Looping Problem

I’m trying to do a perfect loop of rotating helicopter blades, but they keep slowing down before they repeat. What am I doing wrong?

Go into the Graph Editor. The curve probably looks like an ‘S’, which means that it starts slow, then accelerates, and then slows down. You want the F-curve to be a straight line. That means it rotates at a constant rate.
By default the curves are made as an ‘S’ shape (i.e. Bezier) when something is animated , but in the User Preferences under the Editing tab, you can set the F-Curve default to Linear.

Steve S

I still get the same result. Here’s what I see in the Graph Editor.


Fairly new to the graph editor?? You need to do a few things before you can see what is really going on. First, click on the black dot to the left of the ‘cycles’ in the modifier, that will disable the modifier, so now you can see what the curve actually looks like. Then with your mouse in the main part of the graph editor, ctrl-mmb -> move the mouse downward to scale the view vertically. After doing those 2 things, you should see the slight s curve looking animation curve referred to by Steve S.

Anyhow, if all you are doing is constantly rotating the blade, making no changes to speed or anything (like I think your screen shots are telling me), here’s a simple way to do it: from the key menu choose - interpolation -> linear. Now the curve will change from a slight s shape to more of a z shape. At this point, maybe the cycles modifier will work, dunno. What I would do is go into the channel menu and choose extrapolation -> linear. Now your curve will change from a z shape to a straight line. Now the rotation will go on at the same speed for the entire length of the animation.

Getting to know how the animation curves work in the f-curve/graph editor will make life easier as you learn blender. There is no one single source that I know of that explains how it all works, so if need be, ask questions in this part of a forum (animation & rigging), and always supply a .blend file for would-be helpers to look at, so they can help you out better.


Very. I’ve only used f-curve modifiers in 2 or 3 of my projects (not very well, of course). When I was uploading that image, I had no idea how anyone would be able to read that, but I figured that was just because I didn’t understand it.

This worked! Thanks!