I'm trying to make a tube extending with help of curves. I created a NurbsPath and BezierCircle, then put the circle into the bevel object of the path and animated its start bevel factor. Everything like any tutorial says, but I've got a problem. For my specific project I need straight 90 degrees corners, but curves tends to smooth them. So, to overcome this I extruded my curve 4 times in each corner. Just like you do when working with catmull-clark subdivision surfaces and need a straight corner. Now the problem is that the speed of extending somehow depends on the sectors. It is slow at the start of the sector, speeds up to the middle of it and slows again in the end. So after all it is too slow on the corners and too quick on the long sectors. I tried to control it manually by adding additional key frames for corners so they could take only 1 or 2 frames instead of 8 but with blenders own speeding and slowing it all got messed up. I can still play with manual key framing to make it acceptable, but I wonder if there any smart way to control the speed.
Try using free handles on the corners.
You can set the selected control vertex handle(s) to free with V> Free.
You can also set the keyframe interpolation of the selected fcurves to linear with T> Linear in the graph editor to avoid extra smoothing of the keyframe animation.