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Author Topic: falling off the table  (Read 1442 times)

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Offline ccdjr106Topic starter

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falling off the table
« on: July 23, 2009, 10:13:13 AM »
would i be able to use this sensor to keep my robot  from falling off the table    and if it will work how will i use it with a homework board

http://www.robotshop.us/pololu-qtr-1a-ir-reflectance-sensor-3.html

Offline Webbot

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Re: falling off the table
« Reply #1 on: July 23, 2009, 01:30:47 PM »
Since it works on 'reflectance' then it will depend on whether there is anything else on the 'table'. ie if you have some black masking tape on the table then it will probably think it has reached the edge.

Other 'physical' sensors can be 'home made' ie a wire pushed down with a spring onto the table top that fires a microswitch. When it reaches the end of the table the wire falls right down and releases the microswitch. A bit 'mickey mouse' I know - but at least it is responding to physical reality rather than something abstract like the reflective properties of the object it is currently sitting upon (ie just place it on something non-reflective like a carpet and watch it go mad!).

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Offline spizzak

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Re: falling off the table
« Reply #2 on: July 23, 2009, 01:52:10 PM »
How about a Sharp IR sensor mounted on an angle downwards?

Offline ccdjr106Topic starter

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Re: falling off the table
« Reply #3 on: July 23, 2009, 02:06:47 PM »
So what would you reccomend that is not homemade   

Offline SmAsH

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Re: falling off the table
« Reply #4 on: July 23, 2009, 04:28:34 PM »
maybe a sharp ir, or as webbot suggested, a microswitch...
or even an led emitter+receiver pair would do. depends on how much you want to spend...
Howdy

Offline Webbot

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Re: falling off the table
« Reply #5 on: July 23, 2009, 06:59:12 PM »
It really depends on what you need to sense - and how accurately.

A Sharp IR etc may detect a change in reflectance.

I guess you are against my 'home made' solution - and that's fine - but take a leaf from the 'blind' community (of which I have no direct knowledge and so I apologise to them in advance for any over simplification) - but they tend to have a 'white stick' feeler - and not a fancy electronic thing. Their stick is 'binary' - ie 'ok' or 'problem'. And surely an analogue signal, from a Sharp say, would need to be the same - ie 'Im only 40% falling off the table' doesn't mean much.

Of course your main objection may be having a mechanical 'feeler' device mounted on the bot. In which case a photo sensitive device could be a cure - so long as you can live with wrong readings eg where dark = void
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Offline ccdjr106Topic starter

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Re: falling off the table
« Reply #6 on: July 24, 2009, 08:16:47 AM »
so how do i use a sharp ir with the homework board

 


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