Engine type cylinder minor rig problem.

Check the blend file below and run the animation.

The second and fourth cylinders seem to be working okay but there is a small problem with the first and third cylinders.

Whats the difference what method would fix it?

btw blender version is slightly outdated (2.69) so i’m not sure if that would make a difference (just playing around with blender at work,not really allowed to download stuff)

Attachments

Cylinders.blend (547 KB)

Off the top of my head … after looking at your file I would say relign the pivot points… but I have also had this ‘animation slop’ happen to me before using the Tracking Constraint… I almost think there is something wrong with the math in that constraint… that only shows up every now and again… but… Seems like Nathan Vegdahl mentioned some issues with the tracking constraints but I don’t remember exactly what he was saying about them…

sorry I’m proably not helping much

Don’t know if you have seen Revolt Randy’s bone crankshaft Rigg…
It worked great last time I used it…

Thanks,will check it out later.

Do you think there is another way to do tracking using drivers instead?

Throw out the empties and tracking and use an armature with IK. It’s much smoother and more robust. I’ve done two and left two.

Best wishes,
Matthew

Attachments

Cylinders1.blend (602 KB)

@MCollett +

and a tutorial on rigging a piston.

I really like your method of doing this… very elegant solution… thanks for the share! Great STuff!

@DCBloodHound

I think one of the reasons using a constraint of any kind will lend it’s self to ‘slop’ in a Rigg is because of the extended use of matrix math in figuring locations… were as if you use some kind of IK constraint … blender always figures the IK constraint last… and this is what keeps it from having any compound errors…

Here’s Nathan’s Explaination on this …

Allll so… if you look here there is a way to ‘slide’ bones along other bones…

I’m not sure if it will work with a Crank Rigg or not… but here’s some ideas…

Anywayz… take a look at this Rigg and see if you can’t come up with some interesting stuff…

this is a somewhat complex video to follow … the Gist of it is… that in Armatures there is the “location Constraint” in that constraint there is a “Head… Tail” slider…
this slider can be keyframed and animated…
thus you have a way to ‘slide’ one bone along the ‘Y’ axis of the other…
and yep… looks like you can even add a Driver onto this…

Anyway hope this gets you a little closer to what you were looking for…

Many thanks for all the help guys,learned tons (never knew you could use bones like that).Special thanks to Norvman for explaining everything so well.

The propagation of numerical errors is unlikely to be a major problem, unless you have a very long chain of constraints. The ‘slop’ is mainly due to cyclic constraints: at least one bone in each cycle ends up following or tracking to the previous position of its target (i.e. one frame ago) instead of the current position. IK recalculates until it reaches a self-consistent solution.

Best wishes,
Matthew

hummm I"m not sure I 100% follow what your saying… when you say “at least one bone in each cycle…”

plus… wouldn’t the ‘effect’ of one object following another’s ‘previous position’ be caused by a numerical overload in the translation matrix… bumping it into the next frame?
perhaps I have misunderstood the whole cause of the issue…

The Rigging Mechanics tutorial, although comparatively old now, is still definitive.