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Thread: Automatic lap tracking for a go cart

  1. #1
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    Automatic lap tracking for a go cart

    All,

    I'm working with my local high school on a project for their race car, a single-seat electric go cart. The project is a data logger and measures car performance, records to an SD card and sends data to the pit crew for live analysis. It's very cool and works like a million bucks. The data logger and pit display are based on a Teensy 3.2.

    Next step is to have the data logger automatically track laps--and here's where we're stuck. We don't want to rely on the driver or pit to record laps hence some automatic way. I can live with +/- 5 to 10 feet accuracy in when a lap is considered a lap.

    Thought 1 was to have some beam of light by the track and a sensor on the car that will trigger LapCount++; but i for safety I want to avoid anything visible. Maybe an infrared light but not sure about the range of a light source.
    Thought 2 we to have the data logger listen to an inaudible sound but that will be highly inaccurate.
    Thought 3 is to connect a GPS sensor and look at longitude and latitude with a tolerance.

    For a view of our conditions, fast forward to the 29 minute mark to see what the track looks like. Also look at the readout by the cars steering wheel. Maybe seeing the car and track will gel some ideas.
    https://www.youtube.com/watch?v=8wVFj-4ucCg&t=3179s


    Thanks in advance.

  2. #2
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    why not a gps position range?

  3. #3
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    Possible options:
    Light or colour sense the track looking for markings
    Using IR remote library to have one or more senders trackside + IR rx on the cart (strong sunlight will mean big LEDs)
    Ultrasonic sensors would also work in a similar way but would require some hackery since normal design assumes a pair
    GPS works, though you may find precision is not good enough to actual time a lap, just count them
    If just counting laps IMU+magnetic compass and doing averaging of direction and count how many circles.

    Most robust and precise solution is probably a trackside beam break system + RF link to the cart but that means a lot more parts and has means you need to detect which cart broke the beam

  4. #4
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    beware of racoons

  5. #5
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    RFID?

    https://en.wikipedia.org/wiki/Transponder_timing

    Coupled with telemetry you'd get pretty accurate lap timing at both ends as well as exchanging any other useful data.

  6. #6
    Not sure RFID is going to work, the Go-kart is likely to be too far from the pit-wall and adding a loop under the track surface is not an option, unless you own the track.
    I don't know what technology is used by the MSA in the MyLaps transponders, most UK circuits have the trackside hardware, but you might have limited access unless it is a race day and the car-mounted transponder costs 300.
    Most commercial products use GPS, or GPS with accelerometer, and from experience tend to have timing accuracy circa +/- 0.01 seconds, as long as satelitte visibility is not excessivly compromised. GPS is quite well supported in the arduino world so maybe someone has already done the hard-work. You do need a way to input start-line gps co-ords for this, and if you get it wrong you will have no lap times.
    The old/traditional way is with a trackside IR Beacon/transmitter, and a reciever usually mounted low on the roll-hoop on the 'outside' or pit-side of the vehicle. The receiver usually produces a 5v pulse or momentary ground for your data logger to process.
    It is common for circuits to have their own beacon, or for other competitors to also have beacons on the pit wall, so you often just trigger on the first pulse received and then time-out/debounce for a set period of time a little shorter than your best possible lap-time.
    If you are interested at looking inside a receiver, I could break one open and take a picture of the board for you.

    Darcy.

  7. #7
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    a wire loop would be better with fast response times, you can get them from any place that sells gate/fence systems, they can be mounted vertically as well provided there are no big metal objects near.

    a 3x5 grid mounted to a board parallel to the track should detect the car's metal passing by

    the bigger the loop, the greater the range it can pickup ( ex 5x6), and set sensitivity of sensor to highest

    they usually have 1 or 2 contacts where you can activate stuff when a car passes, perhaps you can hook your teensy to it to count laps

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