Hi folks. I'm a newb. My background is primarily in mechanical and fluids, so the electronics/coding is outside my wheelhouse, but not impossible for me. I am working on a small vehicle (about the size of a Roomba, or 1.5' diameter) that's similar to a lawn mower robot. I'm using an Arduino Uno and have had success at the newb level...for example, I have set up the Arduino to make my vehicle go forward (four wheel drive) until it "sees" an object (via sonar sensor), then it stops, turns 135 degrees clockwise, then goes forward again until it sees it's next object, in which case it repeats the above algorithm.
Now I'll talk about what I need help with. I need to set up a perimeter that the vehicle will stay within. My vision is to use an electric wire, similar to invisible fence used to keep dogs in the yard. I've searched these forums and the web but all I have come up with are solutions that are 5-10 years old and require me to fabricate the perimeter wire transmitter/controller with solutions that look questionable in terms of being satisfactory for outdoor use. I'd like to focus my time on my vehicle (as opposed to the perimeter wire), so I am wondering if maybe in the 5-10 years that has elapsed, did somebody develop a perimeter wire solution that I can buy/use off the shelf? And if so, what is the receiver/sensor solution that I would use on my vehicle that detects the perimeter wire?
Here are the details that I think might be useful in developing answers to my question:
*Outdoor use
*Perimeter wire and controller are powered by standard USA household 110 Volts
*Perimeter wire length is 450 feet
*Skill level: I have a technical background but not much with electronics/coding. I have a lot of potential, but I'm still coming up the learning curve. Therefore, use of expert slang/shorthand may be lost on me.
*Budget is commensurate with an amateur enthusiast. I'd be willing to spend around a few hundred dollars (more or less) for the perimeter wire and controller only (i.e., this budget is not intended to cover the receiver/sensor parts that go on my vehicle).
Hey marco_c. Thanks for the input. The link you provided looks doable. I was just hoping for something off the shelf. I'm still in research mode and this looks like a contender for my needs.
hmmm. I didn't figure on that. Don't they use perimeter wire to guide vehicles? At +/- 1.5 meters it would seem like the vehicles would be "all over the place".
Besides building a wall that can be picked up on sonar, is there something else that would give better precision than perimeter wire or geofencing at a low cost, low complexity?
Do you have an almost perfectly flat operating surface that is also protected from weather, ground water seepage, frost heaves, and so on? That's what those industrial robots have.
They would also not just blindly follow the wire signal, they would employ diversity such as inertial sensing etc.
Farm equipment vehicles use RTK GPS positioning, which give cm-level accuracy over a range of about 10 km.
To get started with that, the minimum expenditure is around $400 for a base station and rover pair of specialized GPS receivers. This setup works as advertised: C94-M8P
Just to point out that outdoor mowers (consumer version) are able to use wire perimeter to outline the mowing area and these have got to be more precise than 1.5m.
I looked through the link posted by Marco_c, and it is a great idea!
If you have two or more inductors, at least one on either side of the robot, straddling the wire, I would not be surprised to see cm-level positioning accuracy.
The basic idea has been used for decades to achieve mm level positioning accuracy on line following robots with optical sensors.
Much appreciated, jremington. I’m getting more and more bullish on the perimeter wire solution. The insight and perspective are really great!!!
Subdude
I would avoid the poorly designed receiver circuit recommended and sold by RobotShop.
It could be a place to start, but the overall design is not frequency-selective, the op amps are improperly biased and not at all decoupled, so they are likely to be unstable and lock up or oscillate.