Electrical Sub-system Backup

1 Design of Power Distribution System

The schematic design of PDS includes the following components:

i) A Main Power System that aims at hosting the 7.4V Tenergy Li-ion battery but also accommodates a battery power between 5.5V and 13V and a Battery Monitoring System that is implemented by a voltage divider which feeds the signal into an Analog-Digital Converter (AD Converter) of a microcontroller;

ii) An IMU/MCU/Rotary Encoder Power System that supplies a regulated voltage at 3.3V and a maximum current of 700mA to provide power for one Inertial Measurement Unit (IMU), one Microcontroller Unit (MCU) and up to four Rotary Encoders;

iii) A Motor Power System that supplies battery voltage and a maximum current of 4.1A to powers up to four H-bridge Motor Driver Boards;

iv) A Servo Power System that supplies a regulated voltage at 5V and a maximum current of 400mA to power one servo motor;

v) A General Purpose LED System which can be used to test on board signals.

The layout of the PDS is designed as a 2'' x 4'' board with mounting holes of our Fio v3 microcontroller. We have fuses and status LEDs for each power system and they, along with the General Purpose LED System, are all out of the microcontroller mounting region to ensure easy observation of LEDs and easy changing of fuses. Meanwhile, the routing of the circuits is carefully done to minimize the length of the common power path and the common Ground path of the systems for the minimization of signal crossovers.

2 On-board Electronic Components

1) Flex Sensor

This sensor is mounted to the fiberglass spring and detects the bending angle of the fiberglass under displacement thus enabling the microcomputer to measure the amount of energy stored. 

The flex sensor operates by employing conductive ink printed on the active side of the package.  When the particles get further apart, the resistance changes, and this change can be measured to get a corresponding angle as shown below.

2) Rotary Encoder

This rotary encoder is mounted to the chassis via a small breakout board as shown below.

The wiring schematic for reading the rotary encoder is shown below.

3) Microcomputer Unit

The Arduino Fio v3 was chosen to provide the logic for the RooBot system. It allows for easy access to ZigBee using and XBee shield.

3 Communication between XBee Modules

We implemented a controller and a receiver to imitate the actual remote controller of our robot and the receiving module on our robot, respectively. The controller consists of a XBee, a XBee Explorer, a potentiometer, a button and a LED; the receiver consists of a XBee, Fio v3 microcontroller, two LEDs and a servo motor. On the controller end, users can adjust the potentiometer to a desired position and press the button to send the information to the receiver. Whenever the button is pressed, the status-indicating LED would be lit and the analog value of the potentiometer would be converted to a digital signal through an AD Converter on XBee and then be sent to the receiver. On the receiver end, two status-indicating LEDs were used, one indicating the receiver has received a signal and the other indicating the opposite. If the packet is received by the XBee on the receiver end, it would be deciphered by the microcontroller then converted to signals that control the LEDs and the servo motor, which rotates according to the potentiometer value on the controller end. The picture below shows the setup.

Later we rebuilt the controller circuit inside a nice box.