Electrical Sub-system

Apr 24, 2013

Final PCB manufactured and assembled 

We designed, manufactured and assembled the final PCB. The picture below shows the board layout design.

It is worth noticing that the board serves as the mechanical sidewall of the inner part of the robot in the final design, and the lower part of the board is left almost empty to leave space for physically mounting the planar motion wheels.

March 31, 2013

Second PCB manufactured and assembled 

We manufactured the PCB and soldered the parts onto the PCB. A picture is shown below.

March 2, 2013

Updated second PCB design 

Since we intended to use the PCB to serve as one sidewall of the robot in order to reduce weight, we developed a newer layout that incorporated the dimensions from the mechanical side. The two figures below shows the mechanical drawing of the sidewall and the PCB layout, respectively. It is worth noting that we added one more sensor connector because we decided to use two flex sensors for the dual spring jumping mechanism.

February 14, 2013

Second PCB design

In order to verify the circuits to be built onto the PCB, we performed a breadboard circuit mock up, primarily including the circuit for the motor driver board and the debounce circuit for the rotary encoder, which are shown in the two figures below, respectively.

Source: Pololu website

Source: http://hifiduino.wordpress.com/2010/10/20/rotaryencoder-hw-sw-no-debounce/

After the mockup, we designed the layout which is shown in the figure below. Different from the original size of 2 inch * 4 inch, this board is considerably smaller and has a size of 2.23 inch * 2.64 inch, although the Fio v3 microcontroller board is not constrained within such dimensions.

January 31, 2013

Schematics of the first PCB design

We designed the schematics of the PDS board. The new board constitutes of the following components:

1. A power distribution unit

The power distribution provides power to all the other electronic components in the system. It also constitutes of the main power system, the actuation power system, and the MCU and sensor power system.

2. Microprocessor unit

The microprocessor unit is designed to provide sockets for the microprocessor to be

directly inserted onto the board. This eliminates a large number of physical wires and eliminates the problem of bad connections.

3. Sensor unit

The sensor unit provides accessory circuits for a flex sensor, an accelerometer, and a rotary encoder. Again, accommodating these accessory circuits onboard solves the problem of bad connection using physical wires. It also saves total space of the boards as surface mount components are smaller than the ones we used in the original boards.

4. Actuation unit

The unit includes two dual motor driver boards, which provides power to three motors.

5. Notification unit

This unit includes two LEDs, which are used to notify users of the robot's status.

There are one more properties of this board that is worth mentioning: the board only includes a voltage regulation circuitry for 5V but not 3.3V. This is because the flex sensor, the rotary encoder and the microprocessor all obtains power at 5V. Only the accelerometer draws power at 3.3V and I connected it directly to the 3.3V pin of the microprocessor. This way, by eliminating the 3.3V voltage regulation circuitry, it saves more space. A figure of the PDS schematics is shown below.

November 7, 2012

First PCB design

Today we demonstrated the design of our robot's Power Distribution System (PDS) on the Power Circuit Board (PCB) in Eagle.

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.

On-board electronics 

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.

October 22, 2012

Schematics of the first PCB

The team drafted a schematic for the RooBot's power distribution PCB. The first draft was a sketch, but today we translated the design into Eagle CAD. Below are images of both.

October 17, 2012

Sensor lab

Today we demonstrated the implementation of three sensors: a potentiometer, a force sensor, and  a temperature sensor.  The potentiometer was used to control the motion of a DC motor (which indirectly demonstrated the use of a hall effect rotary encoder.)  The force sensor and temperature sensor were used to control the degree rotation of a servomotor.

In the context of the RooBot project, this lab has informed our choice of relevant sensors. Our project will utilize a force sensor (to detect that the launching mechanism triggered), an IMU (to monitor the flight of the RooBot), a potentiometer (to be used as a power dial on the controller), rotary encoder (to detect the position of the DC motor), and a temperature sensor (to monitor battery hazards such as an overheat condition.

The following is an example of the voltage output for the FSR400 under linearized conditions (i.e., after being fed through an opamp and filtered within software on the Arduino Uno platform.)

Voltage versus Force (Linearized)

Please see Sensor Lab ILR02 under the Project Documents section for more information.

Meanwhile, our team studied the components of each subsystem and their required power. Then we estimated the total regular power and peak power required by the whole system. The information can be found in TeamE_PDSconceptual.pdf in Power Distribution System folder under Project Documents section.