This is the journal/code repository for a physical robot I am working on to test some of the AI software I do in a real system. My intent is to use an Arduino computer for sensor/motor control, with a Raspberri Pi for high-level AI and vision. Hardware is a simple 4-wheel platform purchased as a kit.

The following parts have been used for this robot

• DFRobot 4WD Platform with encoders
• DFRobot Romeo V 1.3 Arduino compatible controller with motor controllers
• 0.1 μF ceramic capacitors (4)
• 3x6x0.025 inch aluminum sheet (to make battery tray)
• 6-32 1-1/2 inch bolts (4)
• 6-32 3/8 inch hex nuts (12)
• Rechargable Lithium-Polymer battery (Turnigy 5000mAh 2S 40C Lipo Pack)
• Bullet connector cable for battery (5.5mm Bullet to 4 x 4.0mm Multistar ESC Power Breakout Cable) [Comment 2]
• 3/8 inch inner-diameter rubber grommets (2)
• LMS303 Tilt compensated 3-axis Compass (DFRobot RB-Dfr-421)

• Attaching compass module to robot

• (5/7/16) Added capacitors and connection wires to motors (Do this before assembly!) [Image 1]
• (5/9/16) Motors, encoders, and wheels added to base. [Comment 1]
• (5/11/16) Tested motors with provided battery pack
• (5/13/16) Added top plate to base. Mounted Arduino board
• (5/16/16) Constructed tray for rechargable battery [Comment 3] [Image 3]
• (5/17/16) Installed tray for rechargable battery (widening of slots needed to install bolts) [Image 4]
• (5/19/16) Drilled holes in upper base for power/motor wires and installed grommets [Comment 4] [Image 5]
• (5/21/16) Connected wires, re-assembled base, tested motor [Code 1]
• (6/14/16) Connected wheel encoders to Romeo microcontroller (digital pins 2 and 3)
• (7/6/16) Calibrated Wheel Encoders [Code 2] [Comment 5]
• (7/13/16) Calibrated Compass from temporary wiring [Code 3] [Article 1]

1. • The instructions for putting on the wheel encoders doesn't place the sensor correctly. There is plenty of hardware provided to adjust the spacing. Play with it till it works. [Image 2]
2. • Rather than make my own bullet connector-to-wire connections, I bought a pre-made assembly and cut what I needed off of it.
3. • I bent 1/4 inch sides on the long edge of the 3x6 inch aluminum, to make a 2-1/2x6 inch plate that was sturdier and had edges to keep the battery from sliding off.
4. • Holes for grommets were 1/2" in diameter.
5. • This took a while. The interrupts for the encoders on the Arduino 'cross-talked' pulses between them. Newer versions of the Romeo use a 32U4 chip, while this version uses a 328P chip. The 32U4 chip has dedicated interrupts on pins 2 and 3, while the 328P can only use a block 'change' interrupt for all digital pins except 0 and 1. Had to add code to check for pin state change in the interrupt handlers, as well as a debounce time.

1. • Initial motor tests. Uses the 5 buttons to stop, go foreward, go backwards, turn left, and turn right
2. • Encoder calibration tests. Uses the 5 buttons to clear eeprom, do a calibration run, check calibration, and put results on serial port
3. • Compass calibration tests. Displays heading, and can display raw data for determining calibration constants. Use S2 button to write calibration constants (hard coded) into EEPROM

1. • Compass Calibration. Describes how to use the CompassTest code to get the calibration coefficients for the compass module

• Image1 - Capacitor and wires on motor:
• Image2 - Mounting hardware used on motor and encoder:
• Image3 - Battery tray:
• Image4 - Battery tray installed:
• Image5 - Wire holes and grommets: