I have been puzzled by this problem for a while and my customer is waiting for a product. If we imagine cookies coming along a conveyor belt, how would this simple mechanism flip the cookies so that every other row is upside down? how do I animate this? I would prefer that the rows be instancers because the cookie will have many polys. Thanks in advance. Here's the blend file. This is definitely not the final blend file but rather a way to get help.enter image description here


  • $\begingroup$ Keep in mind that if I need to, I can hide things (Smoke and mirrors) to make this work. You will not be able to see into the conveyor belt, for example. $\endgroup$ Apr 8, 2023 at 2:49
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    $\begingroup$ Your link is not public, so we cant see your file. Anyway, the drum takes a row of "cookies", rotate them up and than let them slide down along white angled desk back into the conveyor belt, right? $\endgroup$
    – vklidu
    Apr 8, 2023 at 8:43
  • $\begingroup$ Thanks for responding. I changed the Drive access. I hope you can download it now. You got the logic correct on the flow here. Every other row of cookies gets flipped. Thank you for any suggestions. $\endgroup$ Apr 9, 2023 at 2:05
  • $\begingroup$ Probably, but link in your post is still with the same privilege. $\endgroup$
    – vklidu
    Apr 9, 2023 at 11:17

2 Answers 2


There is a more ways to do that ... in general I build a scene by ...

  • Create a mesh line, subdivide a few times, multiply by Array modifier to get a vertex at position of cookies
  • Circle (aka cookie) parent to the line object and under Object Properties enabled Instance > from Vertices (can be done by GN too)
  • Animate movement of lines (conveyor belt), just set a two keyframes with Linear Extrapolation (Shift+E) for continue motion.
  • Add Cylinder (drum) and animate rotation - the first keyframe at state where second line of cookies is bellow a centre of drum and second keyframe of drum rotation at 360° when belt's eight line is passing bellow the centre of drum. Like that you sync picking cookies.
  • Add one line as separate object, this one will be flipping one.

Be sure all F-curves are set as Linear!

version - Follow Path

Create a curve path that matches cookie movement over the drum and line of cookies constraint Follow Path and enable Follow Curve

enter image description here

Go to curve properties enable Path Animation and with timeline at frame 1 set keyframe for Evaluation Time so we can go to F-curve editor to control speed ...

enter image description here enter image description here

Line following curve rotates according to it so it reasonably keeps pink side up. Since we need the opposite at the moment cookies are matched by drum, I animated at that frames line's rotation so it appears as it is hanging on the drum.

Working with curves is always painful for me, rotation and orientation matters and can be tedious to find correct way.

version - Dynamic Parent (addon)

Dynamic Parent addon help you create temporary parent with another object (so the object follows another object). For that, addon by one click adds Child of constraint and keyframes influence value.

  • Add Plane (or just a line) to let slide cookies back to belt. Since I don't use real simulation (Rigid Body) here, just animate this angled object in the angle direction ... similar way as belt (two keyframes with Linear Extrapolation). This part of animation let us to sync speed of belt with delay that cookies get rotating around the drum ... so the cookies end up at correct position (between two existing lines of cookies that continued ride on belt). How to set keyframes? We come to do it later ...

First, let use the addon ... as described on addon page ... select Parent object than Child and press Create (it will create a Constraint with keyframes). Start with drum rotated 45°so the first line of cookies is bellow the drum. Select the belt than second line object and press Create, than move to timeline until this line is bellow the drum, select drum than line and press Create, than move on timeline where line rotated by drum passes the angled plane, Create ...

... here comes time to set first keyframe of the angled plane, move timeline at frame where eight row pass the plane, here add a second frame of plane 's animation.

Now move few frames back at place where line on drum pass the plane on top (drum rot like 225°), select plane than line and press Create (in addon).

Move timeline at frame were line pass belt, select belt than line and press Create.

Now you have finished animation of one row.

Save file as a copy, under addon select Clear > Bake & Clear. Duplikate object and offset in timeline for each ...

enter image description here

  • $\begingroup$ Wow that's great. I'll give it a shot when I get back to my PC. Thank you so much $\endgroup$ Apr 9, 2023 at 17:44
  • $\begingroup$ OK I got the Follow Path (curve) working too ... I would like to see if someone with geometry nodes skills would be able to get it :) $\endgroup$
    – vklidu
    Apr 9, 2023 at 20:21
  • $\begingroup$ UV, the follow path can do it... but how to do it for all the cookies lines (in a reasonable way).. that's where I'm stuck... i.sstatic.net/vm7y5.gif $\endgroup$
    – lemon
    Apr 9, 2023 at 20:24
  • $\begingroup$ @lemon UV? What do you mean? Even intermediate state would be interesting to see for me :) $\endgroup$
    – vklidu
    Apr 9, 2023 at 20:37
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    $\begingroup$ @lemon Ah... OK :) Gif wasn't there in time of asking. Looks good :) I started with Curve modifier, but couldn't solve instance rotation, later I noticed I need a face not a vertex for instancer. So I created one more answer with visual trick that seems to be easier to handle. $\endgroup$
    – vklidu
    Apr 10, 2023 at 21:32

version - Illusion (Geometry Nodes)

Part 1
Animation here is tricked ... cookies on the drum are separate part of system ...

enter image description here enter image description here

The only one issue I have here is the instances are visible at start and end, that is not what we want :/

Part 2
Second part of animation are cookies moving on a belt, lines under the drum become hidden for a few frames and flipped.

enter image description here enter image description here

Node tree is quite dirty but working. I will check that if I will have a time.

enter image description here This anim is result system were Part 1 is done with Curve modifier in this blend file. I will keep it until I (or someone) will find fix for Part1 GN.


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