FIRST PRINCIPLES – DATABYTES
Databytes gives insights to help you improve your data analysis skills each month as Cosworth’s electronics engineers share tips and tweaks learned from years of experience with data systems. Plus we test your skills with a teaser each month
To allow you to view the images at a larger size they can now be found at www.racecar-
engineering.com/ databytes
The truth hertz A
racecar is an exceptionally challenging environment – g forces
of high magnitude and a considerable amount of weight being shifted around very fast demands the highest quality of components. However, the electronics often get overlooked when considering external factors and, as long as the logger doesn’t rattle around and hit the driver, it is generally accepted as being mounted ‘well enough’. Similarly for displays. As long as the driver can see what is needed and the display appears to stay in place, it is deemed good enough. It is, of course, very important to have all parts of the racecar properly bolted in place for the above reason, but also in order to get accurate and good data. There are a few things to be
aware of when mounting any hardware in a racecar. Most chassis are designed to be very stiff, with solidly-mounted engines and drivetrain components all transmitting vibrations at various frequencies throughout the car. This means that extra care needs to be taken when mounting data loggers as the electrical components contained therein can be damaged or their measurements can be inaccurate if they are being shaken around.
ENGINE BUZZ Taking a closer look at the vibration possible in a racecar due to the engine and drivetrain, a racing engine will spend most of its time at the upper limits of the rpm range, typically from around 6000-10,000rpm, depending on application. 6000rpm is
Some suggestions for avoiding data problems due to vibration
equivalent to 100Hz, so with a solid-mounted engine we have a very powerful 100Hz signal generator. There are potentially other sources of vibration induced by the engine too, such as valvetrain noise, gear meshing noises, turbos, induction roar etc but the most powerful could be considered the rotating mass inside the engine, often termed ‘engine buzz’. There is another potentially
large source of vibration from the road wheels. Given a 2m circumference and racing speed of 240km/h, we can then calculate the driveshaft and wheel rotational frequencies at 33Hz. The fundamental chassis-to-
tyre frequency could be in the order of 4-16Hz, depending on construction. This is interesting to measure, but often not affected by suspension tuning. Finally, the lowest vibration is
caused by the driver and race track – typically in the 1-3Hz region as the car undulates over crest and dip and around corners. So we have a myriad
frequencies and vibrations all contributing to the vibration signals on the cars. The job of an accelerometer is to measure these vibrations and the job of a data analysis programme is to try and understand the different vibration measurements. Therefore it is important for
accelerometers to be fixed securely in order to get a representative value for the acceleration being measured. However, it is also important to note that accelerometers will also pick up any vibration in the car. The most common but
unwanted vibration in a racecar comes from the 100–150Hz engine vibration. When this is transmitted directly to an accelerometer, it can saturate and give completely false readings. This can have detrimental effect on the data gathered, as the
February 2012 •
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