Design Question or “Oh boy do I feel stupid”

[edan]

Hello,
I was designing an engine to possibly build after looking at Elmer’s “Opposed Piston Steam Engine”, but I have a problem.

If the model is rotated CW, the left piston with the upper crank throw leaves the cylinder .035 before the right cylinder.

If the model is rotated CCW, the right piston with the upper crank throw leaves the cylinder .035 before the left cylinder.

The crank throws are 180 degrees apart.

If the crank throws are horizontal, both pistons are exactly the same.

If the crank throws are vertical, the error .035 difference.

I know there is a simple explanation for this, but the more I try to find it, the more lost I am. I can see that this model does this, but I can not figure out exactly why.

I think I can adjust one upper linkage rod .035 to correct this, but this would only work for one direction of rotation. I am trying to make this to run in both directions.

Could someone who can see what is causing this please let me know what I am missing?

Thanks you.

 

[mu38&Bg#]

It's just a geometry issue. With all of the linkages one one side of the crank center this is inevitable. You should be able to reduce what you see by adjusting things so that the crank connecting rods are horizontal in your 2 horizontal picture. Currently the rod small ends are below crank center. Adjusting lengths of all rods might be required to eliminate as much as possible. Also changing the center to center of the pivot points or rods lengths such that the intermediate rod is vertical at mid stroke should help. Of course this will change the look of your engine a bit.

 

[edan]

Thank you dieselpilot for your reply.

“so that the crank connecting rods are horizontal in your 2 horizontal picture”

I did what you stated above, rotated the model and came up with a .0001 discrepancy.
Good enough for me.

I basically have a 9th grade education and I struggle with geometry issues all the time. I just don’t have some of the “basics” and I did not see this issue.

Thank you again.