[authors: David Danaher, Sean McDonough, Drew Donaldson, and Reece Cochran]

Abstract

Technology is ever advancing in the world around us, and it is no different when it comes to data acquisition systems used in accident reconstruction. In 2016, the SAE publication, “Data Acquisition Using Smart Phone Applications,” Neale et al. evaluated the accuracy of basic fitness applications in tracking position within the smart phone itself [1]. In 2018, a follow up publication, “Mid-Range Data Acquisition Units Using GPS and Accelerometers,” tested the Harry’s Lap Timer™ application for use in smart phones and compared the data to the Race Logic VBOX [2]. In this paper, another data acquisition system, the MoTeC C185, was tested. The MoTeC C185 data logger contains an internal 3-axis accelerometer and was also equipped with an external Syvecs 50Hz GPS Module with 6-axis accelerometer. A test vehicle was instrumented with the MoTeC C185, Race Logic VBOX, and Harry’s Lap Timer™. Data collected by the MoTeC C185 was then compared to data collected by the other acquisition systems to validate the capabilities of the MoTeC C185. The purpose of this paper is to validate the MoTeC data acquisition system to provide an alternative for use in the field of accident reconstruction.

Introduction

MoTeC designs and manufactures many devices for the automotive industry including engine management systems, dash displays, data loggers, accident recorders, and more. MoTeC devices are often used for data acquisition and engine management on performance-oriented vehicles and in automotive racing environments. The MoTeC C185 utilized in this testing has a customizable full color display which enables the user to clearly see live data, logging status, and more. The MoTeC C185 can be configured and upgraded to fit the needs of the user. The method of obtaining position, distance, speed, and acceleration data utilizing a MoTeC C185 data logging display is advantageous because the device is compatible with numerous sensors, cameras, potentiometers, and other devices.

In previous testing, Neale et al. examined data collected by accessing built in GPS receivers in smart phones running commonly available applications, which was then compared to the Race Logic VBOX VB20SL3 [1]. The testing concluded that smart phone applications would track velocity, elevation, and position reasonably well during situations with non-abrupt changes in vehicle position and velocity. Due to the low sampling rate (1 Hz), error occurred in scenarios with rapid changes in velocity.

Additional testing performed by McDonough et al. compared data collected using a smart phone running the Harry’s Lap Timer™ application [2]. The application allows for the pairing of third-party GPS receivers. For the testing, a Dual SkyPro GPS model XGPS160 was paired to the smart phone, with a sample rate of 10 Hz. [4]. The research concluded that data recorded by Harry’s Lap Timer™ correlated well with data collected by the VBOX for various testing maneuvers. As with the smart phone internal GPS receiver tests, data collected by Harry’s Lap Timer™ using the 10Hz Dual SkyPro GPS XGPS160 slightly underreported peak accelerations during abrupt maneuvers such as a swerve.

This paper evaluates the MoTeC C185 professional data logger by comparing data collected by the MoTeC with data collected by Harry’s Lap Timer™ and the Race logic VBOX. The paper then analyzes the reliability and validity of the data logger configured with a Syvecs 50Hz GPS Module to accurately

report speed and acceleration. Seven tests were performed where data was simultaneously collected with each data acquisition system and compared. These tests are designed to evaluate the use of the MoTeC C185 and comparable data loggers for accident reconstruction purposes, and thus include a variety of vehicle maneuvers such as steady acceleration and braking, slow speed turns, high speed turns, hard acceleration, and hard braking. These maneuvers were tested over both short and long durations.

The MoTeC C185 data logger and Syvecs accelerometer were set up in parallel with Harry’s Lap Timer™ and the VBOX in each test. The VBOX was chosen as the control for this testing due to its use in the automotive industry and in vehicular accident reconstruction. Furthermore, the VBOX is specifically designed to monitor and record vehicle movement [5].

Harry’s Lap Timer™: Features and Data Acquisition

Harry’s Lap Timer™ has four different versions: Rookie Edition, Petrolhead Edition, ToGo Edition, and Grand Prix Edition. For the testing performed in this study, the Grand Prix Edition was used [6]. The Grand Prix Edition allows for an external GPS sensor that can record up to 20Hz and can record video using multiple cameras.

The application is one of several that are designed to record a vehicle’s speed, position, distance, and acceleration. Some other applications designed for similar purposes are Track Attack, Track Master, Dynolicious, Track Addict, and Race Chrono. These applications vary in their features, costs, and what data is collected. The applications also vary in which operating systems they are compatible with. Additional differences include file format types and availability of video logging and data overlay.

