Newsgroups: comp.robotics
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From: rlee@andy.bgsu.edu (Bob Lee)
Subject: Re: Run Rabbit...Run. Cat detectors.
Message-ID: <C2vH6z.K8n@andy.bgsu.edu>
Organization: Bowling Green State Univ.
References: <1mbht6INN2s9@clover.csv.warwick.ac.uk>
Date: Mon, 22 Feb 1993 22:59:22 GMT
Lines: 46

In article <1mbht6INN2s9@clover.csv.warwick.ac.uk> esrbu@csv.warwick.ac.uk (Mr I M Hunter) writes:
>Dear all,
>        I wish to build a small (tennis ball sized) mobile robot that has
>a self-preservation instinct when faced with my cat. That is, it runs away
>from it. The thing is how does it detect where the cat is and whether it
>has pounced upon my poor, doomed robot. I was thinking of attatching an
>infra-red emitter upon the cats head but fear that the cat (Pluto) would be
>more interested in this thing on its head that the small squeaky thing
>being paranoid in the corner as well as well as being accused of crulty for
>my own pleasure. There needs to be a number of these receptors so that the
>robot (which rolls around making cute sqeaky noises) has at least 2 sensors
>that can detect the cat at any time. Any ideas? Processing takes the form of
>"run like hell if the cat is pouncing or whibble around making squeaky
>noises otherwise". Sensors need to be cheap, vague term I know but around the
>20quid ($30 for US of A citizens) mark because there is a price limit to my
>strange pleasure devices.
>                        All comments welcomed, Iain


It sounds to me once again that the matter of proximity comes into play.
IR emitter/sensors are very cheap and using the circuit I mentioned in a
previous article (very recent) minus the schmitt trigger you could use the
filtered signal and check for very sudden changes in IR radiation being
reflected back. This would indicate that your cat is coming. Naturally the
robot assumes that the cat is the only moving object in the area. If you
were to move close to it then the robot would roll away from you too. To
get it to recognize your cat then I thing you would need some complex
object recognition which I don't think you could fit in a ball.

You would definitely need a faster signal then 30Hz, but depending on how
fast your cat pounces on his prey you would have to decide that. Basically
you would just need to check the voltage level of each returning pulse and
when that level changes drastically, enough that you can rule out the
possibility it being noise, then the robot can surmise that something is
moving close to it and it can basically roll like hell!

I think however you would need a lot of sensors to cover the full range of
vision and depending on which sensor gets the drastic level change in a
return signal that will determine which way the ball rolls.

It would definitely require a lot of experimenting and calibrating. I'm
still having a hard time visualizing how you would fit it all in a small
ball that would look apealing to your cat.

-BOB

