For our project, we made a long car and placed the EV3 brick in the middle.  There is one large motor controlling the front two wheels and another large motor controlling the back two wheels.  The two motors are facing opposite direction from each other.  The two axels are attached by two stick-like structures that also supported the weight of the brick.  The motors were secured between these two structures so they stayed in place while the wheels turned.  When the program runs, both motors run at the same time for 5 seconds, allowing enough time for the robot to cross the gap.
 
We decided to make the car long so that even when the front wheels reach the other side of the gap, the back wheels are still on the other side.  We put the weight/brick in the middle of the car so that the car wouldn’t topple when the brick passed over the gap.
 
One challenge we faced was figuring out how to place the weight of the EV3/brick.  When we put it on either end, the car would fall through the gap before reaching the other side.  However, when we put it in the middle, the EV3 made it across the gap while the wheels were still on the original side, then the front wheels were able to pull the car across all the way.
 
We had a slight problem when we were presenting in the class.  Our car didn’t work as planned during the allotted time.  Instead of entirely crossing the gap, our robot only went until the back wheels left the original side of the gap.  The time constraint was certainly a challenge to gather our thoughts, build, and test using the design process—especially since we changed our design plan halfway through the class and had to start over.  Though we realize the time constraint was an important part of the challenge, we still wanted to try our best to make an effective design. We made a few changes after class so that we could successfully solve the problem: we placed the brick in the middle instead of at either end of the car, and elongated the stick structures by one Lego piece.  We also switched out our smaller front wheels for larger ones with better traction.