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timing an RC car

Discussion in 'Electronic Basics' started by Chris W, Jul 1, 2005.

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  1. Chris W

    Chris W Guest

    I want to make a timing gate for an RC car. I don't want to spend more
    than $50. My thoughts would be to have a light beam sensor so it would
    start and stop a timer when the car went through each of 2 timing
    gates. What would be nice is if I could find a cheap stop watch that
    has an external trigger attachment or one that I could open and hack
    into the button with out much difficulty. Any one have any suggestions
    on this or a better way to time an RC car? The goal is to find out how
    fast they are going by measuring the distance between the 2 gates and
    then doing the calculation. But I am also thinking of hooking up one of
    the timing gates up to my camera to take a photo right as the car passes
    by, since my camera (Nikon N90S) already has an connector for an
    electronic remote control I don't think that will be hard once I get the
    timing gates figured out.

    --
    Chris W

    Gift Giving Made Easy
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    give the gifts they want
    http://thewishzone.com
     
  2. Tom Biasi

    Tom Biasi Guest

    Hi,
    You have some sound ideas but as you progress you may go over your $50.00
    limit. If you use a basic start/stop timer with external switches you may do
    it.
    Check these guys out for some ideas : http://www.raceamerica.com/
    Good Luck,
    Tom
     
  3. John Fields

    John Fields Guest

    ---
    Use a couple of modulated infrared LEDs as light sources and two
    infrared receivers to catch the beams. Use an RS flip-flop as an
    enable for a counter and use the output of the first IR receiver to
    SET the flip-flop and the output of the second to RESET it. Manually
    RESET the flip-flop and CLEAR the counter at the beginning of a speed
    run, then when the car goes through the first gate it'll turn on the
    counter which will accumulate clocks until the car goes through the
    second gate, when it will stop accumulating clocks. Display the
    contents of the counter on seven-segment LED or LCD digits, and you'll
    have all the information you need to determine how fast the car was
    going. If you wanted to, you could choose a particular clock
    frequency for the counter and space the gates to have the display read
    out directly in units of speed.

    What kind of speed and accuracy do you need, and do you want a
    schematic?
     
  4. Eric R Snow

    Eric R Snow Guest

    Greetings John,
    Though I didn't post the original message I'd sure be interested in a
    circuit for timing gates. More than once I've wondered how fast things
    were going. I can picture portable gates that could be set up to
    measure anything from skateboarders to bullets.
    Thanks,
    Eric R Snow
     
  5. Chris W

    Chris W Guest

    I would love a schematic, thanks. The speeds will mostly be in the 15
    to 40 mph range but some go over 60 so so up to about 70 mph would be
    good. I don't want to put the gates more than about 50 ft apart. I
    would like the reading to be accurate within +/- 1/2 of a mph. I can
    easily put the gates closer if that doesn't effect the accuracy too
    much. I could move them a little further apart but that would make the
    whole thing much less useful. If the accuracy falls off to say +/- 2
    mph at the high end of 70 mph I can live with that, I mostly want it
    more accurate in the middle range.

    --
    Chris W

    Gift Giving Made Easy
    Get the gifts you want &
    give the gifts they want
    http://thewishzone.com
     
  6. Long time ago when my son was in high school I made some of these
    timers for his science competition. I used laser pointers for a light
    source and photo diodes for the receivers. With the laser source I
    could trigger cmos circuits with just a 20k pull up resistor. The clock
    was a crystal IC and all of the counters were cmos 4518 dual BCD
    counters and displays were BCD led displays. Start/Stop/reset latches
    were cmos NAND gates. The LED displays came from my junk box and the
    rest of the circuits were under $20. Power was a 1000ma 5VDC was a wall
    wort. 12V battery and 7805 regulator was used for outside operation.
    The counter would display up to 99.999 seconds or five stages of
    counters.
    Dave
     
  7. John Fields

    John Fields Guest

     
  8. Eric R Snow

    Eric R Snow Guest

    Thanks very much for the schematic John.
    Eric R Snow
     
  9. John Fields

    John Fields Guest

     
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