Speed IPOs

How do these things work? All kinds of strange things are happening when I’m trying to get an object to go from A to B with constant deceleration.

If I set the speed value at frame 1 to anything other than 0 the object starts at B rather than A and moves backwards?

Why doesn’t a simple exponential decay curve work for deceleration? :-?

I assume the Axes are frame number along the bottom and speed up the side. I’ve set up the location key frames at points A and B 100 frames apart and the object moved fine between those points. As soon as I try change it’s speed everything goes wrong :frowning:

Are you talking about key frame animation or path animation.

Well, for key frame animation there is no speed Ipo. You can set up acceleration an deceleration with the shape of the Loc Ipos. Alternatively you can use a TimeIpo.
TimeIpo X-Axis actual frame; y-axis frame displayed in frame X.
i.e X=10 Y=1 the objet will be displayed in fame 10 in its state in frame 1

Speed Ipos are for path animations only (y-axis fraction of the path lenght) or vertex keys.

I’m using a bit of both, key frames define where the object should be along the path at a particular frame. This may be to do with what is causing the problem.

Like Tordat said, the speed IPO’s y Axis is not Speed, but a fraction of the position on the path. That is, if the Y value is 1, your object is at the end of the path, if the value is 0, it’s at the start, 0.5 at the middle, …
If you want your object to accelerate, you need the rate of the curve. A parabolic curve upward would mean an acceleration, and a parabolic curve downward would be a deceleration (by simple derivation of the Position/Time curve).

I hope that was clear.

Martin

This is likely.

I think that you’ll find good info in this part of a tutorial on path animation.

http://membres.lycos.fr/bobois/Tuts/Courbes/completeRC/complete_RC_3_setting_up_the_speed.html

The time IPO is set using pretty much the same techniques.
Having both Speed for the path and Time for the object can give quite a headache as well as interesting results. Notice that the Loc, Size, Rot, dLoc, dSize and dRot IPO can also be used on the object. Their more direct action may proove less confusing that the indirect (offsetting) ways of Time.

Jean