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My Robot Lawn Mower
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I have wanted to build a robot lawn mower ever since Radio Electronics ran the article on the Lawn Ranger in 1990. In December of 1999 I discovered the mowbot list. I was again inspired to create my own automated lawn mower. I spent a month researching to get as much information as I could. I started to build my creation in January 2000.
I went to a lawn mower shop and asked questions about mower blade speed, weed wacker parts, and different grass cutting methods. The owner of the shop took me back to his junk pile and let me sift through the pile of pieces and parts. I walked out with a MTD Electric mower chassis and a variety of parts. This had me heading in the right direction.
From there I experimented with wheels, casters, and motors. It was a big challenge trying to get the right drive speed to torque ratio to wheel size. After I figured this out I had a mower chassis that could be driven with a battery and some lead wires.
I created a relay circuit board and a wire pendent to control the motors. This proved to me that I was going to be able to at least drive the lawn mower chassis around the yard with a wire pendent. This was a big accomplishment. I felt that the project had momtentom to succeed.
Now I had the task of getting the cutting motor installed and finding a way to drive it. I reverse-engineered an electric mower circuit board and created a way to turn the blade motor on and off with the remote pendent. Another big task accomplished.
At this point I had created a robot that I could manually drive with the remote wire pendent. This was cool but not cool enough. In the spirit of true automation it needed to be automatic and take care of more of the cutting detail with less involvement from me.
I needed a microprocessor to control the logic and drive motors, and I also wanted a wireless remote control. I used the Parallax Basic Stamp II for my processor. I also used the RF wireless link from Parallax. I recreated the remote pendent to include the transmitter. This gave me a remote controlled robot lawn mower. Finally I could sit in a chair and remotely control my robot to mow the grass!
Now I wanted a way to place the robot mower in an automatic mode and have it randomly cut the grass automatically. I did a lot of research on what I could use for a perimeter sensor, looking at everything from switches to lasers to underground wire transmitters. I decided to reverse-engineer a dog boundary fence. Using this kind of sensor gave me a solid system for the perimeter transmitter. I figured out a way to have the dog receiver create a logic signal for the stamp II for it to make a logic decision on. This process was as time consuming as the RF – it turned out that the cutting motor interfered with the RF for the receiver. I overcame this problem by placing the perimeter receiver 12 inches in front of the mower. This separation was enough. After the completion of this step I had a robot that could sense the edge of my grass and turn around and head another direction, thus randomly cutting the grass. The perimeter transmitter was installed in a sprinkler box with a battery and a small solar cell to charge the battery. This gave me a truly wireless device.
To cut the grass I first have to use the remote control to drive the robot out to the yard from the garage. Then I put the robot in the automatic mode and turn it loose to cut the grass. I have built a battery sensor in the robot to stop the operation when the battery gets low. I need enough energy to drive the robot back to the garage to get recharged before the batteries completely die.
Just for fun, I placed a strobe light on the top of the robot that flashes whenever the blade is running. Also I placed a LED light bar across the front to give a night driver look. The robot has built in robot sounds for a fun effect. When the unit is placed in the automatic mode it plays the Starwars theme as the RF sensor moves out and before the blades starts. This adds a cool effect.
Now that I have a solid prototype I need to play with the robot lawn mower and experiment with it, making improvements as needed.
SPECS
Mower MTD 18 inch electric mower
Batteries 24V 17 amp cutting mower
12V 7 amp drive battery low speed
18V 7 amp drive battery high speed
12V 1.2 amp logic battery
Motors 2 x 24v drive motors, 45 rpm, 110 inch pounds of torque
1 x 24V cutting motor, ½ hp, GE motor
Wheels 2 x 8 inch wheels
1 x 8 inch caster
Speed 1.5 feet per second
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