the wheels on the bus go round and round

[Master chief]

ok im making a car of sorts and got the basic model riged but it has ocured to me that i dont know how to make the wheels turn execpt by frame by frame actualy rotating them , is there an easyer way to do this?

[KenH]

Do a search of the forum for Eular constraint.

[John Bigboote]

Basic rigging. Go into bones mode...make a bone that spans the lenght of the car and assign ALL cps to it. Next, in modeling mode, lock or hide all the CPs for the front wheels. Back to Bones mode...make a bone (child of the first bone) that spans along the front axle and assign those front wheel cps to it. Now do the same for the rear axle/cps/child bone of bone 1. Save.

 

In a chor or action, rotate the front axle's roll handle a little to 'activate' it and then look at the rotation properties window. Right click on 'Rotation' and select 'Change drivers to euler'... this will allow multiple rotations. Ketframe the position of your car (start and end) and then rotate the front axle enough times in the right direction to where it looks good. Now, on frame 1...select the rear axle bone and give it a 'roll-like' constraint with the front axle as target... Save and render!

 

Next thing to learn will be to rig the front wheels so they can steer... baby steps...

[phatso]

If you searched for "eular" and got nothing, try again using "euler" with an E.

 

Onnery cuss, ain't I?

[Caroline]

I'm probably missing something here, but is it necessary to use euler in this simple circumstance?

 

Could you just not assign one bone to the wheel, set 4 keyframes for the rotation, then right click the last keyframe, and click Curve > Post-Extrapolation Method > Repeat.

 

This movie is 1 rotation with 4 keyframes, and the 2nd repeated.

wheel.mov

[Rodney]

I like that Caroline.

Can you share the project file?

[Master chief]

I'm probably missing something here, but is it necessary to use euler in this simple circumstance?

 

Could you just not assign one bone to the wheel, set 4 keyframes for the rotation, then right click the last keyframe, and click Curve > Post-Extrapolation Method > Repeat.

 

This movie is 1 rotation with 4 keyframes, and the 2nd repeated.

wheel.mov

im asuming that this is in the pose menu then ?

[T-Dogg]

If you skip to about halfway through this video (after they finish Homer's walk cycle), it shows how to set up a wheel and give it a proper stride length. That should prove helpful for you.

 

http://www.hash.com/ftp/VM/walk_wheel/walk_wheel.html

[Caroline]

T-Dogg - that's a good simple example, and a few less steps than mine.

[Rodney]

T-Dogg - that's a good simple example, and a few less steps than mine.

 

Drat. I almost had Caroline's Project file.

[Fuchur]

You could of course just use an action I think you can even use Has Stride Length with the action and assign the car to an path.

Or you can use a Pose to control it.

Or you can do it like caroline did... this will of course only be functional if the car is driving at the same speed for all the time.

You can of course although try to use an expression which will turn the car-wheels by the translation of the chasi of the car.

 

"Rotation of Carwheel-bone = 2 * PI * Z"

 

Z = (Translation of car on X-axis * Translation of car on Y-Axis)^(1/2)

(works if none of the translation-values are 0)

or Z = Translation of car on X-axis

 

I may miss something there so...

 

Another way to get it done would be to use a Path and an expression and use the ease-value of the Path-constraint instead of the axis-translations.

 

I think the action or the pose-control-methode will be the best once. They give you most of the control while being more or less easy to use:

1.) Give both car-wheel-axis a bone.

2.) Make a percentage-pose.

3.) At 0% rotate the bones a little bit to activate them. Then bring them back to 0°.

4.) At 12.5% set the rotation of both bones to 45°

5.) At 25% set the roation to 90°

6.) ...and so on till you are at 100% and your rotation should be 359°.

7.) Animate the car-wheels by the pose. if the wheels are around once, set the percentage to 0% again (Frame 30 = 100%, Frame 31 = 0%).

