I am in the process of building an autonomous robot for my senior design class and I went with the rover 5 chassis 4WD version with 4 encoders and a Dagu motor controller (red PCB version, which I don't think that makes a difference). I am stuck at square one however when I hooked up my second two motors to channels 3 and 4 on the motor controller board, the motors began drawing too much current. So I further tested by only sending voltage to one motor at a time on channels 1 through 4 and individually they were fine and even channels 1 through 3 receiving voltage at the same time were fine, but when I added the fourth channel they began drawing 4 amps of current. I am not totally sure where to start with troubleshooting this further or what to do to fix it.
Oh I forgot to mention I am using an Arduino Uno if that has any significance.
Haha, of course as soon as I post this I find the problem. Apparently you cannot have the two left hand side motors or the two right hand side motors on the same side of the board together (ie the two left hand or the two right hand motors can't be on channels one and two or on channels three and four at the same time) because they act perfectly opposite of each other and stall each other out causing them to each draw 4 amps of current. As soon as I put the motors on opposite sides of the Dagu board from each other, everything worked perfectly. Hopefully I explained this in an understandable way...
i had the same problem and your solution works fine for me.
Also, if you are using the rubber tracks instead of the wheels, I wouldn't even bother with four motors. I bought the four motor version of the Rover 5, but removed two motors, one on each side, it runs much better .