Speed controller

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  03 March 2013
Speed controller


I have a rig, as seen below, and I am trying to use the center lever to work as a variable controller for the spinning ring on the left based on the rotating ring on the right. My current expresso setup is sort of working, but I am getting backwards rotation and very fast rotation where I really need forward rotation.

Any ideas on a better approach? I'm sure there is some easy way to do this, but I'm not a math or xpresso wizard

I should note that the lever at 0º is the far right and 10º is far left and 5º should be equal speed rotation.

Preview animation of xpresso setup above

Thank you,


Last edited by gdogfunk : 03 March 2013 at 10:01 PM.
  03 March 2013
Set the Outputs of the Range Mapper to Values between 0.5(or 50%) and 1.5(or 150%)

This results in:
at clevis center: speedB = 1*speedA = 100%
at clevis 0 : speedB = 0.5*speedA = 50%
at clevis 10 : speedB = 1.5*speedA = 150%

right ?

  03 March 2013
That is what I am after, yes! But when I try to change the output values as you suggest, I either get no motion until a later keyframe or very very slow motion all around. In addition, the animation from 10 back to 0 is making the output rotate backwards still. In your suggestion, what would the Output Range be set to?

And is simply multiplying the input speed with the range mapper output going to get me the result I am after?

Thank you!

  03 March 2013
Ok, this is the result of what I believe you were suggesting. It's close, but I'm not sure why it reverses or speeds up considerably going from 0-5º. Any thoughts?

Not sure if it helps, but here's the keyframes for rotation:

Preview clip2

I really appreciate the help!


Last edited by gdogfunk : 03 March 2013 at 12:29 AM.
  03 March 2013
Upon further examination, it appears that any keyed rotational value lowering from 10 (or any number) causes a reverse rotation. Is there a way to have additive rotation in a case like this? As in the calculation won't care if the degree value is decreasing and continue to rotate, but just slow down? The range mapper output is showing correctly in a result node, so I am seeing .5 through 1.5 and 1 where I should. I'm not sure why the math is multiplying a lower number as a negative or at least causing negative rotation. Ah, so close!!

  03 March 2013
The reverse rtotation might be a stroboscopic effect. Are you aware the all rotational values inside of Xpresso, COFFEE and Python are radians, not degree? Only in cases like the Range Mapper where you can switch the display to degree you can use 0°-360° values, everywhere else you need to use 0-2PI
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The views expressed on this post are my personal opinions and do not represent the views of my employer.
  03 March 2013

Last edited by littledevil : 03 March 2013 at 10:06 AM.
  03 March 2013
Thanks everyone. I figured it out. I guess I needed to ask the right question to get the right answer. I was looking for a constant rotation with speed control and the 'wheel_setup.c4d' linked in this thread was exactly what I needed:


Since I essentially have two wheels in my setup, I was able to setup a speed control for both wheels, change the slider ranges and match them for my 'neutral' position. Then I range mapped the output slider to the center 'clevis' lever and that now rotates correctly when I animate the output slider. The output wheel now speeds up and slows down correctly!

The wheel solution is actually rather simple looking at it now. Funny how it's easy to over think a problem.

Thanks again,

  03 March 2013
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