Servo control - with or without driver?

[MasterOfPuppets]

Hello guys!

I am going to build simple (or not) robot. I have a question.
Why should I use driver to control servo?
My friend told me, that using driver may provide me more precise control over the servo, is it truth?

Thanks in advance

[mikerr]

Couple of options:

• Directly control a single servo via pi's hardware PWM
  the Pi only has one hardware PWM pin, GPIO18
• Control 8 or more servos by software PWM using pigpio, servoblaster etc.
  In theory this option can cause jitter of servos, but I've found it fine.
• Use an external servo controller board/chip.
  This offloads the "work" to the board, freeing up GPIOs

[mikronauts]

I can recommend joan's pigpio, it worked well for my SPRITE robot.

For more complex robots, I use my RoboPi controller (http://RoboPi.com) which can control up to 24 servos and has eight 12 bit analog inputs. (each of the 24 digital I/O's can control: a servo, or pwm motor, or digital input, or digital output, or ultrasonic distance sensor)

[MasterOfPuppets]

Thanks, one more question.
Whats a difference between DRV8835 dual motor driver and RaspiRobot board?
As far as I know both can hold two motors, but second one is more expensive.

[joan]

The DRV8835 and raspirobot boards are for DC motors not servo motors. Is this in addition to any servos you may be using?

Personally for DC motors I just use the L298N or similar motor driver boards from eBay for a couple of pounds.

[MasterOfPuppets]

I know thats for motors. I just dont understand whats the difference between both (RaspiRobot and DRV8835). Could You answer me?
L298N is a bit cheaper but bit bigger. Thanks for advice.

[Grumpy Mike]

I just dont understand whats the difference between both (RaspiRobot and DRV8835).

They are both H-bridge controllers. The RaspiRobot is built up on a board and uses a L293DNE chip at the heart of it. This uses transistors to do the switching and will give a little voltage loss on the motor drive and has a 1A limit.

DRV8835 is a chip that you will have to build into your own board. It uses FETs to drive the bridge and has a 1.5A limit. It has a 0.35 ohm on resistance so you loose less voltage through the bridge.