Robot Project :: Video of Bot Auto Steering

The bot project is sitting idle no longer - I have replaced a bad photoresistor and tuned the program to improve light detection. This video shows the photovore robot traveling around the perimeter of a wall and autosteering to prevent collision with the wall.

This photovore works by detecting incoming light to two photoresistor sensors, each positioned approximately 45 degrees on opposite sides from a line normal to the robot face. The robot will respond to one of four scenarios: (1) incoming light is approximately the same intensity at both sensors; (2 and 3) light is greater at one sensor than the other; and (4) incoming light is very low at both sensors. In case one, the bot steers straight. For cases 2 and 3, the bot will follow the direction of greater light, and for case 4, motors for both wheels stop running.

Robot Project :: Robot Completed

My first robot project is now completed. It only took a weekend afternoon to complete, but I let it lapse while focusing on my dissertation and research this fall.

The function of the robot is simple: detect light to the left and right and continually drive itself while remaining within an area having light.

I've been able to keep a low budget by finding materials for free or creating parts from what would otherwise by trash. Here's a short list of the components:
- Body: 1/4" thk. PP sheet cut to the size of a compact disc.
- Sensor body: electrical tape.
- Wheels: peanut butter jar caps and rubber bands.
- Attachment: screws (wheels) and velcro (nearly everywhere else).
- Rear stabilizer: Tenergy 2000 mAh 6V battery.

Some of the key tricks/modifications necessary:
- The Hitech HS-311 servos are made stock to only rotate 90 or 180 degrees. The servos must be disassembled and modified to permit 360 rotation; they also must be calibrated to prevent rotation when not desired.
- There were no complete instructions for creating the programmer circuit on the board for the Pololu AVR programmer. Another hobbyist provided some direction with this.
- The C-code needs to be tuned to improve the response to sensed ambient light.

Final verdict: the robot rotates the wheels to move in the correct direction when one sensor is exposed to light and the other is blinded. However, the response to areas of light and shadow in the floor of my apartment are less than the accuracy it needs to work well. This may be due to the shine off my floor or poor lighting. I'll post a video once I find a surface and lighting conditions where it works well.

Robot Project :: Circuit Explained

IMG_1735
Originally uploaded by orangejacket05

With no access to a CAD program, I have not been able to make a good sketch of the circuit diagram yet. Instead, I'll give a description of the circuit components and circuit operation.

What is the purpose of the circuit?
This circuit uses two photoresistors to detect light, read the voltage drop across the sensors, and determine automatically which servo to power using a differential drive setup, thereby steering the vehicle automatically per the user-defined embedded code. The code may be written to make the robot remain within an area, track lines, etc.

Components (from top-left to bottom-right moving down the circuit):
- 3 pin header for battery connections (behind the voltage regulator)
- 5V linear voltage regulator: provides steady voltage to the microcontroller/sensor bus.
- 220 microF capacitor: meets unsteady servo load with peaking power.
- Servo headers
- LED and resistor: circuit ON/OFF signal
- ATMega8 AVR microcontroller: circuit brains, sensor signal processing, program execution
- Sensor headers
- 6-pin programmer headers: designed for the Pololu AVR programmer.

Soldering Completed

IMG_1736
Originally uploaded by orangejacket05

Robot Project :: Workshop Day 3 :: Circuit Complete

IMG_1735
Originally uploaded by orangejacket05

I finished the circuit today and powered it up, and it passed the first tests! No sight nor smell of smoke was emitted from the components or wires.

After finishing all soldering I used a multimeter without an external power source as a first circuit test:
- no connections between the power and ground buses (risk is melting down the battery and causing sparks).
- all intended connections are functional
- no short circuits between adjacent buses
- verify that all connections around the voltage regulator are functional

For my next test, I connected a 7.5 V rechargeable battery with alligator clips to the power input headers. I test the servo power bus and the microcontroller circuit to ensure proper voltages:
- The servo bus read voltages near 7.5 V
- The sensor bus voltages were at 4.95 V
So far, so good. The voltage regulator is working as expected.

Soldering

IMG_1728
Originally uploaded by orangejacket05

Going low-budget on the first robot means more work. I am creating bridges between components using solder and 18 AWG wire since the board has no buses. It is testing my eye-hand coordination without a doubt.

The robot brain circuitry in development

IMG_1726
Originally uploaded by orangejacket05

So far the circuit contains most of the headers, a 340 ohm resistor, LED, and the 18 pin DIP socket.

Robot Project :: Workshop Day 1 :: Starting from the Ground Up

A dream of mine since childhood, building a robot, always seemed like something that I would never find time to complete. Being that Short-Circuit was one of my favorite movies from the 80's as I was growing up, I guess it was inevitable that I'd want to build a robot one day.

At the ripe old age of 27, I have decided to tackle a few of the goals that I've had for years. Having a full workshop and scrap supplies available to me, I no longer have any excuses. Also I have to give credit to societyofrobots.com for their generous advice and forums for this project.

Giving engineering and science education demonstrations in local schools during graduate school has given more reasons to begin building robots. Robot demonstrations are a great opportunity to show students about engineering in a way that is entertaining and educational.

This first bot will be a differential drive robot that mostly performs object-avoidance. I am building the bot from basic components: an ATMega8 microcontroller, resistors, capacitors, servos, photoresistors, etc. I will use an external programmer to download and test various control algorithms.

Workshop day one ...

Soldering for the first time went smoothly for a while, but I eventually learned the hard way how solder wicks can save a project. Today I've finished half of the brains behind the machine; I soldered most of the headers, the 28 pin DIP connector, a resistor, and LED. Since I will be using a newer programmer, the Pololu USB AVR 6-pin ISP programmer, than some guidelines that I have been following, I reconfigured the pin layout from 10-pin to 6-pin based on the programmer module pinout diagram.

Bandsaw skills from ME2110 at my alma mater came in handy as I cut a circular CD-sized disc from a 3/8" thick polypropylene sheet. A nearby machine shop donated the PP sheet.