Harry’s Lap Timer™ is available on both iOS and Android platforms, uses the phone’s internal accelerometer, and uses Doppler shift to determine the vehicle’s speed. Doppler shift is also used by the VBOX data acquisition system, which has been proven to be accurate and reliable [7]. Accelerations are determined using the phones built in accelerometer.

Harry’s Lap Timer™ can also overlay the speed, position and acceleration data onto video taken by the smart phone. The video overlay feature allows the speed and acceleration data to be synchronized with the video as live feedback. The video can also be recorded separately, as its own video file, or as a video file with the data imprinted in the lower left corner.

Since prior testing had been completed using the smart phones built in GPS receiver, testing for this paper was only performed using a paired external GPS. The external GPS used was the Dual SkyPro GPS, a small, lightweight Bluetooth enabled GPS antenna that has a maximum sample rate of 10 Hz with a specified accuracy of ±2.5m (8.2 ft) [8]. Harry’s Lap Timer™ can access the highest available sample rate through the external GPS; for example, if a different antenna had a sample rate of 20Hz, Harry’s Lap Timer™ would track speed and position at 20Hz. Some of the other third-party GPS receiver providers are Dual XGPS ($85-$135), Race Logic VBOX Sport ($320), Push Smartgauge ($400), Garmin GLO ($96), and Qstar BT-Q818 XT ($89).

The Dual SkyPro XGPS160 utilized during testing can access both the US and Russian satellite systems to determine position and transmits positioning data wirelessly via Bluetooth to supported smartphone devices and applications. The XGPS160 can connect to five Bluetooth devices with a range up to 33 feet [9].

Figure 1 shows the Harry’s Lap Timer™ Phone Application home screen along with the Dual SkyPro GPS antenna.

Figure 1 - Harry's Lap Timer™ Home Screen and Dual SkyPro GPS XGPS160.

Accelerometer

The smart phone used in this testing was a Google Pixel 4 XL, running the Android 13 operating system. Harry’s Lap Timer™ accesses the phone’s accelerometer to measure the acceleration of the device directly. The accelerometers in smart phones typically have higher sample rates than the equipped GPS antennas; when Harry’s Lap Timer™ accesses the acceleration data, it samples the data to match the lower sample rate of the GPS. For example, if the GPS is sampling at 10 Hz, the accelerometer will also be sampled at 10 Hz.

VBOX: Features and Data Acquisition

The VBOX 20 Hz VB20SL3 - Triple Antenna (SL3) data logger with accelerometer was used for comparison with data recorded with Harry’s Lap Timer™ and the MoTeC C185. The VBOX is an industry accepted data acquisition system that has been widely used in the accident reconstruction community for measuring GPS location, speed, acceleration, yaw, pitch, and roll angles, heading, and elevation changes. VBOX sells multiple data loggers for different applications [3]. This unit is calibrated once per year to ensure accuracy. Race Logic’s calibration sheet shows a recorded speed accuracy of ±0.06 mph. In the testing performed for this paper, one GPS antenna and an accelerometer were connected to the VBOX. Figure 2 is a photograph of the VBOX unit utilized during testing as configured in the test vehicle.

MOTEC: Features and Data Acquisition

The MoTeC C185 Data Logger was used for comparison to the Race Logic VBOX and Harry’s Lap Timer™, both of which have been validated in previous studies. MoTeC designs and manufactures many devices for the automotive industry including engine management systems, dash displays, data loggers, accident recorders, and more. MoTeC devices are often used for data acquisition and engine management on performance-oriented vehicles. The MoTeC C185 data logger utilized in this testing has a full color display with 250 MB of internal logging memory, and it also has 1000 Hz logging capability, which far exceeds that of the VBOX (20 Hz). The MoTeC C185 has an internal 3-axis accelerometer with a detection range of ±5 g. Furthermore, the MoTeC C185 and Dash Manager software allow the user to wire and configure multiple different sensors such as brake pedal force, linear potentiometers, accelerometers, switched inputs, and more. The MoTeC C185 also has the capability to receive and decode messages from a Controller Area Network (CAN). This feature allows the MoTeC to be connected to a vehicle’s onboard diagnostics system to retrieve additional data from vehicle modules, and it also allows the user to connect sensors that run on a CAN bus system, such as the Syvecs 50Hz GPS Module used in this test. The Syvecs 50Hz GPS Module is an external 6-axis accelerometer and GPS receiver which can be paired to the MoTeC C185 using a CAN bus. The Syvecs GPS Module can record accelerations and elevation changes as well as rates for pitch, roll, and yaw. The Syvecs 50Hz GPS Module is tested and calibrated prior to being shipped to the customer.

