I am banging my head against the wall here. I must be missing something simple but I can not figure out what it is. I have the attached model with 4 rotating rotors. As soon as I set them as children to the rest of the model they show secondary rotation that I do not understand. Any help would be appreciated. drone animation.3dm (7.2 MB)
Hi @Matt6,
I tried to remove the Animation, select the propellers, then type in 7000 degrees again AND uncheck the “Rotate in world space” (which means they rotate only about iut’s own Pivot), and then it worked fine.
// Rolf
Thanks RIL. If you then parent the 4 rotors to the drone body does it still work? Because that is where it all blows up for me. I get as far as you do and then parent to the rest of the drone and then the secondary rotation appears. And there is no good reason for it I can see. I get the same results with and without rotate in world space option.
I was only able to solve this by enabling animate inside of blocks option and treating the rotors as a block. But I see no reason why this needs to be done this way.
I have never seen anything like this before. This is really strange. Could it be that Bongo isn’t very friendly with meshes? I don’t know.
Perhaps @Luc or @marika_almgren have an explanation to this.
// Rolf
I found it has to do with the accuracy of floating point numbers (like the IEEE 754 doubles).
Jussi once taught me:” They look like real numbers but they are only a finite subset of them. Near zero this subset is so dense that one can perform simple arithmetic operations with decent accuracy. But the accuracy of operations gets smaller as operands get further from zero – because the set of doubles gets so sparse.”
The model “to big”.
I scaled the whole by factor 0.001, and everything goes fine. drone animation 001.3dm (7.1 MB) 
Moving the objects closer to the World’s origin (0,0,0) would even improve the matter, I guess.
2 Likes
Interesting. Yes. This model is way out of scale. Thanks for finding the cause. I was going nuts.