I haven't read the entire thread so I am not sure if this has been covered. But once it finds the charger base couldn't you use a light and two photo eyes on each side and use analog inputs to measure the amount of light on each side to center it, and guide it into position.

One mine i am looking at using a laser design (maybe) ,and at the same time i can use it for navigation

COST is should be near about $40 to $50 total for receiver and transmitter

LOOKING at all the ideas and one RICH posted all have good points and bad points like using sonars it has a problem detecting certain materials in the path of it,and IR has a problem with light and same with all other ideas ,each has its problems

And like line following witch is the easest design there is,you have to put a line on the floor Steve what happens if you robot more then a few feet away from the charger,or ever harder the next room.

Thats the hardest to fix,like in my big house,if a robot battery needs to be recharged and in another room i need it to have a system to get it back to the charger and then line up and charged.

SO i am looking at using a second EZB to tell the robot where to go,plus monitor the battery and a lot more.

plus i have many robot designs using different batteries ,i need to charge all of them with one charger

RURAL GEEK thats the idea behind roomba,it uses 3 IR's and a photodetectors , and same on the pololu design also,its i deai bought up ,using one left IR and one right IR and 3rd IR in the center to guide it

Pretty simple design and very low cost ,if robot goes near the left ,then a script tells the motor to turn right and same with the right IR until he is center on and goes forward

@ Robotmaker

The robot uses the sound nav to get to the vicinity of the charger Then uses line folowing to final dock.

Add ir to if you want.

Steve_c

And RICH on your sonar idea you need to remove one or it will pick of the echo,s too.plus a problem with feedback in the circuit also.

Alarms systems use to use that as a break of beam detector using one transmitter transducer and on the other side a receiver transducer,but with sonars they are tied together with a feedback circuit

Only idea may work i have (never been tested) is to cover up the front of the transducer.

@Rural Geek, that hadn't really been covered. In fact the whole lining up last few feet part hasn't really been mentioned. I originally posted my first idea about the dock and using a row of wheels either side of a runway which slowly narrows to line up perfectly but that's pretty much as far as it got with that part. There are a few ideas which would work for that part;

Line following Glyph recognition IR sensors/ultra sonic sensors Mechanical methods (such as the one described above)

Getting to that point however is part that needs the most discussion though, the rest is relativity straight forward.

STEVE ok,i see it works to 6 meter only ,what happen after 6 meters

ALSO lining it up will be very hard.since a photodetector is very small ,and some so small about the size of a pin.like on my heart rate monitor i made in college

Steve on your line following design you need many detectors,i think parallax sells one ,thats like a strip of detectors

line following kit by parallax