WEEK THREE: 4 May to 10 May 2015

Task: Determining the Different Type of Sensors

As there are different parameters that we need to obtain from SunSPEC 4, different sensors are needed. 

Current Sensors

Measurements taken from the following hardware:

• 3x string current after Solar MPPT (Maximum Power Point Tracking) 
• 1x total current from batteries (in 34S 36P)
• 2x current from the 2 motors 

Requirements for the current sensors:

1. Non-invasive so that the circuit need not to be broken
2. Hall effect sensors that measures DC Current
3. Must be compatible with the microcontroller that we are using.
4. Accurate / Sensitive enough for data logging

There are multiple power sources and motors for the SunSPEC 4. Therefore, we are required to have multiple current sensors for data tracking, in order to calculate the power consumption of the solar car. The following are the considerations we took for selecting our current sensors.

1. Bi-directional. The sensors for certain parts of the car must be bi-directional. For example, in the case of the motor, current will be flowing to the motor when driving and current will be flowing out of the motor when implementing the regenerative braking.

2. Non-invasive. For the ease of removing the sensors when troubleshooting and also to minimize the possibility of hot spots due to bad contacts, we have decided to use a non-invasive hall effect sensors.

3. Size. The current sensor must also be of a certain size, in order for the wire to be able pass through the sensor for measurements to be taken.

4. Current rating. The rating of the current that we require would also be considered, as we would not want the sensor rating to be lesser than the rated currents of our systems in the solar car.

Coding for current sensors:

void setup() {
Serial.begin(9600); //initiate Arduino serial display }

void loop() { //to be repeated over and over again

float average = 0; //set average to pin A0

for(int i = 0; i < 1000; i++) {
average = average + (.0264 * analogRead(A0) -13.51); //calibrated current calculation
delay(1);  }
Serial.print(average);
Serial.println("mA"); }

We looked through a few non invasive current sensors which includes Panucatt CS-45AL Hall effect sensor, LEM HO series current sensors and AMPLOC current sensors. Although we favoured Panucatt Sensor the most, it has been out of stock since 2012. The LEM sensors on the other hand consumes too much power. Thus, we decided to continue using the AMPLOC current sensors.

Amploc current sensors were used in SunSPEC3.  We found that the readings obtained in SunSPEC3 was rather accurate which made decision-making easy for the telemetry team. Figure 1b shows the dimension of Amploc sensors. The size of the sensor is able to fit all the wire sizes, measuring the current of motor, MPPT, battery and others.

Shortlisted current sensors: AMPLOC AMP Series (Datasheet)

Voltage Sensing Circuits

Measurements taken from the following hardware:

• 1x system voltage
• 1x battery voltage
• 1x solar voltage

Requirements for the voltage sensing circuit:

1. Able to sense up to 150V
2. To step down until 5V for microcontroller boards to function properly
3. Sensitivity:

For voltage sensing, our team would have to come up with a circuit to measure the voltage and step down into a range of 5V to be input into the microcontroller. 

Temperature Sensors

Measurements taken from the following hardware:

• 4x battery temperatures (to be placed at hot spots in the battery box)
• 3x solar panel temperature (to be placed underneath the solar panels)

Requirements for temperature sensors:

1. Big temperature range
2. Durable
3. Compatible with the microcontroller that we chose.  

Coding for temperature sensor

float temp;
int tempPin = 0;

void setup() {
Serial.begin(9600); }

void loop() {
temp = analogRead(tempPin)/9.31;
Serial.print("TEMPRATURE = ");
Serial.print(temp);
Serial.print("*C");
Serial.println();
delay(500); }

Temperature sensors are easily obtained from various stores. We shortlisted LM35 as it is cheap and compatible with any microcontroller. The reading from LM35 is also rather accurate at 10mV/°C. The pins are also easy to configure. Measurement of temperature ranges up to 300°C. 

Shortlisted temperature sensors: LM35 (Datasheet)

WEEK TWO: 27 Apr to 3 May 2015

Task: Analyzing the Different Types of microcontrollers

During the World Solar Challenge as the SunSPEC 4 is running, we would need constant information about SunSPEC 4's current performance in order to better decide the speed that we should be running at. For that, we would need sensors and microcontrollers to help us deliver the information from the SunSPEC 4 to the chase vehicle.

For a start, we looked at some of the market's most prominent microcontrollers, mainly the Arduino, Raspberry Pi and the Beaglebone.



Arduino UNO

Figure 1. Arduino MEGA board

The Arduino is a very popular microcontroller in the current market. It has a very big community, with many projects and tutorials online, making the Arduino very easy to familiarise with. The Arduino uses the C programming language, the language that most of our team members are familiar with, thus the time taken for us to learn about the Arduino was shorten by quite a fair amount.

