Dan's Vehicle Dynamics Corner - The importance of motion ratios

Summary

In this episode of Dan's Vehicle Dynamics Corner, Director Danny Nowlan emphasizes the critical yet often overlooked role of motion ratios in racecar setup and vehicle modeling. He explains how motion ratios, the ratio of damper to wheel movement, directly impact the spring rate perceived by the tires. Nowlan demonstrates practical methods for measuring motion ratios, including using a car jack and verniers, and highlights the importance of plotting wheel movement over damper displacement. He also discusses the implications of accurate motion ratios for simulations and lateral load transfer distributions, ultimately stressing that correct motion ratios are essential for optimal vehicle performance.

Takeaways

• 🏎️ The importance of motion ratios in vehicle dynamics, particularly in racecar setup, cannot be overstated as they are crucial for getting the setup correct.
• 🔍 Motion ratios are often overlooked but are a critical element in vehicle modeling and should be kept in mind for optimal performance.
• 📉 The motion ratio is defined as the ratio of damper movement to wheel movement, which impacts the spring rate that the tire sees.
• 👨‍🔧 To deduce motion ratios, one should plot wheel movement over damper movement from full droop to full bump to understand the vehicle's dynamics.
• 🛠️ Practical methods for measuring motion ratios include using a car-jack and a table with a level next to the tire for open wheelers and adding a pipe extension on the wheel nut for touring cars.
• 📏 Tools like Verniers are used for plotting wheel movement on damper displacement, providing a direct way to measure motion ratios.
• 🤖 Kinematic programs such as WinGeo and SusProg can calculate motion ratios, but manual measurement is recommended to catch any discrepancies.
• 📊 Approximation formulas can provide a quick estimate for motion ratios, such as using the pickup point to pivot length ratio for lower arms and the contact patch to instant center length.
• 📈 Plotting motion ratios on the fly can help quickly identify mistakes and ensure that the vehicle's setup is on track.
• 📝 An Excel spreadsheet can be used to document motion ratio data, which is useful for comparing actual and simulated vehicle dynamics.
• 📉 Accurate motion ratios are indicated by a linear graph and a close correlation between instant roll and pitch in vehicle dynamics simulations.

Q & A

Who is the speaker in the video script?

The speaker in the video script is Danny Nowlan, the Director of ChassisSim Technologies.

What is the main topic of discussion in this episode of Dan's Vehicle Dynamics Corner?

The main topic of discussion in this episode is the importance of motion ratios in racecar setup and vehicle modeling.

Why are motion ratios considered critical in racecar setup according to the speaker?

Motion ratios are critical in racecar setup because getting them right can significantly impact the vehicle's performance, making everything fall into place more effectively.

What is the formula that relates wheel rate to motion ratio and spring rate?

The formula that relates wheel rate to motion ratio and spring rate is wheel rate = motion ratio squared times spring rate.

How can one measure motion ratios in practice?

Motion ratios can be measured in practice by plotting wheel movement over damper movement from full droop to full bump, using tools like a car-jack, a table for leveling, and Verniers for precise measurement.

What is the purpose of using a table and Verniers in measuring motion ratios?

The purpose of using a table and Verniers is to provide a fixed level and precise measurement of how the wheel moves up and down, which helps in plotting wheel movement over damper displacement.

What are some software programs mentioned that can calculate motion ratios?

The software programs mentioned that can calculate motion ratios are WinGeo and SusProg.

Why does the speaker advocate for measuring motion ratios even when software like WinGeo and SusProg are available?

The speaker advocates for measuring motion ratios manually because there might be a one in a hundred case where the software could be incorrect, and manual measurement can catch such discrepancies.

What is the formula provided for motion ratio approximation in a push rod operated open wheeler arrangement?

The formula provided for motion ratio approximation in a push rod operated open wheeler arrangement is motion ratio = A on B multiplied by sine theta, where A on B is the ratio of the length from the end of the lower pickup point to the instance center, and theta is the angle of the push rods.

How does the speaker suggest verifying the correctness of motion ratios?

The speaker suggests verifying the correctness of motion ratios by comparing the simulated data with the actual data, particularly looking for instant roll and pitch correlation and ensuring there are no massive discrepancies between the two.

What implications does getting motion ratios right have on a vehicle's performance and simulation?

Getting motion ratios right has implications for both the vehicle's performance and simulation accuracy. It helps in understanding the car's behavior, affects lateral load transfer distributions, and improves the reliability of simulations for setup adjustments.