How to make object on the conveyor snap to indexing rotary?

Question

I tried to make an animation for bottle filling automation. when the object smoothly can move on the spinning conveyor, it wont snap/stick to the indexing rotary which will be used as a grabber to place the object to each process (filling water, dropping bottle cap, screw down the bottle cap, and so on).

Answer 1

Bottle conveyor belt - (Blend file below)

EDIT 3/11/2021 (added 2nd movie clip)

This is a bit of a mouthful but I thought it best to describe in detail so it can be done step by step by those without experience. The process itself didn't take all that long.

An alternative to swapping bottles could be to use the 'Child-of' constraint. I personally find duplicate bottles easier in the long term and more straight forward. Either way, you'd still need to Rotoscope.

All of this was animation without physics. All keyframes are using linear interpolation. You may have to go into the Dopesheet regularly to select ALL keyframes, then set them to 'Linear' with 'T'.

The details -

The leading bottle (bottle 1) is keyframed forward so it bumps into the rotary cam. From there it was rotoscoped (see below) to emulate physics (bumps around) and enter the slot where it is visually switched with a duplicate bottle.

That duplicate is located in the rotary cam's slot permanently and parented to it. It and it's siblings are all traveling around with the cam continuously as though on a merry-go-round, but not visible until needed.

At the switch-over frame, the 3D cursor is set to the duplicate's location with SH-S and the original then set to that EXACT position with SH-S again. ( "Selected to 3D cursor" )

The original is switched (keyframed) to invisible in the Outliner and the duplicate switched to visible. The change-over will be undetectable.

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On exit the original bottle is again required to be be at the EXACT location of the duplicate where their visibilities are reversed.

Initially when Bottle 1 enters the slot and switches to invisible, it remains where it is.

The duplicate travels around with the cam, and at the exit frame, will be switched to invisible again.

Bottle 1 however will still be at it's previous location so it needs a keyframe at the exit switch-over frame to place it at the duplicate's precise location. (with SH-S) That makes it casually stroll across to reach the duplicate where it will re-appear in the slot it entered, about to exit.

Once visible again Bottle 1 is rotoscoped a few frames to have it exit 'naturally' before one or more keyframes takes it down to the 2nd conveyor and out of sight.

Play the animation one frame at a time to see how it's done at the entry and exit.

Wobblies -

These are simply VERY slight rotations in X or Y axis every two frames. At 25 fps, that's 12 every second which looks about right. (try every 3 frames for 30 fps)

Once bottle 1 is wobbled this way, those keyframes can be exported to all the others in the Dopesheet. Actually if each bottle is a duplicate of it's leading bottle, it would inherit those keyframes anyway.

Wobbling will be in synch like a chorus line so stagger some by sliding their imported keyframes one frame to the left or right.

A Note here. -

Whilst you might not want 'wobbly' rotation angles however slight when switching between bottles, you'd probably get away with it here because if there is a slight angular difference when switching over, that would probably be seen as just another wobble. If it doesn't look right or 'jumps', re-keyframe Bottle 1's and the duplicate's Rotation to 0,0,0. at that frame.

Rotoscoping -

Is a term I use here to describe the adjustment of a bottle's movement, one frame at a time. (Manually keyframed frame by frame)

Subsequent bottles -

These are also animated to follow the others uniformly until either being bumped into a leading bottle or the rotating cam itself. They can be rotoscoped manually as with Bottle 1 for a few frames to get it's entry looking right and matched to the duplicate's location.

(you'll notice that each duplicate bottle's location in the rotary cam slot is set to appear as though being pushed around by the slot's trailing circumference whilst being 'forced out' against the outer circular barrier)

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4-Bottle Groups -

Once the first 4 bottles are done, further 4-bottle groups can be duplicates of the first. They will inherit all keyframes and their behavior will be identical with the first group. Timing along the first conveyor would need to be organised so the first of any group bumps into the cam at the same cam position as Bottle 1 in the 1st group.

With that achieved, entry behavior for each 4-bottle group should be the same as the others, requiring no further Rotoscoping unless appearing a little too linear. If so, tweaking of individual bottles every so often is a simple matter of a little extra movement to one side or the other and keyframing that but not too much otherwise they'll be seen to 'jump'.

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Whatever action behavior is required, when the physics engine won't behave as you wish, animation allows you that freedom and without instabilty. When unsure how to go about it, use the physics engine on a dummy object to give you the action it produces. You then have a reference you can copy manually. (if it's usable)

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Bottle Transparency -

The clip was rendered using OpenGL (direct from the viewport in vers 2.77) so the transparency may have to be re-organised in 2.8+ .

Conveyor Rollers -

These were a hurriedly done array and rendered as a pic. That was used to texture the conveyor sections and their Diffuse keyframed to vary - cyclic fashion. A much more effective solution would be to render a rotating array of rollers and use that for texture, or even place 3D rollers there direct.