# How to make an object accelerate and *then* rotate at a constant speed?

Say I am designing a mini-gun. One of the key things it does is spin up, and then continue to spin at a constant rate. I'm having trouble making it look consistent when this transition happens from the 'acceleration' motion to the 'constant speed' motion.

For the sake of round numbers, say I am using a Bezier interpolation from frames 0 - 50, as I want to control the slope of the acceleration. Then, I transition to a linear interpolation from frames 50-100. The problem is that the rotation speed coming out of the bezier curve is awkward, because there is still that easing.

Basically I want it to rev up, then continue at a constant rate (though I'd like control over how long it takes to rev up).

I saw this answer but I don't understand drivers well enough to know if it solves my problem or not.

## 1 Answer

The tangent to the curve reaching frame 50 must be exactly in line with the linear progression after frame 50. Also the 1-50 curve must also stay to the left of the linear ascension otherwise it will look like it accelerates before getting to the linear part.

• This solves my problem, thank you! To be a pain, is there a way to make this more automatic than eyeballing the handle of the frame 50 key? I'd be really interested in making this more consistent.
– Rug
Apr 23 '20 at 15:09
• Other than selecting the last 2 keyframes and rotating them like on the GIF I attached, not that I am aware of... Apr 23 '20 at 16:31