 

The action-methode should work like a character who is walking along a path like it is described in the manual.

 

Hope that helps...

*Fuchur*

[Caroline]

OK, I give in, but it's really not elegant.

 

wheel.prj

 

It's probably missing the decal, but it should show the 4 keyframes and the post extrapolation.

 

(Sorry to those people who downloaded it with hair - accident)

[Rodney]

Thanks Caroline. You're the best!

[phatso]

Now, to totally upset the applecart...

 

The problem I find when making a rotation out of four keyframes is that it isn't smooth unless I do a lot of tweaking. Doing it the Euler way pretty much automatically means you get "x" degrees of rotation for every frame, all equal.

 

Maybe I'm doing something wrong. Wouldn't be the first time.

[Fuchur]

Now, to totally upset the applecart...

 

The problem I find when making a rotation out of four keyframes is that it isn't smooth unless I do a lot of tweaking. Doing it the Euler way pretty much automatically means you get "x" degrees of rotation for every frame, all equal.

 

Maybe I'm doing something wrong. Wouldn't be the first time.

 

What exactly do you mean by isnt smooth? That may depend on the frames you are giving A:M to work with...

if you use 4 frames (00:00-00:04) you will get 90° per frame. You can scale the keyframes down to smaller numbers, but a frame is the smallest number you will see later (A:M is actually calculating inbetween the frames, but the output wont show anything that). That means that you will see jumps of 90° per frame. Normally that isnt a problem because the eye cant cache up with more than 25 frames per second.

 

If you are after a more blurred look of the wheels you can however use Motion Blur to smooth things out.

Have a look at your render-settings (make sure to use the advanced-settings, not the one with the images). There you will find a motion blur-setting. Play a little bit around and render it out.

 

*Fuchur*

[detbear]

So do any of you know how to exactly get an expression to automatically rotate the wheels in correlation with pulling a main body bone forward?

 

 

 

 

Now, to totally upset the applecart...

 

The problem I find when making a rotation out of four keyframes is that it isn't smooth unless I do a lot of tweaking. Doing it the Euler way pretty much automatically means you get "x" degrees of rotation for every frame, all equal.

 

Maybe I'm doing something wrong. Wouldn't be the first time.

 

What exactly do you mean by isnt smooth? That may depend on the frames you are giving A:M to work with...

if you use 4 frames (00:00-00:04) you will get 90° per frame. You can scale the keyframes down to smaller numbers, but a frame is the smallest number you will see later (A:M is actually calculating inbetween the frames, but the output wont show anything that). That means that you will see jumps of 90° per frame. Normally that isnt a problem because the eye cant cache up with more than 25 frames per second.

 

If you are after a more blurred look of the wheels you can however use Motion Blur to smooth things out.

Have a look at your render-settings (make sure to use the advanced-settings, not the one with the images). There you will find a motion blur-setting. Play a little bit around and render it out.

 

*Fuchur*

[robcat2075]

hmmm... now I dont' know if an expression can do this or not but I think the algorithm would be something like this:

 

1-from the previous frame to the current frame you find the distance the center point of the wheel has moved horizontally. this is a pythagorean theorem calculation using x and z coordinates.

 

2-that distance divided by the circumference of the wheel gives you the portion of a complete rotation the wheel will turn if it is aligned exactly inthe direction of movement.

 

3-some formula probably involving a sine function would scale that rotation portion from 0 (the case where the wheel has skidded sideways, causing no rotation at all) to 1 (the case where the wheel is aligned exactly with the direction of movement) based on a comparison of the orientation of the wheel with the actual direction it moved.

 

4-add the resulting rotation value to the wheel's previous rotation value.

 

repeat for each new frame.

 

Of course this would only work on level ground; bumps, hills, potholes would be beyond this simple formula.

 

 

I suspect this is all doable in A:M expressions but I dont' know enough about the exact syntax of A:M expressions.

 

Some interested expression writer may want to try it.