The authors could not find previous research or validation studies for the MoTeC C185 nor the Syvecs 50Hz GPS module. MoTeC provided calibration accuracies for inputs such as the analog voltage inputs utilized for many sensors. The C185 User Manual lists the analog voltage inputs as having a resolution of either 1.33 mV or 3.66 mV depending on the inputs used, with a calibration accuracy offset of +/- 6 mV [10].

This paper aims to validate the data logging capabilities of the MoTeC C185 internal accelerometer and Syvecs 50Hz accelerometer and GPS Module by comparing data to the previously researched and validated VBOX and Harry’s Lap Timer™ applications.

Figure 2 - Image of VBOX VB20SL3.

Procedure and Test Setup

Testing was performed on a 2005 Subaru Legacy GT. The vehicle is equipped with all-wheel-drive, a 2.5 liter, 4-cylinder engine, and a five-speed manual transmission.

For the testing, the Google Pixel 4 XL was mounted on the inside of the windshield near the center of the vehicle. The Bluetooth Dual SkyPro GPS antenna connected to the smart phone was placed on the dashboard of the test vehicle as close to the center of the dashboard as possible.

The Race Logic VBOX accelerometer and Syvecs accelerometer were mounted in the center of the vehicle as close to the center of gravity as possible. The accelerometers were placed in parallel with the X, Y, and Z axis of each accelerometer facing the same direction. The VBOX controller was placed on the front passenger seat.

The MoTeC C185 was positioned on the center console of the vehicle in between the front seats, keeping the internal accelerometers in line with the Syvecs and VBOX accelerometers. A photograph of the test vehicle is shown in Figure 3. Locations of the smart phone, Dual SkyPro GPS, VBOX, and MoTeC devices are shown in Figure 4.

Figure 5 shows a top-down view of the VBOX and Syvecs accelerometers mounted in the test vehicle.

In the Harry’s Lap Timer™ application there is a help section that shows how to set up the phone to record data, and there are also multiple guides and instructional videos on the application’s web site [6]. The process requires minimal setup, such as connecting the phone via Bluetooth to the GPS antenna and configuring video recording settings. The smart phone was then mounted on a suction cup mount and rotated to have a level landscape orientation with a view through the windshield. Positioning the phone on the windshield allows the user to properly level the phone and record video with the phones built in cameras. Leveling the phone ensures that the lateral and longitudinal accelerations are reading correctly. An acceleration circle is shown in the bottom left corner of the phone, which shows the live accelerometer reading. The phone was adjusted until the acceleration circle showed zero acceleration prior to each test. The live data overlay displayed by Harry’s Lap Timer™ is shown in Figure 6.

Figure 3 - Exterior of test vehicle.

Figure 4 - Interior of test vehicle.

Figure 5 - Accelerometers mounted in test vehicle.

The VBOX was set up with the accelerometer mounted centered within the test vehicle, as shown previously in Figure 5. The VBOX accelerometer was zeroed and set up using the VBOX Test Suite software. A GPS antenna was connected to the VBOX, which was centered and mounted on the roof of the vehicle using a magnetic mount.

The MoTeC C185 was set up with the Syvecs accelerometer mounted in-line with the VBOX accelerometer, also shown in Figure 5. The MoTeC C185 dash was placed on the center console between the front seats. Sensors and accelerometer readings were zeroed using the MoTeC C185 Dash Manager software to account for any offset or variation in the angle of the accelerometers when mounted in the vehicle. The Syvecs 50Hz GPS module was attached to the MoTeC C185 via a CAN bus. The Syvecs module records GPS position in ten-thousandths of a minute of arc, and records speed in centimeters per second. To match the units of GPS position recorded by the VBOX and Harry’s Lap Timer™, unit conversions were configured using the MoTeC C185 Dash Manager software. The unit configuration ensured that live data being displayed on the MoTeC could be directly compared to live data shown on Harry’s Lap Timer™ during testing.

