How to sense pool cue relative position?

Hi everybody,
I am trying to build a device that will measure and visually report a billiard cue’s position relative to the ground table. It’s meant to be an aid in correcting players’ cue stroke. But I still don’t know how can I sense the cue’s poisition. Maybe you could help with some suggestions.

I thought about a device made of a base plate and two vertical plates within which the cue will move longitudinally.
The cue will move horizontally and vertically too, that’s what interests me more. The horizontal and vertical movements are to be considered a mistake in player’s stroke and have to be minimized in order to have a more precise stroke. That’s why I want to measure it in some way and play a real time visual feedback to the the user while practicing.

See attached picture for details.

The cue stick is made of wood, and I’m willing to attach other stuff to it if needed (I’m thinking about metals, magnets, reflective stuff …) by the measuring sensor. But I’m not going to brake open the cue, make the modification permanent and damage it.

Do you have any idea how can I approach this situation? I’m willing to consider different solutions. I’m open to any suggestion at the moment.

The wooden cue’s diameter is approx 3cm and Id like to achieve a 1mm resolution.

I’m trying an HC-SR04 ultrasonic distance sensor that I had at home (and never used before); it works with wooden fine but minimum distance is 2cm and resolution is poor.
I wonder if there are other cheap ultrasonic sensors around with higher resolution and lower range to play with.

The fact that ultrasonic sensors work with wooden is a plus I like :slight_smile:

I've given up with the ultrasonic sensor, I can't find a reasonable high-resolution/low-range sensor that works for me.

I'm considering a hall effect sensor (or an array of them) now. I may wrap a solenoid around the cue stick and place an array of sensors at short distance at its sides. It may takes some calibration but if things are done right I may be able to "sense" distance variations (which is my main concern, being the absolute distance not the point of it at all). I wonder if I will get consistent and usable measurements. Any hint in that direction is well appreciated :slight_smile:

I'd install two lasers pointers at the back end of the cue. Setting some angle between beams, two lasers dots projected on the wall would be split on some distance, depends on the angle and distance between cue's end and wall. Having stationary camera (high res. may be required, and I think may be 5 of them or more if players interfere in fields vision) you always can measure dot's position, and calculate precise cue whereabouts.
Example project, though in your case hardware setup should be different.
http://coolarduino.wordpress.com/2011/12/07/arduino-laser-3d-tracking-range-finder/

Magician:
I'd install two lasers pointers at the back end of the cue. Setting some angle between beams, two lasers dots projected on the wall would be split on some distance, depends on the angle and distance between cue's end and wall...

Interesting suggestion. I'll be looking into that. I'd really like to keep it low profile at first though, and this solution seems a bit overengineered to me.

Anyway, one laser only, projecting a dot onto the back wall may suffice in my case, because my main concern is to evaluate Horizontal/Vertical movements. Correlating it with the Longitudinal displacement would be a well accepted plus, of course :slight_smile:

Chewing idea, may be you can reduce complexity installing only 1 cam, just above a table. Than two led rings at both ends of the cue would be sufficient to track in 2D, 4 rings - 2 pairs spaced 5-10 cm at both ends will do 3D.