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Data Analysis Fundamentals: Speed

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Speed

03.45

00:00 - To do much useful in the way of analysing the data, we're going to need to know how fast the car is going at any particular point on the track.
00:09 The speed of the vehicle should be thought of as the result of everything that has been done to the car or by the driver in order to seek out improvements.
00:18 And hence it's one of the most vital places to analyse performance.
00:22 We'll be coming back to this channel many times through this course.
00:25 A speed signal can come from a wheel speed sensor that's fitted to the car and wired to the datalogger or it may be possible to interface your logging system with the ECU that controls the operation of the engine and receive the data from this.
00:39 This is possible with aftermarket ECUs that are common in purpose built racecars as well as standard factory fitted ECUs where the data can often be retrieved via the onboard diagnostic port.
00:52 While a single wheel speed sensor will get you a speed input, the best option is to monitor wheel speed on all four corners.
00:59 This adds to the complexity if you need to add sensors to your car however as I've mentioned, this information is often available already from your car's ECU for free.
01:11 You just need a way of retreving it.
01:13 As with our lap timing, GPS is now a viable alternative when it comes to measuring speed on the racetrack.
01:20 By constantly differentiating the changing GPS location, speed can be calculated from a moving vehicle.
01:27 This greatly simplifies our logging installation because now we have the potential to get two of our vital pieces of data straight from the same source.
01:36 And GPS can be completely standalone in respect to the rest of the vehicle's electronics.
01:42 Of course, nothing is perfect though and the downsides of GPS have already been discussed in the previous module.
01:49 The other issue with GPS based speed is that you have no way of detecting wheel spin or lockup which is very obvious from wheel speed data.
01:57 As with the use of GPS for lap timing, it's almost certainly going to be more than adequate here for our purposes at the hobbyist and semi professional level.
02:06 In this example of wheel speed data we can see the typical saw tooth pattern that we would expect to see when analysing the speed signal from a lap around a typical racetrack.
02:16 Any time we have a rising line, this represents acceleration while braking is indicated by the speed trace dropping sharply.
02:24 Looking a little closer at the individual wheel speed traces during braking, we can see the telltale signs of wheel lock up where some of the traces drop sharply below the speed trace from the other wheels.
02:37 Note that this data was generated from a car with ABS so the lockup is somewhat limited.
02:43 Likewise if we look at the data of a slow speed corner where the driver is a little aggressive on the throttle. we can see the telltale signs of wheel spin where the rear wheel speed spikes up above the speed trace from the front wheels.
02:56 If we look at the speed trace as the car accelerates down a long straight, we can naturally see that from low speed, the speed line rises more sharply but as the speed continues to climb and the driver shifts through the gears, we see the speed line begin to nose over as the rate of acceleration drops.
03:14 Speed data makes it easy to see at a glance what the minimum and maximum speeds are at a given track as well as getting an indication of the track characteristics.
03:24 In other words, this lets you know if a particular track is predominantly high speed with long straights and fast corners or a tight twisty low speed track.