AddWorldOffset changes scale all the time

I want to do a relatively simple animation: A robotor whose parts go straight on rails in x,y,z direction. For that I set up Timelines and AddWorldOffset. At first it looked good, I just guessed the amounts till I got it right but then I found out that the amount it changes its location by, keeps changing when I make changes to other settings. E.g. I add a transformation to Part B to happen after 10 seconds but suddenly I see that Part A’s transformation in the beginning got e.g. three times as extreme. That way it’s virtually impossible to set up the thing because once you got it right it’s all wrong again 10 steps later. How is that possible?
Interestingly enough, the thing moves only a 10th in the simulation than in the playable game.
To explain the scene: The robot is supposed to go up to the top of the lower rail, then adjust slightly y to laserscan it and then go x,y,z to the screws on the big box to adjust it.

I’d be grateful for your help!