Hello everyone,
I have an interesting challenge that I am stumped on and wanted to come to see if anyone may have any ideas that may be able provide some guidance. I would like to track the position of sensor 2 relative to sensor 1 in the attached image. I'm thinking I will need 2 Arduinos to do this (1 for sensor 1 and 1 for sensor 2). Would like to keep it to 2 if we can and not involve other devices like a phone or other objects outside of the 2 objects in the picture. Ideally I would like to be able to track sensor 2 regardless if sensor 1 has a change in yaw, pitch, or roll but I realize that this may be pretty difficult so I have two scenarios in which I can work with, but of the two would like to see if scenario 2 is possible. In the case that I can't get scenario 2 to work I will have to try to settle for scenario 1.
Scenario 1: I don't allow sensor 1 to change pitch, yaw, or roll and stays in the same spot. Sensor 2 moves around freely within 25 feet of sensor 1.
Scenario 2: I allow sensor 1 to change pitch, yaw, or roll and stays in the same spot. Sensor 2 still moves around freely within 25 feet of sensor 1.
I'd be happy if either one of these is possible. Is there is a pair of sensors that can work with two Arduinos that can somehow accomplish this task. Does anyone have any ideas on a type of paired wireless sensor that can help me do this?
Thanks in advance for reading and pondering.
What is the normal distance between the two?
If out of doors, GPS is about your only option to measure absolute locations, accurate to at best +/- 2 meters with consumer grade GPS units.
If indoors, there are a few rather expensive solutions for device location, such as Posyx.
The normal distance will be 15 feet, but it will vary greatly. could be 3 feet, could be 25 feet. Every few seconds sensor 2 will move. Definitely don't want a GPS of any kind. Pozsyx is definitely too expensive, but seems to do what I would want with the exception of needing 4 anchors. Surely there must be some kind of paired sensor combination that can do relative distance and position from one object to another?
This is surprisingly, one of those really difficult challenges. It looks easy to a human but it's staggeringly complex for a computer to do it.
Isn't there a thing called Microsoft Kinect? I've never used one but I think the basic system is available in a way that perhaps an Arduino can access the data. There may be other gaming-related systems that can be adapted. They may not meet your maximum range goal.
Surely there must be some kind of paired sensor combination that can do relative distance and position from one object to another?
This question is asked every few days on this forum, so there is a lot of interest.
However, if you try to buy a sensor that does what you want, you will find that nothing exists, at least for a decent price. That is a hint as to the difficulty of the problem!
I feared it may be one of those challenges that looked easy to a human but is surprisingly challenging 
I will keep looking around and do some more research. If I do happen to find a relatively cheap way of doing this I will update this post. Otherwise, if anyone happens to think of anything please do let me know. Thanks for taking the time to ponder.
It would be good if you found an answer because no one has yet in the eight years I have been here.
The mimio board is impressively accurate; in the centimeter range for whiteboard-sized areas. The pens/eraser make a buzzing noise when pressed on the writing surface and two microphones triangulate the position.
In retrospect there must have been an IR element in there as well.
By any chance if anyone knows how I could pull this off cheaply with 2 stationary sensors I think I would settle for that also. (Perhaps another sensor called "Sensor 3" located within 10 feet of "Sensor 1" that didn't move?)
Also, I think if sensor 2 could track its movement along the X / Y planes accurately that would be acceptable also. Just wanted to throw those two other options that I am pondering on. Thank you to those who responded an initially pondered on this thus far.
I had about the same problem as ArduinioPig. At the time, I tracked it with three sensors, as two of them were too inaccurate for precise positioning. [ :- Today I would also track with three.
If you have line-of-sight from two fixed positions to the moving object you might be able to use an IR beacon on the moving object. With bright enough IR LEDs in the beacon you should be able to get your 25-foot distance. At the fixed locations you would use three or four IR sensors and baffles to determine which way to move the baffles to point them at the beacon. Do that at two positions a known distance apart and you can get a rough triangulation and a 3D position. If you only need 2D position you only need two IR sensors at each station.