Build a Raspberry Pi Telepresence Rover

Here's my Raspberry Pi telepresence rover robot. You can make one yourself and explore your house from your web browser, iPad or iPhone. Just read the tutorial

Overview

The setup is simple, using readily available hardware and software for motor control and streaming video. The rover consists of a Raspberry Pi in an enclosure sitting on top of a tracked chassis. Low voltage motor controllers are driven by the RPi GPIO pins controlled by REST services called from a control webpage via JQuery.

Meet Dragon. Streaming video top. Controls, bottom.

A web cam provides visual feedback using mjpg-streamer visible on the control webpage. The rover runs off of a 3600mAH NiMH battery feeding into a switched 5V regulator board. The RPi uses a wifi dongle for LAN communication.

Let's start building the Raspberry Pi robot from the bottom and work our way up.

You'll Need

• 1x Raspberry Pi Model B
• 1x MicroSD card with Raspberry Pi Wheezy
• webiopi software for Raspberry Pi
• mjpg-streamer software for Raspberry Pi
• EDIMAX USB wifi
• 1x Pololu 30T track kit
• 1x Pololu idler wheels
• 2x 150:1 Pololu gear motors
• 1x Pololu Step-Down Voltage Regulator D15V35F5S3
• 1x Pololu motor brackets
• 1x Sparkfun 3.3V FTDI breakout board
• 1x Microsoft LifeCam HD6000 (or equivalent, low power USB Webcam)
• 16x #10 nuts
• 4x #10 x 1" screws
• 2x #10 x 3/4" screws
• 1x 3/4"x1/2" aluminum 1/16" thick L-bracket cut into 2x 4" lengths
• 1x 1/2" aluminum 1/8" bar stock, cut to 5" length
• Hookup wire, various colors
• 30x Multicomp 2226TG (includes extras just in case)
• 1x Multicomp 2226A-02
• 2x Multicomp 2226A-04
• 3x Multicomp 2226A-06
• Cyntech Raspberry Pi enclosure
• Polycarbonate (Lexan) cut to 4" x 4" square
• 6C NiMH battery (or you can use 2S LiPo)
• Deans/Tamiya/XT60/Traxxas/etc. battery connectors

Chassis, motors, and motor control

The chassis is built on the Pololu 30T track kit. It comes with tracks, a pair of idler wheels and a pair of drive wheels. I added another pair of Pololu idler wheels and mounted the idlers on short sections of aluminum L stock.

The drive wheels are mounted onto 150:1 Pololu gear motors which in turn are mounted to the top of the L stock with Pololu motor mount brackets. Solder 6" wires on the motors and attach female crimp connectors (Newark: Multicomp 2226TG) on the ends.

I assembled each side independently, then cut a Lexan (polycarbonate) base. How do you cut polycarbonate? Carve a straight groove with a wood carving tool (like one of these) and a straightedge, then bend it in a vise for a clean break.

Mount each aluminum L channel to the Lexan base with 1" long #10 screws and nuts. Extra nuts raise the base above the motors.

Note the wires: female crimp ends with heat shrink

The RPi is enclosed in an injection-molded plastic case from Cyntech which I consider to be one of the prettiest, nicest-looking plastic cases made for the Pi. It comes in several colors. Attach the Cyntech enclosure to the base with its built-in slotted mounting holes. Drill holes in the four corners of the polycarbonate base so you can access the enclosure screws.

A Pololu DRV8835 motor controller handles the tricky task of driving the motors. Install 0.1" pin headers on the board. Using Pololu's diagram, insert your motor wire crimp connectors into a 4-way housing (Newark: Multicomp 2226A-04) and plug the assembly onto the motor controller board.

Image from Pololu.com

Battery, Power Supply

The robot runs off RC Car batteries like a Reedy Wolfpack 3600mAH NiMH battery. Why antiquated NiMH battery technology? Because I happen to have an automatic NiMH charger that I plan to hack into a docking station. Drive the robot up to it and charging begins.

A Pololu Step-Down Voltage Regulator D15V35F5S3 converts the battery power to a usable 5V for the Raspberry Pi and the motor controller. This is the same switching voltage regulator powering the electronics on Data Bus, my 20 mph autonomous RC rover. Install two 4" lengths of wire to the regulator to connect to the battery. On the other end, install whatever connector your battery pack requires (Tamiya, Deans, XT60, Traxxas, etc.)

Cut off a few inches of a micro-B USB cable, strip the wires, and connect the power wires to your regulator board output. This cable plugs into and powers the Raspberry Pi.

For powering the motor controller, cut a 3-5" length of black and red wire respectively, add female crimp connectors, and insert into a 2-way female housing (Newark: Multicomp 2226A-02). Plug this assembly into the VCC/GND pins on your motor controller board.

Battery mount is aluminum bar stock mounted lengthwise

To secure the battery, mount a section of 1/2" x 1/8" aluminum bar stock underneath the Lexan base longitudinally. Use 3/4" #10 screws with an extra nut next to the Lexan to create a gap between the bar stock and the base. The gap is required so you can use velcro straps or elastic cord to secure the battery.

