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Is it possible to connect 6 dc motors and 2 dc servo motors to an Arduino Uno? I intend to control the Uno with a Raspberry pi connected through USB.
Assuming every motor to be bidirectional, how many L293 or L298 motor driver boards do I need? Is there any other better option than using multiple driver boards?
TI is only one of the many manufacturers who make some really nice motor control chips. The DRV8835 is one such device: it will drive two motors at voltages up to 11 Vdc at currents up to 1.2 Amps each. Each channel requires two control lines: enable and direction.
Pololu sells this chip already mounted to a carrier board for a rational price.
You will need a total of (6 motors * 2 lines per motor) = 12 i/o lines PLUS two more lines to control your servos for a total of 14 i/o lines from your controller.
Normally a full H-bridge (for one motor in bi-directional mode) will need 3 ouput pins. You can potentially force the enable pin to a constant level but that means you will always draw current for your motors even when they don't move, which is probably not what you want. ou might also wire all 6 enable pins together to one Arduino pin just to control power of all motos altogether.
In addition, each servo will need one output pin (typically 9 and 10 for both servos).
Hence in the worst case, you would need 20 pins overall. You have them on Arduino UNO but this means you don't have anyhting else left, even Serial communication!
If you can wire all 6 enable pins together, then you will need "only" 15 pins.
Also, note that if you want to control the speed of the DC motors, you will need PWM pins, but then you won't get enough with a UNO.
Regarding drivers ICs (L293 or L298), each of them has 2 full H-bridges, hence can drive 2 DC motors in bi-directional mode, so you will need 3 of them overall.
