ultrasonic ground speed detection

Using Arduino Project Guidance
1

Hi
I wish to use ultrasonic, or some other similar sensor to give the ground speed of a moving child vehicle.
Like this
http://www.fisher-price.com/img/product_shots/W2880-thomas-and-friends-kid-tough-trike-d-1.jpg

It doesn't have to be extremely accurate.
I do not wish to use magnets etc, the sensor needs to point straight to the ground and be able to determine the ground speed.
The sensor would be no more than .5 meters of the ground.

Thanks for your help.

2

Think ball-less mouse.
I don't know if IR will work at 50 Cms, though. I suspect that it will depend on the surface.

3

I don't think a device that measures speed using ultrasonics and presumably the Doppler effect exists as a hobbyist module.

I know the principal is used to measure the speeds of liquids e.g in a pipe but have not heard of it being used to measure speed of an object in air.

Henry_Best's idea of using the same technology as used in optical mice may work, but those mice use a camera and in front of it is a lens that is focused less than 5mm below the base of the mouse.

I guess you could experiment with taking one of those mice to pieces and possibly replace the lens, but you'd still have the issue of needing a USB host

4

You might be better off using a doppler radar. Have a look on eBay. Search for "doppler radar". There are some doppler radar units (HB100 is one) that are meant to sense motion for opening doors or lighting lights. They are under $10.

5

Hall effect sensor on one of the wheels....

6

@lar3ry

Interesting Idea, but it looks like those modules need external electronics :frowning:

7

Henry_Best:
Think ball-less mouse.

I was reading this: Optical Mouse Hacks: 2D Micropositioning using cheap mouse cameras « Outguessing the machine

I wonder if you could replace the lens system in a mouse's optical imager to focus on the ground 15cm below and just use the mouse's movement outputs to read the speed, direction, distance traveled and so forth.

I have a vague idea to try placing a parallax ping style sensor at a 45-degree angle to the direction of travel and see if there is a detectible shift in the distance it reads with relative movement. That would be a simple experiment to try, even if it is unlikely to be successful.

8

rogerClark:
I guess you could experiment with taking one of those mice to pieces and possibly replace the lens, but you'd still have the issue of needing a USB host

There were, and probably still are, ball-less mice with a PS2 connector. But I wasn't suggesting using a mouse, merely the principle of reflecting IR off the ground.
ANY reflective system needs to take into account the surface over which it will travel. Tarmac, concrete, grass, carpet, vinyl and wood will all have different reflective properties to any wavelength of both sound and light. The OP hasn't told us anything about the surface(s) he want to use it on, so were just guessing here.

9