View Full Version : IK Pushrod Help

11-27-2013, 12:01 AM
I have a handle that pivots on bank +/- 30 deg from a 30 deg initial tilted forward position. Connected to it is a pushrod that is connected to a flap. The handle pushes/pulls on the rod which in turn pushes/pulls on a horn/arm extending down from a flap, rotating the flap on bank.

This is basically a modified form of a piston and crankshaft, which is easy to setup, except instead of pushing/pulling a piston up and down, my pushrod makes the end flap object rotate up and down.

Can someone load up the attached simple layered object and scene with defined pivots and parents and get this to do the above action with IK? Been banging my head on this for hours trying different permutations. Can't get it to work. Works perfect when the flap object's motion for X position is set to IK, but not Bank... the flap barely moves (rotates) because the Link and Goal nulls pull apart.

11-27-2013, 03:29 AM
I think you'll find that its ust the extreme proportions of the thing that the IK solver doesnt like (as in one very short "piece" connected to a very long one)... If you grab the pushRod object and move it further away on its Y channel, you get proper reaching to goal as you'd expect... In short, its just a limitation of the IK solver.

In this case, and for something that only has a limited range of motion, you can use some constraints to do it... letting you dictate what drives what and by how much.

Its a bit awkward as Ive done it (using that link null as an inbetween)... that's why its best not to use positioned pivots/parented parts, but just use bones, or parent parts off to nulls as you can get your base alignments easier.

11-27-2013, 06:45 AM

I was running 11.5, so loading your scene I recv'd numerous Input Node plugin failures, so I uninstalled and installed 11.6. No errors, but I cannot find where you applied all those node Inputs. Nothing in motion mods, obj. props, graph ed mods, etc.

Step me thru the setup. I mean I SEE what you've done, but I guess I'm too dense to understand what a Pole is, how they work, and thus how to use them. To me a pole is something you hang a flag on... hehe.

Actually, I see NOTHING in this setup that is awkward. I see complete simplicity! IK without the use of goals... baffled.

11-27-2013, 08:01 AM
The node thing is a default attribute in 11.6, Ive not actually added any, so ignore that.

As for what Ive done... its just a same as item constraint to drive the flap from the handle, the pole targeted back (or poled since its on bank, which is what pole is... targeting for bank axis), and then the sai factored to give the correct response reaction.