Raspberry PI based robot - Part 6

Enabling the servo’s

In this post, we will explore enabling the servo motor drives of the robot. This will allow us to move the camera mount on the robot, without moving the entire robot. It will also tilt movements, which are up and down movements of the camera. The pan movements will allow the camera to move from side to side.

If you have successfully followed the instructions provided in the video tutorial Pan and Tilt Sensor Mount Assembly for Arduino and Raspberry Pi, you will have the camera setup on the pan tilt mount, with the 2 servo motors connected.

We will get started with programming the server motors. For that, we will use the servoblaster package.

We will be following the instruction provided by MJRobot here: https://www.hackster.io/mjrobot/iot-raspberry-pi-robot-with-video-streamer-and-pan-tilt-f50e53

Download the package:
$ sudo git clone https://github.com/richardghirst/PiBits
$ cd PiBits/ServoBlaster/
$ cd user/
pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $ sudo make servod
gcc -Wall -g -O2 -L/opt/vc/lib -I/opt/vc/include -o servod servod.c mailbox.c -lm -lbcm_host
pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $ sudo make install
[ "`id -u`" = "0" ] || { echo "Must be run as root"; exit 1; }
cp -f servod /usr/local/sbin
cp -f init-script /etc/init.d/servoblaster
chmod 755 /etc/init.d/servoblaster
update-rc.d servoblaster defaults 92 08
/etc/init.d/servoblaster start
pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $
pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $ sudo chmod 755 ./servod
pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $ sudo ./servod

Board model:                   3B+
GPIO configuration:            P1 (40 pins)
Using hardware:                PWM
Using DMA channel:              14
Idle timeout:             Disabled
Number of servos:                8
Servo cycle time:            20000us
Pulse increment step size:      10us
Minimum width value:            50 (500us)
Maximum width value:           250 (2500us)
Output levels:              Normal

Using P1 pins:               7,11,12,13,15,16,18,22

Servo mapping:
     0 on P1-7           GPIO-4
     1 on P1-11          GPIO-17
     2 on P1-12          GPIO-18
     3 on P1-13          GPIO-27
     4 on P1-15          GPIO-22
     5 on P1-16          GPIO-23
     6 on P1-18          GPIO-24
     7 on P1-22          GPIO-25

pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $

For our project, we are mapping P1-15 (GPIO22) and P1-12(GPIO18), to the PAN and TILT servo’s respectively.

We will connect this as per the below schematic:

Run the following commands to test the servo setup:

pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $ echo p1-15=40% > /dev/servoblaster --- TILT
pi@raspberrypi4:~/work/PiBits/ServoBlaster/user $ echo p1-12=60% > /dev/servoblaster --- PAN

At these positions, my camera is pointing straight ahead.

Let us now integrate this solution with a web page.

We will start the camera at the boot up of raspberry PI by adding the following line to /etc/rc.local

sudo nano /etc/rc.local

LD_LIBRARY_PATH=/opt/mjpg-streamer/ /opt/mjpg-streamer/mjpg_streamer -i "input_raspicam.so -fps 15 -q 50 -x 640 -y 480 -vf" -o "output_http.so -p 9000 -w /opt/mjpg-streamer/www" &

Now, even if we restart the PI, the camera streaming will be turned on.

We will now enable the buttons on the webpage to both PAN and TILT the camera.