Wiring Raspberry Pi IO

You'll need nine 4-6" wires with female crimp connectors on both ends of each wire. Six of the wires are for the motor controller. One is for 3.3V motor power (the motors don't draw much current), the other five are for control. The remaining three are for serial communications.

Motor control: Following the Pololu diagram above, and Raspberry Pi pinout, insert 3.3V and control wires into a 6-way socket (Newark: Multicomp 2226A-06) and plug into the Raspberry Pi. At the other end, insert the wires into another 6-way socket. Connect Raspberry Pi GPIO pins to motor controller pins as follows:

• GPIO11 to MODE, 
• GPIO9 to AIN1/APhase, 
• GPIO10 to AIN2/AEnable, 
• GPIO21 to BIN1/BPhase, 
• GPIO22 to BIN2/BEnable.

If you have a Revision 2, you'll need to use GPIO27 and tweak the software accordingly.

Serial comunications is really handy. I use a Sparkfun 3.3V FTDI breakout board with 4 pins: 3.3V, TXD, RXD, GND. Insert one end of the remaining three wires into a 6-way female housing, the other end into a 4-way female housing. You'll connect the wires from RPi to FTDI Breakout as follows: GPIO 14 to RXD, GPIO 15 to TXD and the nearest RPi GND pin to FTDI GND.

Raspberry Pi Setup

Now that everything's wired, you can set up the Raspberry Pi. You can connect a monitor and keyboard or you can set it up using your FTDI connector and a terminal emulator on your PC.

I used a standard Raspbian Wheezy distro. I installed an EDIMAX USB wifi dongle for wireless connectivity and I configured it with a static IP address. You'll need to install webiopi and mjpg-streamer.

Controlling IO

Now that everything's wired up, and the Pi is set up, it's time for software to take control. I've made the entire source available (see below) so you can just download it and put it in place on your Raspberry Pi.

The DRV8835 motor controller uses a mode pin and four PWM pins. Details on how to use the board are found on the product page. I'm using webiopi to control PWM on the four motor GPIO pins to move the robot. Here's how it works.

The web page includes rover.js which I wrote. It contains jQuery functions for controlling direction: fwd(), stop(), spinLeft(), spinRight() and rev(). These functions are called when control buttons on the web page are clicked (more on that momentarily).

In turn, these functions call the appropriate webiopi functions available by including webiopi.js. Webiopi jQuery functions call REST services to set PWM parameters on the GPIO pins. Here's an example of how I'm calling webiopi from within the direction functions.

Web Interface Buttons

The web interface has an HTML table with cells forming buttons for each of the available directions (forward, reverse, stop, spin left, spin right). We use jQuery to detect when those buttons are clicked and call our jQuery direction functions.

But our table cells aren't buttons. Normally, clicking a table cell doesn't make it blink. Also, double-clicking a cell will select the contained text. We can make the cells act like buttons with a little CSS and jQuery.

The following CSS disables text-select in popular web browsers.

html {
-webkit-touch-callout: none;
-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
-o-user-select: none;
user-select: none;
}

The following CSS makes the entire text cell change color from grey when you click on it. Every cell is given a class of "button".

td.button {

width: 80px;

height: 80px;

font-family: Arial;

font-size: 20pt;

font-weight: bold;

color: black;

background-color: grey;

}

td.button:active {

background-color: red;

}

Now, bind mouse events to the cells and call our jQuery direction functions when those events occur.

On desktop/laptop web browsers, one uses the mousedown and mouseup events to detect mouse clicks on the buttons. Browsers on the iPad and iPhone first fire touchstart and touchend events when you press and release a button and then they fire mousedown and mouseup. If you don't disable the mousedown event, the Rover will move, stop, then move briefly again as if you clicked the button twice.

Bind mousedown/mouseup, touchstart/touchend like this, to call our direction functions and to disable mousedown for iDevices:

  $("#F").bind("mousedown", fwd);

  $("#F").bind("mouseup", stop);
  $("#F").bind("touchstart", function() {
    fwd();
    $(this).unbind("mousedown");
  });
  $("#F").bind("touchend", function() {
    stop();
    $(this).unbind("mousedown");
  });

Examples of our direction functions, fwd(), rev(), stop(), spinLeft() and spinRight() can be found above.

Streaming Video

Streaming video originates from a Microsoft LifeCam HD-6000 with it's annoying, unnecessary autofocus disabled. The web streaming is made possible with MJPG-streamer. It runs its own web server on the RPi.

My control page simply includes an IMG tag:  <img id="streamimage" src="http://192.168.0.4:8080/?action=stream" /> to display the streaming image.

Screen capture from today's cat observation mission

The camera is mounted with double-sided tape to a section of aluminum bar stock I bent into an L shape. That in turn is mounted to the RPi enclosure.

Source

Full source is on the Bot Thoughts Google Code Repository, here

Future Plans

In addition the docking station I'd like to add servo pan/tilt for the camera, battery meter circuitry so the RPi can display power statistics on the control page, streaming audio so I can hear what is going on. I'd also like to be able to speak through the Rover.

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