BSquared White-Paper Series: Basic Dampers Analysis Part 1

Hi All,

In this series, we are going to discuss damper analysis with respect to driver’s inputs. It will give you a bigger picture on the behavior of your car as a whole.

Dampers are velocity dependent, meaning they work by resisting velocity of the strut, not the displacement of fluid. If you push a damper very slowly, it does not require that much force to compress the damper. However, if you try to push the damper very quickly, then a lot of force will be required.

To measure damper velocity, you need a linear potentiometer on each corner, as shown in Figure1. A linear potentiometer is a sensor that measures the change in distance of two points and translates that into an electrical signal. You must calibrate and validate the sensor to ensure that you will be getting accurate reading. We will discuss in-depth the best practices for mounting the sensors in future Bsquared articles. For now, let’s take a look at how to use damper data to characterise the vehicle.

Figure 1: Linear Potentiometer on Formula car

The damper position is an output parameter of the vehicle. The damper position is the result of:

1. The previous vehicle state.

2. Steering input.

3. Brake input.

4. Throttle input.

5. Clutch/gear input.

6. Ambient conditions.

7. Road input.

8. More...

Damper potentiometer data is not often observed during the track day. Due to the complexity of damper analysis, there are better things the drivers and engineers could be doing to yield better and quicker improvements. That being said, experienced drivers and engineers are easily able to detect damper or grip anomalies during the session/stint. For example, they would come off a hot lap and know immediately that their car loses grip in Turn X during corner entry specifically because of the damper setting. Subsequently, they would focus on analyzing the data for the problem section in Turn X. For those of us who are not aliens and can’t detect damper anomalies while driving, the best way to analyze the data is to look at the points of a heavy braking event, throttle, and steering input. A combination of observing the damper data and experimentation will over time make you as a driver be able to detect even small changes in the dampers.

Let us now analyze some sample data below. Figure 2 shows the typical raw data from a working potentiometer. First step to understanding the data is to apply a low pass filter to split the low and high frequencies (basically meaning, just the important data curves remain). Dampers oscillate due to body movements and road vibrations. Body movements create low frequency movements in the dampers and road vibrations create high frequency movements in the dampers. Typically, the low pass filter frequency can be 1 Hz which is acceptable for most race car applications (think of the frequency at which body roll/pitch occurs).

Figure 2: Potentiometer raw data from all 4 corners

Figure 3: Filtered data with 1Hz low pass filter

As seen in Figure 3, Damper FL/FR low speed (the top two graphs) shows damper movement with frequency less than 1Hz. Damper FL/FR high speed (the bottom two graphs) shows damper movement with frequency more than 1Hz.

This means that the first two graphs are low speed damper movements such as body roll, pitch, and heave. The last two graphs are high speed damper movements such as curb, road undulations, wheel hop, etc.

This data was obtained from Assetto Corsa data at Silverstone. The techniques that we will use will not only work in real life but can be practiced in simulation. We will analyze one section of the track which is turn 3-5 in Silverstone, shown in Figure 4. This section is chosen because our data shows oscillatory braking motion combined with erratic throttle application.

Figure 4: Silverstone track.

Figure 5: Driver's input at turn 3 to turn 5.

In Figure 5, we can see the three graphs on the bottom are vehicle inputs (throttle, brakes, steering angle) and the top four are the damper data. The cursor position on the top section is located at the point at which the FL damper was at peak compression. The corresponding vehicle input that caused that compression is shown at the cursor position of the bottom section of Figure 5. What does this mean? Well we can see the driver has already been braking for quite some time before the FL peaks in compression. The front weight transfer from braking took some time to develop. Ideally you want the load transfer to develop instantaneously with zero oscillation when you press the brake pedal. However, in the real world, this lag is typical, especially in production vehicles. In a racing application, the driver may prefer a more instantaneous response. The information from Figure 5 may help us guide our driver-engineer conversation to fine tune the dampers to optimize grip and handling.

If you are a professional racing team, you will have a lap time simulation with a validated dampers model to determine the optimal target. For most of us with no access to hundreds of engineers, the only solution is to experiment. The takeaway from figure 5 could be to try decreasing/increasing the damping speed and observe if this timing difference decreases/increases. Observe how you, as a driver, feel when the damping is different and check it against the lap time. Perhaps, you will not feel a difference, but the lap time improves. Do not fall victim to confirmation bias during experimentation.

As well in Figure 5, you can see the brake pedal oscillation on brake release points. These oscillations will contribute to poor grip development and may cause further problems when at the limit of the vehicle. The driver here should be told to practice being smooth with the heel and toe technique before moving on to any advanced damper analysis.

The biggest takeaways from the analysis done so far are:

1. The driver’s braking application is not smooth thus it induces load variation among 4 dampers during a braking event.

2. There seems to be a time delay in front compression to the driver’s input.

With the above two observations, the biggest gain in lap time can be achieved by applying a smooth and gradual brake release. Adjusting damping with inconsistent braking inputs will result in even more unpredictable vehicle behavior that may hurt your overall lap time.

The intention of this paper is to display some of the basics of looking at damper data. Remember, the damper’s job is to control loading speed - that’s all. So when evaluating damper data, take a look at how quickly the damper reacts to your inputs. Take caution when making changes to your damper to correct an issue in one corner, as that change may not improve the performance of the vehicle in other corners of the track - you may even introduce new unwanted behavior in other corners too. As always, make sure the driver is consistent first, before moving on to damper analysis.

We will further discuss damper potentiometers in Part 2, so stay tuned and shoot us a message at info@b-squared.io for questions or comments.

If you want to learn more about dampers and also how to use data acquisition to become faster in a safe and efficient way, send us an email or book a strategy session. We are now accepting applications to our next batch of students, don’t delay!

BSQUARED TEAM #drivebetterbebetter