• Get -> Primitive -> Cube
• Scale it to .2, 1, and .2
• In Ctr mode, move the center to the top of the cube. This is the bicep of an arm. Or maybe it's the pendelum in a clock, I don't know.
• Duplicate the object, translate it down in Y and scale it slightly so it looks like this. Call it forearm. Make bicep the parent of forearm.
• Add a hand if you like, the same way you added the arm. Make forearm parent of hand.
• Now if you branch select the bicep and rotate it in Z, the whole arm should move like a stick, (locked).

• Get -> Primitive -> Sphere, size 1. Name it arm_flap. This will be your arm control slider.
• Translate it out of the way of the arm. Go to Effects -> Freeze Translations
• Go to Motion mode. Select the bicep object. Go Expressions -> edit.
• In the affected element box, enter bicep.rotz
• In the expression box, enter arm_flap.etrnx * 10.
• Click O.K.
• Now select the arm_flap shere, and move it in X. Note how the arm object rotates.
• Select the arm_flap sphere again. Go to Model mode, Info -> Transformation Set-up. Select Trans and check X, User Defined and DRG.
• Activate User Defined Transformations from the Preferences menu.
• Now when you select the arm_flap element, (in single mode), the X translation is automatically selected.
• Get another sphere, move it out of the way, freeze transformations, and call it elbow_flap.
• Select the forearm object, and in the expression editor, in the affected element box, enter forearm.rotz, and in the expression box, enter elbow_flap.etrnx.
• Now, moving the elbow flap slider moves the elbow.
• Select the elbow_flap sphere. In the expression editor, make the affected element elbow_flap.etrnx.
• In the expression box, enter at_frame (Fc - 5 , arm_flap.etrnx) * 4
• Now try moving the elbow_flap slider. You can't because it is locked to the arm_flap slider.
• Move the arm_flap sphere. The whole heirarchy still moves like a stick. There is no extra rotation in the elbow. That's because your at_frame expression requires that the referenced object have some animation.
• Select arm_flap object again, and save a keyframe in X.
• Go to Motion mode,Fcurve select -> Object -> Explicit Translation -> X
• Go Fcurve edit -> Expressions. (Note: The source controlling object must have actual keyframed animation. You cannot enter an expression from the Motion -> Expression dialogue box, or the affected elements won't move.)
• In the dialogue box, enter sin (Fc * 10 ) * 5
• Now play the animation. Note how the arm swings, and the elbow has a slight lag as it swings. Try changing the value after the Fc in the expression. See how the lag changes. Note how the elbow_flap ball lags behind the arm_flap ball.
• Now, lets add a switch so we can make the elbow move automatically, (with the bicep), or manually, (independant of the bicep).
• Get -> Primitive -> Cube. Scale it, move it out of the way, freeze transformations, name it Switch.
• Select elbow_flap sphere. Go to Expressions -> Edit. Copy and paste the existing expression in the Affected Element dialogue box to Local Variables B. Copy and paste the expression in the Expression dialogue box to A.
• Now replace the expression in the dialogue box with: cond (switch.etrnx < .5, A, B)

• Click O.K.
• This expression says: If switch is less than .5 in X, (off, or set to auto), then use the value of A, which is the value of the bicep rotation, plus the offset, (the Fc - 4part of the expression.) If the switch is more than .5 in X, (on, or set to manual), use the actual value of A, which is the elbow's actual rotation value.
• Now go back to the animation. Play it. Move the switch back and forth in X. Note how the elbow is linked to the forearm when the switch is set to Auto, (about zero in X), and how it you can manually control it, (or even animate it) when it is set to manual, (about one in X). Now it's up to you to build a pretty interface for this thing. See the hints below.

Animating Transitions Between Automatic and Manual

Sometimes you will have to have your character go from full automatic to manual. For example, maybe the wings of your character are flapping nicely in Automatic, and then you have to have your character wave one arm.

Go to the frame that you want to begin manual operation. Select all the sliders and icons that you will be animating from that frame on, (lets say frame 50). Save a keyframe here. Now go to the frame where you want to begin the transition from Auto to Manual, (say frame 40). Save another keyframe here. Now go to the object that switches between Auto and Manual. Go back one frame, (frame 39), and save a keyframe, (should still be set to auto). Now go ahead one keyframe, (frame 40), move your switch to manual, and save a keyframe. Now you can go to frame 50, and move the individual sliders so that the character's arm is in the position it should be after the transition. When it's all said and done, you should have a smooth transition between frames 40 and 50, (auto and manual).

Hints and Tips

• Multi-select all components of your control panel and go into Info -> Mental Ray. Deselect everything so that your panel won't render if it happens to get in the way.
• I moved my panel -400 units in Y so that it would be out of the way of any action, and won't clutter up your view when working. Save out a viewport preset so you can return to your panel quickly and easily.
• Use named selections, (Select -> Set Named Selection), so you can quickly and easily turn on and off your control panel. With SP1, you only have to select the Named Selection Icon, and then h + u on the keyboard to turn the display of Named Selections on or off.
• As I mentioned before, use the User Defined Translation option under Info -> User Defined Translations. Make sure to select User Defined Translations in the Preference menu too. That way, when you select a slider in single mode, the appropriate translation channel will be automatically selected.
• Select the parts of the panel that you don't want to be able to select, then go to Select -> Selectability -> Toggle Selection. Now when you select your sliders, you can't inadverdantly select frames and such in your control panel. Unselectable icons are represented in the schematic with a box around them. Of course, they can still be selected in the schematic window.
• Of course, instead of using geometry as I did to make your interface, you can use an image map. I found it took too long to load on my O2, so I've gone with geometry.
• All of these constraints and expressions will slow down your interactivity somewhat. I have also noticed a problem occasionally with the animations updating properly when command-line rendering when you have a lot of expressions.

This page by Sean Lewkiw.
Copyright 1998, Sapporo Japan.