I am trying to animate a skateboard doing a trick called a hardflip. The trick involves the skateboard rotating 180 degrees and flipping once. If I animate the whole trick with two keys, it make it look weird because it involves the flip and rotation. To solve this I split it up and put two keyframes. Then on the second one, I rotated the board halfway, and flipped it over halfway. Then I put a third key and on that one I flipped and rotated the board the rest of the way. The problem is, since the animation is split into three keys instead of two, it looks like the board rotates half way, slows down a bit, then speeds up into the second half of the rotation. Is there a way I can make it look smoother? The image shows the timeline, and circles are over the main 3 keys. The other are just to adjust poses.
The pacing for an animation is controlled by the proximity of the keyframes over time. In the Dopesheet or the Graph Editor windows you can select keframes and move them horizontally. If the keyframes are moved closer to each other the movement will happen faster. If the Keyframes are moved away from each other, then the movement will happen in more frames and will take longer. Additionally you can use graph editor to adjust the animation curves which will affect the pacing of motion.
The hardflip is quite a complex movement: not all motions occur with the same timing, and the number of keyframes needed to describe it is not the same for all axes, and is different for location, rotation and tilt.
The location movement is quite simple for the X axis: the board keeps travelling forward even when it is in the air, but at a lower speed, then lands and picks up a bit of speed again.
Heightwise the motion is almost a parabola, but there is a sharp movement down once the feet touch the board pushing it down back to the ground.
The rotation is the complex part:
On the X and Z the movement is 360 on X and -180 on Y, and they both start almost immediately after the board is kicked on the back to raise it, but the rotation ends while the board is still in the air and the feet of the skater stabilize it and push it down.These rotations can be described with only two keyframes per channel and are basic bezier curves.
On the Y axis it is a very different story because the movement is sinusoidal to describe the hard initial kick and the landing with the back of the board first and then landing the front last.
So, going back to the original question... Once you have the keyframes you need, then you can control the pacing for the animation by moving the keyframes closer or further away from each other...
Additionally you can fine tune movement by playing with the control points and its handles on the curves on the Graph editor window.
Here's the file used for this example:
Select your object and then open the Graph editor in a new window. You'll see a series of coloured lines going across the window with little square nodes on some of them. Those nodes represent your keyframes, and the lines represent the transform values for your object over time.
Play your animation as you watch the graph editor. You'll see that the curves/angles of the coloured lines coordinate with the location/rotation of your object as it moves.
Locate the line(s) that represent the rotation values and find the little nodes on it and play with their positions to get an idea of how the shape of the curve affects the object's movement. You can also affect the shape of the curve by playing around with the handles attached to the sides of each node. Use these handles to adjust the curve shape between nodes.
Once you have an idea of how the shape of the curve affects the motion of your object, you should have no problem figuring out how to smooth out the movement of your object.