Pivot - Rotation issue

[terry.lee]

Hi.

I have a cylindrical tube that I need to animate moving 180 degrees around a central axis remote from the cylinder.  I also want to create a circular motion locally for the cylindrical tube as it follows the 180 degree arc.

I planned on creating the 180 degree rotation first and then the local circular motion second.

When I created the first motion I tried to use an object (another cylinder) as the transform centre for the rotation.  As soon as I click on "Auto-key" the "Use transform centre" option is greyed out.  I therefore moved the cylindrical tubes own pivot to the required position for centre of rotation.  After I created the 180 degree rotation I moved the pivot back so that I could create the local rotation.  At this point I find that the original motion has now changed to suit the new pivot point.

Any ideas please how I can get the "Use transform centre" option to work in this instance?  Or am I approaching this the wrong way altogether?

Many thanks,

T 

[Steve_Curley · Accepted solution]

Put the Pivot Point of the Cylinder back where it belongs first. Create a Dummy (or a Point) Helper object at the centre of the rotation (away from the Cylinder). Select and Link the Cylinder (child) to the Dummy (parent). Animate the Rotation of the Dummy - the Cylinder will follow. You can still animate the Cylinder around its own Pivot Point if necessary.

[terry.lee]

Thanks very much Steve, that's great.

[terry.lee]

Hi.

I have created the circular motion about the vessel axis.  I then moved the pivot point of the cylinder just off to one side.  I set up a rotation about the Z axis of the cylinder pivot expecting to see the cylinder rotate smoothly around this parallel axis as it also moved around the 180 degrees.  Instead I get a series of jerky movements that are not anything like I expected.

I started off creating 4 x 90 degrees.  When this didn't work I put the 45 degree intervals in too but that didn't really help.

The attached has a JPEG showing the positions and a short avi clip of the movement.

Any ideas how I can get the movement that I am after?

Many thanks,

T 

[Steve_Curley]

You're trying to make it look like the Cylinder is rolling?

Unlink the cylinder, remove any animation.
Position it along either the X or Y axis.
Hierarchy Panel > Affect Pivot Only > Center to Object (deselect the Affect Pivot button).
Utilities Panel > Reset XForm (you may need to click "More").
Animate the Cylinder's rotation (will be X or Y, not Z).
ReLink it to the Dummy.

If you offset the Pivot from the centreline of the object it will not only rotate (as if rolling) but will also rotate about the pivot making it move up and down as well.

[terry.lee]

Hi Steve.

Yes, I want the tube to be rolling, but around a line just offset (see attached).  So the tube moves around inside the cylindrical wall (large arrow on right) and at the same time rolls about an axis (red line) offset from tube.

Hope that makes sense.

Many thanks,

T

[terry.lee]

Hi Steve.

A while for the penny to drop but I think I got it.  I need two dummies.  Link the tube to dummy 1 for rotation around an axis and link dummy one to dummy 2 for the rotation around the wall.

Thanks for your help.

T

[terry.lee]

Ha!  Spoke too soon.

Looked like it worked when I did a quick test file.  As you can see from the attached, still some "eccentricity".  Although I am rotating the new helper about it's local Z axis, it seems to be rotating about a point?

Cheers,

Terry 

[Steve_Curley]

2 Dummies is the way to go.
You have 3 separate motions, so you need 3 sets of rotation.
The first one you have - the original Dummy.
The 2nd will be the new Dummy - this needs to rotate around it's own central pivot.
The 3rd you (should) already have - the cylinder spinning on it's own axis.
Link the Cylinder to the 2nd Dummy but then offset (move) it with respect to the dummy.
Link the 2nd dummy to the 1st (original one).
Don't offset any of the Pivot Points - move the objects with respect to their immediate parent in order to create an offset.

[terry.lee]

Thanks for that Steve.

Still unsure about a couple of things.

1.  Does the cylinder need to rotate about it's own axis?  I am picturing it just being rotated around  dummy 2 pivot.  Therefore if dummy 2 can just rotate about one axis (it's own Z axis - see JPEG) I think all would be correct?  The cylinder is just offset from dummy 2 so it just rotates around it with dummy 2's movement.

2.  How do I get dummy 2 to only rotate around its own Z axis as opposed to it's pivot point (which it appears to be doing).  When animated there are  X and Y rotation keys as well as the Z keys that were set.  I tried deleting the X and Y but the animation just went haywire.

My Zip file was too big so I will post another reply with second Zip file.

I included a clip that shows dummy 2 unlinked and just showing it's own rotation.  I set this to rotate only about Z but still wobbles.  Ay ideas how to lose the wobble?

Thanks,

T

[terry.lee]

As promised, 2nd Zip.

