# Correct Connections between parts in Assemblies

#### willblatt

##### New member
I'm trying to set an assembly with six pistons converging to a single point at the same rate. Rather than moving each one individually I wanted to make connections between them on axes which are at 45 deg angles (12 total, 2 fixed to each piston) I can't seem to get the correct combination of connections to constrain them all together. I've tried a Slider connection for the first one and Cyliner connection for the others but no luck, any suggestions?

##### New member
Can you post a picture? I'm not sure I understand this problem. You say the six pistons converge to a single point. Do you mean that they converge to the same line of action (e.g., axis)? Are they radially or linearly located with respect to one another?

Are you sure your set of connections leaves the appropriate number of DOF unrestrained? If I understand your problem the way I think I do, each piston should have 1 DOF (translational) unrestrained. What about the other components, like crankshafts and connecting rods?

Basically, figure out how many DOF should be unrestrained for all your components, and make sure the mechanism satisfies that. The formula is:

#DOF = (6 x number of components) - (6 x number of rigid components) - (5 x number of pin connections) - (4 x number of cylinder connections) - (4 x number of planar connections) - etc. and so forth for all the different types of connections

David Martin

#### willblatt

##### New member
You were right, my dof were off. The idea was to have six pistons, each on a seperate axis(one on the postive y, negative y postive x, etc...) each moving similtaniously to the origin of the six. By setting one as a slider to its main axis, I was able to set the other five as children by an angular slider connection (Tie rod set at 45 deg, four per piston) and a cylinder connection to its main axis. so when I move the parent piston, all six move jointly.

Thanks for the tip.

##### Member
can you upload the model for us ?

karavasilis

#### willblatt

##### New member
Sorry, I can't upload the model because of work restrictions but I'll try to put a simplified version on soon.