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Determine car's speed and acceleration — Parallax Forums

Determine car's speed and acceleration

AltaierAltaier Posts: 3
in Learn with BlocklyProp
I have an application where I need to determine the instantaneous speed and acceleration of a moving car , I need to know which sensor to use ?
Would an accelerometer do the trick ?

Comments

  • hatallicahatallica Posts: 175
    Welcome to the forum, Altaier!

    I do not believe that you will get a satisfactory result from an accelerometer. It will measure the applied forces, but there is not a tidy way to translate that into directional speed.

    There are a few ways to go here, which include various amounts of fiddling with the car. If you search for "speedometer sensor" on-line, then you will see how many modern cars derive the signal for the speedometer. Please use your best judgment regarding your ability to hack into this without causing an unsafe condition.

    An additional sensor could be added one of the wheels, to act as an optical or hall effect encoder. Again, please use your best judgment.

    Finally, a GPS could be used without any vehicle modifications. This may be ideal for using with multiple vehicles.
  • AltaierAltaier Posts: 3
    Thank you , hatallica .
    I think I'll go with the GPS or the hall effect encoder since I'm trying to make a standalone system and i want to avoid manipulating the car's system at this stage .
    I shall look more into it , Thanks again :)
  • kwinnkwinn Posts: 8,697
    GPS may not work very well if you want the "instantaneous" speed measurement to be over a short period of time ( a few seconds or less). You could use a hall effect sensor to measure the time it takes for the ribs in the center of the disk brake rotor to pass the sensor. That would be about as instantaneous a speed measurement as you can get with fairly simple hardware.
  • DavidZemonDavidZemon Posts: 2,973
    Hi Altaier,

    As the other two have mentioned, there are lots of different ways to do this. I think the options they give are great.

    However, there might be even better options if we know more about your requirements and restrictions. Does this need to work with any production vehicle? Any production vehicle newer than 2000? Any Toyota? Your own car and nothing more?

    As kwinn pointed out, it would also help to define "instantaneous speed" in more detail. If you're willing to deal with the delay of a GPS system, and your car is 1996 or newer (in the USA, not sure about laws outside USA), reading the OBDII port would be even easier than installing a hall-effect sensor. It requires reading the car's systems, but not manipulating.
  • AltaierAltaier Posts: 3
    Thank you kwinn and DavidZemon .
    The thing is I don't actually have a car right now , I'm trying to develop a system that can be installed on any car and it'll still work .
    This is my first phase of the project , so reading the OBDII port can't be done at the moment , maybe in future phases .
    I think the hall-effect sensor would be the most convenient in my case .
  • kwinnkwinn Posts: 8,697
    Altaier wrote: »
    Thank you kwinn and DavidZemon .
    The thing is I don't actually have a car right now , I'm trying to develop a system that can be installed on any car and it'll still work .
    This is my first phase of the project , so reading the OBDII port can't be done at the moment , maybe in future phases .
    I think the hall-effect sensor would be the most convenient in my case .

    You might use a bicycle sprocket for your proof of concept/prototype. We used the front wheel hub assembly from a car for our prototype. Having the entire assembly made mounting the sensor and motor much easier. The sensor bracket was welded on to the brake cylinder mounting.
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