I am brand new to Blender after discovering it a week or two back and need to catch up very quickly - feels like the world has passed me by!

Problem is, I am a mechanical engineer and the first thing that I try and model, which comes natural anyway, is bogging me down. I have decided to model a piston-cranking mechanism as in a piston running in a vehicle engine. I still need to sort out the actual model but that is less important than being able to animate the setup by rotating the crankshaft for now. I therefore beg for your assistance in this regard - a thousand apologies if the request seems trivial.

I have opted for the constraint philosophy and used an empty (A) to determine the crankshaft center and defined that through a parent-child relationship with the crankshaft centre. Next I defined an empty (B) for the crankshaft radius with parent-child relationship at that point - this is also the point around which the big end of the connecting rod will pivot on the crankshaft. Another empty © to define the piston pivot point where the piston turns around the small end of the connecting rod (the empty C being a child of the piston). Everything behaves as should when you turn the crank, that is, the empties are turning as expected.

I then constrained the following:

  • A as the independent point that will manipulate the model at different angles when rotated and the empty axis rotate accordingly
  • B follows around the radius as A is turned and the empty axis remain upright (right I expect)
  • I defined the centre of the connecting rod at the small end centre and tracked that to point C and vice versa tracked point C to the small end centre.

Problem is, everything seems to work fine although I cannot for the life of me get the small end to remain in place, it is in the middle of the piston being only able to move up and down as it should. It keeps on rotating with the crankshaft radius!

Won’t somebody please do a tutorial on this as I believe it is a universal concept and finds application in virtually everything, please? You are welcome to go slow and in detail…I won’t be offended.



Thanks, I tried to shortcircuit the whole armature setup by using only the modelled objects with constraints and I gather it should be possible still? That is actually how I ended up at this forum because I searched for piston-crank setup but could only find one for full rigging. Thanks for taking the time to help me out…I will definitely explore the forum more.