Make a rotation of an object accelerate

[kasjorg]

Yes this must be very easy - but I´ve tried to make my object rotate slow in the beginning and just go faster and fatser and I can´t stop it from slowing down at the end of the spin! I made a key in the beginning and one at the end telling my object to spin 2000 degree on the z axis. When I put both the keys on linear my object turns at the same speed all the way - but then I ´ve tried all the combinations of smooth in and out and my object slows down at the end of the spin with all the time, please help me!

Kasper

[rylleman]

You have to set more keyframes inbetween, each accelerating.
Since the interpolation doesn't work properly you won't get a smooth passing between the keys, the motion will slow in to the keys and then accelerate out from them even if they are just passing positions in one direction...

[kasjorg]

Yeah tried that as well - but the spin gets very not- smooth when I use smooth interpolation setting on the keys- and very bumpy when I use linear! . Is there no way to make the interpolation smooth while speeding up?

[jeff]

You can do what you're after, but unfortunately, it isn't as straightforward as it might be. You can fiddle with the graph mode available in the timeline and by adding extra keys, you can get a reasonable amount of control over your moves, but you never get exactly what you want since (as Rylleman points out) the only choice of move allowed between keys is smooth or linear whereas as what you want is exponential or similar.
You don't say how long this move is to be. If it were fairly short, I would be tempted to simply create values by hand for each frame. This means entering a rotation value by hand for each frame, which doesn't take long to do.
Basically, you can do this the stupid way (my way, I'm afraid), that is: choose numbers that look about right - that is they increase steadily over time without big jumps, or you can do it the clever way and use mathematical formulae. There are some smart folk on this forum who will probably help you out with this if you ask nicely.
If the move is too long to use the above approach, I suggest you use the graph mode and add keys until you get as close to the curve you want as possible.
To overcome the forced "smoothing" effect at the end of the acceleration, add more keys bunched at the end and make sure they are all linear.

I'd be interested to hear if anyone has a better solution.

Jeff

[SJMarky]

Try using bones rather than rotating layers. I needed to make wheels spin smoothly and ran into the same problem when I just tried rotating the layers. I tried it in a bone layer instead and viola! - wheels spun smoothly and easy to key-frame speed, bounce them up and down, etc.

[jeff]

Hate to disagree, but the problem is in the way Moho handles inbetweens and this applies equally to how bones work. Using bones can have many benefits, but they won't make it any easier to do what Kasper wanted - to steadily increase the speed of a move over time.

Jeff