Parts and Materials Used

Arduino Mega 2560

The Arduino Mega 2560 micro-controller board was selected for the operation of the drive system and physical controls.  It boasts a 16 MHz crystal oscillator, 54 digital IO pins (14 of which can be used as PWM outputs, 16 analog pins, and is highly versatile and easy to use with its opensource design and plethora of breakout boards and available libraries.  We also chose this board specifically because we had one readily available and because its libraries help inexperienced coders like us develop advanced projects in far less time.  

USB Host Shield

The USB Host shield is an Arduino compatible shield capable of communication with USB devices using the SPI bus through the ICSP header.  It supports device classes including, but not limited to, game controllers, HID devices, USB to serial converters, digital cameras, storage devices, and Bluetooth dongles.  We chose this breakout shield for its ability to communicate using Bluetooth dongles and its available Bluetooth controller libraries allowing communication with a Dualshock 4 controller.  

Sony DualShock 4 Controller

  

The Sony DualShock 4 controller has 12 digital buttons (2 are triggers, 1 is used for a power button, and 4 are used for the 8-direction D-pad), 2 analog triggers, two analog joysticks, an LED, a touchscreen pad, two rumble motors, and a gyroscope.  We chose to use this controller because we have the ability to communicate easily using a Bluetooth dongle and the USB Host shield libraries and also because we (and many people) have them readily available.  

MultiMoto 4-Channel Motor Driver

The MultiMoto by Robot Power is a low cost four channel H-bridge motor driver designed for small robots.  It is extremely versatile with a 6V to 36V battery voltage range with the ability to supply 6.5A continuous current on each channel.  The motors and battery are protected from dead shorts, it has full current limiting and over temp limiting, and programmable current limiting for each channel.  This board was chosen for pretty much all of these reasons.  Mainly, it is extremely versatile and has the ability to run 4 motors, at low cost, in a small package.

Pololu Gear Motors

The Pololu gear motors are powerful, 12V, brushed DC motors with a variety of gear ratios available.  They have 6, M3 threaded mounting holes and a D-ring shaft for easy setup with aluminum stamped L-bracked, and the Pololu 6mm universal mounting hub makes mounting wheels take minutes.  The 19:1 gear ratio chosen has a free-run current of 300mA , a stall current of 5A with 84oz-in of torque, and a no load speed of 500 rpm at 12V.  We chose this motor because we didn't need high torque for our application and we wanted to be able to make it as fast if we wanted.  In retrospect, a gear ratio of 100:1 or even 131:1 would have better suited our application because when the chassis is inside the ball, the ball won't be able to go extremely fast without disrupting the head mounted on top.  The higher gear ratio would have slowed down the top speed significantly and helped us to overcome the deadband of the motor at low PWM values.  

12V NiMH Battery Pack

This nickel-metal hydride battery pack is a 12V, 3000mAh rechargeable pack consisting of ten 1.2V cells.  It comes with an XT-30 connector and an in-line 20A fuse.  When choosing a battery pack there were many options to start, but they narrow down quickly.  Lead acid was too heavy. NiCD batteries are slowly disappearing because of their memory effect.  Li-ion do not supply enough current.  This left us with a choice between LiPo and NiMH.  While LiPo may be the best choice of battery, they are more expensive and extremely dangerous if not charged properly.  While we were confident enough to use the LiPo battery without injuring ourselves, we decided to go with the NiMH as it was less expensive and suited our needs adequately.  The price, capacity, and weight for the cost was hard to beat, and they are quickly rechargeable.

Wantai 42BYGH801 Stepper Motor

We chose this stepper motor to control the head because of its precision turning. With 200 steps per rotation we are able to turn the head in 1.8 degree increments if necessary. At 12V and .4A the motor is not very fast however its only job is to precisely turn the head which it does very well. The motor has enough torque to overcome the pull of the magnets against the ball. The motor can be driven in either direction. The motor seems to be a little big for the job and takes up a lot of space below the upper chassis however its weight helps to lower the center of mass inside the ball.

L298N Dual H-Bridge Motor Driver

The L298N dual H-Bridge stepper motor driver was perfect to control the Wantai stepper. The driver can operate anywhere from 5-35V and can supply up to 2A per channel. With our 12V motor this supplied more than enough power to drive the stepper. Another feature of this driver is the 5V supply pin that allowed us to power the UNO from this driver. This feature is nice because the main supply is wired to the driver instead of the UNO lessening the chance of power spikes inside the UNO that could damage components. There are numerous dual H-Bridge motor drivers on the market that would have worked for our application. However previous experience with this specific driver lead to our decision to use it. 

Elegoo UNO R3 Board

The Arduino UNO was chosen to control the movement of the head. Using an ATmega328P microcontroller the UNO is very versatile. The board runs on 7-12V and can supply up to .5A. The UNO runs at 16Mhz and has 32kb of flash memory on board. With 14 digital I/O pins and 8 Analog inputs this board has more than enough I/O's to control the motor driver. The UNO may have been to much for simply controlling the head however we had some on hand and decided to use them instead of something smaller. With more than enough space on the chassis to mount the boards the size was not a deciding factor. 

Raspberry Pi 3 Model B

The Raspberry Pi 3 Model B was chosen to control the ultrasonic rangefinder, process the data, and communicate with the Arduino Mega.  The Raspberry Pi 3 boasts a powerful 1.2GHz ARMv8 CPU, 40 GPIO pins, WiFi and Bluetooth on board, and draws around 600mA when idling. It runs Raspbian, a custom distribution of Linux based on Debian. It is small, lightweight, and powerful.

HC-SR04 Ultrasonic Rangefinder

The HC-SR04 is a fairly common ultrasonic rangefinder. It runs off 5V DC, takes a 3.3V trigger signal, and returns a 5V echo signal.  The model we used is accurate from 5cm to about 2.5m, is very easy to work with, and is readily available.