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VIEWS

Workshop 5- How to validate your FSAE racing car?

Speaker I Ping, Huang and Pai-Chen, Chien

Editor I Yi-Shan, Hsiao

Posting time: Apr. 09 2024

Speaker Introduction

 

Huang Ping

Currently working as Performance Systems Integration Engineer at General Motors, and also serving as a FST judge. Expert in sports car system integration and racetrack simulation.

 

 

 

Jian Baichen

Currently studying at the Department of Electrical and Electronic Engineering of Imperial College of Technology, and serving as a design reviewer for the FST mechanical group. Proficient in vehicle dynamics and automatic control. Served as the head of the chassis group and the person in charge of the design report of the Taipei University of Technology team in 2019.

Part 1. How to certify your Formula Student car?

Why verify?

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  1. Verify whether the car meets the design target

  2. Verify that the vehicle meets the requirements set initially

  3. Verify that the car's results match the initial simulation

Before vehicle certification - do a safety check first

Regardless of the type of testing and simulation performed, vehicle safety must be ensured first. This includes the following points:

  1. Confirm that the switch function of the large power is normal

  2. Make sure the tire is firmly fixed

  3. Make sure all parts are secure

  4. Make sure the driver is wearing qualified safety equipment, including helmets, seat belts, racing suits, etc. Ensure compliance with FSAE and FIA regulations and never use expired equipment

Longitudinal dynamics validation: straight-line braking, straight-line acceleration and coasting

Straight-line dynamic verification items include straight-line braking (Deceleration, straight-line braking), acceleration (Acceleration, straight-line launch) and coasting. Coasting is the most important verification item in the mass production stage, but it is not a key item in FSAE .

How do I verify my brake system?

Straight-line braking is usually tested in three categories. Braking performance indirectly determines the performance of the vehicle on the track:

I. Test the maximum value of the braking G value (gravity acceleration).

II. Test the brake stability. Test whether the car is stable and whether the rear end will swing when the brakes are applied hard. Braking stability determines how fast the driver can drive on the track. An unstable braking system will result in an inability to increase speed on the track.

III. During the tire lock test, the following data can be collected for further analysis:

  • Cylinder pressure : How high does the tire pressure have to be before it locks?

  • Tire pressure : monitors the overall pressure during braking and observes changes in tire pressure during heavy braking.

  • Ambient temperature : Record the temperature on the day of the test and compare it with the temperature on the day of the competition. Because tire pressure changes with temperature, if the test is conducted in February or March when the weather is colder, and the competition is in July or August, the data from the test may not be applicable to the situation during the competition, and may even bring unexpected results. In this case, if the settings used during the test are still used during the competition, the results may not be as expected.

  • Wheel speed / vehicle speed : Record the best wheel speed slip ratio %.

  • Ride height : Observe the height of the vehicle when braking. Does the front axle touch the floor when braking? If it touches the floor, it does not meet the competition rules.

How to verify the acceleration system?

Straight-line launch is a common test item with the following three categories. The performance of the acceleration also indirectly determines the performance of the vehicle on the track:

I. Test the maximum G value during acceleration.

II. Test the acceleration stability. Is there any stability problem when the accelerator is fully pressed and the car accelerates at full speed? Does the rear end of the car sway? Does the steering wheel pull?

III. Test the wheel slip condition. If there is a wheel speed sensor, the maximum slip condition can be recorded. During the test, the following data can also be collected for further analysis:

  • Tire pressure : Observe the changes in tire pressure during acceleration.

  • Ambient temperature : Record the temperature on the day of the test and compare it with the temperature during the competition

  • Wheel speed/vehicle speed

  • Wheel hop/vibration : Observe whether there is wheel hop when the accelerator is depressed to the bottom. In severe cases, the drive shaft may break due to vibration. This should be avoided.

  • Powertrain torque request : Observe whether the motor provides the expected power when the accelerator is fully pressed. For example, in some cases, the motor can reach a maximum of 400 Newton meters (Nm), but when the accelerator is fully pressed, it is only mapped to half, 200 Newton meters (Nm).

  • Ride height : When accelerating, be careful not to let the rear axle touch the floor

Lateral Dynamics Validation

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I. Constant steer ramping at different speeds

At a specific speed, or at different speeds, slowly turn the steering wheel, for example, one degree per second or two degrees per second, keeping the steering rate consistent (such as one degree per second or two degrees per second). Such a test can produce interesting data, such as:

  • Understeer Gradient (RWA vs Ay) : The Y-axis is the average steering angle of the two front wheels, and the X-axis is the lateral acceleration.

  • Roll Gradient (Roll Angle vs Ay) : The Y axis is the lateral rolling angle, and the X axis is the lateral acceleration.

  • Understeer Angle (UA vs Ay) : The Y axis is the understeer angle, and the X axis is the lateral acceleration.

  • Steering Sensitivity (SWA vs Ay) : The Y axis is the lateral acceleration, and the X axis is the steering wheel angle.

(For detailed instructions, please see the video at 17:15)

II. Cone Test (Slalom)

III. Timed Test (Autocross)

Part 2. FSAE dynamic simulation introduction and examples

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There are two main types of simulation software widely used in FSAE competitions: CarSim and CarMaker. The former is widely used in the United States and Japan, while the latter is mainstream in Europe. Seniors shared that since the logic between the two is similar and the models can be converted to each other, it is impossible to judge which one is better. Subjectively, I think CarSim's user interface is more user-friendly, but on the other hand, CarMaker provides free use rights for FSAE teams.

Why use commercial simulation software? What are the advantages and disadvantages? The following uses CarSim as an example.

Advantage 1: Convenient, time-saving, and error-reducing

The advantage of using commercial software is that it can save a lot of modeling time and reduce the chance of errors. The software has built-in FSAE sample vehicles with hundreds of degrees of freedom in parameters. If you manually write code in the development environment, it will be very easy to make mistakes and time-consuming.

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Advantage 2: Can simulate race tracks and roads

The FSAE program built into CarSim can simulate different working conditions and tracks, but the simulation of tracks and roads is more difficult to complete manually in a self-developed environment.

Advantage 3: FSAE Example

Several FSAE project examples are included with CarSim, along with a simple user interface for easy setup adjustments.

Advantage 4: Supports integration with external software

For example, you can connect CarSim with a control method written in Simulink to perform a joint simulation.

What are the disadvantages of using a commercial simulator?

Commercial software cannot directly set up some special suspension systems or special mechanisms that are not commonly found on vehicles. In addition, CarSim and CarMaker are not the strongest simulators when it comes to laptime optimization, so they are relatively weak in this regard.

CarSim modeling example of the sixth generation car of the National Tsing Hua University Racing Factory

In this section, the senior uses NTHU06, the car of the 2022 German race of National Tsinghua University, as an example to introduce how to set vehicle parameters in CarSim and provide suggestions on how to obtain parameters. At the same time, the impact of each parameter on the entire vehicle is also discussed.

Vehicle configuration and key parameters (For more details, please refer to the wonderful introduction in the video!)

  1. Mass Property

  2. Aerodynamic

  3. Powertrain

  4. Suspension

  5. Steering and Brake

  6. Tire Model


CarSim simulation includes Skidpad, Autocross, and Endurance

Please see the video at 00:54:03


Q&A Session

How to verify the authenticity of the simulation? See the video at 01:08:32

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