Noted K-bob, steinywi and 1Qwk.

Okay we continue....

Basic Sizing
Based on the DLE222 engine mount plate, we know already that we can only play around with gears that have a diameter of between 60 to 70mm. Larger than this it will interfere with engine stand offs. Yes we can always design a larger plate to accommodate a larger diameter gear, but it’ll be a non standard mounting pattern of the engine. This proves to be a problem for some who have already mount the engine to the firewall.

Gear productions vary with different standards, but the most important thing is to have its teeth cut to an involutes shape. One can search out what the term involutes is, but put it simply; the involutes profile of each individual teeth will not cause any point on the surface of two meshing teeth slides with each other. In another words, a point A on a tooth surface will always meet a point A on a meshing tooth, it will not meet at any other points. This concept will prevent pre-mature wear of gear teeth due to sliding action between two surfaces.

Now we have calculated that we need a ratio of 32 to 45 times of step down. Let us assumed at this moment we are going to make only one stage step down ratio of 38 (average of the 32 to 45 ratios). Say the final input gear is 60mm, then the pinion that drives this gear should be, 60/38 = 1.58mm. Will it be possible? No way… Typically a 1000W rated motor shaft alone will be 5mm diameter.

Looking at this we have to design several stages of step down. Let us assumed a 2 stage step down, then per stage of step down ratio will be square root of 38 = 6.16. If the final gear is at 60mm diameter, then the pinion will be 60/6.16 = 9.7mm. Not to say not possible, but is it too small? Then let us add one more stage, then per stage step down will be 38^1/3 = 3.36. At this ratio, if the final drive gear is 60mm, then the pinion is 17.9mm. This is more like it!

Now we know for a good sizing, at least we require 3 step down stages. How much this exact individual ratio will be, will have to depend on how we can arrange the stages so as not to interfere with each other but as guideline, we know it should be around 3.4.