Still trying to get the L293D to work...
You only need to connect one of the grounds, unless you're powering motors that draw close to the limits of the chip's current capabilities. In that case, it makes sense to connect all 4 grounds, because the grounds also act as the heat sink connections to draw heat away from the chip.
The two voltages, Vcc1 and Vcc2, are different -- Vcc1 is the one that powers the L293D's logic circuits, and Vcc2 is the voltage that is fed to the motors. Vcc1 should be connected to the 5v from your microcontroller, and Vcc2 should be connected to the battery positive. If you're using a separate battery for the motors, then Vcc2 should be connected to that battery.
As for the 4 outputs, obviously you shouldn't connect all four of those together :) 1Y and 2Y should be connected to the two motor leads of one motor, and 3Y and 4Y go to the second motor.
I didn't use a capacitor on the SN754410 on Little Drum Machine, but I did use them on Little PIC:
(The SN754410 is the bottom chip). Basically, it never hurts to add capacitors to motor circuits, and it almost always helps. You should get in the habit of just always using them. Buy a bunch of 0.1 uF capacitors and sprinkle them around like candy :)
For months now I haven't been able to get my BullyBot to move -- I had soldered one 0.1 uF capacitor across each of the two motors in the Tamiya dual gearbox, so I thought that couldn't be the problem, but still when I sent the command to the Pololu motor controller to drive the motors forward, they'd pulse for a second and then the system would reset. Finally I added two more capacitors to each motor like Pololu suggests (even though in this thread I had mentioned how I didn't understand what the point was), and once I had the three capacitors on each motor, the problem cleared right up. I can't believe I struggled for months when all I needed was a few more capacitors :)
The mitor controller is going to want a zero-impedance voltage source at its inputs. I am running off of a protoboard, and power traces are fairly long so when the motor would try and switch on the motors, I am assuming the voltage at the motor chip would dip below a cutoff and then shut the chip down until the voltage rose again.
I was experiencing jerky motor problems. I was also running off of batteries. I can see how using a cap may be a problem for some builders, but I , in all honesty, probably own over 400 caps of different sizes/voltages. I have 'em to spare, and they are only like 10 cents each.
In response to your question, a capacitor is not always nessecary. It was for me. Pardon my spelling.
Ok, so I connected and it worked fine, proving that my L293D board is not the problem its my connections,
Blue and white are obviously outputs
And can anyone tell me the outputs connected on the Picaxe 28x1 Board where I can run the code from Fritsl's YDM tutorial page with the GM10 as the head?
This looks amazin