SparkFun Forums

[james89]

Hey everyone,

I'm working on a toy tank project that uses these 2 parts:
Serial motor driver - http://www.sparkfun.com/products/9571
Dual motor gearbox - http://www.sparkfun.com/products/319

I'm having trouble getting the motors to move when VCC for the driver exceeds 4V, even though the drivers are supposed to run from 5-16V and the motors from 3-6V. I'm sending the commands using a MSP430F5438 dev board through UART pins. At 4V the motors operate correctly most of the time, but other times only 1 motor will run and I have to send the command again before the other motor starts. At 5V or above VCC every time I send a command the motors start to run but then suddenly stops. I made sure I have a common ground and even tried adding capacitors to the motor connections thinking it might be noise but no luck.

I'm pretty lost at this point, the only thing I can think of is that these 2 parts aren't compatible or the motors aren't getting enough torque. Any ideas?

[esklar81]

James,
That sounds like a power supply problem to me. Your comment "the motors aren't getting enough torque" may well be a step in the right direction. To oversimplify vastly: for a brushed DC motor, voltage is speed and current is torque.

Here're a few things to get you started:

1. What are you using as a power supply?
2. What happens to the voltage across the driver board input terminals when you try to run the motors at different voltages?
3. Do you get the results you reported with or without mechanical load on the motors? If you have had mechanical load on the motors, try running them at various speeds without anything attached to the motor shafts.

Post your answers and someone here will probably be able to help you.

Happy Hunting,
Eric