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View Full Version : Controlling accerleration in Graph editor



iggy21
11-29-2005, 09:04 AM
Im using graph editor to move a car around a city scene. I can easily control XYZ and all rotation in Graph editor, but im having a hard time animating a realistic accel/deaccelaration around corners, and at stop signs.

(i have to time the car's entire path exactly, so I created a spline path and converted to motion path to attach to the camera--which i stretched to my accuarte time) Now i need realistic stop/start/slow down. speed up areas.

Does anyone know how control the acceleration values with graph editor or a plugin?

Thanks.
iggy

Wonderpup
11-29-2005, 09:12 AM
Hi iggy21,

The shape of your curves between keyframes in the Graph editor controls the way the object moves between them. The best way to get the feel for how this works is to make a simple bouncing ball animation and play around with the curves a bit.

iggy21
11-29-2005, 09:45 AM
ive got the entire animation down, but i need to add stopping points, starting points, etc.. This is where i run into problems. More or less, im finding that its difficult to manually adjust the cars acceleration sing the graph editor (which im doing by sliding/stretching key frames). Its difficult to get that smooth transition between motions.

UnCommonGrafx
11-29-2005, 11:40 AM
William "Proton" Vaughn posted a GREAT piece on how to use some of the extra features in the graph editor.
http://www.newtek.com/lightwave/tutorials/videos/index.php

On this page you will find the vid, "Velocity and Speed Curves". Check it out, as well as the other gems on the page.

iggy21
11-29-2005, 03:11 PM
Thanks, that velocity/speed tutorial helped alot.. although, it would be even easier if there were some way to control velocity directly with keyframes (but it may not be feasible)

loki74
11-29-2005, 06:05 PM
Well, lets consider this mathematically...

If the curve denotes the position of the object, where time is measured along the X axis and the value is measured on the Y, the slope of the line is the speed.

Acceleration and deceleration of an object can be thought of as tapering off the speed. So we slowly decrease (or increas) the speed as time progresses. This means that you must slowly decrease or increase the slope of your curve in the graph editor.


I whipped up this thing real quick to try and help explain
http://i8.photobucket.com/albums/a8/loki74/accelerate.jpg

To get the smoothness in the second graph, I increased the tension until lt looked smooth enough.

I do not totally understand how these things are made programatically, but it seems to me that velocity cannot be set on keyframes because knowing the velocity of an object will not give you the position in which it exists in 3D space. LW uses the X, Y, and Z coordinates to determine where to place your 3D object. As in real life, velocity is determined by the amount change in any of these coordinates over a given amount of time. The velocity curve is useful in that it can show you the velocity achieved by the various coordinates assigned to your object by keyframes.

Good luck!