Ledge Detection

[pomprocker]

Does any one have any recommendation for ledge detection sensors that I can mount underneath my robot pointing at the floor?

i don't want him to fall down the stairs 

[cooldog]

the irobot rommba uses ir range finders that measure really close distances

Edge detection:
You mean like detect when its hovering over the edge of a stair case? You can use a simple IR range finder that can measure extremely short distances (0cm to like 30cm) so that when suddenly its sensor range goes from ~3cm to really anything over 100, it knows that it could get damaged due to a fall if it continues any further.

[frodo]

whats ledge detection?

[cooldog]

it is so your robot when driving if it comes to a ledge like if it's on top of a table or if it it's going to go down the stairs it will know to stop and go back

[want2learn]

Build a basic 38khz generator with a 555 or with a 74hc04, feed the output to some IR leds.

Use a modulated IR reciever (38khz too).

When the IR reciever is recieving light you will have a 1 or 0 output depending on which one you use. Hook this up to a pin on your mcu. When you stop/start recieving a signal from the reciever you're at an edge.
One reciever and led setup at each end of the bot (tilted at a slight angle if you need extra reaction time) and you're sorted

[airman00]

non-tactile ledge detection or tactile?

[pomprocker]

non-tactile ledge detection or tactile?

What do you mean?

[want2learn]

tactile means touch

[pomprocker]

oh, non tactile would be preferred

[SciTech02]

I remember doing a setup with my old BOE-Bot so that it could detect edges (it was one of the projects in the book that came with the robot).  It basically worked the same as obstacle avoidance, except it turns away when the left, right, or both IR detectors did not detect anything (they were aiming at the ground immediately in front of the bot).  This worked fairly well, until it fell of my dining room table one day; it survived with no damage, but I never tried that again (I think the table messed with the sensors, it was a glass one).  It may also had to do with the sensors still pointing forward instead of directly down at the ground beneath the bot.

So using IR detectors (not Sharp IR rangefinders or sonar sensors) make the most ideal ledge detectors.  Their cheap and take little programming and power to use.  Unless you really want to know exactly how far the ground is below the bot (for topography perhaps?), I would go with two IR detectors.

[Soeren]

I would go with at least 6 detectors and LED's (which could be driven from the same oscillator) equally spaced around the perimeter of the 'bot, as otherwise, you would still fall (too late detection), if going towards the ledge in an angle.

[strydom]

Does any one have any recommendation for ledge detection sensors that I can mount underneath my robot pointing at the floor?

i don't want him to fall down the stairs 

what program did u use to make the desing of that robot

[HDL_CinC_Dragon]

what program did u use to make the desing of that robot

Google Sketchup

Gift from the Gods, AKA Google.

[frodo]

going off topic a bit here but Dragon, type into google google god and click on i'm feeling lucky.

[HDL_CinC_Dragon]

Omg I cried from laughing so hard...

[Canabots]

Have you considered trying these?
http://www.hvwtech.com/products_view.asp?ProductID=95
http://www.hvwtech.com/products_view.asp?ProductID=97

According to the description they're meant for surface detection, though they need to be fairly close to the ground (about .5cm I think). Though that might be ideal for you, since it will detect nothing at a ledge and you can program your robot to back away at that instance.

I hope your robot doesn't harm itself! 
 
Canabots

[MaltiK]

Any IR ranger at a 45 degree angle downwards with the horizon will do the job fine. Just gotta change the code a bit to use triangulation of the signals differently and place it closer to the front/bottom.