Ive just recently built my motorshield and my L293s get hot , really hot (to the point i think theyll probably burn up) when driving my motors. im using a 3V motor driven by my 7.2V nicad battery and my 7.2-8.4V motor.
Both motors cause the chips to heat rapidly and when running the test program will often not go as far in reverse as forwards.
Im think maybe i have damaged the chips in soldering and so will go buy some spare ICs today and this time put on sockets :).
1 thing is the external power on the mshield has a + and GND terminal, the GND would be the -ve terminal from my battery right? or am i doing this wrong. also do i have to ground the shield to the chassis or anything?
Yes, GND, negative battery terminal and 0V are all the same thing. You need not connect GND to a metal chassis, although it may help if you ground the motor cases (if they're metal) to help with screening.
Are there heatsinks on the L293 chips? If so, how big? Do you know how much current (Amps) the motors draw at full power? And if so, how does that compare with the L293's ratings?
The ICs are probably not damaged by soldering heat.
If your motors are trying to draw 1 or 2 Amps, then you've exceeded the L293's maximum rating of 0.6A. That will definitely make them get hot! You'll need a bigger driver chip, such as the L298.
well solved the problem by using 4 AAs instead (5.2V) the chips are still hot but no where near as bad. only trouble is now the motors dont seem to like going from forwards to reverse? (ie sensor saying there is a wall). it seems to just stall or take ages to reverse and when it does it about 30% the speed of going forwards!