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View Full Version : Rigging a mechanical scissor link disc (or Hoberman Disc)



Matus_1976
05-03-2015, 07:58 PM
Hi,

I'm working on a project and am stuck, looking for some advice. I'm modeling a series of cross linked members which are like scissors, but they are linked end to end, so when the links close the whole assembly gets longer. Think of the those gags which the punching glove of the end of linked metal bars which look like X's linked together, or the gates they use at Home Depot to block off an aisle. Mine is a bit different in that the link is bent so it forms a disc, when the parts move, the disc gets larger in diameter. There is a toy that does this called the Hoberman Disc, he also has a sphere version of it. It's easy enough to model, but I'm trying to rig it so I can turn a control null which causes all the links to expand, increasing the radius of the disc. I've tried setting the pivot at the center of the link, then using channel follower for he opposing link, saving the pair and adding the files from the scene, but the parenting gets very messed up. Is there a tool / plugin that would help with this? Thanks!

Matus1976

Matus_1976
05-03-2015, 08:06 PM
Here is an image of the collapsed disc surrounded by the larger disc128095

Slartibartfast
05-04-2015, 10:24 AM
Hi!

I would do like this (attached scene).

128111

Matus_1976
05-04-2015, 01:36 PM
Hi!

I would do like this (attached scene).

128111

Thanks, that looks perfect! I'll dissect it to try to figure out how it was done.

Slartibartfast
05-04-2015, 02:12 PM
Thanks, that looks perfect! I'll dissect it to try to figure out how it was done.

Just ask if there is any problems! Main idea is every bone is 'same as item' on heading. Every other bone with a multiplier of -1. It's kinda tedious to assign a weightmap to every part for each bone but that's what i did.

lertola2
05-04-2015, 02:14 PM
You could animate one pair of scissors then make clones and rotate each by 30 degrees. The attached scene takes that approach.

http://forums.newtek.com/attachment.php?attachmentid=128117&d=1430770270

128116

squarewulf
05-04-2015, 02:31 PM
It all appears to be linear motion, you could just use a morph.

lertola2
05-04-2015, 03:43 PM
It all appears to be linear motion, you could just use a morph.
Yes that might be easier.

Matus_1976
05-05-2015, 08:21 AM
Thanks all for the suggestions! I've played around with doing it a couple different ways, so far either the morph or animating a single pair and copying it seems to be working best for me. I've done alot of modeling but not as much animating. Some minor issues I've run into so far is the morph options seems to slightly distort the length of the links and the parenting option is tedious to make it controlled by one single Null. I'll try some more variations tonight.

seghier
05-05-2015, 12:41 PM
i create simple example based on disk shape with 6 sides ; i used two morphs
than i apply array in layout

https://www.youtube.com/watch?v=VZB0Io7kjH8

128147

spherical
05-05-2015, 02:58 PM
Seems that your segment arms shrink and grow in length, which wouldn't happen in a physical Hoberman Disc or Linear Pantograph.

JoePoe
05-05-2015, 04:01 PM
If you’re careful when modeling then just ONE morph, right! (a la squarewulf).

No stretching here. (edit: whoops, I think I spoke too soon. A very small amount of squashing as it nears/leaves 50%. Start and end are perfect)


http://youtu.be/voyF39kNDz0

seghier
05-05-2015, 08:41 PM
Seems that your segment arms shrink and grow in length, which wouldn't happen in a physical Hoberman Disc or Linear Pantograph.

you are right because i create disc shape with 6 sides and use bevel
i just want show the idea ; maybe he will make it better or use splines with metalink
for animations like that i prefer rhino

seghier
05-05-2015, 10:38 PM
new test : lines guide created with rhino and shapes with lwcad for more precision


https://www.youtube.com/watch?v=K63yJatMgYQ

128154

spherical
05-06-2015, 06:11 PM
That looks really good.