Robot Positioning Systems? 26
CyberLeader asks: "As a hobby I've been developing a small robot to mow the lawn (giving me more precious hours to read Slashdot, of course). The intended brain of the 'bot is a small Linux-based on-board PC. To be able to operate the 'bot as desired, the PC needs to be able to accurately identify the robot's location to within about 10 centimeters, but I can't find any decent system to do this that falls within my cost constraints of a few hundred U.S. dollars. The position doesn't have to be global; it can be relative to radio beacons or similar devices placed around the yard. Any suggestions?" Ah, the mischeif I could have caused if I had had one of these as a teenager...
radio signals? (Score:1)
i know there are systems for yards with a similar setup. although the sgnals are used not to control or give a position, but to keep a dog within the specified area (it will shock the dog if it tries to leave)
kill all humans (Score:2)
Another thing might just be to program very precise geometrical measurements into the bot. Go forward 10 feet, make a left turn, go forward 1 foot, left turn, forward 10 feet, etc.
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Just use your eyes, and don't void your insurance (Score:3)
I'd say something about Cliff having misspelled mischief, but that would just about guarantee that I'd misspelled guidance.
Well... (Score:2)
The geek in me, however, has thought about the same idea. I think it's a neat idea and I've always wanted to try it myself. One of my ideas was to lay out a "track" of sorts - a wire through which runs some low current which you can perhaps have the robot follow, perhaps by detecting the magnetic fields or something. Maybe I'm f.o.s. since I have no idea how to implement this (I'm only a programmer - no electronics experience), but Lego Mindstorms gave me this idea when the book encouraged me to try to build a robot that follows a black line on the floor. In this case, of course, you use the optical sensor to have the robot turn one way if it sees black, and the other way as it sees white. The end result is a robot which jerkily makes its way round the oval they provide on a poster-sized sheet.
So instead of trying to use radio positioning or precise measurements, maybe there's a way to lay out a track that it can follow. A bit of work, but if done properly you'll only need to do it once, right?
Re:radio signals? (Score:1)
Radio Beacons (Score:1)
Spinning laser beacon. (Score:4)
Make sure you have >> 3 recievers so you can have an overdetermined solution, so that if one reciever is blocked by a person, tree, or errant butterfly, you can still determine the position.
This *does* work, as long as you don't get too far from the sensors. The farther the sensor is away, the less accurate the position solution. You might want to implement multiple sorts of sensors, including compass and whatever else you can, and feed them all as inputs to a Kalman filter, which should give you a more robust solution.
If you'd like to talk about this, de-obfuscate, and drop me an email. I'd love to have a system like this for my *own* lawn.
unattended lawnmower (Score:1)
Sears, and probably others, sell a lawnmower using nylon string trimmer blades.
You might even be able to adapt a normal string trimmer for this.
Re:kill all humans (Score:2)
> bot. Go forward 10 feet, make a left turn, go forward 1 foot, left turn, forward 10 feet, etc.
Ah! a lawn-mowing robot programmed in LOGO.
I bet Seymour Papert never envisioned *that* as an application for his language!!
Here's how others did it (Score:2)
construction systems (Score:1)
Invisible Fence? (Score:1)
Re:unattended lawnmower (Score:1)
Power would be a large concern, but *shrug* i'm not even on the right topic here.
Re:unattended lawnmower (Score:2)
Re:Well...Modified line following bot (Score:1)
If you really want to go cheap, just tie the lawn mower to the tree in the yard. As it circles the tree, it cuts smaller circles. If it does run over the cat, it was already dead.
Re:Differential GPS cost (Score:1)
Re:Radio Beacons (Score:1)
BTDT (Score:2)
Three IR LED beacons, mounted on the gateposts. Each one bleeped a simple ID code (TV remote chipset, with a button permanently down).
On the two 'bots, were scanner heads. These were dead simple, a stepper to rotate it and a pair of IR detectors and lenses as a simple 1-axis discriminator. By stopping, then scanning the head around a bit, the bot could take a bearing on each of the beacons. Some triangulation and it then had a position fix. Crude, inefficient, lots of software, but the hardware was cheap & easy.
Control was a couple of nested state machines.
One beacon had few bits of data link in the code as well; just a simple "Wander around the garden", "Come home now", "'Bot A get into the kennel" code.
"Home" was a kennel in the conservatory, with the coded beacon mounted directly above the door. When "homing", they just did a home on the beacon until they were nearby to it. To get them through the kennel's bot-flap there was a buried wire inductive guide. Each bot 'was called through in turn, at which point it homed as close as possible to the beacon, until it picked up the wire field and then line-followed that through the flap. Indoors there were actually two separate wires, so the 'bots could park side-by-side and charge up.
The 'bots themselves were just little diamond chassis, with a single powered wheel each side and a castor at each end. In the middle was a plantpot (that being the function of the whole malarkey).
Battery life was OK, as they didn't move much. They weren't mobile 'bots, so much as randomly re-positioning on an intermittent basis.
Stuff they should have had:
Dallas Semiconductor's TINI board [ibutton.com] is cool for this sort of thing.
Re:Just use your eyes, and don't void your insuran (Score:1)
Bury wire arround the perimeter. (Score:1)
Re:Just use your eyes, and don't void your insuran (Score:1)
If you want, you could put tiny arms holding tiny tweezers and cut the grass by tearing out six bites from each blade of grass...
Linkathon (Score:2)
Typo Corrected (Score:2)
More clarification (Score:1)
Thanks for the responses so far. Some clarification to some of the points raised:
Re:Invisible Fence? (Score:1)
instead of shocking your lawnmower
Nah, shock the little tin bastard. Those 'bots will be getting uppity enough before too long. Best keep them in their place now.
Radio - not a hope (Score:1)
Radio just isn't going to cut it for this. Simple and reliable 'bot positioning at this time needs an absolute position indicator. Open the box, place the 'bot on-site, boot it up for the very first time and it should be able to work out where it is. Anything that requires it to be placed in a "known position", then track movement from their is just too painful to contemplate.
Doppler radio systems might deliver some velocity information (but it's difficult), but it cannot do absolute positioning.
Radio multi-station phase-tracking systems were developed during WW2 [danshistory.com] (Gee [lineone.net], Oboe [tripod.com]) to give absolute positions. The trouble with these is that they only work over long distances. They work by timing path length differences between fixed stations, so they can only work if the path lengths differ by more than the shortest time interval you can measure, multiplied by the speed of light. With radio wavelengths in a garden - forget it !