Have you heard of #twitchPlaysPokemon? Well that was some of the inspiration behind this project #googleMowsMyLawn. This project was an idea that my brothers and I had and wanted to do for a little while. When StartFest had a hackathon, we were provided with the perfect opportunity to build it.
The rules were simple: make a gigabit app. That means that it either had to be low latency or that large amounts of data were to be transferred. We were given 24 hrs to complete the project. Other stipulations that we had imposed on ourselves were that all the products that we used had to be off the shelf. So the implementation we used was not the only way to accomplish these things, but it was the fastest. We now hope to improve and expand on this project's abilities.
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Step 1: Parts List
1. Eletric Lawn Mower
Ryobi 20 in. 40-Volt Lithium-Ion Brushless Cordless Walk-Behind Electric Lawn Mower 499.00
2. Two Drills
Ryobi 18-Volt ONE+ 1/2 in. Cordless Hammer Drill 69.00/ea
3. Ryobi 18-Volt ONE+ Compact Radio with Bluetooth Wireless Technology 39.97
4. Three Batteries high performing
Ryobi 18-Volt One+ High Capacity LITHIUM+ Battery 99.00/ea
5. Two metal casters 5.48
3 in. Steel Swivel Caster
6. Two 4in Hole Dozer Hole Saw with Arbor 12.97/ea
7. Raspberry Pi 2 micro Computer 35.95
8. Eight channel relay board 18.10
9. Tripod with iPhone Mounts
10. Two iPods 199.00/ea
11. 18-Volt One+ 6-Port SuperCharger 79.00
12. Zip Ties
13. Four 3"-1/4 bolts with locking washer and nut
14. Eight 1/2" 1" bolts and nuts
Step 2: The Lawn Mower
We chose this lawnmower because it was in the family of Ryobi products and it had enough space to work on the inside. We wanted to keep everything inside the same family of products so that we could swap batteries for any part of our project.
First you need to take off all the unnecessary parts. You are going to need a set of star screw drivers to do this. There are several screws all around the lawn mower holding the green plastic body on to the lower chassis. You will need a star screw driver to get these screws off. Once removed you can take the outer shell off but there is one cord that is attached form the top and bottom pieces. Luckily, there is a quick release clip that you can squeeze to release it. Once that is off, you will see the inside of that race-car-looking lawnmower is composed of nothing more than a motor power distributor and a clip to the battery connection on the top half.
There is a wire that runs up the handle so that you can instruct it you are going to mow and have both hands on the handle. You will unscrew all the plastic tabs holding that on and take apart the button mechanism on the handle. There are 6 star screws on the back. You only need to take out the bottom 4. Once open you can take the two switches out and feed the wire all the way back into the main chassis. This will later be bypassed and hooked up too our relay board so that the raspberryPi can control it.
Now you can remove the two bolts that hold the handle on. It should be looking like a sweet race car. Remove the back flap by popping off the clip on the end of the metal rod that acts as a hinge for the door. Slide that rod out and the door will fall off.
Step 3: Front Wheels and Steering
Normally when you mow your lawn, to make a turn you push the handle down so the front end lifts up and you rotate the lawn mower. That will not work here as there wont be a handle on the finished product. So we need to remove the front wheels and the axle that connects them too the chassis.
Once they are removed, take the metal casters and attach them to the plastic that protrudes out the front of the lawn mower. These wheels swivel a full 360 degrees making them perfect for enabling better movement of the lawnmower. Drill 4 holes that line up with the hole pattern on the casters. Then take 4 1" bolts, a locking washer and a nut for each to secure the wheels to the mower. This is one thing that we will be changing on the next iteration because this lifts the lawn mower a considerable distance off the ground.
Step 4: Onto the Drills
The drills are the most important part of the project. First you need to take the drills apart. We need to make it so we can trigger the drills. The easiest way is to create a trigger between the batteries and the motor. Once you have the outer casing off you can see there are three main parts: the Motor, the trigger mechanism and the battery terminal hook up. We want to disconnect the battery so we can toggle it with our relays giving us the ability to drive. Disconnect the black wire from the trigger mechanism to the contacts.Then take two wires and solder one end to the black wire. Take the other wire and solder an end to where the black wire attaches to the trigger mechanism. Then you can put it all back together inside the drill and just drill a little hole for your wire extensions to make it out. I made my wires about 15" long so I could house the electronics inside the lawn mower.
Step 5: Attaching the Rear Wheels
Once you have taken off the rear wheels, we need to attach them to the drills. This is where the whole saw bits come into play. So take the 3" hole saw bits and line them up with the center of the wheel. There are these awesome holes conveniently on the back to line the up. Take a 1/4" bit and drill into the wheels. Then take some 3" 1/4 bolts and pass them through the bit and then though the wheel. Take a washer, a locking washer, and a nut to secure it and tighten them down. Now you can take the bit and put it into the drill and tighten it down just like any other bit.
Now you're ready to attach the drills to the chassis.
Step 6: Attaching the Rear Wheels to the Chassis
Now that you have the entire drill assembly put together you can secure them to the back of the lawn mower. You want this to cut grass so make sure the clearance is 1 - 2". There is an attachment that comes with the drills that bolts on an external handle for more control. We heated this up to get the nut out of it and then used the bolt to secure the drill to the back of the lawn mower.
Drill a 1/4" hole mid level of the lawn mower then take the extra attachment bolt and slide it through the Drill and lawnmower. Place a washer and the nut on the other side. Drill another hole at the same height on the opposite side for the other wheel and attach the other drill. This makes a pivot point. To keep the drills from rotating drill some more holes and pass zip ties through to tighten them down.
Step 7: RaspberryPi and Relay Board
Time for the brains of this whole thing. We used the raspberryPi to control all of our logic and a relay board to let us trigger the motors for driving. We had ours hooked up to a chat room and used "w","a","s","d" for directional controls. People could login to the chat room and send commands. The raspberryPi then would interpret the commands and drive the motors.
The rest is simple soldering for hooking up the relay board. Take the wires that we attached to the drills and place them in the relay terminals, securing them by screwing the terminals down.
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Check out my other intractable https://www.instructables.com/id/Fix-Hover-Board-Swagway-Glyde-Stick-Red-Ring-of-De/
First Prize in the
Raspberry Pi Contest