Solar Speed: Stanford University Solar Car Races Coast-to-Coast Down Under

IRVINE, Calif. – FUTEK Advanced Sensor Technology, Inc. – As a group of eager Stanford students awaited the announcement that would detail this year’s engineering challenge, chatter among the group predicted that 2013 would be most formidable to date. And, being some of the best and brightest, it should come as no surprise that they were correct.

The mission they were given was to design, build, and pilot a racecar that could compete against some of the top racing teams on Earth. Not only must this vehicle survive, but it would have to win a transcontinental endurance race straight through the heart of the Australian Outback. And, there was the kicker: their racecar would have to complete the entire 1850 mile voyage on less than one gallon of gas.

Surprisingly, this absurd fuel restriction was the only part of the challenge that did not raise an eyebrow. It was actually expected. Because these students are the Stanford Solar Car Project (SSCP) and their mission is the 2013 World Solar Challenge. And everyone in this contest knows that being the fastest without a drop of gasoline is the only path to victory.

An important distinction between a solar racecar and conventional automobiles is that a solar racecar stores its potential energy electrically. This allows sunlight to be converted into mechanical energy in real time. The energy used by an internal combustion engine does begin and end in the same forms but, since the potential energy is stored chemically, the conversion process takes hundreds of millions of years.

With just a glance, the extreme speed at which a solar racecar transacts this process becomes immediately obvious. While an ordinary racecar can be littered with corporate exclamations, Xenith, the SSCP’s 2013 racecar, wears only a dark cloak of photovoltaic panels. Since the energy input to this system is its primary limitation, painstaking strategy insures that the distribution of these panels will maximize the amount of sunlight that is converted into electrical energy.

Electrical energy generated by the panels is pumped directly into an array of high tech lithium batteries. These batteries are a necessary intermediary between the solar panels and the drivetrain because they condition the power before consumption by the motor. Obviously, the batteries are also double as an energy reservoir so racing can continue under overcast skies and into the night.

The process is complete when the motor transforms electrical energy from the batteries into mechanical energy. For any racecar in this contest to be a true competitor, it is crucial that this stage be executed with perfect refinement. The torque and power output of the motor must be maximized without squandering a blink of its precious energy allowance.

The SSCP set out to make the motor within Xenith the most powerful and efficient to date. And, based on models and simulations, it appeared their new design showed promise to deliver. But, theory alone cannot satisfy a team that is hungry for a win- this critical component would need to prove itself empirically. Only through direct measurement could the team refine the acceleration, speed, and energy economy Xenith would ultimately command on race day.

In practice, effectively characterizing the performance of a motor turns out to be a particularly challenging measurement application. This is in part due to the dimensions at play having complex relationships: rotational frequency is the independent variable of this system; toque and power are both nonlinear functions of rotational frequency but independent of each other. Another complexity of this test is that the motor must be securely situated so that the crankshaft is able to rotate indefinitely while being subjected to variable opposing loads.

To emulate what the motor will be subjected to on race day, a test system called a dynamometer (aka dyno) is used. Generally speaking, a dyno consists of three basic components: a test stand, an energy absorber, and measurement instrumentation. The test stand securely situates the motor during testing and dampens vibrational modes. The energy absorber applies opposing loads to the crankshaft, approximating what the motor is subjected to when in service. And the measurement instrumentation must capture useful data during the test so it can be analyzed.

The SSCP team wanted to add a clever twist to their dyno: implement one of Xenith’s regenerative breaks as its energy absorber. This setup would allow them to simultaneously study the efficiency of their regenerative breaking system while testing their motor. But it was unclear if such an improvisation could be made to this standard. To gain perspective on if this approach could be realized, the SSCP Team called on the experts at FUTEK Advanced Sensor Technology.

Consulting with Solution Engineers at FUTEK made it clear that their dyno would need a TRS605 Rotary Torque Sensor as the center of its measurement system. The TRS Series sensor integrates a rotary encoder with a freely spinning torque transducer; this single compact device can satisfy what would have otherwise required multiple sensors. The TRS605 could then be situated directly between the motor’s crankshaft and the regenerative brake allowing the both torque and displacement measurements to be simultaneously captured by a single sensor.

Signals from the TRS605 sensor would need to be converted into data for analysis; for this, the FUTEK instrumentation portfolio brought several compelling options. The IHH500 Elite digital handheld display is always a contender in rotary torque applications because of its durability, portability, and outstanding performance specifications. Using the USB320 and USB410 USB modules in concert would give the measurement system Plug-N-Play PC connectivity at an aggressive price point. Or, the groundbreaking USB520 module has redefined possibility by allowing both the torque and angular displacement channels to stream into a computer though a single USB port. In terms of performance, the USB520 module takes everything that is legitimately impressive about a USB320 / USB410 system and cranks it up to eleven.

Test data would then need to be graphed and analyzed so that the complex relationships among the measurement parameters could be studied and fully understood. Naturally, the entire FUTEK instrumentation portfolio offers seamless compatibility with the powerful SENSIT™ Test and Measurement Software platform so that data to be logged, graphed, analyzed, and reported with ease and flexibility. And, although sensors themselves can only measure basic dimensions such as the torque and angular displacement of a crankshaft, SENSIT can automatically determine and graph derived parameters such as power (HP) and rotational frequency (RPM).

By implementing a powerful measurement solution from FUTEK, the SSCP used their innovative dyno concept to push Xenith’s drivetrain beyond its original performance targets. Now, it is just a matter of time before the world will know if Xenith can distinguish itself from some very stiff competition and earn the SSCP a view from the podium when 2013 World Solar Challenge concludes….

FUTEK is delighted that our advanced sensor technology continues to assist the world’s leading minds in progressing the world’s leading technologies. We believe bold endeavors like the SSCP that navigate along the bleeding edge of technology are necessary precursors to the breakthroughs of tomorrow and beyond. Regardless of if the mission is across the bottom of sea, deserts of the Outback, or deserts of the Moon, FUTEK is proud to play a part in this ongoing human enterprise.