Micro Dual Serial Motor Controller issues

I’m having what seems to be a common problem: the motors will run for a second or so before cutting off. Sometimes they’ll run for ten or twenty seconds, sometimes only a fraction of a second. This isn’t a heat issue. This isn’t a power issue. The only other thing I can think of is interference, but for the life of me I cannot fix this problem. I’m using the 70097 twin motor gearbox. Each motor has a 0.1uf capacitor bridging the terminals, and 0.1uf capacitors leading from each terminal to the motor casing. The motor leads are twisted pairs.

Using different motors is not an acceptable solution. Pololu’s dual serial motor controllers are sold bundled with the tamiya motors and gearboxes; I expect them to work together.

Is there anything besides the twisted wires and capacitors that I’m missing?


The motors that come with the Tamiya gearboxes are very noisy and draw more current than the micro dual serial motor controller can deliver, so we recommend using different motors or the low-voltage dual serial motor controller.

However, the noise issues will be there even with the higher-current controller, and that is a common and difficult problem. Do you have access to an oscilloscope to look at what the various power and signal lines look like? Without seeing the noise, it’s hard to see if what you are doing is helping or hurting. What are you using for power and for the serial signal source?

- Jan

I don’t have access to anything more complex than a digital multimeter, I’m afraid.

Originally I had the controller connected to a BS2 Board of Education. While tinkering, I connected the motor controller to a Basic Stamp I project board and the 70168 gearbox. Low and behold, it works fine in this setup. The motors don’t have any caps across the terminals, the power leads are overly long, and not twisted pairs. Doesn’t really help me, though. I’m not going to dedicate a micro controller to controlling a motor controller.

The BS1 draws 1mA while running. The BS2 draws 3mA while running. I don’t see how it could be a power issue.

EDIT: Missed the last couple sentences of your post. The motor controller logic supply is the same regulated 5v source powering the BS2. The motor supply is 6v unregulated from 4 alkaline AA’s. The BS1 setup is the same.

Thanks for the quick reply, by the way.

EDIT AGAIN: Perhaps I should have listened to professional advice, eh? The BS1 configuration, when fully taxed, starts running, then stops and starts again, and repeats. So you were right about the motors being too demanding.

I’ve ordered the solarbotics motors for my robots.

Again, thanks for the help.

The difficulty with noise is that it can be dependent on the whole system. As you’ve seen, the motor controller can work with the motors you want, and the BS2 can work fine with the motor controller with other motors, but bring everything together, and there might be new interactions that cripple the system.

Noise can also show up on the power supply, mixing the two issues. In your case, it sounds like the AA’s are powering both the motors and the logic. Things might improve dramatically if you separate the supplies. If that is not an option, additional capacitors across the regulated supply could help. All it takes is a microsecond glitch to reset either the motor controller or your main controller.

In this case, the motors are 3 V motors, so you might be best served using a separate 2-cell battery pack for the motors. That will also significantly reduce the current the motors draw, possibly making the motor controller usable.

Of course, it’s easiest if you just don’t have the noise to deal with. We’re always looking for better motors and gearboxes to offer. The Tamiya gearboxes are fairly nice; it’s just unfortunate that they don’t include slightly better motors with them. But, they are meant for simple mechanical switch connections to batteries, and I guess Tamiya wants decent performance without requiring a lot of cells.

- Jan

Thanks, running the motors on 2 cells helped a lot, though not to the point where I’d trust the bot to run correctly. It spun in circles on the desk for about five minutes before the controller froze up for one reason or another.

How does the typical interference of a 6v solarbotics motor compare to the tamiya motor running on 3v? Will the solarbotics motor at 6v still be an improvement?

Yes, the other motor at 6 V will probably be an improvement. For some reason, the ones that come with the Tamiya gearboxes are really bad.

- Jan