Pro Mini 5v with Adafruit motor shield v1 power sharing problems

Question

I am trying to convert a RC car into autonomous car using Arduino Pro Mini 5v 16 Mhz. I have done this with UNO and Adafruit motor shield 1.0 with 4 gear motors and one micro servo for mounting range finder sensor. That worked fine.

Need to mention here that originally the RC car was using 5 AA cells for 2 motors and its RC reciever which looks like a customized motor shield as well.

I tried to move everything to Arduino Pro Mini 5v, and motor shield v1 to reduce space. Now how I wired everything.

1. Uses 8 AA cells to power the motor shield on EXT-PWR input.
2. From EXT-PWR in motor shield one wire goes to RAW in Pro mini.
3. From Pro Mini, VCC connected to +5v on motor shield.
4. One micro servo having range sensor getting its current from motor shield.
5. Motor shield has to run two motors, 1 for rear wheels and 1 for turning front wheels. (they are small motors look like 3v)

Now when I turn on the power the motor sometimes run and sometimes sound like bee and no movement. That also cause the L293d chip on motor shield becomes very hot and I think I have burnt one yesterday and replaced it from another motor shield. Same for servo it sometimes move or not move but sounds like hmmmmmmmm. The Arduino power light on and red. But sometimes it flickers and other light is also on and off.

At this point I have no idea whats wrong here. I changed the input voltage to lower but no progress. Tried to disconnect the 5v input from Pro Mini to motor shield and give 9v input to motor shield but nothing works. Please suggest best or correct power distribution in this case.

Thanks

Qazi

Answer 1

I would check each motor without the motor shield to see if the motors are ok. Check the motor shield motor supply, should be around 12 volts with 8 AA cells. You might run a simple test program to see if the motors run full power forward and full power backward with the motor shield. Check the servo with a simple program like the Arduino Knob program. I suspect the Pro Mini 5 volt regulator is overloaded, causing the buzzing sound, but you have to find out why. One possible reason is that you are dropping from 12 volts to 5 volts via the pro mini linear regulator, creating all kinds of heat. The additional load of even a small servo might push the power dissipation spec over the edge.

Answer 2

Sounds good, a more capable linear regulator with heat sink. Another possibility is to get a DC to DC converter (buck regulator from 12 volts to 5 volts), that way is more energy efficient than a linear regulator. They cost just slightly more than a linear regulator on ebay, and don't need a heat sink.