Prefabbed Drive Train

[John16]

We recently purchased an AndyMark nano-tube drive chassis. We've hooked up 4 CIMs to it, two to drive the rear four wheels, and two for the front two wheels. When reversing directions quickly, we seem to be able to drop the voltage low enough to reset the router, but only with either of the two front motors connected. Disconnecting the two from, we can run all day without the issue. Any ideas why this is happening, and how to overcome it?

We've previously used four CIMs in our drive train before, but with chains. We weren't sure if the previously not experienced sudden current draw was coming from the almost zero lag of the gear system.

We greatly appreciate any and all assistance in understanding this. Thank you.