animation rotation problem

Ok I thought Id have a go at a simple animation by rotating a wheel. My problem is that half way through the sequence it reverses the rotation and I cant see what Im doing wrong. Here is how it is set up:
number of frames 100
frame 1 set using just “I” - loc/rot to initialise its position.
frame 50 set to rotate 180 degrees using “I” again to set its position.
frame 100 rotated a further 180 degrees to complete the cycle using “I” again to finalise its position.
When it rotates it goes correctly to frame 50 but then reverses to 100. If I remove frame 50 and set 100 to 360 degrees it doesnt do anything (no movement). If I set frame 25 to 90 degrees and 50 to 180 degrees it does nothing till it reaches frame 25 then speeds through 180 degrees to frame 50.
So what am I doing wrong? Am I using “I” loc/rot when I should be using another option?

dont rotate it more than 180 degrees and ‘rot’ it or it will spin in the other direction. rotate it by 90 degrees and half the time.
if it is not that im stuffed

Take a look at the Ipos by opening an Ipo curve editor and selecting the cube. You’ll be able to see exactly what’s happening there.

The easiest way to rotate an object is to simply set two keyframes, rotated slightly, select the Ipo of the rotation (for example, RotZ if you’re rotating around the Z axis) and go to Curve>Extend>Extrapolate. This will make the object rotate endlessly around the Z axis. Making sure that the first and last frame repeat on a multiple of 360 degrees will make it so the animation repeats.

In any case, the secret is in the Ipos, and plain old rotation should never require more than two keyframes.