Why is my animation's shadow bouncing

[GregHeumann]

Learning everyday. I think I'm in week 2 but I can't remember when I started. I set myself the task of drawing this 4-throw crankshaft with cam - I added the brown "bearing" so I could animate it. The rotational animation works and is reflected in the shadow. But the shadow is also "bouncing"....why? There is only one "joint."

I tried to use the "camera" icon in this message editor to put the video in - that didn't seem to work. I tried to "embed" by putting in that code from Youtube - got overruled. 

SO here's the URL - I guess I can't embed the video here: https://youtu.be/2Vj4JY6oNxM

(The video goes by fast - I was trying to keep it small. May have to set it to run slower to get a decent look.)

[JHRendon]

That's normal when an object is moving. If you do not want that you can unselect that option. 

[GregHeumann]

Thanks- however that turns off the shadow entirely. The crankshaft is rotating - I like seeing the movement of the crank throws on the shadow. It is just that it is ALSO suggesting a straight up and down vertical movement - like the entire assembly is getting further from and then closer to the ground plane.  I thought maybe it was some invisible dumb thing I did to my model......

I have another model with a crankshaft driving a piston in a cylinder via connecting rod. When I animate that - the shadow reflects the movement I see on the screen but does NOT bounce up and down at the same time.

Could I have some part of the crankshaft locked to the ground plane? And if so, where to look to find that and unlock it?   (EDIT: I checked - no components are grounded. I tried grounding the crankshaft - didn't make a difference in the bouncing shadow.)

[JHRendon]

That's how it works. Shadow will move if the object is moving. You can see that in this animation too. Anyway, that how it looks in the workspace design. When you render it as a motion study. You can edit those things like ambient, light, etc. in the render workspace. 🙂

[TrippyLighting · Accepted solution]

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@JHRendon wrote:

That's how it works. Shadow will move if the object is moving. 🙂

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That is obviously not what the OP is referring to.

@GregHeumann The reason for the shadow bouncing up and down is because the default ground plane always attaches itself to the lowest point of the geometry in a model.

So create your own plane/box etc. far enough below your object to function as a ground plane.  

[JHRendon · Accepted solution]

Only change the offset of the ground plane. 👽🖖 You do not need to create another thing. 

[GregHeumann]

Brilliant! Thanks for the explanation. I created an offset plane - 1st at a greater distance, it cured the problem - but I kept reducing the distance to 1" (which makes the shadow look about the same distance away as it did before.) That completely stopped the bouncing but does let me see the shadow showing the actual movement of the part. Thank you.

[GregHeumann]

I spoke too soon - I ASSUMED your solution would work too but it did not for me. (Is there a way to "unaccept" a solution?)

I tried this at a few distances - the shadow still bounced. However the "offset ground  plane" trick DOES work - that construction must, however be visible. Here's a short video that shows it more clearly than my 1st one: https://youtu.be/VqlW8sJirsg