I have just recently purchased the micro dual serial motor controller. I have had some problems with the chip set overheating (typically it seems to be the bigger of the two chips on the board) I have the motor ground and logic ground connected. I am running the same twin motor gearbox depicted in your robot examples.
I set the reset high, then toggle low then set it high with pauses between. I have a 1k resistor between the reset and my controller pin. I have also tried connecting the reset through the resistor to high directly and in both cases the chips get hot.
The system runs ok. I can control the speed and direction of the individual motors alright. Its just that after a minute or less the controller seems to get too hot so I shut it down.
My motor supply is 2 rechargeable C batteries at 1.2 volts each (2.4V total) I am using a basic stamp 2e as well.
The larger chip is the motor driver, so it is normal for that IC to get warm during operation. The chip does have a thermal shutdown feature, so if that does not get tripped (you would see the motors turning on and off at approximately 1 second intervals), your motor driver is not necessarily too hot.
However, it is possible that the motor driver will overheat if you keep running it with the current configuration, and there are a few things you can do to improve the situation. It is worth noting that the stall current of the motors you are using is over 2 A and thus well beyond the limit of the motor driver. The gear ratio you use can affect how much the motor draws; we use the higher gear ratio with the smallest wheels (truck tires), and it’s close to the limit. If you use a lower gear ratio or larger wheels, you might be drawing quite a bit of current. You can help the motor by making sure the gearbox is well-greased and free of debris.
You can also put a heatsink on the larger IC (the motor driver). You can get small heatsinks at most electronics stores, but any piece of metal with a bigger surface area than the chip should help. (Just be careful not to short any of the pins across the heatsink!)
Finally, you can help the situation by altering the behavior of your robot. Instantaneously changing direction causes a large current demand, which increases the heating in the motor driver. Inserting a small pause when changing direction can help a lot. For example, if you are moving forward, and you want to switch to backward, instead of sending the backward command immediately, send a stop command, wait a few milliseconds, then send the reverse command. Of course, there will be times when you won’t want to do this (to prevent driving off of a ledge, for instance), but there are often places in your code that can be modified, and anything you can do to prevent 4 amps from going through the motor controller helps.
