Help rotating bone in relation to spinning wheel without keyframes

[GuitarGuy (Sarosh Chinoy)]

Hey all!

I’ve never done rigging before and spent all of yesterday on youtube tutorials trying to understand rigging.
I’m starting to understand it but I’m stuck trying to figure out how I can simultaneously rotate and face an object differently to its rotational position.

Here’s what I’m going for:

Specifically, the joint in yellow on the left.
One end of it rotates along with the wheel, the other end of it rotates slightly slower, generally facing the middle of the wheel.

I’m trying to get that same spinning motion I’m sure I’m missing something obvious, but here’s what I have so far:

TrainWheelHelpRig

I tried adding an empty in the middle of the wheel and having the object constraint set to “track to” - it almost worked, but it kept flipping the object halfway through the rotation like this:

There’s 3 armatures in all. One for the bar going across all three wheels, one for this problematic circling object, and another for the arm it should connect to while it rotates.
I don’t want to use keyframes for this, I’m guessing there’s an easy way to do this with just the bones?

Is there a particular video anyone could point me towards that shows how to do this? Or if anyone could nudge me in the right direction here - I appreciate any help

[ajcdfin]

Hey, If you search this forum specifically the ‘Animation and Rigging’ part for ‘train rigs/ing’ there are some helpful posts and files. there are also posts related to specific parts/actions/rigging of it too. Not long ago some one posted about that particular action of the part that the rod is hooked to - it has an action that is hard to replicate/create. Otherwise post a file for a bit more help.

[DNorman]

I would keep it all in one rig, the end goal is to be able to drive everything with the wheel rotation, the tricky part of these gears is in the combination lever, as it has to combine the movement from the radius rod and the union link with a fixed pivot. The trick is to use a very large upright bone that fixes the pivot point and combines the horizontal movement.
I uploaded a version of the gear here in my last post:

How to rig this piston-like mechanical setup?

Sorry I did not see your post until today. I also came to a similar conclusion as you after watching this video: [Blender Tutorial: Walschaerts Valve Gear Animation] by Locomotivist. I did not use any empties or constraints - only bones and Ik’s. Edit: to get the pivot point of the link sliding I created a third IK system, which points to the center of the radius of the link’s curve that maintains and slides the pivot point in the groove of the link. You can change gear by rotati…

Feel free to download and use but I do recommend you try to understand and replicate the mechanism yourself.
edit:

@GuitarGuy

There’s 3 armatures in all.

Bare in mind that the whole gear is one mechanism and that the valve piston movement is dependent on all the other parts!
Edit 2
To answer your specific question I recommend you start with a drive bone (that will drive the rotation of the wheel). In my file the drive bone is called “driver”, it starts in the centre of the wheel and extends to the eccentric crank, the eccentric crank is a child bone of the drive bone and inherits its rotation. The eccentric rod is a child of the driver bone but does not inherit its rotation. The main rod has an Ik system that uses a child of the eccentric crank as its Ik target.

[ajcdfin]

@DNorman

Feel free to download and use but I do recommend you try to understand and replicate the mechanism yourself.

LoL, Thats a good one

@ajcdfin

Not long ago some one posted about that particular action of the part that the rod is hooked to - it has an action that is hard to replicate/create.

Hey that was you…

[DNorman]

Yes I was involved in that thread, the “action” was resolved in this video https://www.youtube.com/watch?v=5AMmhKgi8qU by Locomotivist. My final gear was based on it, although I simplified a bit getting rid of the empties. I am now modelling a full train and will post a work in progress soon I find these gears fascinating.