How to set a perimeter for an autonomous robot?

[cesarito160]

m team and I are building a robot that will autonomously pick up tennis balls, we would like to set a rectangular perimeter of maximum 10m, can you give me some ideas how to make the robot not leave that perimeter and only pick up the tennis balls that are inside of it? what kind of sensors will i need to use? Our robo uses a camera to recognize the tennis balls, we could program it not to leave a white line but its too much programming. Do you have any more ideas? thank you.

our robot design is something like this
http://tennisrobot.org/wp-content/uploads/2010/03/capPic.png

[random robots]

i think hall effect sensors with a magnetic fencing around the proximity should work.

[Conscripted]

I think I would run a wire around your perimeter and use a hall effect sensor to detect the magnetic field created by the current running through the wire as stated by random robots. Good luck with your project and let us know how it goes.

Conscripted.

[Razor Concepts]

Does anyone know proper calculations for what kind of current goes through the wire for the hall effect sensor? I know it should depend heavily on wire resistance.

[madsci1016]

My senior Design robot had just such a method of containment.

Florida State University IEEE SouthEastCon 2009 Robot Design Test Runs

While the suggestion of hall effect sensors seems good on paper, once you do the math, you will realize there are no hall effect sensors sensitive enough to do what you need. We even tested that to prove it.

What you can use is an inductor. I will have to dig for the schematic of the sensor I designed in school, but it was basically an inductor, tied to a few stages of Op Amp amplification and notch filtering for just the frequency of the wire running underneath the grass.

We did not design the circuit for the fence itself, it was part of the course given to use. All we knew was it was a sawtooth wave at 10KHz.

It worked decently, although motor noise and dropping battery voltage was still a problem sometimes, until I added an auto-sensor calibration cycle at the beginning of each run that sampled the noise floor and set the threshold just above it.

[Soeren]

Hi,

Two coils in front of it, angled somewhat to both be directed towards the wire, if you need to be able to discern the position accurately.
A single coil will do if you go by the amplitude and never need to cross the fence.

The fence itself should just be a single wire with an audio signal - preferably a sine of say 2..10 kHz

In effect, it's an inductive loop as used by the telecoils in hearing aids - doesn't take much power, 5W should be ample, but the output amp needs to have a reasonable low output impedance.

[madsci1016]

A single coil will do if you go by the amplitude and never need to cross the fence.

Exactly what I did! We just had two so we could determine the best direction to turn away from the fence.

[kd5kfl]

1) an intense light source, at a specific wavelength, directed around the rectangle. a laser, with three mirrors
2) a sensor, mounted top center, that senses that wavelength
3) circuitry to reverse the robot when the sensor triggers.

easy enough to say, if you're the guy that doesn't have to make it work.

[klims]

Is this robot being made for practical purposes? As in will it be operating on a tennis court?

I ask this because tennis courts are usually a pretty consistent colour that would be noticeably different to the surroundings. Would be pretty easy to keep a robot on a tennis court using image processing.