I decided to use a Fiji Water bottle as the robot's exoskeleton because Fiji Water is an environmentally conscious company and Fijibot recharges its batteries via a solar panel. Plus, I think the round-edged rectangular shape and the (see through) clear bottle make a really cool looking robot!
Step 1: Materials & Tools
1 - 1.5 Liter Fiji Water Bottle (I actually used several bottles during my trial and error stages, but at least I had plenty of great water to drink!)
1 - Hacked RC car
1 - Arduino Uno (Radio Shack #276-128)
1 - Arduino Proto Shield (Adafruit #51)
1 - Break-away pins (Adafruit #392)
1 - Female/Female jumper wires (Adafruit #266)
1 - 6 Volt solar panel (Radio Shack #277-052)
2 - Parallax Continuous Rotation Servos (Radio Shack #273-457)
2 - Parallax 4-6VDC Standard Servos (Radio Shack #273-441)
1 - Parallax Ping Sensor (Radio Shack #276-136)
1 - 4-AA Battery Holder (Radio Shack #270-391)
1 - 9 Volt Batter Holder (Radio Shack #270-324)
4 - Photoresistors (Radio Shack #276-1657)
4 - Panel Mount LED Holders (Radio Shack #276-080)
4 - 10K ohm resistors (Radio Shack #271-1335)
1 - 1N4001 Micro 1A Diode (Radio Shack #276-1101)
Step 2: The Brain
Fijibot includes four servos: one continuous servo for each rear wheel, one standard servo to turn his head (the Ping sensor), and another standard servo to move the front axle left or right for turning.
Considering working in the tight space of the Fiji Water bottle, I decided I wanted to be able to easily connect and disconnect everything (sensors, servos, etc.) from the Arduino board. So I purchased a Proto Shield, male breakaway pins, and 6" female/female jumper wires from Adafruit. I soldered the pins to the proto shield and hooked up everything with jumpers!
The middle section of the proto board has two parallel rails connected to +5V and GND. To the right and left of these rails are 3-terminal perpendicular pads. I took advantage of this arrangement by mounting 5 (3-terminal) breakaway pins across the two rails and into the perpendicular pads. This basically gave me power, ground, and signal pins for each servo and the Ping sensor. Then, I added 4 (2-terminal) breakaway pins to the +5V and signal pads for the plug-in photoresistors.
NOTE: Notice in the photo that I did not solder the pin headers (that came with the proto kit) to the analog pins or the second bank of digital pins. I left these out so I could solder wires directly to the pads.
I connected wires to the digital PWM pins (for the servos) and to the analog pins (for the photoresistors). I also added a 10K resistor to ground for each photoresistor.
I connected wires from pins 7 & 9 of the proto board to the positive terminals of the green and red LEDs respectively.
In order to run the four servos and the Arduino, I used two separate power supplies. The Arduio runs on a 9v battery connected to Vin. The four servos and the Ping sensor run on a 4-AA battery pack, which is wired in parallel to a 6v solar panel for in-circuit charging. Since the solar panel and battery pack are closely matched, I just wired a diode between them to prevent back current.
I ran both power supplies through a DPST switch so I can power him off completely, but still leave the solar panel connected to the 4-AA battery pack. This way he can charge his batteries even when not in use.
Step 3: The Sensors
Since the photoresistors would be mounted to the chassis via LED holders, I needed a quick and easy way to disconnect them from the circuit board during and after construction. So I just connected one end of the female/female jumper wires to each photoresistor lead and the other end to the pins on the proto board. The rubber spacers in the LED holders keep the leads from touching each other and shorting out.
Step 4: The Chassis
I decided to use the rear wheels for power and the front wheels and suspension for stearing. I attached two continuous servos to the back of the water bottle using double-sided tape. I also used double-sided tape to secure the servos to each other. Then I cut a small slot in the plastic bottle to feed in the servo cables.
For the front end, I attached a standard servo to the suspension system so that it could turn the front wheels left or right. Then I cut a rectangular hole in the water bottle and drilled four holes. Next I slid the servo into the opening and mounted the assembly to the bottle using 6/32 nuts and bolts.
I cut a flap on the back label side of the bottle to allow me to work inside. I was worried it would reduce the stability of the bottle, but it's still actually very sturdy. I used a strip of Velcro to reseal the flap. Then, I drilled four 5/16" holes in the front, rear, and two sides of the water bottle and mounted the LED holders.
Fijibot's head is a Ping ultrasonic sensor mounted to the top of a standard servo. I drilled a hole in the top of the bottle for the servo gear to meet up with the Ping mounting bracket and then added four holes for 6/32" bolts to secure the servo to the bottle.
Finally, I ran all of the wires out of the flap and labeled them accordingly for connection to the circuit board.
Step 5: The Program
While looking for light to charge his batteries, Fijibot avoids running into things using ultrasound (via a Ping sensor). The main program loop is constantly checking for obstacles within a specified range (30 inches). If something is detected, Fijibot stops, looks left and right (using a standard Parallax servo), and decides which direction is clear. If he's blocked forward, left, and right he will backup for half a second and try again.
The source code is available at https://github.com/mikesoniat/Fijibot
Step 6: Putting it all together
First I connected the jumper wires from the servos and sensors to the male pins on the circuit board. With the flap secured open via a Velcro strap, I attached the two battery packs and organized everything inside the bottle. I also used Velcro strips to secure the circuit board and battery packs inside the bottle.
Finally, I installed the wheels and solar panel and I was ready to test him out!
I setup my garage with two low-hanging spot lights and placed a plastic recycle bin between them. The plan was for Fijibot to find the closest light source and position himself underneath it. Then, I would turn that light off and see if he can find the remaining light source without running into the recycle bin.
Good news, he passed with flying colors! Check out the video below!