Forum Groups
  All forums
    Help & Feedback
      Questions
      Work in progress
      Finished Art
      Non-Max related
    Community
      Offtopic
      News
    Hardware
    Photography



Maxunderground news unavailable

 
First page  Go to the previous page   [01]  [02]  Go to the next page  Last page
 
Four bar linkage
show user profile  dinant
I am drawing the experimental setup we have in our lab. I am now making a robot arm, which is some sort of four bar linkage and I need it to move accordingly. I tried placing the pivots in the right axes and linking connecting them. Yet, it doesn't move. I also tried using the Create>Systems>Bones option and then linking it to the robot arm.
So I need to make that 1) per joint only movement is allowed around the z-axis and 2) for two elements to rotate around the same z-axis.
This way it should be that I get a four bar linkage with two degrees of freedom.

I am not very experienced in 3dsmax and not at all in making linkages.




read 1791 times
8/19/2009 1:34:33 PM (last edit: 8/19/2009 2:08:32 PM)
show user profile  Reality Man
might help...scroll down to Groteys last post:
(you need to make an IK chain,basically...that's what you left out)

click link below


http://www.maxforums.org/thread.aspx?tid=478607

read 1784 times
8/19/2009 1:36:39 PM (last edit: 8/19/2009 1:42:22 PM)
show user profile  dinant
I think I tried that to.. I'l have a look.
read 1768 times
8/19/2009 1:47:58 PM (last edit: 8/19/2009 1:48:39 PM)
show user profile  dinant
Ok, I am almost there.
http://s648.photobucket.com/albums/uu203/dinantk/?action=view¤t=robot.flv

I have a dummy connected to the brown arm and have a lookat constraint from the blue arm to the dummy. I can't figure out what I need to do to make a fixed axis between blue and brown.


read 1737 times
8/19/2009 3:36:43 PM (last edit: 8/19/2009 3:37:18 PM)
show user profile  mrgrotey
I'm guessing that you want to control the arm via the end of the brown section and not by rotating each part separately?

If so I've done this rig




Here's the max7 file
http://www.divshare.com/download/launch/8237986-81e


Make sure the pivot points for the brown bar and the two dummies are all vertically level.

Pivot locations:
Green bar: left
Pink bar: top
Blue bar: top
brown bar: left
dummy objects: center

Linkages:
blue bar --> green bar
big dummy --> blue bar
brown bar --> small dummy
small dummy --> pink bar
pink bar --> green bar

Orientation constraint:
blue bar --> using pink bar as target

look-at constraint:
brown looking at large dummy (change axes in options for correct orientation)

IK Chain (HI Solver)
from green bar to brown bar



Then just move the IK Chain crosshair




read 1691 times
8/20/2009 3:04:06 AM (last edit: 8/20/2009 3:16:34 AM)
show user profile  dinant
The famous Mr Grotey!
Thanks a lot.
I am getting closer...
I assume you meant:

pivot location:
green bar : right (iso left)
brown bar : at the end of pink bar (iso left)

The only issue is now that the brown and blue bar separate a bit when moving the IK Chain crosshair
read 1665 times
8/20/2009 10:36:16 AM (last edit: 8/20/2009 10:36:16 AM)
show user profile  parkerfamily
woohoo, the engineering box thingy.... can't remember it's name, but by changing bar lengthes you can get like 1000 dif uses.
read 1662 times
8/20/2009 10:37:33 AM (last edit: 8/20/2009 10:37:33 AM)
show user profile  mrgrotey
"I assume you meant:

pivot location:
green bar : right (iso left)
brown bar : at the end of pink bar (iso left)"


UMM... no I meant it as I said it ;)

the pivot point of the green bar is on the far right as you see it
and the pivot point fo the brown bar is of the far left as you look at it.

download the max file I posted and have a look at it




read 1657 times
8/20/2009 10:46:20 AM (last edit: 8/20/2009 10:48:18 AM)
show user profile  dinant
Getting into serious mental problems here...
I have all the pivots and links as you did, yet the blue and pink bar don't move when I move the IK crosshair.

All the orientations of the pivots are set equal.


read 1641 times
8/20/2009 12:19:25 PM (last edit: 8/20/2009 12:22:27 PM)
show user profile  mrgrotey
Not sure where you are going wrong, maybe I wrote it down wrong. Here's a simpler explaination







read 1622 times
8/20/2009 1:46:11 PM (last edit: 8/20/2009 1:46:11 PM)
show user profile  mrgrotey
and it would appear I forgot to do the look-at constraint and it still works so don't bother with that bit ;)

and as that part isnt needed then you dont need the large dummy either




read 1615 times
8/20/2009 2:16:27 PM (last edit: 8/20/2009 2:18:10 PM)
show user profile  dinant
I was in fact already wondering why I would need that as it should "follow" mechanically from the IK link.

I am starting to feel very stupid though...

I have remade the robot arms to be sure to have the exact dimensions. I have placed the pivots accordingly and made all the links. It is pretty much moving as it should move, yet the brown and blue bar detach. The brown and green bar should be parallel and they aren't always as can be seen on the vid. Pretty please sugar on top, Mr Grotey what do you think?

read 1610 times
8/20/2009 3:10:12 PM (last edit: 8/20/2009 3:27:18 PM)
show user profile  dinant
Hey Mr Grotey, still around?
I am sorry to bother again, but I think there is still something missing. I rebuild and used your simple rig and it also does what my problem still is: the rotation point change. Within a small range of motion you can hardly see it. Watch the rotation point of the brown and pink bar:



I remade it with exact parameters, and it seems not to be a problem of accuracy.


read 1600 times
8/20/2009 4:43:51 PM (last edit: 8/21/2009 1:07:40 PM)
show user profile  mrgrotey
Sorry for the late reply, ive fixed it now using a slightly different and easier method

Hopefully you're still around








read 1553 times
8/22/2009 3:08:09 AM (last edit: 8/22/2009 3:08:09 AM)
show user profile  dinant
Hey Mr Grotey!
Good that you are back.
This works very well and makes indeed way more sense as now the system is determined.
I played around with the same setup of pivot points and 2 IK links, but I didn't come up with ur magic trick: linking the first IK chain to the brown bar! Really good man.
Here my working model:



And thanks again Mr!
read 1509 times
8/24/2009 12:15:28 PM (last edit: 8/24/2009 12:16:10 PM)
 
First page  Go to the previous page   [01]  [02]  Go to the next page  Last page
 
#Maxforums IRC
Open chat window


Support Maxforums.org