AXE120 speed control misbehaving

[Dr_John]

Is is a hardware fault or am I using it wrong.

I have put in the simple line-following program from http://www.rev-ed.co.uk/docs/axe120.pdf and most of the time it does what it says on the tin,

But ocasionally

one of the motors goes full speed in reverse.

Normally the motors run at half speed (128).
I've checked the PICAXE outputs 4,5,6 & 7 whilst it is doing this, and they are all zero!

Any thoughts?

Thanks
John Fisher

 

[BeanieBots]

I may have this wrong because I have no experience of the AXE120 but you say that you have used the "line follwing program" and that "Normally the motors run at half speed (128)." The example does NOT use speed control, so the motors should be either full on or full off.
Are you sure that you have not put in the other (not line following prgram) by mistake. This program could easily give the symptoms you describe depending on what you have done with the inputs.

Short of that, and the fact that you say that the motor outputs are all low when it happens, it would suggest that the L293D is latching on. I've never known one to do that and don't have the required information to know if it is even possible. Check that the noise suppression caps have not fallen off either of the motors.