In previous testing, it was observed that Harry’s Lap Timer™ would record at less than the 10 Hz for the first 2-3 seconds (when connected to an external GPS sensor), therefore a protocol of remaining stationary for the first five seconds was established [2]. Once the VBOX, MoTeC, and smart phone were set up and ready to collect data, logging was initialized on each device and the vehicle was held steady for approximately 5 seconds to ensure that logging had been successfully initiated on each device.

Figure 6 - Acceleration circle and data overlay.

Testing

The tests were performed on both open roadways and a closed course. Open road tests allowed for longer time periods traveling at a steady speed while closed course tests allowed for abrupt maneuvers. Four groups of tests were performed: 1) steady acceleration and steady speed, 2) left and right turns, 3) hard acceleration and braking, and 4) slalom maneuvers. For the open road tests, a course was set up with multiple turns and acceleration and deceleration areas. A portion of highway was also used for longer duration acceleration and constant speed testing. An aerial view outlining the low-speed test locations is shown in Figure 7.

Figure 7 - Aerial view of low-speed test area.

The course shown above was traveled in a clockwise direction, and each section of data recording began with the test vehicle stationary. Tests were stopped while the vehicle was traveling in a straight line at a constant speed.

The location used for the highway test is shown in Figure 8. The test was performed traveling southbound without changing lanes. Recording was initiated at a signal located on the on-ramp and was stopped part way down the exit ramp.

Figure 8 - Aerial view of highway test area.

Data Export

Prior to exporting the data collected from Harry’s Lap Timer™, the speed, acceleration, and path data was overlaid onto the recorded video using the application. The collected data was also exported individually as .CSV files. An example of the file produced from the tests is shown in Table 1.

The exported data includes Date, Time, Lap Time, Latitude, Longitude, Speed (in both kph and mph), Elevation (in meters and feet), Heading, Distance (in km and miles), and Lateral and Linear Acceleration in g. Additional data is provided which documents the status of the GPS, including the number of detected satellites. Data can also be obtained through a Bluetooth On-Board Diagnostics II (OBD II) reader that gathers information from the Controller Area Network (CAN) for the subject vehicle. Information obtained from the CAN data is related to engine parameters and was not recorded during testing.

Test data recorded by the Race Logic VBOX was exported using the VBOX Test Suite software. The software allows a user to view the recorded data and live parameters such as the acceleration, recorded GPS satellites, and more. Data recorded by the VBOX was exported as a .CSV file. An example of the file produced from the tests is shown in Table 2.

Test data recorded by the MoTeC C185 was exported using the MoTeC C185 Dash Manager software. The data was then imported into the MoTeC i2 Pro Analysis software. Once imported into the software, the data was split into individual tracked runs and exported as .CSV files. An example of the file produced from the tests is shown in Table 3.

Table 1 - Partial Harry's Lap Timer™ exported data.

Table 2 - Partial Race Logic VBOX exported data.

Table 3 - Partial MoTeC C185 exported data.

While all three devices were equipped with GPS receivers and captured positioning data during testing, the accuracy of GPS devices has been validated in previous published research and therefore was not analyzed for this paper.

Results

A total of seven tests were performed, which are listed in Table 4 below. Each test was designed to evaluate a specific parameter such as longitudinal/lateral acceleration, speed, and distance/position.

For test runs 1 through 3, the test vehicle was driven in a normal manner with acceleration and deceleration rates typical of an average driver. These tests were designed to document the accuracy of each data acquisition system at varying speeds and accelerations. Test runs 4 through 7 were performed near the limits of the test vehicle, with hard acceleration and deceleration. These tests were designed to document the performance of each of the data loggers during rapid acceleration, braking, and quick changes in direction.

Data Filtering

After being exported from each device, filtering was only performed on the acceleration data. Prior to being exported, Harry’s Lap Timer™ data can be smoothed within the application: noise reduction settings can be adjusted directly within the Harry’s Lap Timer™ application. Within the application, noise reduction is described as an up-front smoothing of measured data. A factor of 0.1 averages roughly 10 values, and a factor of 1.0 turns noise reduction off.

On the Google Pixel 4 XL utilized in this test, the noise reduction is set to a factor of 0.1 as a default, which was utilized for this testing. Noise reduction features can be adjusted within the “Expert Settings” of the application. At the time of the testing, Harry’s Lap Timer™ was sampling at 10 Hz which equates to 10 samples per second. With the smoothing set at 0.1, the measured accelerations during rapid maneuvers, such as those performed in a slalom, will underreport the peak accelerations. It is recommended that when performing rapid maneuvers that the smoothing is set to 1.0.

