newsletter May 2019
All systems go Text: Martin Berger Photo: Erik Brettingen Johansen
On the unveiling, our race cars looked finished, but there were still some not so noticeable things left to do for our members. On highly technological race cars there are a lot of systems both electrical and mechanical. All of these have to work in concert and it is a complex and time-consuming task to make them do so. This has to be done before the race car can zip around on a track with breakneck-acceleration. During the month of May, these systems have been worked on and the car has been tested to validate that everything works as it should. The complex systems also have to be documented. What was the reason for choosing to create the system in that way; what are the positives and what are the negatives concerning the respected system? There are at least two good reasons for doing so. The first is that there is a part of the competition called Engineering Design. This is where we tell the judges about the race car and have to give reasons for why we have made the design choices we have. For example, why did we choose that number of battery cells or why did we choose that layup for molding the carbon fibre parts? This always has to be backed up by tests showing that the design choice chosen is the best of the ones we have looked into.
The second reason is that good documentation ensures that the next team has a good foundation to start from. Ensuring progress by making sure they know where the potential for improvement is. One example from this year is the tests performed on the crash box. We ran some tests on an experimental design. These were promising and they give next years team the possibility of working on this design even though we do not have the time to implement it into Nova. In the end, the systems have been finished, checked and documented. We are very excited about the coming month and the time leading up to the competitions. Because we have all systems go and are ready to drive!
Sensors on Nova Text: Marius Hamre Nordrik, Martin Palm, Viktor Korsnes, Erik Brettingen Johansen, Odin Aleksander Severinsen & Bo Willem Woelfert Photo: Ă˜yvind Storvik Ingebrigtsen & Martin Berger, Illustration: Bo Willem Woelfert
IMU (Inertial measurement unit) Nova has an Inertial Measurement Unit mounted at each wheel. The units are of the type STIM300 which we received from Sensonor. The IMUs provide measurements of acceleration, and rotational velocity in three-axis, which allows us to accurately estimate the forces acting on each wheel and the resulting motion. The estimates are used to utilize the grip in the tire through our control systems and to better understand how our suspension behaves.
INS (Inertial navigation system) The INS unit is a VN-300 provided by Vectornav, it is a light package, perfect for race car applications. It is used to get accurate positions of the car as well as the heading. This is done by utilizing its dual GPS system. The position and velocity measurements are heavily used to analyze the performance of the car, and the heading and its derivatives is used by the control systems on the car to help the driver through corners by the use of torque vectoring.
Pressure cells on the brake pedal The pressure cells on the brake pedal measures the pedal force. We use the data for mapping the Kinetic Energy Recovery System (KERS). Our car has two separate braking systems; a hydraulic system and a KERS. KERS turns the electric motors into generators, both
charging the battery and slowing down the car. The load cell from FUTEK lets us make these systems function as one, so that the driver is confident in the brakes. By directly mapping KERS to the pedal force we can charge the battery during normal braking, and engage the hydraulic system for harder braking, and keep a smooth transition between the two.
Linear potmeter The linear potmeters we received from Arrow measures the linear distance the spring in the suspension system has been compressed. It is also used on the accelerator pedal, to measure how much acceleration the driver wants. The measurement gives an inkling to the forces acting on the wheel. However, as
the forces are absorbed in different places, such as the rubber on the wheel. The data is used for both analyzing the car, and the torque allocating algorithm to give optimal torque for each wheel at all times.
Temperature measurements A lot of systems on the car are dependent on temperature in some way or another. You can read about some of them on the next page. Brake disc: The brake disc is a critical component that is exposed to many risks. To make sure the brake disc is not overheating we have to track the temperature. In addition, the different temperature gradients can indicate whether the disc is in the right position or not. If the position of the disc is just slightly off, the fast rotation and the forces exerted can quickly lead to material failure. Tire temperature: Each tire is monitored by a sensor, which measures the temperature across the width of the tire surface. The distribution and amount of temperature can be used to tune our suspension and dampers to make sure that we keep the tire within the operating limits and don’t cause excessive wear on the inner or outer sections. Gearbox oil: Inside the upright, we have placed sensors to keep track of temperature changes. The main reason to do this is to make sure the gearbox is functioning properly. In case there are big temperature increases, it could indicate that there is something wrong with the gearbox, and we will be able to take action before it ruins too much. Cooling system: There are four sensors on our car to track the temperature of our cooling system. They are situated right before and after the radiators, which means we can measure the temperature of the fluid and how well our radiators are working. Too high temperatures of the fluid means increased chances of overheating.
Battery cells: This is the system with the highest consequences of overheating. It is therefore critical that we have complete, real-time information of the temperatures in each cell of the battery.
Current measurements
Accumulator: The DC current from the accumulator, which is the battery of the car, is measured by the onboard battery monitoring system, called AMS, with a Hall effect current sensor. This data is used to calculate the energy consumed and recovered during a race in order to iterate on the energy required for later seasons. In addition, it is being used to protect the cells from overcharge and -discharge.
Inverter: Each inverter has two PCB mounted Hall effect current sensors that measure two of the three phase currents used to control a motor, where the last phase is calculated with Kirchhoff ’s current law, as the motor is a closed circuit. The current measurement is used in the internal motor control algorithm, as the RMS of the AC current delivered to a motor is proportional to the torque outputted by the motor.
calculate the angle of the front wheels. This data is absolutely essential for our torquevectoring, as the algorithm needs to know what the driver wants from the car to be able to improve its performance. The data is also a core part of how we analyze the performance of the car to both mechanically tune it for optimal running, and what we use to create a new and improved suspension design each year.
Other Sensors
Tire pressure: With one wireless tire pressure sensor mounted inside each rim, we are able to predict the tire performance with much higher accuracy. The pressure decides how well the tire performs along straights and during cornering and influences how the heat buildup of the tire behaves. Thanks to our sponsor el-watch, the sensors are as light as possible and adapted to our very specific requirements.
Steering wheel position: The steering system is equipped with two high-resolution halleffect sensors. These measures the rotation of the steering wheel, which we can use to
Ride height: Four ride-height sensors from Panasonic, one mounted in each wheel, measure how far the wheel is from the ground. With this information, we can calculate how much the tire is squished. This data is used to estimate the forces in the tire and helps us improve the accuracy of the torque vectoring. In combination with the damper position measurements, we know what the position of the monocoque and suspension is in relation to the racetrack. With this knowledge, we can more precisely predict how the suspension and aerodynamics are performing.
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