View Full Version : Keyframing correct speed of car

04-22-2004, 06:46 AM

LW 7.5 Scenario:
I have a car traveling around a driving course with multiple turns and straight stretches.

I'm having severe trouble getting the correct speed of the car driving through the turns and straight aways. I need to simulate braking and speeding up.

My keyframes are excactly 10 frames apart from one another with an equal distance of 50 feet beween them. “In theory” I should be traveling at a constant rate of speed, Right? Wrong. The motion between my keyframes are all screwed up.

The readings I'm getting from the speedometer are off the charts. I start going into a turn at 24m (45 Mph) and after passing through it shoots up to 100m which would be something like 200 Mph (obviously not accurate). Every time I play with the TCB controls and/or time values it messes up my motion path and changes my curves. I have my path nailed down but my speeds are off.

Is there any way to speed up or slow down motion between keyframes
without affecting your motion path. Any plug-ins out there? Cruise Control didn’t work.

Someone please help, I’ve got deadlines to meet!

04-22-2004, 07:39 AM
Hey, just a few questions for u:

are u using 2d or 3d space?? (X,Z) or (X,Y,Z)?

If so, you need to do the math for distance between 2 points.

As for going around a curve, that distance is also different, especially if your object changes on the Y axis.

ALSO Make sure u use LINEAR and not Bezier curves in graph editor!!

If that doesn't work:

3 solutions:

1: get a calculator and do 3d math to get the proper placement of the vehicles

2: I believe EKI was working on a plugin that set a constant speed

3: I made my own plugin to set constant speeds, BUT I need to know what speed you are wanting to use so I can recompile the plugin (if I can find it). ALSO, my plugin ONLY works with keyframes, so there for on a curve you will get straight lines and some adjustment will be needed!

04-22-2004, 07:44 AM
Oh, and Flay.com is a 4th option:

This is a plugin found in flay:


04-22-2004, 07:44 AM
This is not a solution, but it helped me with my Hummer race (http://onthez.com/animation/hummerH2.wmv) .

In the graph editor you can right click on a channel and choose show Velocity or Show Speed. I used this as a reference for smoothing out my keyframes using TCB and number of frames between keyframes.

Good luck!


04-22-2004, 09:13 AM
If Monday wouldn't be too late...
I could have a colleague of mine run an actual traffic simulation, with dedicated software, it's simulation is perfect, right down to deceleration/acceleration during gear shifts etc...

Only takes a second to set-up, run and export (thanks to Al Street), but she's (my colleague) not back in till Monday...

04-22-2004, 10:36 AM
Worley's Polk set includes VelAccel (which lets you keyframe velocity and acceleration). I haven't used it but it sounds perfect.

04-22-2004, 11:20 AM
...and also SpeedLimit, which does what it says.