Creating A Variable Motor Control

[The_Waffleing]

I've been trying for the last three hours to come up with a way to control the motor speed with every tote that I pick up. So for instance I have a stack of 3 and we push a button to grab the fourth one and get that under the stack of three that we already have and while that is going on the motors then get limited by a certain amount so that it's not going as fast as what it was before that fourth one is obtained but is more stable and has a less chance of spilling the crates when it suddenly breaks or get's hit by one of your alliances robots. Does anyone know of a possible way to create something along those lines? Even if you know a small bit of how to possibly do that I would very much appreciate the help? Many thanks in advance.