RE: DLE222 Starter System - The Project
Structure consideration
The part that needs consideration is the final gear and the final gear pinion shaft. If we choose steel gears, automatically we are bounded by this material shear strength i.e. at around 186MPa (Mega Pascal or 10^6 N/m^2) where this value will be compared with designed dimension loading.
Without dwelling into in-depth analysis, we only consider the base area of the gear teeth. For additional info many good literature out there provide various approaches towards predicting load capacity for a given gear and it involved rather complex mathematics which I try to avoid here in RC world (we are definitely not designing things for human occupancy, if one do so please look at what being presented here as the most basic foundation only). But whatever it is we still can’t run away from high school maths…
Okay, if we designed the final gear diameter to be 60mm then the radius is 30mm or 0.03 meter. We already calculated that in order to successfully turn the engine per compression stroke (at 180 degrees), a torque of 57.8Nm is required. What does it mean? It means that at 1 meter length we apply 57.8N of force. Now to balance it out, at 0.03meter, we should apply how much? The answer is a whopping 1926.67N!
Now if we designed the gear tooth width to be 2mm or 0.002m and thickness to be 3mm or 0.003m, then we have an area of 6 x 10^-6 meter square. Now if we take the applied load 1926.67N and divide this against the area, we’ll have roughly 321MPa of shearing stress on the gear tooth. The limit as we know it to be only 186MPa. For a gear teeth this size, the loading imposed will definitely shear off our gears….
This is where the problem is, we have to juggle those numbers in meeting at least not more than half of the strength limit i.e. 186/2 = 93MPa (half here is meant for safety factor of 2) but roughly from first calculation we already know that we are off target by a third. Now if we increase some of the parameters say by 60%, sooner or later we’ll arrived at a good solution.
I leave that for forumers to come out with solution.