Rotation rate problem

Still working on a camera shutter. Curious problem illustrated in the attached file.

If I slide the timeline carriage back and forth between 35 and 45, the shutter opens and closes as it should. The rotating slotted disk that drives the individual shutter blades is shown to be working correctly. The shutter blades’ studs slide up and down inside the drive disk slots.

If I slide the timeline carriage back and forth between 23 and 28, the shutter opens and closes correctly, just as before. But the shutter blades’ drive studs are not captured within, nor sliding within, the slots. They begin and end well, but wander in and out of the slots.

The problem is – How do I confine the studs to straight line travel within the slots when the carriage is moved between 23 and 28?

The keyframes for the slotted drive disk were copied back (in inverse order) to 23 and 28 from 35 and 45. The keyframes work fine at 35 and 45, but the studs jump out of the slots between 23 and 28.

A puzzle to me. rotation rate problem.3dm (320.9 KB)

Thank you for your insights.

Hi Michael,

First of all in the model you posted the keyframes are at 45 and 50. But indeed when the keyframes are moved to 35 and 45 there is a difference noticeable.
This is the result of the Tweening settings and the Automatic easing. The default settings make that the rotations don’t run linear. But even when all tweenings are set to Linear and every Automatic easing is disabled (as in the 001 model in attachment) you can still see the studs travel outside the slots.
rotation rate problem 001.3dm (348.4 KB)
The problem llies in the nature of your mechanism. You cannot expect that the relation of the rotation rate of the wheel and the rotation rate of the shutters is linear. However my knowledge of mechanics and/or mathematics isn’t enough to explain this in theory.

In model 002 an IK-structure has been deployed to manage the relation between both rotations as the result of the ‘stud and slit’ mechanism.
rotation rate problem 002.3dm (413.8 KB)
Maybe IK is somewhat complex to grasp for a beginner but hey… take a look at the model and have a peek at the tutorial on


Many thanks Luc.

Your video on the whys if 1K is excellent, I watched it several times. I will guess that the slot centerlines are the Constraints in this model. Perhaps the actuator disk is the Driver.

I wonder if it would be possible to re-post the file, “rotation rate problem .002.3dm” as a Rhino 5 file? It was apparently created in Rhino 6, and I am unable to load it into Rhino 5.

Thank you again for your time and help, Luc. From your examples I am getting a much better sense of what can be accomplished with Bongo 2.0. It is very impressive.

Best, Michael

Thanks for your kind words.

rotation rate problem 002.3dm (386.5 KB)
is a V5 version of the IK-model. Indeed a line in the centre of the slots takes care of the constraint, while the disk is the ‘driver’. If some questions remain, feel free to ask.


PS. As for the Tweening setting – maybe I went a little fast. I hope you know those setting can be found in the KeyframeEditor

Re the camera shutter animation, from studying the Bongo Object Properties a couple of basic questions have come up. Thank you again for your help in understanding how this animation is made to work.

The first question is about constraints.

A slotted disk is the Driver of the five camera shutter blades. The midlines of the slots are not identified as constraints. They are simply children of the slotted disk.

The actual “constraint” is called out as the point that slides along the slot midline. This point is also an object. How (or where on the Bongo menus or displays) is the “constraint” point instructed or programmed to faithfully follow the slot midline?

Second question: The motions of the blades of the camera shutters are governed by the IK feature – they have no corresponding timeframes. However, the shutter blades are each listed as a numbered object in the animation manager.

How were these objects entered into Bongo?

I thought that in order to create an object, it was necessary to first Select it and then click Animate, creating a keyframe in the process. Apparently, it is also possible to create an object for which there exist no keyframes.

What is the method or procedure for typing these exceptional objects into the list displayed on the animation manager?

Thank you for your insights. Michael

  1. Indeed the point objects are “constrained” (“bound”) to the midlines, thus forcing them to ‘faithfully follow’. The IK settings (joint types and contraints) are managed in Bongo’s Object Properties panel.
  2. Indeed altering an objects properties (Position, Rotation ….) in Animation mode is only one way to initiate animation.
    Another way is to create a hierarchical link between 2 objects (make one child or parent of another).
    And the also you can simply click on the “Bongo” button in the Utilities toolbar, hence making the object appear in the Animation Manager.