I have wired up a little four motor tank. I'm using the SN754410 chip to drive it--everything works fine, except I can't get the motors on each side to go in opposite directions.

Forward works
Back works.
Turn right, only fires left side motors.
Turn left, only the right side motors fire.

What I would like, is if turning right--the left motors go forward and right motors go back. Making a zero point turn.

I'm a hack, and content with it. But, I'm obsessing over this detail.

 

You need another SN754410. Then each motor has its own H-bridge. The chip logic doesn't allow both directions to be on at the same time.

 

Awesome. I thought it was a chip logic issue. I just didn't have the smarts to deduce it. Again, thank you. I have another another H-bridge, so it's a simple fix.