Does anyone know any good reason to connect the enable pin to the microcontroller on the L293 motor driver?
Connecting this pin to 5V shouln't be enough?
This way I can use the microcontroller pin for any other use.
Now I am a bit confused. I am going to assume when you say "modified servo" you mean you took ALL the brains out of the servo and are using it as just a geared motor now. If this is the case, then yes, braking stops your wheels pretty gosh-darn-quick.
If you are using a continous rotation servo (with brains, and with 180 stops removed) then you don't need the L293D at all. Your servo is still a servo and contains its own motor driver.
In general, braking is like 4wd or air conditioning. You really don't need it, but it is sure nice to have. If you are doing any kind of "precision" motion, (I.e. encoders on your wheels) I would say brakes are 100% needed.
Yes It has no brains. Now comes the tricky part. For more info, i'm gonna say that I'm using a PIC16F84A, and that i'm trying to design a circuit with two L293 to drive four motors. (That why I needed to do without the enable pins, because I needed to save some PIC pins).
As you can see in the picture below, a single pin from the microcontroller drives two pins (one on each L293). I can imagine that this could drive an excess of current from the pic so I'm thinking on some switching transistors. (if anyone can help me with that... :P) or if you know of a chip that can handle four motors....
Current draw to drive the inputs on the L293D is not an issue it is in the microamp range per input.
Tank you very much. One more question. It's about the "No brakes, coast only" part. Using a modified servo would I notice the difference?
If you're using a moded servo, you really don't need the 293 at all. If you're using 4 motors you'll really want the PWM signal though. There's statistically very little chance that they'll all be within a close enough tolerance to eachother that you won't have problems going straight or worse, ripping the motors off the chassis because the front and back wheels on the same side are trying to go different speeds.
I don't know for sure, but, I would imagine you might get a braking effect by sending a number just past center opposite the direction of motion.
As I was writing the above, I realized that plastic gears might not like fighting that much force, and, rather than a braking reaction you might get a breaking reaction. :P
by using a NOT gate between the two input pins per motor like http://letsmakerobots.com/node/32462
is PWM , you can control the speed of your motors with 2 PWM channels and 4 digital I/O's . this becomes important when you wont to use servos or tone as they use the internal timer/s . im assuming your using an Arduino uno it has 2 timers i think 1 on pins 10 and 11 and 1 for the rest 3,5,6,9 (correct me if wrong) . i would use pins 2,4,7,8 for direction , 10 and 11 for the enables
i have also thought that it would be cool as well but it made more problems than it solved
note it's good for driving steppers
Basically, your question is to use a 4-pin system or a 6-pin system. Here we go:
4-pin with enables pulled high (Direction pins: one is a digital i/o, one is a PWM)
6-pin (4 digital I/O pins for direction, 2 PWM pins going to enable)
There is more but that is probably what you wanted to know.