7 cylinder Radial engine, optimised main rod

thingiverse

Not only you have to have and odd number of pistons but as well it is known, or it is time to learn being a mech eng teacher I am proud to be usefull, that on the master rod, called hub here, the attachments of the rods are not evenly spreaded around the part. they happen to be closer as you go away from the main rod. This is very well explained at http://patrice.courtade.pagesperso-orange.fr/etudesw/etoile/etoile.html. It is in French, but to sum it up I'd say that the three pivoting points have to be aligned for every rod when the corresponding piston is at its peak. This is not the case when the spreading is even around the circle. Seeing my screen copies might help to understand. Values must depend on the ration between the lengths of rod and rotor. I made a model with plusalphaDesigns model and find the following values : 64.99° ; 119.86° ; 161.76°. I made the top and bottom models of the new hub. All works great exept that the two bottom rods have to be filled by hand a little bit as there linking points are closer. Enjoy. Post your makes