Maze Robot Buggy help

[SaintSoulja]

Hey evry1.

I have a picaxe 18X. I wud like to make a robot buggy which completes a maze on a table with a white surface and black finish point ground surface. However instead of the normal mazes i am going to include empty walls where it can fall off, which i want the buggy to avoid.

So my question is what kind of model will be suitable. I.E. which sensors can I use and where would i position them.

So far I have thought of using IR range fnders as though their beam is quite narrow it needs to either avoid a solid barrier or not. I thought of placing one at each side, and one at front. Then program to go left, or striaght or ryt in that order based on where and how many walls surrounding it.

Then to stop it from fallin i was gnna use another IR sensor underneath but near front, b4 the wheels... u can guess how thisl work.

Finally from my research an IR range finder can also tell difference from black or white surface based on how they reflect. so gnna use another in middle which will stop the buggy when on the black spot.


Does this sound like it will work? or is there another alternative, prefereblay cheaper, cos I have not bought the IR range finders yet, an would like to save money where i can.

Thanks,

SaintSoulja

[rbtying]

If you're going to use Sharp IR rangefinders, realize that they have a few important limitations:
  1) minimum range (this will probably be the biggest problem)
  2) narrow beam width (you could just mount it on a servo...)
  3) nonlinear output

For detecting walls, a simpler/more reliable setup would be a set of ultrasonic rangefinders, because their field of view is usually plus/minus 20 degrees - enough to create a "bumper" system; and also because some of them have no minimum range limit (big plus).  Since sonar isn't as cheap as IR, you could mount a single sensor on a panning servo and just turn the sensor to view the three sides (left-front-right). 

For detecting the floor, you probably want an IR-LED/phototransistor pair, which will be able to tell you the color of the floor.  Sharp IR rangefinders are essentially incapable of this because of the minimum range issue, and are much too expensive for this purpose anyways. 

P.S.: Just a personal pet peeve - just because this is an internet forum doesn't mean you can avoid typing in english - "chat" or "IM" abbreviations are not standardized, and will confuse people - or make them think that you actually did not know how to spell the word (which I doubt, so it's probably intentional)

[Soeren]

Hi,

So my question is what kind of model will be suitable. I.E. which sensors can I use and where would i position them.

So far I have thought of using IR range fnders as though their beam is quite narrow it needs to either avoid a solid barrier or not. I thought of placing one at each side, and one at front.

Plain English please.

If you want to go with an IR rangefinder, a single one can be scanned with a servo (just like an U.S. sensor) and that will be cheaper.

For maze work, you don't really need distance info, just if there's a wall or not right in front of you (or to the left, right or behind you).
This can be accomplished much cheaper with a simple modulated IR and an integrated IR receiver of the continuous wave receiving type.
This can be scanned as well but it will be cheaper to build 3 or 4 of them, than one plus a servo.
For detecting the black floor a LED and an LDR (or photo transistor) will be just the ticket.

What do you mean by falling?  Off the table or what?

[SaintSoulja]

Hey,,

Thank you for your replies. Sorry if my english is not that good, ill try and write more formally now.

rbtyping, I am a bit confused. If i used one ultrasonic rangefinder and put on top of a servo then in order to check which walls are there (left, in front and right) wouldnt it have to stop and wait till it scaned around to make a decision? Also what is a "bumper" system. Im sorry if i sound really dumb, but ive just got into using microcontrollers.

I think im going to go with soerens suggestion of 3 simple modulated IR and integrated IR receivers. Also yes, it would have been silly to use IR range finder for detecting floor, so thanks to both of you for phototransistor idea. 

And yes soeren, i meant falling off the table.

[rbtying]

A "bumper" would just be setting a constant distance, where:
  if (sonarReading < bumperDist) { wallIsThere = true; } else {wallIsThere = false; }

It would have to wait for the sensor, yes, but this can be done while moving.  It's not the best method, but probably the easiest (and 3 sonars is quite expensive). 

The modulated IR is more than many people are willing to build on their own - it's certainly a cheaper method, though.  Just remember to calibrate the circuit for the distances you want.