Tag Archives: Raspberry Pi

Raspberry Pi Robot #2

I’ve connected the [amazon &title=Raspberry Pi&text=Raspberry Pi] to an L298N and two 6V DC Motors, which have been in the Makeblock Starter Kit. I’ve had some issues with the WPA2 Enterprise TLS Network, which is why there is an cable attached.

IMG_20140521_164828

I’ve also written a small geometry/Twist controller for ROS-compatibility,for controlling the robots movement with keyboard interop like I did before.

Before I dismantle this little robot, I’ve like to share a little video:

As soon as possible I will use the arduino micro and the two 250rpm stepper motors – for that I am planning to use a Arduino Motor shield that I’ve already ordered.

Rasberry Pi Robot with ROS, Xtion and working base_controller teleop

Before I dismantle my little [amazon &title=Raspberry Pi&text=Raspberry Pi] Robot #1 , I wanted to have a little video of its base_controller working together with the turtlebot teleop. It uses the geometry/Twist messages to transmit moving information like a lot of ROS Robots do.

As you see there is a little acceleration control implemented which makes the robot start smoothly and stop after gently after no key is pressed anymore. In case of emergency its possible to hit e.g. the space bar for a instant full stop.

This robot isn’t very fast – but the next one will be. So this was a successful ROS-learning robot which I can recommend to everyone who wants to know how ROS Robots work.
Its a bit hard to get all of the source compiled on the small arm cpu, and there are nearly no precompiled packages – but it takes away all the fear from compiling errors in the future 🙂

 

Raspberry Pi Robot with ROS, Xtion, OpenNi2 and rviz providing 3d point cloud data

That’s one small step for a man, one giant leap for a small raspberry powered ROS robot.

Okay – maybe thats a bit too big – but I am in a good mood. I compiled the latest openni2_camera ros driver on the little arm cpu of the [amazon asin=B00LPESRUK&text=[amazon &title=Raspberry Pi&text=Raspberry Pi]]. Before that, I used the driver provided by kalectro (see source), which is an older fork but prepared for raspberry.

As a result of that, I’ve got some new features like the IR-Image stream I visualized with rviz :

Raspberry Pi Robot with ROS

Raspberry Pi Robot with ROS

or the handy little parameter with which it is possible to skip some frames which reduces the load a bit:

set param name="camera/driver/data_skip" value="300"
rosrun openni2_camera openni2_camera_node

Now, running roscore on my laptop – I had some sensor_msg/Images I needed to convert into 3d depth data. After some little issues with faulty XML-launch files, I finally got openni2_launch up and running, which is a handy little launchfile using rgb_launch providing every data format you’ll can get out of the [amazon &title=Xtion&text=Asus Xtion].

roslaunch openni2_camera openni2.launch

Now I’ve had a /camera/depth/points topic, with a pointcloud2 datatype. Which is really nice because rviz can visualize it:

Raspberry Pi Robot with ROS - Xtion

Raspberry Pi Robot with ROS – Xtion

Houston, we’ve had a problem.

Yes, there were times when it was possible to land on the moon by the power of a daily life calculator – but todays robots need more than that 🙂 So my aged Intel Centrino Core 2 Duo ASUS-F3J with 1,7Ghz each core isn’t able to do more than I reached today. It pops to 100% processing and after some time it collapses totally.

So todays lesson learned is:

Robots are distributed systems – by every measure.

So I’ll need more power.. again…

Controlling two 28BYJ-48 Stepper Motors with Raspberry Pi

I’ve taken some code written by Stephen C Phillips and added/modified a few lines so its possible to run two motors at once, even with different directions.

#!/usr/bin/env python

# This code is written by Stephen C Phillips http://scphillips.com.
# and modified by Paul Petring http://defendtheplanet.net
# It is in the public domain, so you can do what you like with it
# but a link to our websites would be nice.

# It works on the [amazon &title=Raspberry Pi&text=Raspberry Pi] computer with the standard Debian Wheezy OS and
# the 28BJY-48 stepper motor with ULN2003 control board.

from time import sleep
import RPi.GPIO as GPIO
from thread import start_new_thread
import sys

class Motor(object):
    def __init__(self, pins):
        self.P1 = pins[0]
        self.P2 = pins[1]
        self.P3 = pins[2]
        self.P4 = pins[3]
        self.deg_per_step = 5.625 / 64
        self.steps_per_rev = int(360 / self.deg_per_step)  # 4096
        self.step_angle = 0  # Assume the way it is pointing is zero degrees
        for p in pins:
            GPIO.setup(p, GPIO.OUT)
            GPIO.output(p, 0)
    def __exit__(self, type, value, traceback):
       self.clean_pins_up()
    def _set_rpm(self, rpm):
        """Set the turn speed in RPM."""
        self._rpm = rpm
        # T is the amount of time to stop between signals
        self._T = (60.0 / rpm) / self.steps_per_rev

    # This means you can set "rpm" as if it is an attribute and
    # behind the scenes it sets the _T attribute
    rpm = property(lambda self: self._rpm, _set_rpm)
    def clean_pins_up(self):
        GPIO.output(self.P1, 0)
        GPIO.output(self.P2, 0)
        GPIO.output(self.P3, 0)
        GPIO.output(self.P4, 0)
def move_to(self, angle):
        """Take the shortest route to a particular angle (degrees)."""
        # Make sure there is a 1:1 mapping between angle and stepper angle
        target_step_angle = 8 * (int(angle / self.deg_per_step) / 8)
        steps = target_step_angle - self.step_angle
        steps = (steps % self.steps_per_rev)
        if steps > self.steps_per_rev / 2:
            steps -= self.steps_per_rev
            print "moving " + `steps` + " steps"
            self._move_acw(-steps / 8)
        else:
            print "moving " + `steps` + " steps"
            self._move_cw(steps / 8)
        #self.step_angle = target_step_angle #in case you want to keep track of the position
        self.step_angle = 0

    def _move_acw(self, big_steps):
        self.clean_pins_up()
        for i in range(big_steps):
            GPIO.output(self.P1, 0)
            sleep(self._T)
            GPIO.output(self.P3, 1)
            sleep(self._T)
            GPIO.output(self.P4, 0)
            sleep(self._T)
            GPIO.output(self.P2, 1)
            sleep(self._T)
            GPIO.output(self.P3, 0)
            sleep(self._T)
            GPIO.output(self.P1, 1)
            sleep(self._T)
            GPIO.output(self.P2, 0)
            sleep(self._T)
            GPIO.output(self.P4, 1)
            sleep(self._T)
        self.clean_pins_up()
def _move_cw(self, big_steps):
        GPIO.output(self.P1, 0)
        GPIO.output(self.P2, 0)
        GPIO.output(self.P3, 0)
        GPIO.output(self.P4, 0)
        for i in range(big_steps):
            GPIO.output(self.P3, 0)
            sleep(self._T)
            GPIO.output(self.P1, 1)
            sleep(self._T)
            GPIO.output(self.P4, 0)
            sleep(self._T)
            GPIO.output(self.P2, 1)
            sleep(self._T)
            GPIO.output(self.P1, 0)
            sleep(self._T)
            GPIO.output(self.P3, 1)
            sleep(self._T)
            GPIO.output(self.P2, 0)
            sleep(self._T)
            GPIO.output(self.P4, 1)
            sleep(self._T)
        self.clean_pins_up()
if __name__ == "__main__":  
    GPIO.cleanup()
    GPIO.setmode(GPIO.BCM)
    m_l = Motor([2,3,14,15])
    m_r = Motor([10,9,11,25])
    m_l.rpm = float(sys.argv[1])
    m_r.rpm = float(sys.argv[1])
    print "Pause in seconds: " + `m_l._T`
    i = 1
    while i < 5:
       start_new_thread(m_l.move_to,(int(sys.argv[2]),))
       start_new_thread(m_r.move_to,(int(sys.argv[3]),))
       sleep(2)
       i=i+1
    GPIO.cleanup()

run the code with the following command:

sudo python motor.py 10 +90 -90

10 stands for rpm (rounds per minute) and +90 -90 as the amount of degrees each motor should turn. I figured out that, with this code and motors the max RPM is around 16, which results in a speed of 16 * 2 * Pi * Radius of your Wheel in cm / m.