Inherent noise in the data made it necessary to filter the acceleration data for comparison. A four-pole Butterworth lowpass filter was used for acceleration data recorded by the MoTeC and VBOX. Reported speed data from each source was smooth and therefore did not need to be filtered. Figure 9 is a comparison sample of the filtered and unfiltered VBOX accelerometer data, collected during Run 4.

Table 4 - Testing list.

Data Synchronization

At the onset of each test, the VBOX, MoTeC, and phone were started manually and therefore began recording at slightly different times. Due to the differences in start times, as well as differences in sampling rates, synchronization was required to determine the offset of the data. Data from each of the seven runs was offset based on the first instance of a speed reading on each device.

Figure 9 - VBOX Accelerometer data filtered and unfiltered.

During Runs 1 through 3, data was inconsistently recorded by the VBOX due to GPS connectivity and logging issues. Therefore, portions of these test runs are missing data. All other tests using the VBOX were recorded correctly and have consistent data throughout the entire logging period. Intermittent data recorded during these runs was consistent with data recorded by the other devices, however the lack of data made it difficult to properly synchronize the VBOX data for these runs. An example of the inconsistent recording of the VBOX is shown below in Figure 10, recorded during Run 1. Speed data points recorded by the VBOX are plotted based on the determined time offset. MoTeC speed data is shown in orange, and Harry’s Lap Timer™ speed is shown in gray. Due to the limited data, individual recorded VBOX data points are displayed and labeled with blue triangles.

Figure 10 - Run 1 speed, inconsistent recording of VBOX data.

As seen above, data points collected by the VBOX correlate well with those recorded by the other devices; however, large sections of data are missing. Despite the missing sections of VBOX data, Runs 1 through 3 show that data collected intermittently by the VBOX is valid. One of the downfalls of data acquisition is the possibility of having intermittent connectivity to sensors that cause the recorded data to drop out for periods of time, as was experienced with the VBOX during testing. The MoTeC data acquisition system is intended as a replacement for the VBOX system utilized during testing and validation in this paper, partially due to the missing sections seen in the VBOX data shown above. It is important to note that this VBOX, when recording properly, does in fact record accurate data, and it is a valid control for comparison with Harry’s Lap Timer™ and MoTeC data for the purposes of this paper.

Speed

Each of the three devices utilized in the testing presented in this paper (MoTeC, VBOX, Harry’s Lap Timer™) uses Doppler shift to determine speed. The VBOX was calibrated by the manufacturer prior to use and was verified to fall within the reported accuracy of ±0.06 mph. Harry’s Lap Timer™ has been verified in comparison tests with the VBOX presented in previous research. The Syvecs 50Hz GPS module and accelerometer are tested and calibrated by the manufacturer prior to delivery. For ease of comparison, conversions were made such that the data collected by the Syvecs accelerometer was displayed and logged in the same units as those recorded by the VBOX and Harry’s Lap Timer™. The following section outlines findings from the test runs.

A plot of the test vehicle’s speed comparing the unfiltered data from the VBOX and MoTeC with the smoothed Harry’s Lap Timer™ data is shown in Figure 11. The test shown in the plot is Run 2, which included multiple areas of acceleration and deceleration. The VBOX data is shown in blue, MoTeC data is shown in orange, and Harry’s Lap Timer™ data is shown in gray. Speed plots created from the other tests are shown in Appendix A.

Figure 11 - Comparison of the unfiltered speed from Run 2.

Further analysis of the speed data shows good correlation throughout the entire run, with maximum recorded speeds differing by approximately 0.2 mph. Changes in speed shown above are due to changing gears during acceleration. Acceleration and deceleration for the test were steady and typical for most driving scenarios.

Lateral Acceleration (Slalom Test)

In addition to the speed comparison, the testing included comparing lateral and longitudinal accelerations from the MoTeC C185 and Syvecs GPS Module to Harry’s Lap Timer™ and VBOX. The acceleration and braking tests (Runs 4 through 6) were designed to document longitudinal accelerations, while the slalom test (Run 7) was performed to document lateral accelerations. Acceleration data collected during each of the seven tests was analyzed. For the comparison, the VBOX and MoTeC acceleration data was filtered as previously discussed, and Harry’s Lap Timer™ data was smoothed within the software. The following section outlines findings from the test runs.

