A data logger for drag racing

John Bond

Hi Guys
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I put together a 2 axis logging accelerometer over the weekend. It displays the data on a LCD and logs 3500 records, approximately 10 per second. One can then download these to a PC and graph them in Excel. It was one of those fun projects where everything worked 1^st time and I could just copy and paste the code from Parallax’s various examples (accelerometer, LCD, flat EEprom, Comms – Thanks Jon and others!!!).
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There are a lot of car fanatics round here. For some time now, I’ve been thinking about a logger as my next project. It would record acceleration, road speed, RPM and time. Later, I’d like to add information on the position of the gas pedal (accelerometer on a strong magnet to clip onto the airflow quadrent). The device must be portable so that each racing maniac can clip it onto his hot automobile and drag up and down the road for 30 minutes. He then downloads the information and we analyse it. The device is put on the next vehicle and we do it again.
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The device would replace the old, expensive and very inaccurate dynamometers that are only available in Durban which is over 50 miles away. I believe the information would be more accurate and much more useable. It looks like you’ll be able to see flat spots and bad ratios much easier by just looking at the rate of acceleration at any choice of speed/gear/gradient/Pedal position. (Memsic have a paper on how to calculate both acceleration and gradient at the same time – the math is a bit beyond me but I’ll go to the nearest university)
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My question – How do I read road speed? GPS is too inaccurate round here. I can use a 5^th wheel and I have suitable (industrial) encoder but fitting it to the car each time is a hassle. Is there some other inexpensive option?

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Kind regards from Kwa Dukuza (Where ever that is?)
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John Bond

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Unsoundcode

Hi John , a friend of mine recently bought a comercial logging unit for his dragster. These units vary in price depending on the number of sensing points. I think his has exhaust temps , engine speed , propshaft speed , acceleration , battery voltage , gear selected·, spring compression and possibly a couple of others. Anyway the propshaft speed is measured with a ring that has 2 or 4 magnets (depending on which you buy) and hall sensor.The ring·clips around the propshaft and the sensor has a bracket fastened to the chasis, these rings are fairly universal and pretty quick to fit. Might be an option for you to consider.

Jeff T.

John Bond

Thanks Jeff, clocking the driveshafts is an option. Measure the diameter of the tyres and put in a factor.

Most of the cars in South Africa are front wheel drive round here (Japanese, Korean, or small German and French). Quite a number still have cable drive speedo's. All the racing vehicles have non standard tyre and wheel sizes. This is why I preferred a 5th wheel to measuring driveshafts or Speedo impulses.

Also, spinning the wheels is actually counter productive. That is why the really high performance cars have traction control. I would also like to measure this spinning (by comparing RPM to actual road speed - I'm told that under 10% slip between tyre and tarmac gives the best traction).

The speed cops round here use radar and infra red. Can I somehow do this in reverse but bounce some signal off the tarmac (pavement or whatever you call it)?

I'm very keen to try and avoid an impractical 5th wheel.

Kind regards

John Bond

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Unsoundcode

Hi John, I never really thought about front wheel drive I guess I was focused on the system I had seen. The sensors he had fitted do exactly what you describe, the spring compression sensor is a linear pot that gives a reading as the back end goes up and down giving an indication of traction. The engine speed compared to prop speed would give a value of losses in the transmission which put against the gear indicator would indicate the best rpm to be changing gears The temperature sensors help in determining fuel mixture.

My friend does a lot of racing and his system is a permanent fixture to his dragster. But you might be interested in the sensors available which are sold separately and if I remember are not too expensive. I'll post the link when I find out which system he has

Even if you want to manufacture your own sensors it might give you some ideas.

Jeff T.

John Bond

Thanks Jeff

We're a 3rd world country so as an engineer (and quite a senior one too), I don't earn a lot. I will probably copy a sensor rather than buy.

I got the spark plug sensor for measuring RPM to work on my development board last night. I'm going to have to do some thinking because I'd hoped to sample all data every 50ms on but a spark only occures every 200ms on a 4 cylinder engine at an idle speed of 600 RPM. Possibly measure every 50ms, average and record every 100ms, interpolate if there's no new data.

How to measure road speed is still bugging me...

Kind regards

John Bond

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kelvin james

This is a canbus device that might be worth a look, auto-detects the vehicle make.

www.racelogic.co.uk/?show=VBOX-Products-CAN_Speed_Interface

John Bond

Thanks Kevin - Very Interesting for me from a professional point of view. I work for a factory that manufactures the wiring harnesses for a range of Toyota, Ford, Isuzu (and we're hoping also GM) vehicles sold in Africa, the Middle East, Australia and parts of Europe. Only the large Ford 4L LDV (smaller than your F150) has a bastardised 1 wire Canbus. It also has 2 LinBusses. Toyota uses the LinBus. The new Corolla -March 2007 - has a couple of proprietary LinBus busses. I assumed that Canbus was dead-in-the-water when it comes to cars.

It looks as though you Yanks need to use·CabBus in your "Battle Ships"· I suppose one needs different systems when automobiles are 8 foot wide and·25 foot long, ours are only 5 foot 8 wide and 12 foot long. You just need run a couple of short wires.

John Bond


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MikeS

John,

I have a 1953 Ford 4 cyl tractor and·I would like to build a tacometer for it. I am interested in the circuit and code you are using with your spark plug sensor. Do you mind sharing?



MikeS

John Bond

Hi Mike

Sorry about the delay in responding

I used the attached circuit. Stuff out my scrap bin. I'll probably use an optoisolator between this and the microcontroller on the final circuit.

I intend timing from positive edge of the (spark) pulse to the next positive edge. I did the trials on a BS2 only to checked for signal. I'm using an SX on the final device. Unfortunately the spark doesn't occure frequently enough for me to count the spark pulses.

Hey there are a few of those old Fords round, the Brittish made ones though. Also quite a number of the old Masseys from the mid 50's, some still doing work. You can still buy some Massey Fergeson spares. I saw a head gasket set, valves and petrol pump being sold to an old black farmer about a year ago. The farm I live on has a number of Catapillar D40 (+-1937). They are dead but there are enough of them to build a couple of running crawlers. Plenty of the Brittish (stationary) Ruston Oil Engines from the 1920's - There must have been a good Ruston salesman up here about then. They were used to drive water pumps gensets and mills.

Kind regards from Kwa Dukuza in South Africa. I hope you enjoy your Trekker...

John Bond

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