Joints for Oscillating Engine

[etotheix]

Hi folks. For a starter project I am attempting to Model the Elmer #2 V twin wobbler, a simple oscillating engine that runs on compressed air. I've got all the components modeled, but I cannot figure out how to joint the crankshaft and the piston. 

The motion should look like this wikipedia animation, the bit I am having troubling with is the equivalent of the connection between the blue and green links.

In my case I have constrained the cylinder to revolute about the hole where it will be bolted at the bottom, the crank to revolute about the crankshaft, and the piston to slide, but then any joint I attempt between the piston and crank pin either over-constrains the motion, or does something else weird. The thing that should be happening is the crank pin and the end of the cylinder should travel in a circle about the crankshaft, while also free to rotate about each other.  Do I need to change one of my existing constraints to make this work? 

Thanks!

Thanks!

[jhackney1972 · Accepted solution]

You are real close, all you had to do is add a joint between the piston yoke and the rotary pin.  I would use a Cylindrical Joint since you need rotation and determining the distance along the pin length is touchy.  The Screencast will show.  Model is attached.