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Getting Connecting Rod and crank to moe together


New member
I am trying to create and engine model. I have drawn a crankshaft, a connecting rod, a piston, and a connecting pin. I want to start out trying to get the crank to stay put but rotate around its axis. Then i want to have the connecting rod travelling on the crankpin. I don't know how to use connections to make slider connections or angular connections etc. I also don't know if I need to make any parent child relationships. Any help would be appreciated. Thanx

here is a picture:

View attachment 132


New member

As you start your assembly your first component will be a 'ground' body, so it will not move. Therefore, you should put something representing the engine block or a main bearing. Next, you can place the crank with a 'pin' connection to the bearing/block. A pin is just a combination cylinder/planar. Then, you can assemble a connecting rod the a crank journal, again with a pin connection.

You have to be careful not to take the connection refs from different models. For example, a pin connection cannot take its axis/cylinder reference from one part and the planar reference from another. Well, it can, but it won't move. In order to correctly constrain the conrod you're going to need something representing the piston or else (just like real-life) the conrod will just thrash around. The piston will be connected to the conrod with a pin connection and to the cylinder bore with a cylinder connection.



New member
Hello Mustang,

First you need an engine block or something to represent an engine block, like Peter said that will be your ground part when you apply a servo motor.

Next, assemble the crankshaft using a pin connection.

Next, assemble a connecting rod to the crankshaft using a pin connection remembering what Peter said about not crossing the references with other parts. You're only going to use the 1 pin connection but rotate the connecting rod around so the top of the rod is center to the cylinder bore.

Next, create 2 cylinder connections for the piston to the cylinder bore and to the connecting rod to the piston.




New member
OK I dont really understand what a pin connection is. I made an engine body and a piston but I dont know if I am supposed to make these constrains in assembly mode or if they are supposed to be in animation mode. I Dont understand a pin connection in either mode


New member

I have to ask the obvious question: Do you own the Mechanism Design Extension (MDX)? If you do not, you will not be able to create a pin connection (or any other mechanism-type connection, for that matter). This functionality will, however, be available in the Foundation-level license of Wildfire 2.0, minus the ability to create drivers and analyses.

If you have MDX, when you assemble the component you will see in the Component Placement dialog box a highlighted banner 'Connections' with an arrow. When you click on the banner, the dialogs will change to allow you to apply pin, slider, point, etc. If it doesn't change, and you do have MDX, select Tools>Floating Modules and grab the Mechanisms license.



New member
Great pics and explanations Moroso!


Contact me offline if you'd like me to send you several ppt

slides that define all the connections in pretty plain english.

We have found these definitions very helpful in our effort

to educate ourselves not only the connections themselves

but also what they mean as they relate to degrees of

freedom they provide or take away.



New member
I don't know about the Pro/MECANICA simulation functions, but we build a simple 2 dimensional curve network as a skeletion. We work out all the givin details like crank diameter, rod length and jug/sleve/cylinder angles in simple Pro/SURFACE style curves. Each of the piece parts then becomes a detail. If interested I could email or post a simple model.

Bart Brejcha