Data collected from each device was synchronized to account for differences in logging start times using the same procedure that was used with the speed data. Plots of the test vehicle’s lateral accelerations were created, which compare the Butterworth-filtered data from the VBOX and MoTeC to the software-smoothed data collected by Harry’s Lap Timer™. The slalom test (Run 7) was chosen for comparison due to the large peak lateral accelerations and quick changes in steering direction. Figure 12 shows the lateral accelerations recorded by each device during Run 7, with slalom cones placed 50 feet apart. The VBOX data is shown in orange, Syvecs data is shown in yellow, MoTeC internal accelerometer data is shown in green, and Harry’s Lap Timer™ data is shown in brown. Lateral acceleration plots for test runs 1 and 2 are shown in Appendix A; lateral acceleration plots for runs 3 through 6 were omitted because the vehicle was traveling in a straight line during these tests.

Figure 12 - Comparison of lateral accelerations from Run 7 - slalom test.

Data collected by the VBOX and MoTeC correlate well, with reported values within 0.05 g for peak lateral accelerations during both left and right turns. While the data collected by Harry’s Lap Timer™ closely follows the trend of the VBOX and MoTeC data, Harry’s Lap Timer did not achieve the same results for peak lateral accelerations. Furthermore, as can be seen above, accelerations recorded by Harry’s Lap Timer™ appear to slightly lag behind the VBOX and MoTeC data.

Further analysis of the hard lateral acceleration data shows multiple testing parameters which may contribute to the offset between Harry’s Lap Timer™ data when compared to the VBOX and MoTeC. The factors which may contribute to the offset in data include the 10 Hz sample rate, smoothing settings applied within Harry’s Lap Timer™, and the phone mounting location within the test vehicle. The 10 Hz sample rate is lower than the 20 Hz sample rate utilized for the MoTeC and VBOX, which can contribute to underreported peak accelerations during maneuvers with quick maneuvers and changes in direction, as experienced during the slalom test. Additionally, smoothing applied within the Harry’s Lap Timer™ application averages previously recorded data points. During maneuvers where the lateral accelerations are relatively constant, such as a long radius turn, the recorded data points used for smoothing have a small separation. Maneuvers with inconsistent and abrupt changes in lateral acceleration, such as the slalom maneuver, create a larger separation in the recorded data points used for smoothing, and therefore may increase the difference between the raw and smoothed recorded data. Furthermore, the phone mounting location may also affect the peak acceleration recorded as well as the lag time. For testing, the phone was mounted on the windshield of the test vehicle above the dashboard, while the VBOX and MoTeC accelerometers were mounted on the front cup holders. When the accelerations were relatively low, such as 0.2 to 0.3 g, the body of the vehicle stayed relatively flat; however, during aggressive turning maneuvers, the body roll became more noticeable. The phone’s mounting location is higher than the VBOX and MoTeC accelerometers and was therefore positioned further from the roll axis of the vehicle, which may affect the peak recorded acceleration as well as the lag in recorded peak acceleration. Therefore, due to the sample rate, application smoothing settings, and phone mounting location, peak accelerations may be underreported during rapid changes in accelerations. If the testing does require rapid changes in acceleration, the above should be considered and accounted for in testing setup and data acquisition system selection. These findings are consistent with those determined in the publication “Mid-Range Data Acquisition Units Using GPS and Accelerometers” [12].

Longitudinal Acceleration (Hard Acceleration and Braking)

Longitudinal accelerations were also recorded and compared as part of the testing. Runs 4 through 6 were designed to compare the longitudinal accelerations seen during hard acceleration and braking events. Acceleration data collected during each of the seven runs was analyzed and compared. As with the other tests, acceleration data from the VBOX and MoTeC was filtered as previously discussed, while the Harry’s Lap Timer™ data was smoothed within the software.

Figure 13 - Comparison of longitudinal accelerations from Run 6 - hard braking and acceleration test.

Data collected by each data acquisition system was synchronized to account for differences in start times. A plot of the test vehicle’s longitudinal accelerations was created, comparing the Butterworth-filtered data from the VBOX and MoTeC to the software-smoothed data collected by Harry’s Lap Timer™. Figure 13 shows the longitudinal accelerations recorded by each device during Run 6. During the run, the test vehicle was accelerated from a standstill to approximately 30 mph before hard braking to a stop. The VBOX data is shown in orange, MoTeC Syvecs data is shown in yellow, MoTeC internal accelerometer data is shown in green, and Harry’s Lap Timer™ data is shown in brown. Longitudinal acceleration plots for the other test runs are shown in Appendix A.