Cheers,

T

[Steve_Curley]

Mine doesn't wobble at all. Dummy 2 rotates around it's own centre point, the cylinder rotates with it, but offset. Would be useful to have the scene - or rather a copy of the scene with everything except the dummys and the cylinder removed (especially the particles!).
It's difficult to work out what's wrong without knowing exactly what you're aiming for, so if you have any reference material showing what this should be doing it would be useful to see that.
You can see from the attached scene that the cylinder itself is not rotated - it inherits the rotation from Dummy2.

[terry.lee]

Hi Steve, thanks for that.

Yes, I can reproduce what you have no probs.  The only difference in the set ups is that I have a cylinder that is at an angle and I have angled dummy 2 to suit.

I found that the excess "wobble" could be reduced by inserting a lot more keys at shorter intervals.  If you look at Curve editor for dummy 2, as  well as the Z rotation that I created, there is also an X and Y rotation (presumably to do with the angles?).  If I could lose these then I should be able to time it so that I get the desired effect of spraying the wall in a circular motion (see JPEG).

Please find attached Max file.  Also JPEG shows intended path, a circular motion that goes around the wall.  When particles are used there will obviously be a divergance so that all the gaps are filled and the wall is completely sprayed.

I am going to show a few passes of this so I will need to alter the angle of the cylinder (spray gun) for each one (as though the cylinder is being hand held).

Hope this all helps,

Many thanks,

T

[Steve_Curley]

Nonono - don't rotate the dummy, rotate the cylinder with respect to the dummy, if the cylinder itself is not rotating (which I suspect it doesn't need to do, as in my example). Rotating an object on more than 1 axis is what is causing your wobble. That's why there's an extra dummy - to keep the axis rotations separate. If you do actually need the cylinder to rotate (along its "length" axis) then introduce a 3rd dummy between the 2nd one and the cylinder.

[ads_royje]

Hi Terry,

Attached a video of what I understood that you're trying to achieve.

Hopefully i've got it right.

Important to keep in mind is that animation is always relevant to parent space, specially true in rotations.

So for your secondary motion, your outside cyclinder, should have a parent that is oriented the same way, that is how you'll get your local cylinder rotation on a single axis not to wobble.

You may want to use euler rotation controller to achieve this with ease. You can edit fcurves with clarity for any further edits.

If you still get wobbles, do check for Scaling values, should always be 100% on the 3 axis. If scaling is the issue, you'll have to use the ResetXform as Steve explained.

In the video, the central parent has rotation on Z axis.

Child1, same position as Parent, has rotation on X axis.

Child2 (is child of Child1) is positionned at the circonference and oriented as the Child3, no anim.

Child3 (is child of Child2, represents the Cylinder) has a rotation on Y axis.

Hope that can help! 🙂

[terry.lee]

Thanks Steve.

I'm a bit more confused now!

If we go back to the first post I made on this, when I press Autokey the transform defaults to "Use pivot point centre" and is greyed out.  I therefore cannot use anything else for the centre of rotation of the cylinder (and therefore can't rotate the cylinder with respect to the dummy).  It was at this point I created dummy 2 to rotate in order to link the cylinder to it.

The example Max file you sent me has dummy 2 rotating and the cylinder linked to it.  Which made sense (but are you saying this only make sense in the horizontal with no angle?).

I don't need the cylinder to rotate on it's own axis, just around an external/parallel one, but as I said, I cannot pick anything because the transform option is greyed out.

Thanks,

Terry

[terry.lee]

Hi JT.

Looking at your video I think you may have it a little more complex than it actually is.

Attached is a clip showing the main rotation of the cylinder in the front view.  Although the cylinder is angled it stays in the same horizzontal plane for 180 degrees.

Does your Child 1 X-Axis rotation "lift" the cylinder away from this plane during the animation?  If dso, than that is not what I am after.

The JPEGs show the additional rotation that I am looking for, which is the cylinder rotating around an axis parallel to it's own.

Many thanks,

T

[ads_royje]

Hi Terry,

ha, I think I see. Yes it was up-lifting.

Attached another video. Keeps same plane.

Cylinder has an angle offset to the floor but rotates locally on it's own axis.

I do select parent to child in the start of video.

Hope this is the motion you're after.

So, the Cylinder rotates on local axis (animation is on point helper but could be on the cylinder).

The important thing there, is the oritentation of the parent of your cyclinder must be the same orientation as your child (cylinder). Your cylinder rotation exists (is executed) in it's parent space coordinate.

For your question about external axis during Animate is ON, you can go in Customize > Preferences > Animation Tab, toggle OFF the "Local Center During Animate". Although i do not suggest using this option OFF as you may end up adding position keys and may not get the motion you're expecting. That's up to you to decide.

Hope this can get closer to your expectation!

🙂

[terry.lee]

Hi JT.

Thanks.  I tried to open the file but it says "the file is not a valid Zip archive".  Any chance you could resave/resend please.

Many thanks,

Terry

[terry.lee]

Hi JT.

It's OK.  I just tried again and it opened.

I'll let you know.

Thanks,

T