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Developing a Telemetry System for a Solar Car

"We chose CompactRIO because it combines real-time data acquisition oncustomizable input channels and can record and transmit data."- Neo Wei Ren, School of Mechanical Engineering, Nanyang Technological University

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Author(s):Neo Wei Ren - School of Mechanical Engineering, Nanyang Technological University

The World Solar Challenge is a biannual competition where universities from around the world design and build fullysolar-powered vehicles that can travel 3,000 km across Australia at average speeds of more than 80 km/h. The aim of thiscompetition is to promote research for sustainable transportation. Key areas of interest are aerodynamics, solar conversionratio, battery technology, low-rolling resistance tires, and electric hub motors. A well-planned race strategy is also pivotal towhether the solar car can survive the full distance of the journey across Australian terrain.

The Purpose of TelemetryThe World Solar Challenge is different from other solar car competitions because it requires the team to travel 3,000 km fromDarwin to Adelaide, Australia, which means that a problem could arise that determines whether the solar car completes thejourney. Using the CompactRIO configurable chassis and NI LabVIEW software, we developed a telemetry system to monitor,log, and transmit data reflecting the real-time health of the solar cells and batteries (Figure 1). The real-time data helps thesupport team develop an optimized race strategy and reduces troubleshooting time because the monitored data triggers alarmsto prevent problems before they arise. The drivers actions can also be monitored and logged to perform postrace analysis.

Our FocusEven though the solar car produces mechanical and electrical data for collection and analysis, our primary focus for building ourvehicle was the electronics because they were the determining factors for completing the race. We used the data collected fromthe battery and solar cells in the design process to battery size and performance curves. Real-time data collected during roadruns helped us optimize the performance of the vehicle and compare how different the actual specifications of the car were fromthe design specifications. Also, our race strategy team used the data to calculate the optimum travel speed with reference to theweather forecasts. We logged all the data in the CompactRIO built-in memory for postrace analysis to improve future projects.

Using CompactRIO with a Reconfigurable ChassisWe chose because it combines real-time data acquisition on customizable input channels and can record andCompactRIOtransmit data. The NI 8-slot chassis allows can be customized with the modules that cater to our unique monitoringcRIO-9104needs. With the range of NI modules we could adapt our chassis as the project progressed and we focused on different aspectsof our solar car. The onboard memory and multiple I/O types on the NI real-time controller provide flexibility of thecRIO-9014interface and secondary data storage.

Our customized chassis includes an to provide real-time vehicle position; an serial interfaceSEA cRIO-GPS+ module NI 9870module to capture data from our battery monitoring system, which has a RS232 interface; an NI 9401 digital I/O module tocapture vehicle speed from the motor controller terminals and data output; four analog I/O modules for monitoring theNI 9219throttle, brakes, currents, and voltages of the solar array; and an thermocouple module for temperature sensing aroundNI 9211the vehicle. We used an NI 9219 universal analog I/O module to monitor multiple data types including voltages, currents,temperature, and resistance with high accuracy and resolution.

Programming with the LabVIEW FPGA ModuleWe quickly and easily programmed the system using the . Also, the express VIs provided shortcuts forLabVIEW FPGA Moduleusers to quickly change the program to suit their needs. In addition, we ran our program at start up of the CompactRIOcontroller, which made the whole system wireless, eliminating the need to connect to the system to manually start the programprior to the race. Our team had limited programming experience, but the intuitive graphical icons and wires that resemble aflowchart made programming fast and fun for a team of amateurs. With the field-programming gate array (FPGA) programmingmode, we integrated all eight modules, because not all of the modules can be used in CompactRIO Scan Mode. We viewed allthe collected data in real time in the chase car and optimized our race strategy according to a formulated program (Figure 2).\

The Challenge:Developing a low-power, real-time monitoring system for a solar car traveling 3,000 km in the World Solar Challenge to monitor thehealth of the vehicle and help optimize our race strategy.

The Solution:Using an NI CompactRIO controller and an 8-slot chassis to monitor the voltage, current, temperature, and speed of the vehicle andtransmitting this information wirelessly using a 2.4 GHz modem to a chase vehicle following the solar car.

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Figure 2. Real-Time Data as Seen on Chase Car

Our ApplicationIn the design phase of the project, we used the CompactRIO controller to record the performance of the solar cells to developthe performance curve of the cells in different weather conditions. We hooked the batteries up to the system to determine theirdischarge curves at different temperatures, and monitored the actions of the drivers for each test run so the support team coulddetermine if they were performing the correct actions.

Because the vehicle is completely solar-powered, we minimized the use of power in our electronics and directed the main bulkof power to the motor to complete the race. The customized 8-slot chassis captured data such as GPS, battery information,solar cell condition, motor performance, and driver actions. We recorded all the data in the 2 GB onboard memory in thecRIO-9014 real-time controller. Simultaneously, we formatted the same data to a text string using LabVIEW VIs and sent itusing a low-power 2.4 GHz radio modem to a chase vehicle behind the solar car (Figure 3).

Figure 3. Block Diagram of Our Telemetry System

This provides ample storage in the real-time controller and the laptop in the chase car. In the chase car, the race strategy teamanalyzed the collected data and determined the speed to travel with reference to external factors such as the road, driver, andweather conditions.

After each road test, we analyzed the data and fine tuned the mechanical components of the solar car such as adjusting thewheel chamber, steering sensitivity, suspension, and tire pressure to improve the performance of the vehicle. With LabVIEW,we simulated the different weather conditions we may encounter in Australia so we could better gauge the level of power oursolar array could provide. Also, we will conduct postrace analysis using the recorded data to make improvements to future solarcars.

ConclusionBecause this project was the first time we used a real-time monitoring system, we were initially unsure of what our main focuswould be because there are many areas in a solar car that we can acquire data from. As the project progressed, we usedCompactRIO for the race and design phase of the project to chart the battery discharge rates at various temperatures and todetermine the performance of our homemade solar array. It benefited our team in all phases of our project from design to theactual race to postrace analysis. We successfully used CompactRIO to develop a monitoring system for our solar-poweredvehicle, and plan to reuse the same chassis and controller as we carry out more solar projects in the future.

Author Information:Neo Wei RenSchool of Mechanical Engineering, Nanyang Technological University

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Figure 1. Using CompactRIO during Testing of Our Solar Vehicle

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