Un-Named Engine

[vederstein]

Here's a cross section of the engine at its most advantageous torque. As you can see from the free body diagram, the the torque "arm" (L) is only 0.066". So the torque applied to the crankshaft from each piston is:

T = L * F
T = L * Press * A
T = L * P * pi*r^2
T = 0.066 * 55 * 3.14 * .313^2
T = 1.1 in-lbs

.187

If the piston is offset from the camshaft, the "torque arm" can be significantly increased but it's to the detriment of higher cam forces on the return piston stroke. In the illustration below I offset the the piston 0.188" which is the centerline of the cam at 90 degrees. You can see here that the "torque arm" goes from 0.066" to 0.188" which would change the applied torque from 1.1 in-lbs to 3.2 in-lb at the same pressure, a 290% increase in torque which would decrease the air pressure requirements from 55 psi to a more reasonable 19. The stroke would increase significantly as well.

Based on this analysis, it appears the biggest improvement would be a change in geometry. But I'm not going to re-make this engine. Remember back from the beginning: if it runs, it's a success.

I'm always trying out new ideas on this hobby. I can leave it to other to optimize...

...Ved.

 

[vederstein]

I've started a different thread with the plans for this engine. You can obtain the design files for this thing here:

https://www.homemodelenginemachinist.com/threads/four-square-engine-plans.33841/#post-372431

 

[Steamchick]

Ved: Your post #21. Well done! A good bit of design work! Noting that the line of force is actually at an angle to the axis of the piston (Radial in the roller follower, but not in the line of the piston), this force can be resolved into the thrust from piston through the cam follower etc. to camshaft bearings, but also a thrust that is a reaction perpendicular to the axis (motion) of the pistons. This side thrust is higher from the high pressure of the air on the power-stroke, but lower on the return stroke when it is only working against the mass of the piston, spring, and residual pressure as the cylinder is evacuated. This side thrust on the piston can also be calculated and plotted to optimise the friction to a minimum, by reducing the peak value (power stoke) and allowing an increase of the side thrust on the piston where is is likely to be significantly lower - I.E. the return stroke.
Perhaps this design work will encourage you to make a second model, with "optimised" geometry" for power/friction, and if you can measure the performance of this engine, then compare the performance of the "optimised" engine, you'll appreciate how good this engine can be. But I concur with your drawing a line to define success. It runs, it achieves objectives = Success!
But the mental exercise and drawings of alignment on cams versus piston roller you have done has already given us most of the answers. So again "Well Done sir!" - and thankyou for sharing your time to explore some question I had raised. I do appreciate the work you have done.
K2