Overheating Dual Serial Motor Controller

I’m using the dual serial motor controller to run the motors in a Tamiya Double gearbox. I have .01uF caps across the leads on each motor, and and using 4AA batteries (6V) to drive them. It works fine, but after a few seconds of operation the motor controller heats up, and then the thermal cutoff kicks in. Should I be able to drive these motors using this controller? If so, what do I need to do to fix the problem.


The short answer is that the Tamiya motors draw too much current for that motor controller, which is why we made the low-voltage version (https://www.pololu.com/products/pololu/0120/). It can run with motor supplies down to 0 V (practically speaking, it means you can use one cell) while supplying the high currents that these low-voltage motors draw.

However, if you’re getting a few seconds of operation, you might be able to improve things a bit to just get by. Basically, you need to reduce the current used and get rid of the heat. To reduce the current, consider different gear ratios, cleaning the gearbox, making sure it’s greased, and running at lower speeds. To get rid of the heat, you can glue a heat sink to the motor driver (the bigger chip).

Also, be careful with your 4 AA batteries. Alkalines aren’t great, and your voltage might be fluctuating and dropping below valid levels. A better solutions for getting 6V on a robot is a 5-cell NiMH or NiCd pack, but keep in mind that those will be around 7V when fully charged (and higher voltage means more current and more overheating).

- Jan

ok, well how is this bot (https://www.pololu.com/projects/prj0001/) getting away with using that controller?

I put a 7805 voltage regulator in, and it warms up and handles the current so the motor controller doesn’t have to. It’s better equipped to handle the heat though, as it has a heat sink.

The project uses the micro dual serial motor controller. It can support a low motor supply; at 3V, the current is lower so there is less overheating. As noted in the project, overheating can be an issue.

I’m not sure what you’re doing with the 7805, and statements like “it warms up and handles the current so the motor controller doesn’t have to” certainly don’t make sense. If you’re using the motor controller, the current is going through it.

- Jan

The voltage regulator limits the current being drawn from the power supply to 1A (well below the limits of the motor controller). Anyway, it is a temporary solution to allow me to test the code on the PIC. I’m thinking about replacing those motors with ones that will draw less current. I believe these: http://www.radioshack.com/product/index.jsp?productId=2102828&cp=&origkw=motor&kw=motor&parentPage=search
should work. They draw .25A max, but I don’t know yet if they’ll fit in my gear box. It looks like they will. I’ll have to use a lower voltage power supply.

I didn’t see the current spec., but in my experience, the 1.5V - 3V rated motors tend to draw a lot of current. If you’re happy lowering the supply voltage, the stock motor should give you similar results.

- Jan