Rocket Flight

[Shotster]

I'm trying to animate a cylinder along a spline. The longitudinal axis of the cylinder must remain tangent to the spline. (It will eventually be a rocket in flight, but I want to make sure I understand the animation fundamentals first.)

Immediately after adding the cylinder object to the scene, it behaves as expected - i.e. the Z axis remains tangent to the spline. The problem is that the Z axis is perpendicular to the longitudinal axis of the cylinder. I therefore went into pivot mode and rotated the axis 90 degrees so that the Z axis is parallel to the cylinder's longitudinal axis. The problem is that now the silly thing does somersaults along the spline!!!

Can someone PLEASE tell me how to get the cylinder to travel along the spline so that its longitudinal axis remains tangent to it?

(C3D file is attached. I don't think a "rail" spline is needed, but it's there just in case.)

 

[frank beckmann]

Not exactly sure why it isn´t working in first place - but:
Delete rocket cylinder
Take new cylinder - adjust height - add transform-modifier: rotation"P"itch= -90° - needs to be minus z-axis
Add spline-tracking tag - add helix to spline tracking tag - Check Adjust just heading - No rail spline needed here - keyframe "position".

Cheers
Frank

PS: there are 2 example files in the help: 1 under "Animation": Spline tracking.jas and 1 under "Particle": Cartoon Jet.jas

 

[Shotster]

Thanks, Frank. Yeah, so a transform modifier is all that was needed. However, that makes me wonder if my understanding of pivot mode is lacking. The user manual says...

Use this mode when you want to move the object coordinate system.

...which seems to be exactly what I needed.

That raises a question though. When/how would one use pivot mode? Can you (or someone) provide an example?

Should the existing behavior with respect to pivot mode and spline tracking be reported as a bug/issue? If so, how does one go about reporting an issue?

 

[Shotster]

Use this mode when you want to move the object coordinate system.

Ok, so taken verbatim, it seems to state that pivot mode pertains only to position and not orientation/rotation. Maybe that's the key? Still a bit puzzled, but oh well...

EDIT: I don't mean to beat this to death, but in what situation would pivot mode enable me to do something that couldn't be done with the transform modifier? I think an example would help drive home the distinction between the two features for me.

 

[frank beckmann]

A simple example you can find at Help: Cheetah3D samples->Dynamics->Rigid Body Pivot.jas

Cheers
Frank

 

[Shotster]

Ahhhh, I see. That's really helpful. Thanks!