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Rotary Engine Con Rod Crank Pin Assy

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sbwhart:
I've been chewing arround the best way to configure the con rods on the Three cylinder Rotary I'm building.

I'm aware of three there may be more, please shout if you know of any others



1:- Is the method used by Elmer for his three cylinder rotary, what you've got is a spool that centres on the crank pin, with the con rod equaly spaced around the spool on their own crank pin.

2:- Is the method used in the Haylo, what you've got her is a master con rod attached to the crank pin, with the other two con rods attached to the master con rod.

3:- Is the method used in the Cygnet Royal what you have her is a master con rod with a extened bearing bush attached to the rod that roates around the crank pin, the other two rods run on the outside of the bearing bush with cranked con rods.


Like most things all these designs are comprimises 1:- Is compact but not very robust, and you don't have a stright action on the pistons 2:- again is compact but you don't have a straight action on two of the pistons3:- Is not as so compact but you have a straighter action.


What I've had in mind is to modiified version of option 3:-

4:- Instead of having the extended bearing bush, just have a short bush on the crank pin master con rod with the same on the cranked con rods all bearing round the crank pin:- like this




Any ideas, comments, criticism will be welcome.

Cheers

Stew

tinkerer:
Check this out. I don't know how you coould improve on this design concept.
http://upload.wikimedia.org/wikipedia/commons/a/ab/Radial_engine.gif

bogstandard:
Stew,

As you know, I have built the Cygnet Royale, and the crank shown on the plans works very well.

You have to be very careful when going over to another crank system, especially with shorter rods. The whole geometry of the crank swept area can change.

The only real way to do it would be to put what you propose into a CAD package and when animated, see if any obvious problems show up.

The usual problems are that the conrods can hit the bottom edges of the cylinders because they are sweeping over a larger angle, and length of strokes can change, causing either too little or too much movement of the piston, which in turn could require a cylinder length change and maybe timing adjustments.


John

kvom:
While a CAD emulation is nice to have, you can calculate most of the critical factors yourself, and using a spreadsheet lets you experiment with various dimensions.

The stroke will be just twice the distance from the rod end to the crank pin regardless of the configuration.  The angle the rod makes is at a maximum when the crank pin is at 90 degrees to the cylinder centerline and can be calculated with a bit of trig.

A nice thing about a radial like Halo is that the input and output ports are all at the top of the cylinder, so that as long as the piston stays within the cylinder boundaries it will run.

Russel:
Keep in mind that configuration number one, Elmers, the hub is soldered or brazed to one of the rods, so it also has a master rod. The halo version, number two, the hub and master rod are machined in one piece. 

I realize that you are probably considering the differences in machine methods required, more that the configuration of the designs. I just thought I would point out that the Elmers version has a master rod also because it isn't super apparent in your diagram. (I know it took me a little while to grasp how a radial engine could connect all the rods to one hub without destroying itself while it was running.)

Russ

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