hobbies sells them and Ralph(RCIgnion) sometimes has some surplus from his operation. Your Robin has a 11mm shaft and the Zenoah has a 12mm shaft. You want the taper to be right. I make a sleeve to shim the difference. You need the shaft, special bolt and nut. I add the timing magnet from my local Radio Shack. I use CH Ignitions and their timing wheel to set everything up.

You can see the engines run at YouTube (poor quailty but gives you the idea)

http://www.youtube.com/watch?v=Wo70lJYLA34

I will also try to get some video of the big G62 on the Citabria to show a larger engine starter.

Here is file showing the starter for a G38/Q42