Circular Motion

[ednachman]

I am attempting to show a ball following a circular path such as an orbit. I have 4 frames to show a change; East to North, North to West, West to South, and South to East to the beginning. I have smooth transitions at North, West and South but at the East it appears to be a 90 degree angle and not smooth as the other points. Any suggestions?

[MonroePoteet]

The splines need data outside your sequence to calculate smoothing across the end points. You can add keyframes outside your sequence to provide the data. For example, if your sequence is from frames 0 to 60, with keys at 0,15,30,45 and 60, make a duplicate of key 15 at frame 75, and a duplicate of key 45 at -15 (minus 15). That provides the smoothing at the endpoints.

However, I've found it difficult to get accurate circular or elliptical motion with constant velocity from the spline-based motion paths, so I tend to use MathMotion (legacy plug-in) to get circular or eliptical motion. If you set the X position and Z position as follows, you get a perfect circle in 360 frames. "f" is the MathMotion representation of the current frame.

Position X = sin(f * 3.141 / 180.0)
Position Z = -cos(f * 3.141 / 180.0)

You can also create Expressions in the Graph Editor to do the equivalent, using the keyword "Frame" in the Expression instead of "f", providing appropriate expression names, and applying them to the appropriate channels. MathMotion may be a little easier, but it doesn't appear to be Added by default in V8.2. It can be found in the C:\Program Files\Lightwave [8]\legacy_plugins\layout\lwmath.p plugin.

If you want a faster circle, multiply "f" by some scaling value (e.g. f*2 gives a circle in 180 frames). If you want an elipse, multiply one of the expressions by a small real number.

mTp

[ednachman]

Thanks MonroePoteet. However one problem.
I've located the plug-in lwmath.p but cannot get it to initiate in Layout. I click on "Add Plugins" locate the file, select open, get the message "8 plugins have been successfully added.", click OK. I clicked on "Addtional" under "Plugins" under "Utilities" and cannot find the plugin. I can see it when I click on "Edit Plugin" under "Motion" but that's it.

[MonroePoteet]

MathMotion is an "Item Motion" plug-in. The type defines which locations within LW it's available. "Item Motion" plug-ins are only available in an Object's motion panel.

1) Select the object, then press "m" to get the Motion panel.
2) Under the "Add Modifier" pull-down, you should see "MathMotion"
3) Select the plug-in, then double-click to bring up the panel for options
4) The "Channel" pull-down defines which aspect of the object's motion or rotation or scaling you want to affect.
5) Enter the equations from the previous post in the "Value" window to implement circular motion.

mTp

[ednachman]

Thanks again MonroePoteet.

I'll be experimenting all weekend.

Ed Nachman