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Thread: "ALMower" [was: Robotic Lawn Mower]

  1. #11
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    Re: Robotic Lawn Mower

    I would definitely recommend using a wire to define the perimeter. You install it by staking it down on the top of the grass, and over time the growing grass causes it to migrate to the bottom of the sod naturally. As long as you use the right kind of crimp connectors for any joins (the wrong kind can fail over time, I learned the hard way!) it's pretty indestructible.


    The Robomow does no mapping of any kind. It has no idea where it is and only a rough idea of what direction it's headed. That said, the heuristics for getting out of corners could certainly be better. If it knows, for example, that it hits the perimeter going forward and it hits the perimeter again going backward a few seconds, then it could try turning left and if it hits the perimeter going forward there then it knows the lawn is directly behind it. It would probably have the same problem with closely-spaced trees that the Roomba has with chair legs.

    I like the idea of mapping a lawn using RFID tags. Would they survive buried in the dirt? And would they have enough range for the robot to be able to triangulate its position?

  2. #12
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    Re: Robotic Lawn Mower

    Passive RFID could be buried, yes. I have one implanted. But they don't have near the range to do it.

    Active is where you need to go for that. Controlling the range is the hard part and it wouldn't be buried - not going to punch through that dirt. It would have to be in a water tight PVC (or other material transparent to the frequency) box. Again, though, figuring out how far away from it you are is the hard part.
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  3. #13
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    Re: Robotic Lawn Mower

    Thanks you all for your suggestions guyz. I really appreciated it.
    Can you please help make a list of components (sensors, motors,motor drivers etc..compatible with PIC 16f877A)so that I can buy them from the trossenrobotics store?I am planning to build the robot like robomow(friendly robotics), that is, with the perimeter wire and simply a "Go" button ( and the rest of the mechanism is like meta described). The weight of the robot should be no more than 10 kg.

    Any one got an idea how to build the perimeter wire circuit and make the microcontrolle sense it when the robot approaches the wire?

    Please bear with me coz I'm a debutant in practical electronics/robotics

    Thank you all
    Last edited by revoltage; 08-05-2008 at 09:45 AM.

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    Re: Robotic Lawn Mower

    I'm a beginner myself, but maybe I can offer a suggestion.
    You may not need to actually hook the bot up to the ground wire, just run a constant current through it. They install a Current Sensor onto your bot. Assuming you have no other lines in your yard, the robot could then detect that it had reached the edge of your yard once it sensed the current from the buried line.
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  5. #15
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    Re: Robotic Lawn Mower

    Edit: You could probably do the same thing with a Magnetic Sensor

    And actually, now that I think about it, another interesting idea would be use an onboard IR detector and strategically placed IR emitters to box in your yard. It would probably take some trial and error to get it right, but it would use less electricity, and would be pretty cool! Plus, you could take a picture of it working with an ir lense, and it would look cool.. lol
    Last edited by Electricity; 08-05-2008 at 08:58 AM. Reason: Real edit this time, sorry about the double post, thought I was editing the first.
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  6. #16
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    Re: Robotic Lawn Mower

    That current sensor would require direct contact with the wire.
    That Hall Effect sensor might be usable, but you'd be wanting to bury an electromagnet or one very large ring magnet.

    As I pointed out, the IR emitters are a bad idea.


    What you want is an inductive sensor. http://en.wikipedia.org/wiki/Inductive_sensor

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  7. #17
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    Re: Robotic Lawn Mower

    Quote Originally Posted by revoltage View Post
    Can you please help make a list of components (sensors, motors,motor drivers etc..compatible with PIC 16f877A)so that I can buy them from the trossenrobotics store?I am planning to build the robot like robomow(friendly robotics), that is, with the perimeter wire and simply a "Go" button (and the rest of the mechanism is like meta described). The weight of the robot should be no more than 10 kg.
    There are so many variables that need to be addressed on the subject of motors and motor controllers that IMHO that will be your first design challenge and will dictate the rest of the project. The "average off the shelf" robot propulsion system simply won't do for yard work.
    If these were available back when I started, they would have gotten a serious look http://www.trossenrobotics.com/store...ontroller.aspx
    Now assuming those would work (for discussion), your next step will be to determine your power needs. My guess is you will have some sort of DC motor spinning the cutting device, and you will need to power it as well as any electronics. So, depending on the "cutting motor" you have a minimum power draw of 12 - 23+ amps during the time spent mowing (lets assume 20 amps average). Ideally depending how big or small your yard is you will need a battery capable of running enough hours (or fractions there of) to mow the whole yard in one cutting. To keep things simple lets say it will only take one hour to mow the whole yard. You now need, at the very least, a 20 amp hour battery. A quick google search and it looks like a small 32AH gel cell will weigh 26lbs or 11kg (if my quick in the head math works) and that is just the battery.

    Now I am not suggesting for a second that your original plan to keep things under 10kg is impossible. What I am suggesting, in what now has become a very long winded post, is that you will need to sort out the drive system first and the rest will follow.

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    Re: Robotic Lawn Mower

    Quote Originally Posted by Adrenalynn View Post
    That current sensor would require direct contact with the wire.
    That Hall Effect sensor might be usable, but you'd be wanting to bury an electromagnet or one very large ring magnet.

    As I pointed out, the IR emitters are a bad idea.


    What you want is an inductive sensor. http://en.wikipedia.org/wiki/Inductive_sensor

    I can poke at the digikey catalog after I have a soda and wake up.
    heh I guess you could use a metal detector, and bury enough wire/metal to be detectable..
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  9. #19
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    Re: Robotic Lawn Mower

    A metal detector is a form of inductive sensor. But that's painting with too wide a brush for me. It's the rare yard that doesn't have construction debris 5" under the soil, very inductive water pipes <18" down, sprinkler-system wires, ...

    I'm advocating a tuned inductive probe running on something like an electric fence transformer scaled down.

    One could probably use a capacitance plate and look for the 50/60hz hum too, but having built a 3D sensor using capacitance I can attest just how hard it really is to filter environmental noise from that.

    The more I think about it the more certain I am that Meta's toy uses a tuned inductive probe.
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  10. #20
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    Re: Robotic Lawn Mower

    I'm a bit confused now what to do...
    The motor I was planning to used to cut the grass is also a dc one. I planned to use 250 square metres of the available flat lawn area to carry out the test.

    From what I see from this website I guess the parallax motor mount wheel kit would work. Please give me some clue guyz
    Last edited by revoltage; 02-28-2009 at 11:39 PM.

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