Longitudinal acceleration data collected by the VBOX and MoTeC correlate well, with recorded peak accelerations differing by approximately 0.02 g. As with the lateral acceleration tests, data recorded by Harry’s Lap Timer™ slightly underreports the peak accelerations.

As with the slalom test, longitudinal acceleration data shows that the location of the phone during testing compared to the locations of the VBOX and MoTeC accelerometers, along with the smoothing performed by Harry’s lap Timer™, may contribute to an offset in the data. The same factors as previously mentioned for testing involving maneuvers with rapid changes in acceleration should be considered with longitudinal acceleration and deceleration testing as well.

Discussion

Overall, testing data collected by each of the data acquisition systems correlates well with the other devices, however some error can be seen in peak accelerations and timing for maneuvers with quick changes in acceleration. The rate of change in acceleration is known as jerk [g/s], which is the derivative of acceleration, and it reaches a maximum where the greatest changes in acceleration occur, such as during the onset of a maneuver. Analysis of the data recorded during the hard acceleration, braking, and slalom tests showed a lag between the recorded speed and the acceleration in the Harry’s Lap Timer™ data. This lag was not seen in the tests with lower jerk (Runs 1, 2, and 3). The tests with noticeable lag were analyzed to determine if the lag time was consistent between runs. It was determined that the average lag time between the speed and acceleration data was approximately 0.4 seconds for Run 4 through Run 7. As part of the analysis, Harry’s Lap Timer™ data was adjusted to compensate for the lag seen in these tests and to better determine the correlation between the other devices.

Additional test runs were performed to verify whether the lag seen in Harry’s Lap Timer™ data was caused by data smoothing within the application, the external GPS receiver paired to the device during initial tests, or some other factor. Harry’s Lap Timer™ was set up in the test vehicle in the same manner as the first set of test runs. The VBOX was also positioned with the accelerometer in the same location. Two hard acceleration and braking tests were performed. Both tests utilized the internal GPS receiver on the smart phone, which is limited to 1 Hz. For the first test, filtering was turned on within the application, and for the second test it was turned off. Both sets of test data showed the Harry’s Lap Timer™ data lagged behind the VBOX just as in the initial tests with the external GPS. Further testing is required to determine whether features within the application can be adjusted to limit the data lag, or whether app software updates released by the developer have affected its capabilities. Although there was a lag between the speed and acceleration data, the overall data is reliable within the given parameters discussed previously in this paper.

To further analyze the data, a coefficient of determination (R2) value was determined for each of the seven tests. The coefficient of determination is a measurement which explains the variability between data. The values range from 0.0 to 1.0, with values closer to 1.0 showing better correlation. For these tests, the coefficient of determination was analyzed individually by comparing the data to the VBOX. Due to the inconsistent VBOX data recording on Runs 1 and 3, a coefficient of determination was calculated only over the intervals where the VBOX recorded data. The coefficient of determination for Harry’s Lap Timer™ was determined for both the original synchronized data set and the data adjusted to offset the lag seen in test Runs 2 through 7. Table 5 shows the coefficient of determination for each of the runs performed during this test, with the values for Harry’s Lap Timer™ runs that were adjusted to compensate for lag labeled as “adjusted.” Runs with inconsistent VBOX data are labeled with an asterisk. Additionally, runs in which only straight-line testing maneuvers were performed show only correlations for longitudinal (X-direction) accelerations.

For the purposes of accident reconstruction, average acceleration values are typically used for analysis. Therefore, the data was analyzed to compare the average accelerations recorded for each test maneuver. Average acceleration is commonly found in equations used for accident reconstruction, such as the equations for a lane change or swerve maneuver listed in John Daily’s reconstruction textbook [11].

Table 5 - Coefficient of determination (R2) values.

Table 6 - Average accelerations.

Lateral acceleration averages were calculated using the slalom test, and longitudinal acceleration averages were calculated using the straight-line hard acceleration and braking tests. The average accelerations were determined based on the absolute values of the data, in order to average the magnitude of accelerations experienced by the data loggers during testing. Calculated average accelerations for each test are shown in Table 6. Runs with an asterisk indicate runs where the VBOX intermittently recorded data.

