How to rig this sliding arm?

Hi guys,

I’m used to rigging with empties but for this I think I might need bones which I’m not too clued up on.

Here’s a few pictures of the problem I have.

The red line represents slide 1, the blue is slide 2, and the orange is something that would be great if it would only face forward regardless of the position of the arm.

What’s the best way to do this? I’m not sure I want to do a stretch-to constraint because while the second arms are metallic, they will be rusted and textured so I don’t want any stretching going on.

I could probably do this with empties and constraints but when it comes to animating there are a few problems, such as putting locks on positions but the cursor can still travel and this messes up timings.

Any help would be appreciated.

Could you upload a blend? You don’t have to supply the mesh objects but suitable stand ins would help us help you. IK constraints and an armature would be the easy way to rig this or any arm.

I agree with @DanPro - IK Constraint, single Armature, lock off some IK axes in the bone panel, use “target” bones for the two parts of the cylinder so they slide apart not stretch (so you make this in two parts hint, hint) and one simple control bone to activate it all.

Simple Blend file please and I will see if DanPro get it right… (just kidding Dan)

Cheers, Clock.

Hi guys, thanks for your attention, here is a simplified version of the arm. The sliding has me stumped. It needs to stop after a certain height but im a noob with bones


rigHelp.blend (540 KB)

Hey DanPro, just subbed to your Youtube channel. You have a good youtube instructor voice, I’m Jealous. I sound like a pre-pubescent choir boy and I’m 36 :@

Thank you very much for the compliment and the sub.

I’m running into an issue with your setup. The issue has nothing to do with the rig but the mesh. It’s not possible to rig this in the way you intend. The reason is, both pistons are perpendicular. One piston (the lower one) needs to be able to rotate to compensate for the arc between the end pivot points. Or, a cam is needed at the lower pistons upper connection point to deal with the arc.

It may be better if I just record this. I have a half working rig. Just need to figure out how you want to fix the pivot issue.

Give me an hour or two to fix this up.

BTW, Clockmender is being a bully by leaving this to me. He’s the engineer…

Hey cheers for the reply. If the two pistons have to work in union and not separate then it’s not the end of the world As I really don’t want to remodel it, not because I’m being lazy but because the visual design is what I’m after. It’s actually a background asset for an animation with a few close up shots.

See the thing dangling at the tip, that can rotate too so that should fix that particular problem…i think

Here is the video:

It could be better, but it’s a good starting point to build from. Let me know if you have any questions.

Good luck!

Hey Dan. A big thank you for the video, it has really helped a lot. I’m going to have a crack at it and once it’s rigged and textured I’ll post a video. And wow you’ve tought me about that annoying thing where the position of an empty or bone is still recorded even though it’s been locked off. It was worth watching just for that alone!

DanPro!! Who - Moi - scare bleu wouldn’t dream of doing such a thing. You posted first, you should be left to provide the answer, it would be rude of me to post anything after you said you would do a tut.

Anyway, I watched your video - very nice, really impressed with the detail and concise explanations you did on this. You should seriously consider doing a series of these and putting them in the Hint & Tips or getting a website together with your tutorials on, or even charging for them!

I cannot do video tutorials, I always end up getting tongue tied and swearing, it’s hard for me to talk to myself or a computer for that mater, although often I am sure you find as well, talking to yourself is the only way to get a sensible answer.

Cheers, Clock.

While I’ve got your guys attention can I pm you another issue I’m having? It’s to do with moving a circle over a rugby ball shaped object but keeping it flat against the surface.

Sure. Send me a PM. I might be away for a bit this weekend, so no promises when I can get to it.