Let's Make Robots!

Homing method

The only base-homing method I know about that works fairly well is the one that Roombas and the RBs use-namely an odd number of IRLEDS pulsed at varying rates on the base that the bot can detect so it knows if it's to the left/right of center or heading right for it.

Sabre explained a little bit of how the Hero 2000 does it, but I didn't get the meat of it. Of course there are "cognitive" systems like Loki uses, but that's not perfect:any number of things can throw off the sensed relative location.

So I guess I'm asking what other systems and methods you guys like for homing, and can you give an explanation of it that an average TV viewer would understand?  

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Since you ask for homing methods in general I'd like to mention the low-tech method of a light source homing beacon. That worked for me. Two LDRs are sufficient to let the robot find out if the light is stronger or weaker. If its stronger, go ahead. If its weaker than turn until it knows where it is stronger. Then go ahead. So light intensity is the bearing.

The cognitivity you can also get when this homing starts when the light source has reached a specified threshold. When the intensity is higher than the treshold the homing behavior kicks in and takes over as a higher level behavior. If it is lower then the homing behavior does nothing.


Nowadays, I would use a WiiCamera to track a point (or a couple points) of IR light and triangulate from there. In the past, I have had pretty good success with a "shielded" 38khz IR sensor. I have set up a "standard" IR system --the kind you would use to control your bot via a TV remote control. A IR led puts out a signal and it is read by a 3-pin, 28khz sensor and microcontroller. For docking, the IR LED is just that, a IR led, putting out a steady signal (it would be the same as holding down "pause" or "2" or "stop" on a regular remote.) This is your homing beacon and would be placed in a given, known spot.

The 3-pin sensor is placed in the end of a narrow tube with the inside of this tube painted black. The outside of a pen is about right. The sensor is sealed so it can only detect a IR signal from not only the front of the tube, but also only when that IR signal is comming in parallel with the tube. This will give you directional sensitivity. Stick this thing on top of a servo and you can now scan for the beacon and also know what angle the beacon is at based on the position of the servo. 

Depending on the diameter of the tube, you can get the sensitivity down to that of the servo. I.e. accurate down to one servo "click"