The unique part of Arduino would be the Shields that are available on the market. The Shields are like add ons to the Arduino boards, adding to the functionality of the Arduino boards. This unique feature of Arduino enhances the Arduino's flexibility, making them extremely useful when we need the Arduino to perform various tasks that a normal microcontroller would not be capable of.



Raspberry Pi

The Raspberry Pi is a mini computer, with many capabilities. The Raspberry Pi does not need a computer for programming, as it takes care of that by receiving instructions directly from the user by allowing them to program through the connecting a monitor, keyboard and mouse.

Although the Raspberry Pi may appear good in the market, it is unsuitable for use in the SunSPEC 4, as it would require a output display when we want to make changes to the program, making troubleshooting very inconvenient. Also, the Raspberry Pi only possesses digital I/O ports, making it unsuitable for taking outputs from the sensors which would require analog ports from the microcontroller.



Beaglebone

The Beaglebone is a relatively new microcontroller. It is a microcontroller with a powerful processor and many different interfaces for connections, such as the CAN bus and SPI bus. With many I/O ports, it is capable of taking in many different inputs from the various sensors that we would have on the SunSPEC 4.

However, as the Beaglebone is relatively new to this market, there is not much information we can learn about the Beaglebone's programming and functions. Although the Beaglebone may be a very good microcontroller for the SunSPEC 4, we do not have much information to start working with it.

WEEK ONE: 20 Apr to 26 Apr 2015

Task 1: Familiarization with World Solar Challenge Rules and Regulations

As we're doing the electrical section of the solar car, we have to be familiar with the rules and regulations, especially on the electrical side. 

According to the WSC R&R, our gathered the following points that we thought is most important for us to keep in mind all the time.

In 2.19.1, any voltage higher than 60V must be isolated and protected by covers or protection grills that are reliably secured and marked with the approved high voltage symbol. 

This means that we must isolate battery and solar panels voltages.

In 2.19.6, exposed carbon fibre is considered to be an exposed conductive part and so must be isolated from the energy storage system and from the solar collector. 

Carbon fibre is also an RF shield. Thus, when attaching our modem for transmission of data, we must be extra careful with the carbon fibre.

In 2.20.3, all wires, connectors and electronics modules (such as MPPTs) which remain at high voltage when in Safe State must be double insulated.

Double isolation is necessary for solar panels and battery.

In 2.22.10, for Cruiser Class Solar EVs, if the energy storage system is a secondary electrochemical battery then the sum of the nominal cell masses, as specified and endorsed by the cell manufacturer and approved by the Chief Energy Scientist, may not exceed the following limits: 

• Li-ion 60.000 kg 

• Li-Polymer 60.000 kg 

• LiFePO4 120.000 kg.

Base on this rule, we can only configure the battery in 34S 36P. 

In 3.6.3, a warning sign not less than 900 mm x 300 mm with black lettering on a yellow background, clearly visible from a distance of 30 m, must be displayed on the rear of the Rear Escort Vehicle, stating "CAUTION: SOLAR VEHICLE AHEAD"

This is for the safety of our drivers and passenger 

Task 2: Understanding What Telemetry Is

Telemetry is the wireless transmission and reception of measured quantities for the purpose of remotely monitoring environment conditions or equipment parameters. There are two parts to telemetry: monitoring the performance of the car and planning race strategy. 

Monitoring the Performance of Solar Car

In order to monitor the performance of the car, several parameters are to be measured. During the actual race, the car will run from 8am to 5pm daily over the span of 6 days. We have to measure various parameters in order for us to plan and aim to complete the race. 

Measurements taken from Solar Panels, Battery, Motor and the System will be input into the microcontroller boards (e.g. Arduino MEGA / Beagle Bone etc.) After which, these information will be transmitted via a RF modem to the chase vehicle. A data logger will be required to keep all these data for any future reference. 

Planning of Race Strategy

Race strategy focus mainly on the energy management as our car has limited energy from solar panels and the batteries. The real time measurement attained from the solar car will be send to chase vehicle via RF transmission. The telemetry team in the chase vehicle will have to analyse the data and decide on the actions to be taken. For example, if the power consumption is too huge, we will advise the driver to slow down.

Referring to the road route and the route profile analysis from the 2013 challenge, planning can be done even before we are in Australia. 

Introduction to Telemetry

2015 World Solar Challenge will be held from 18 - 25 October. SunSPEC 4 is participating and in the progress of building. SunSPEC4 consists of electrical and mechanical systems. One of the electrical system is telemetry.

What is telemetry?
Telemetry is the wireless transmission and reception of measured quantities for the purposes of remote monitoring environmental conditions or equipment parameters.

Telemetry system is important in a solar car as it measures information of the car and transmits them to the team. Crucial and real time information can be obtained during the race, which allows us to come up with strategy to complete and the race. Monitoring of SunSPEC can also be done through telemetry.

Further updates on telemetry will be here soon!