Let's Make Robots!

Motors not working correctly

I've been following the "First Robot" tutorial, and I'm very close to getting my first working version, but have got stuck right at the end. Everything, including the sensors and servo, have been working fine, but the motors are not. If I enter

high 4
low 5

Then one of the wheels turns as expected. But if I do

low 4
high 5

The wheel turns in the other direction, but only really slowly. And the Motor Driver IC becomes very hot. If I try the same with 6 and 7, the other wheel doesn't turn at all, but the Motor Driver IC still gets very hot. If anyone can tell me from this description what exactly is going wrong with my robot, I'd be very grateful. Do any of my parts need replacing? Thanks!

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Congratulations.  Glad it's working.

You were right, I had solder bridges on the motor connections. And now it works! Thanks for the help, I'll make sure to post pics if I have more issues.

It sounds to me like there are solder bridges on the motor connections.  But that is a shot in the dark.  Please post more info.  GOOD, close up photos of your work, including BOTH sides of the board and all the parts.  An EXACT list of parts you are using, preferably with links to the motors you are using and any other relevant parts.  Any more information that might be helpful.