Milton,
I'm doing some talking with a few manufacturer at this moment... so see how it goes with it, about the installation picture, maybe after the deal is made.

Barracuda,
Thanks.

Marcin,
I saw that ROTO 50 twin config, rear carb design... if there are internal drawing of that engine, i may figure something out for you.



To those who are interested in designing their own starting system, i list down something here which may help,

1. Pressure x Volume = constant(provided the temperature remain constant)
=> P1 x V1 = P2 x V2, where P1 = ambient pressure, V1 = Initial Volume, P2 = End Pressure, V2 = End Volume
=> Using Engine data, (BORE x STROKE) + Squish Volume = V1 (initial volume), where V2 is just the Squish Volume alone, one may determine the final pressure P2, if twin just times 2 of this figure.
=> The torque to overcome by the system = P2 x BORE x 1/2 x Stroke (if you did not times 2 for twin engine above, then the 1/2 here can be omitted)
=> Now to satisfy quick and confirmed cranking of your engine, you may need at least twice this torque for your system(don't forget, as the engine poured with fuel, those piston rings seal better)

2. Depending on typical idle rpm, you may need to crank the engine to at least 10% of this rpm. Say in my case, DLE111 can idle at around 1300rpm, so at least i need 130 cranking rpm.
=> Power required(kW) = [Cranking speed(rpm) x Torque(N.m) x 2 x pie]/60000
=> Find a suitable motor that can provide such power requirements.
=> Look-up the motor data for typical voltage per rpm output.
=> From there you can calculate the step down gear ratio.(based on the input voltage and expected motor rpm, but can at least handle the power required as above)
=> But have to at least add in 10% losses per gear contact, the more number of gears the heavier the losses. So choose the motor as such it can provide higher torque but enough rated power as above. So that we lower the number of gears, yet maintaining the right ratio.

3. Gears
=> The number of teeth vs pitch diameter constitute the gear teeth base surface; based on the material used, this base must be large enough to overcome the shear stress of system.
=> Highest teeth load will be the final drive gear to your engine shaft, this load can be calculated as per, Load = Torque/radius of the pitch diameter of the gear.
=> Shear stress = Load/Base surface of gear teeth, compare this with known data of the material, if it fall within 1.5 times less than ultimate strength, then your gear teeth will hold!

4. Gear shafts and bearings
=> The size of the final gear shaft is critical, even with bearing mounted shaft, side loading amounted to LOAD calculated above will be experienced by this shaft. Check for shearing stress of these shafts(load/shaft correctional area).
=> As above item 3, compare against material data. This process again needed for the bearings(data can be found from bearing manufacturer)

5. Bracket Structure
=> Again depending on material use, the thickness of this bracket can be determine by factoring in the LOAD.


So, all these design approaches that i just mentioned is to ensure you'll have a good and reliable on-board starting system, but if one just choose to do it simply by machining things, no problem also but you can't simply know for sure whether the system you're making will be lasting yet economy enough in terms of it's additional weight.