First of all, thanks everyone for so much help so quickly!
The precision isn't a huge deal, it doesn't need millisecond precision, a second or two + - would be tolerable. Although, obviously precision isn't a bad thing either so if the digital counter circuit is more effective, and not that much more complex (read: expensive), and doesn't need any programming, then that may be the way to go.
I understand the 555 one shot circuit that MisterT suggested, but just a few questions. First, how could I prevent misfires, etc. after the first pulse of the output? Does it matter if the input (push switch signal in this case) is held open, say by a triac? then there could be a NC push switch to cut off power to the triac and 'reset' the circuit ready for it's next use/reversing the motors. Oh, but that 555 circuit wouldn't drain the batteries if the switch was held open would it?
Is there a simpler way to do this? maybe make the reset and reverse function one in the same?
And a mechanical switch to reverse the direction of the motors is fine, as long as they go for the same period of time in reverse as they went forwards. Also, I don't entirely understand how to apply the 555 circuit to control the motor. What is with the high-side and low-side circuits? Why couldn't the output just be directly connected to the motors? Am I missing something really obvious? (I assume so
).
@ajsivsan, unfortunately the two switches (to start it and reverse it) need to be separate. And the triggering switch needs to be protected/held open, as it will be a noisy push switch signal that will probably cause misfires otherwise. Could the circuit you're thinking of accommodate for that?
Sorry there are so many questions, I'm trying my best to get my head around all this stuff!
I think the 555 circuit would be the best bet (mainly because I sort of understand it
) as long as the precision thing is not too big of an issue. Now I just need to understand how to apply it to motor control, and incorporate the whole switch protection and reverse and stuff.
oh, and I've been thinking, I think the voltage would be more towards the 6v level, but it depends if I can get motors with high enough torque in that voltage.