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Author Topic: Wire guidance for robot lawnmower?  (Read 8054 times)
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I'm looking for a wire guidance transmitter and sensor system (similar to an invisible dog fence) to control the route of a  robot lawnmower.  A transmitter puts a RF signal on the buried wire and sensors on the robot pick up the signal and follow it.  This type of equipment is used a lot in industry but industrial grade electronics is very expensive.  I am looking for a low-priced transmitter and sensors.  I have googled and found nothing.  Please don't suggest I paint a white line all over my lawn and use photo sensors.  A GPS system is only good for about plus or minus 5 meters, I want plus or minus a few centimeters.  Any other suggestions?  Maybe I will buy a used invisible dog fence and open up the dog collar and see if I could get a signal from it.

Useful links:
http://www.philohome.com (I would like a pre-built plug-in block)
http://www.instructables.com/id/Lawnbot-Learning-Experience/
http://www.agve.se/page/by_desc/inductive-guidance
http://www.robotshop.se/micro/wwwrc_us/indext.htm

Anyone know where I might buy hobby robot wire guidance controls?
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Thats a lot of wire to bury. Previous lawnmower post.

https://www.google.com/search?hl=en&as_q=lawnmower&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=http%3A%2F%2Farduino.cc%2Fforum&as_occt=any&safe=off&tbs=&as_filetype=&as_rights=
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I'm not sure yet if I should use the wire for full guidance or only as a lawn edge detector and let the mower move randomly within the lawn.  I would lay the wire on top secured with big staples and let the grass grow over it.
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I'm not sure yet if I should use the wire for full guidance or only as a lawn edge detector and let the mower move randomly within the lawn.  I would lay the wire on top secured with big staples and let the grass grow over it.

I've run low voltage wire on top of the ground under the grass without mowing issues. laying the wire can result in a really sore back!
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If you definitely must go with a wire (as opposed to say, magnets and hall-effect sensors, or something else) - a cheap way to do it would be to use something like this to energize the wire and pick up the "tone":

http://www.harborfreight.com/cable-tracker-94181.html
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Thanks cr0sh.  What a great idea!  I'll check into it. smiley-grin

I looked into it. Seems that the tracer sensor needs to be within a few mm of the wire.  I need a sensor distance up to about a meter. smiley-cry

Thanks anyway!
« Last Edit: August 18, 2012, 10:04:29 am by warren631 » Logged

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Thanks cr0sh.  What a great idea!  I'll check into it. smiley-grin

I looked into it. Seems that the tracer sensor needs to be within a few mm of the wire.  I need a sensor distance up to about a meter. smiley-cry

Thanks anyway!

Well - a meter would be problematic; but a few mm seems misleading (I used one of these to trace wires in the walls of my house; I certainly wasn't anywhere near "a few mm" of the wires).

Anyhow - that might just be a question of amplification? Maybe you could amplify the output in some manner of the toner transmitter (or amplify the receiver audio)? For as little as such a device cost, it would be worth experimenting with...
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Update:
My solution was to buy a pet invisible fence (http://www.hisgadget.com/waterproof-electronic-fencing-system-transmitter-collar-w227-one-to-one.html) and hack into the dog collar unit to get a 0 - 5 VDC signal for how close to the wire (edge) the mower was getting.  It was easy and works well.  The signal was a little jerky so I had to do exponential smoothing on it.  The perimeter wire is buried or out of sight.   On a timed basis the mower follows the edge wire (getting close but not over the wire), sometimes it does random patterns, sometimes it does spirals if it finds enough space.  It also has a IR receiver for remote manual control using an old TV remote (I use this to move it back to the garage - it is heavy!),  scanning ultrasonic ping sensor for object (people) avoidance and three bump switches.  I used an old power wheel chair ($100 on Craigslist) base for the chassis, battery and charger (the owner had just bought new batteries before he died), wheels, drives, gears, and powerful motors included.  All I had to do was remove the chair part, add the cutters in front (4 string cutters), add brains (Arduino Uno) and sensors.  The wheel chair maker says it goes 18 miles between charges!
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warren
I'm very interested in your approach. I'm building a lawn mower myself right now.
Do you have some visuals?
Best regards
Jantje
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Sounds like it was a great success - do you have anything showing it in action?
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Well done I have a friendly robotics lawn mower that I would like to hack with your approach.

My lawn mower starts to spin the wheels when it tries to go up a hill steeper than 15 degrees...It would be nice to detect slippage of wheels and change direction when this is detected. 

Does your yard have many hills?  Maybe the weight/wheel chair wheels don't have this issue
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Paulware
My 2 cents: replacing the wheels by more grippy ones may be easier.
Best regards
Jantje
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Well done I have a friendly robotics lawn mower that I would like to hack with your approach.

My lawn mower starts to spin the wheels when it tries to go up a hill steeper than 15 degrees...It would be nice to detect slippage of wheels and change direction when this is detected. 

Does your yard have many hills?  Maybe the weight/wheel chair wheels don't have this issue


I've got one of these, but I haven't taken the time yet to hack it (purchased it used off of Craigslist for $50.00!); surely there is some place on the motor driver board that is monitoring (or can be made to do so) the current to the motors; look between where the motor wires connect and the output h-bridge drivers - you might have to do some probing. Basically, you are looking for a point on the board where you can monitor a voltage representing the current consumption of the motors; it will be lower when the wheels slip. Good spots to probe for are any place marked "TPn" - where "n" is a number (stands for "test point" and is used for troubleshooting the boards, usually). Testing will be another thing (you'll want to build a pony brake with adjustable slip, and test the motor without the gearbox).
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Here is my "RoBoMo" in action:  See my previous description posted somewhere herein above.

http://youtu.be/bmf7OF1B-lo  and http://youtu.be/T9WiJkRTDTo

Still improving on it.  The speed and navigation need improvement.  It goes too slow up hills and too fast down hills (sometimes it overshoots the invisible dog fence wire boundary) so I need to add some kind of speed regulation - maybe I need 'IR Compensation' on the DC motors, or feedback to a PID control from tachs or encoders on the wheels?  I will try something simple first such as a tilt switch to switch between low and high speed to give more power when its going up a hill.  Any other suggestions?

What I have learnt for others:  Orientation of the four DC cutter motors was critical to minimize RF noise interference to the dog collar sensor.  I had a big problem trying to eliminate motor brush noise (using shielded cables, proper grounding, capacitors, etc.) then I noticed that if I just rotated the motors to a certain point, found from experimentation, I could almost eliminate the noise problem.  

The power wheel chair's joystick was very complicated using four hall-effect IC sensors on the joystick and a 'fly-by-wire' custom network cable down to the drive motor controllers.  So I used two servos (in the white inverted ice cream box on top) to actually move the joystick for speed (X servo (including forward and reverse)) and direction (Y servo).  This seems to be a simple solution.
« Last Edit: October 24, 2012, 07:28:29 pm by warren631 » Logged

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Nice video, I'd like to suggest a magnetic azimuth sensor to make straighter lines, but maybe it curving because it detects the doggie wire.  Very impressive.  What kind of cutter device are you using?
Thanks,
Paul
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