QuadServo – Control 4 DC servo motors + 8 RC servos

4pics

quad_servo

 

One QuadServo board being used to control 3 custom servo motors

 

Hardware

For a robotics project I needed a way of controlling at least 12 motors with analogue feedback to turn then in to servo-motors. I needed a separate board for each of the 4 ‘legs’ of the robot which have 3 motors each.

I designed a small PCB (36mm x 33mm) around the Atmel ATXMega32 and 2 x TB6612FNG dual motor drivers. This allows each board to fully control 4 x DC motors and with analogue feedback turn then into servo motors. I added access to the spare pins which were later used to control 8 x RC servos using the standard PWM servo protocol (https://en.wikipedia.org/wiki/Servo_control).

I had 8 PCB’s manufactured with PCB-POOL (https://www.pcb-pool.com/), it cost €93. They are certainly not the cheapest but the quality is excellent and I got the boards in a week.

Hardware features

  • ATXMega32 @ 32MHZ
  • USB for programming or debug UART
  • ISP connector for programming and debugging
  • 2 x dual DC motor drivers
  • 2.5v reference for analogue feed back

Design

PCB was designed in Eagle, it fits with the free version limitation.

schematic
Schematic
Board layout
Board layout

 

 

OLYMPUS DIGITAL CAMERA
Front of PCB, half populated
Back of board
Back of board
Populated board
Populated board

 

Software

quad_servo1

The software is written in C using Atmel Studio. The diagram above shows a simple representation: Commands come in through the UART and are buffered in a fifo, the main loop just looks into the fifo and decodes the commands as they come in. The DC servo motor control is done in a timer interrupt, it reads the ADC and performs a PID control of the 4 motors. Another timer is used to generate the RC servo outputs.

Software features

  • PID control of 4 x DC motors with analogue feedback
  • Control of 8 x RC servos on the spare 8 output
  • ..or use spare I/O for GPIO control
  • Use USB as debug or comms serial port

Files

Hardware and software files are here:

https://github.com/emileb/QuadServo