Table 6 shows that the differences in average speed and accelerations between the data loggers is minimal. Due to the inconsistency in some VBOX datasets, average speed and acceleration were only compared between the MoTeC and Harry’s Lap Timer™ for Run 1 and Run 3. Data from Run 2 and Runs 4 through 7 were compared directly with the VBOX averages: the data from these runs shows that both the MoTeC and Harry’s Lap Timer™ speed averages were within 1% of those recorded by the VBOX.

Based on all the testing performed (speed, lateral acceleration, longitudinal acceleration), The MoTeC C185 internal accelerometer, Syvecs accelerometer, and Harry’s Lap Timer™ accurately reported data when compared to the VBOX. Longitudinal and lateral accelerations were recorded accurately when the jerk was kept below approximately 2 g/s, as seen during Runs 1 through 3. The location of test instruments, test procedures, sample rate and body roll of the test vehicle should all be considered when evaluating test data. Additionally, due to the possibility of intermittent GPS signal and data recording errors, as seen in the VBOX data, redundant test runs should be considered. For purposes of accident reconstruction, the authors recommend turning off the smoothing filter in Harry’s Lap Timer™ by changing the noise reduction to a value of 1.0, allowing the user to manually filter the data.

Conclusion

Overall, the authors found that all three data loggers and configurations (VBOX, MoTeC, and Harry’s Lap Timer™) provided useful information for all maneuvers performed throughout testing. The data can have its limitations, as outlined in this paper. However, each of the three data loggers is capable of recording data at an accuracy which is sufficient for performing most accident reconstruction tasks.

Furthermore, the data recorded shows that the Syvecs accelerometer paired with the MoTeC C185, along with the MoTeC C185’s internal accelerometer, show strong correlation with the validated and widely accepted VBOX. Values recorded by the Syvecs accelerometer and MoTeC internal accelerometer were typically within 0.2 mph and 0.05 g of the values recorded by the VBOX.

Knowing the capabilities and limitations of the devices in relation to the testing parameters and vehicle maneuvers, an accident reconstructionist can determine which data acquisition system is sufficient. The strong correlation of data between the different systems when performing maneuvers with steady-state accelerations shows suitable functionality for use in the field of accident reconstruction.

Acknowledgments

We would like to thank David Danaher, Sean McDonough, Drew Donaldson & Reece Cochran for providing insight and expertise that greatly assisted this research.

References

1. Neale, W., Danaher, D., McDonough, S., and Owens, T., “Data Acquisition Using Smart Phone Applications,” SAE Technical Paper 2016-01-1461 (2016), https://doi.org/10.4271/2016-01-1461.
2. McDonough, S., Danaher, D., and Neale, W.T., “Mid-Range Data Acquisition Units Using GPS and Accelerometers,” SAE Technical Paper 2018-01-0513 (2018), https://doi.org/10.4271/2018-01-0513.
3. https://www.vboxautomotive.co.uk/index.php/en/products/data-loggers/gps-measurement-systems
4. https://www.dualgpssolutions.com/explore-by-product/xgps160
5. https://www.vboxautomotive.co.uk/index.php/en/applications/performance-testing/speed-distanceverification
6. http://www.gps-laptimer.de/products ($5-$28)
7. Certificate of Calibration, Race Logic. Date of certification 1/27/15
8. Dual XGPS SkyPro GPS Receiver Specifications, https://www.dualgpssolutions.com/explore-by-product/xgps160
9. https://www.dualgpssolutions.com/explore-by-product/xgps160
10. https://www.motec.com.au/c185/c185downloads/
11. Daily, J., Shigemura, N., and Daily, J., Fundamentals of Traffic Crash Reconstruction Volume 2 (Institute of Police Technology and Management, July 2014)
12. McDonough, S., Danaher, D., and Neale, W.T., “Mid-Range Data Acquisition Units Using GPS and Accelerometers,” SAE Technical Paper 2018-01-0513 (2018), https://doi.org/10.4271/2018-01-0513.

Appendix A

Appendix A contains graphs comparing data recorded for each of the 7 runs performed during testing. The graphs include comparisons of speed, lateral acceleration, and longitudinal acceleration data collected from the data loggers. Note that lateral acceleration graphs are not shown for tests involving only straight-line testing maneuvers.

Run 1. (NOTE: Due to the limited data collected by the VBOX, individual data points are shown.)

Run 3. (NOTE: Due to the limited data collected by the VBOX, individual data points are shown.)

Run 4.

Run 5.

Run 6.

Run 7.