The main components for BalanceBot are :
- Two geared motors with quadrature encoders
- A Motor controller
- An Arduino Uno for a brain
- A 9 DoF sensor stick to provide the IMU
- A custom board to interface the quadrature encoder counters
- A 12v rechargeable battery.
The motors are Pololu metal gear motors and Pololu have a nice motor controller shield that matches the requirements of the motors. The motor shield has a built in regulator to power the 5v Arduino from the motor power coming from the battery, so I could power everything from a single 12v rechargeable battery. A perfect fit. Pololu also sell mounting brackets for the motors and wheels. So that’s the mechanics covered in a single order.
The brain is an Arduino Duemilanove with an ATmega328p microcontroller but this is essentially the same as the newer Arduino Uno.
I read a lot about various IMUs and considered using an all-in-one unit with a built in CPU and code. I have an UM6-LT Orientation Sensor from CH Robotics for a different project and they are easy to interface to and do all the Kalman filtering for you on board, but I needed it for the other project, and they’re expensive, so I decided to use a raw 9 DoF sensor board and do the data fusion and filtering in code on the Arduino.
These 9 DoF boards are cool from FreeIMU but at the time I was researching this, there weren’t many online stores selling them, so I decided to use a SparkFun Sensor Stick. The FreeIMU site provides a GNU GPL license library for Arduino which supports not only the FreeIMU boards but also the SparkFun boards and the DIYDrones ArduIMU.
I was hoping to find an existing 3rd party Quadrature decoder Arduino shield, but I couldn’t one. I found some quadrature counter ICs LS7366 with an SPI interface. These count the quadrature pulses from the motors so the Arduino can read the count totals using SPI. I prototyped a shield for them using wire wrap and then manufactured a custom PCB using BatchPCB.com.
The frame is made from MicroRax which gave me the flexibility to build the frame to any dimensions to mount the motors and controller boards. Its strong and easy to construct and it also meant I could change my mind 🙂
The other components are from Maplins. A standard sealed 12v battery and some switches.
Finally, to make it look more professional I have some custom acrylic sheets laser cut for the base and top. These made mounting the PCBs and switches easier and made it look less Heath Robinson.
A sad note, Fabio Varesano (http://www.varesano.net/) the 28 year old student behind FreeIMU died suddenly over Christmas last year. Such a terrible shame for such a talented young man. He invested so much effort designing and developing FreeIMU and provided lots of support and encouragement to the robotics community. The information from his site was part of my research for this project and I’m sure he will be missed by the community. My heartfelt sympathy goes to his family and friends.