This code only demonstrates how to turn the motors with a certain speed and degree. Its not made for rotating wheels yet..

Have fun experimenting 🙂

Raspberry Pi Robot #1

I’ve completed a new version today. It is a bit smaller and heavier, but already running ros hydro (I will write a small tutorial soon how to achieve that) with OpenNI2 and the ros-package openni2-camera. With that its possible to stream data to another computer visualizing the depth image of the [amazon &title=Asus Xtion&text=Asus Xtion] in rviz. I had some trouble solving and compiling all drivers, dependencies like ros-packages and libs like openCV (see Howto).

When the camera node is running the Raspberry is faced at with a processing load of 100%. The used network bandwidth is about 200-300 kb/s.

I suppose the raspberry Pi needs to be replaced by something stronger soon.

But for my first week in robotics, it’s something 🙂

 

Controlling a stepper motor 28BYJ-48 with a Raspberry Pi

Actually there is no need to explain more about stepper motors than that video does:

Currently I am using this python code to get the motors running:

#!/usr/bin/env python
 
# import required libs
import time
import RPi.GPIO as GPIO

GPIO.cleanup() #cleaning up in case GPIOS have been preactivated
 
# Use BCM GPIO references
# instead of physical pin numbers
GPIO.setmode(GPIO.BCM)
 
# be sure you are setting pins accordingly
# GPIO10,GPIO9,GPIO11,GPI25
StepPins = [10,9,11,25]
 
# Set all pins as output
for pin in StepPins:
  GPIO.setup(pin,GPIO.OUT)
  GPIO.output(pin, False)

#wait some time to start
time.sleep(0.5)
 
# Define some settings
StepCounter = 0
WaitTime = 0.0015
 
# Define simple sequence
StepCount1 = 4
Seq1 = []
Seq1 = range(0, StepCount1)
Seq1[0] = [1,0,0,0]
Seq1[1] = [0,1,0,0]
Seq1[2] = [0,0,1,0]
Seq1[3] = [0,0,0,1]
 
# Define advanced sequence
# as shown in manufacturers datasheet
StepCount2 = 8
Seq2 = []
Seq2 = range(0, StepCount2)
Seq2[0] = [1,0,0,0]
Seq2[1] = [1,1,0,0]
Seq2[2] = [0,1,0,0]
Seq2[3] = [0,1,1,0]
Seq2[4] = [0,0,1,0]
Seq2[5] = [0,0,1,1]
Seq2[6] = [0,0,0,1]
Seq2[7] = [1,0,0,1]

#Full torque
StepCount3 = 4
Seq3 = []
Seq3 = [3,2,1,0]
Seq3[0] = [0,0,1,1]
Seq3[1] = [1,0,0,1]
Seq3[2] = [1,1,0,0]
Seq3[3] = [0,1,1,0]
 
# set
Seq = Seq2
StepCount = StepCount2
 
# Start main loop
try:
  while 1==1:
    for pin in range(0, 4):
      xpin = StepPins[pin]
      if Seq[StepCounter][pin]!=0:
        #print " Step %i Enable %i" %(StepCounter,xpin)
        GPIO.output(xpin, True)
      else:
        GPIO.output(xpin, False)
    StepCounter += 1

  # If we reach the end of the sequence
  # start again
    if (StepCounter==StepCount):
      StepCounter = 0
    if (StepCounter<0):
      StepCounter = StepCount
 
  # Wait before moving on
    time.sleep(WaitTime)
except:
  GPIO.cleanup();
finally: #cleaning up and setting pins to low again (motors can get hot if you wont) 
  GPIO.cleanup();
  for pin in StepPins:
    GPIO.setup(pin,GPIO.OUT)
    GPIO.output(pin, False)

it is based on code by matt.hawkins but with some improvements I did.

Please be sure you set your GPIOs accordingly to your [amazon &title=Raspberry Pi&text=Raspberry Pi] Revision. So mine was REV 2.0.

Run the code with

sudo python nameOfTheFile.py

and hit [Ctrl]+[C] to stop it. All pins will be set to low afterwards.

In case you want control two motors of this type see another post I made here.

 

For a different version see:
http://www.intorobotics.com/control-stepper-motors-raspberry-pi-tutorials-resources/http://www.elektronx.de/tutorials/schrittmotorsteuerung-mit-dem-raspberry-pi/ 

Raspberry Pi Robot #0

I am trying to build my own [amazon &title=Raspberry Pi&text=Raspberry Pi] based robot. Someday, it shall be able to drive autonomously based on data from its [amazon &title=Asus Xtion&text=Asus Xtion] (a smaller version of an Xbox Kinect) and with the help of ROS (Robot Operating System). For today, it is only capable of driving straight forward.

PiRosBot #Zero

Parts:

  • [amazon &title=Asus Xtion&text=Asus Xtion] Pro
  • a [amazon &title=Raspberry Pi&text=Raspberry Pi] Model B Rev.2.0
  • WLAN USB stick
  • two Stepper Motors 28BYJ-48 Datasheet PDF 5V controlled by an ULN2003A Chip
  • an easyAcc Powerbank with 10.000mhA with an MicroUSB Cable supplying 2A of power
  • some metal toy constuction set parts including 3 wheels
  • 8 old female to female jumper wires
  • 2 Y female jumper whires (to share positive and ground of the raspberry with the motors)

With this setup, the raspberry i able to run at least 8 hours by the power of my already a little bit aged powerbank. Driving at an unbelievable slow speed of about 30 seconds per meter (full torque mode of steppers).

For documentation (and for fun, because I never did this before), here a small video of the very first test drive:

 

Howto: OpenCV 2.4.9 on Raspberry Pi from source

OpenCV is a powerful tool for building computer vision based applications. For one of my projects, I needed it to be compiled on my Raspberry.

Installing it from repositories was not an option because of its too old version.
If this wouldn’t bother you, consider using: sudo apt-get install libopencv-dev

Here is how I installed it on my Rasbian Wheezy from source:

prerequisites:

sudo apt-get -y install build-essential cmake cmake-qt-gui pkg-config libpng12-0 libpng12-dev libpng++-dev libpng3 libpnglite-dev zlib1g-dbg zlib1g zlib1g-dev pngtools libtiff4-dev libtiff4 libtiffxx0c2 libtiff-tools libjpeg8 libjpeg8-dev libjpeg8-dbg libjpeg-progs ffmpeg libavcodec-dev libavcodec53 libavformat53 libavformat-dev libgstreamer0.10-0-dbg libgstreamer0.10-0 libgstreamer0.10-dev libxine1-ffmpeg libxine-dev libxine1-bin libunicap2 libunicap2-dev libdc1394-22-dev libdc1394-22 libdc1394-utils swig libv4l-0 libv4l-dev python-numpy libpython2.6 python-dev python2.6-dev libgtk2.0-dev pkg-config

after that:

downloading the zipfile into a folder located in $HOME

mkdir ~/opencv
cd ~/opencv
wget http://downloads.sourceforge.net/project/opencvlibrary/opencv-unix/2.4.9/opencv-2.4.9.zip 
unzip opencv*.zip
cd opencv*
mkdir build
cd ./build/
cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D BUILD_PYTHON_SUPPORT=ON -D BUILD_EXAMPLES=ON
make
sudo make install

Make took about 6-7 hours on my Raspberry Pi, so be sure you have a stable connection or consider using a tool like ‘screen’.

Please also see:

For  openni2_camera it’s not necessary to go further like other posts suggested.