Me and my project partner are doing a new design of two suitcases that are attached to each other for easy traveling.
The two suitcases are almost the same size in a way that one of the suitcases will be inside the other and the user can decide if he want to use one or two suitcases.
We need help with the way to put the suitcase on top of the other when both of them are full in stuff. When one is on top of the other, the suitcases will move like a stroller to manage the weight of them.
In additional, if you have an idea for a good material for the suitcases to be light and strong we will be grateful
If I got your idea right and you want only to roll them together you can use spring to hold the smaller suitcase from falling. The materials is not my field but it seems like you need hard cover to hold it.