Hi,

I'm building and disigning my own robot using the mbed as the basis for control. At the moment I'm working with two motors (Mabuchi FC-260SA). The schema I use is from Solarbotics. When I lay it out on a breadboard and I measure de voltage between L1 and  L2 (motor + and -) it reads about +/- 7 V (vs 9 V). However when I attach the motor the reading drops to +/- 0.5 V and the motors won't run. Any ideas about what I'm doing wrong?

Bon.

What power supply are you using? If it's a small battery with high internal resistance or a current-limited bench supply that could explain the problem. IIRC the L298 is a bipolar transistor H-Bridge so you could expect up to around 2-3V drop across the pair of transistors in the current path when loaded at a couple of amps.

Does it get hot? Do any of the diodes get hot? (Either could happen if something was connected wrong).

I'm using a dc regulated 1.5 A powersupply. The Voltagedrop is so drastic that the motor doesn't spin at all. There's no component getting hot. According to the datasheet of the L198N, the drop should bu in the range of 1.8 to 3 volts. I will rewire the breadboard to assure the correct wiring.

Try measuring the current output by the power supply. If you're accidentally drawing more than 1.5A the power supply might be shutting down or browning out.

Hi,

I found the problem a faulty schottkydiode was causing the voltagedrop. Replaced it and now it works the way it was ment to do.

Thx for your tips.