Probly been asked before but I can't find a reference to it.

I want to make a mechanical arm controlled by a hydraulic piston. The piston sections are children of the lower arm, the upper arm is a child of the lower arm, but then the upper arm would also need to be a child of the piston.

This would leave the upper arm with two pivot points; one on the 'elbow', and one where the piston joins it. YIKES!

I've tried hacking the CR2 to add weld and parent statements, but can't get both joints to be active at the same time - either one or the other works, but not both.

Can this be done in Poser?

I think it must be possible, I'm sure I've seen someone do a Poser figure of a mechanical digger with a similar setup

But How?

Does anyone know of a tutorial that covers this?

regards

peejay

Urg:) Can you give us a picture of it? Can't quite imagine... H:)

Good question

Yes you can do it. Quite easily Hopefully the hydraulic parts have unique names. The solution is simple but takes a bit of fiddling because you have to get the joint rotation angles right. I've done it with my terminator and powerloader models so I know it works. Parent each piston part to the relative arm part that it is a child of. Set the rotation (green/red crosses) so they are central to the rotation centres. Green for rotation control red for rotation end. This is important. Also the xyz axis needs to match that of the arm so when the arm moves the piston moves with it. Once you've done that and the hyrdaulic ends are aligned. You need to "point at". Select upper piston part "point at" lower part. Select lower part and "point at" upper part. Problem solved. If you need more information and a couple examples how this works. email me at Questor@shalako.demon.co.uk and we'll talk about it. You can do this with props or by having the hydraulics as part of the main figure provided they have unique names.

Example image using the terminator arm. The pistons on this figure are a part of the main object, not seperate props. The naming is the key. But this will give you an example how it works. The rotation centres (green) are at the hinges where the piston meets the arm parts, the rotation ends (red) are at the end of the piston parts. Both pieces then use "point at" so they know what they're supposed to follow. Left image is the arm at rest, right image is the forearm bent at 60 degrees forward, you can see how the pistons have extended and collapsed to follow the arm position.

Thanks That's exactly what I wanted to do. Cool model by the way!

That T-800 is a masterpiece of Poser virtual engineering, Questor. Stan Winston would be proud.

You can do it with ERC, too. No need for any parent child relationship. You turn the elevating screw on the cannon I have in Freestuff and not only does the screw unthread out of the carrage properly, the tube tilts AND the sight rotates to match the tube's elevation (like a proper sight should). No parent/children at all, super trick, what? (ERC is the "master" name for all the Joint controled stuff, in this case the screws rotation also does Y trans for the same part, plus rotation for two other parts. Wasn't super-hard to setup, you can download the Napoleon to see the details in the CR2)