View Full Version : Jet Exhaust TVC & "LookAt" Constraint

11 November 2010, 06:34 AM
I have tried so many combinations but I can't get it to work,I mean the animation of the thrust vectoring control of the Su-30MKA exhaust nozzles I'm working on.

This is what I want to achieve:

AL-31F TVC (

I thought the LookAt constraint in 3Ds Max was the way to go,apparently no.

With this constraint,I can get the nozzles to close and open but only horizontally as you can see below,I did a rotation array of simple blades and used a sphere as a dummy :confused:

Grouping,arranging the pivots and rotating them to fit the exhaust of my model doesn't work,as every blade will go solo.IK systems means animating each blade on its own...And building it the reversed way (sounds crazy right?) to get the opposite effect gives nothing.

Scrimski suggested to create an IK system for each blade and clone it...

Is there another or easier way to anim those nozzles (Closing/opening and rotating +/- 15 degrees) ?

Thanks for the help.

11 November 2010, 10:50 PM
Interesting... ok, so I'm new to rigging but I think I have an idea that would work for you (of course the experts in this forum may have a more elegant solution). I'm not in front of 3dsMax to test myself, but here it is:

1. Go ahead and add an HI IK solver on each blade object (turn off the swivel angle -- I don't think you'll need it).

2. Create a circle at the default diameter you want the nozzle to be opened and position it at the end of the nozzle (coincident with blade tips) centered on the "thrust" axis. Add an editable spline modifier to it to turn it into a spline object (make sure it has knots uniformly distributed that line up with the mid-points of your blade tips). Add an Xform modifier to the top of the spline's stack.

3. Place point helpers at each of the spline knots (either constrain directly or use a certain % along path with a path constraint if necessary) and link each blade's IK goal to the corresponding helper. To expand or close the nozzle you will vary the scale of the Xform Gizmo's two axes that corresponds to that open/close plane of your nozzle blades.

4. (Note: you may be able to omit the need for a look-at target) just move your spline object and the IK chains should cause the blades to follow. (...again I'm not in front of Max to test this idea right now. So try translating the spline and see if it works like that.)

5. Manipulate your gizmo's planar scale to have the nozzle expand and contract.

At least I hope that is what happens. Good luck!

11 November 2010, 06:32 AM
Thanks a lot Archangel!

Your idea is quite logic,I have had it in mind but didn't know how to translate it.I'm at work right now,will try later and let you know how it works.

11 November 2010, 09:42 AM
It works!

Actually I have combined your method with the "LookAt" constraint:

- Create the blades rotation array and arrange the individual pivots
- Create a circle with knots matching the blades tips and add an Xform modifier to it
- Create helpers for each knot
- Create a lookAt constraint for from each blade to its corresponding helper
- Manipulate the spline gizmo scale to control the nozzles opening

Thanks a lot!

11 November 2010, 05:47 PM
The scaling on your circle spline looks non-uniform to me... (some points staying behind when reducing and non-circular when expanding...) did you convert the circle to an editable spline or add an Editable spline modifier? And then add the xform modifier? It seems to me the circle should scale uniformly when you manipulate the planar scale gizmo handle. Could you post a screenshot of your circle object's modifier stack? (I'll try and play around with it in Max this evening when I get home from work.)

Bottom line, if you're happy with the results-- that's all that matters.

11 November 2010, 07:13 PM
You're right,the scaling is causing a strange deformation of the spline,but this deformation is uniform,and all the helpers are moving as I want.
I have converted the circle to an editable spline,and refined it by adding 4 vertices to get 8 helpers (for 8 blades).
I have tried another approach,very much similar, by deleting the spline,creating any new object with an Xform modifier,keeping the helpers and linking them to that object.Same result,scaling the object will cause the nozzle to expand & contract (but no deformation in this case).
I'm on night shift,so I can't give any other details,but I would be curious to see your own approach,even if mine is working,I'm always willing to learn other ways.


11 November 2010, 08:37 PM
Simpler way:

1.- Create a bone and its nub.
2.- Make a HI IK Solver from that bone to its nub.
3.- Copy this in a circular distribution.
4.- Create a circle, and link all the IK's to it.
5.- Scale the circle.
6.- There you go! :buttrock:

11 November 2010, 02:09 AM
Thanks for the interesting approach.Looks easier indeed,will try it!

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