Because mowing many acres is time consuming.
And kinda dull.
And because it's a good test-bed for other agricultural machines. The mowing deck could be replaced with other things - a bucket to carry tools / rocks / weeds / spray tool / weeding instrument, a camera .. etc.
Non-autonomous (manually controlled) mowing robot ('GizMow-1') initial test
Non-autonomous (manually controlled) mowing robot ('GizMow-1') mowing grass (turn down your volume!) medium small
Non-autonomous first test around the house paddock ('GizMow-2') [and yes, the control box is only attached by a loose strap]. medium small
Autonomous simple grid test in house paddock ('GizMow-2') 8x speedup. small
A rotary mower is a better solution- it won't put as much stress and strain on the gearbox. This one is a battery operated electric rotary mower. These are easier to use with a robot than a petrol-powered mower.
They run on batteries already, and could even share the batteries with the drive mechanism.
They are generally lighter, and hence easier to work with.
They can be turned on and off with a relay, and are therefore easier to fully automate.
The controller can monitor the motor current to detect stalling, near-stalling, or thermal cut-out.
But there are also disadvantages of a battery mower.They are not good at getting through thick grass.
One of the issues with a standard push mower is stalling. If you hit a thick clump of vegetation, the mower is prone to stall. A human operator will intuitively either lift (tilt) the mower or reverse it to prevent the stall. Further, a human operator tends to adapt the speed of pushing the mower according to the toughness of the vegetation - the mower gets pushed more slowly through the thicker grass.
Many modern mowers reduce the need for this process in several ways. Firstly they have a governor, which effectively tries to keep the motor at constant speed. It's like an auto-throttle which revs the engine when it starts to slow down. Secondly, they use swing blades mounted on a disk, instead of the 'rotating machetes' model.
With swing blades, only a small amount of grass is actually being cut at a time. Too much grass, and the blades get pushed back (though the are unlikely to in the photographed example because they are so badly rusted). This might reduce the quality of the cut, but it means the motor is less prone to stalling.
This is both good and bad news for a robot mower - it may not stall, but the robot won't get good feedback to enable it to slow down on thick grass to get a good cut. A servo-controlled throttle could be installed, but it would have to interact with the governor in subtle ways (or the governor would have to be removed).
This would be a good reason to monitor the RPM of the engine.
|Box||EBay||A box. A big box. Always use a bigger box. Jaycar don't stock good boxes this size, and ordering them online is almost as much as buying locally because of the size.|
|Raspberry Pi-3||Core Electronics||The brain of the rover.|
|Voltmeter||EBay||Monitor battery charge and generally check that the voltages are okay.|
|Latching Panic Button||EBay||This is essential. Rovers are temperamental, and large rovers are dangerous.|
|Step-down Power Supply||EBay||To (back-)power the Raspberry Pi. Don't use one of these, they are not reliable. Use a proper automotive one.|
|Sabertooth 2x25||Dimension Engineering||Main drive motor controller. These are great.|
|Arduino Nano||EBay||Arduinos are better than Raspberry Pis at talking to 5V peripherals (like the EasyDriver), and doing repetitive grunt work to take the load of the Pi.|
|WiFi Dongle||EBay||For communicating with WiFi network (including the RTKLIB base station).|
|Warning Strobe||EBay||Robots are dangerous. Warn people about this.|
|50A Anderson Plugs||EBay||May be required to connect battery or drive motors. Cheap when bought in bulk.|
|Pneumatic Wheels||Bunnings||Far better than the ones which came with the wheelchair. I had to take out the centres of these with an angle grinder and a vice. In the end they fit pretty well. Some people complain that these cheap tubes don't hold pressure, but I haven't had any problem.|
Most of the paraphernalia which comes with an electric wheelchair is useless unfortunately. The only parts of the chair that were re-used for this project were the motors (including the gearboxes and axles), and the batteries.
Some wheelchairs actually have water-resistant battery cases for the batteries. These are great for rough or wet terrain. Unfortunately They are also sometimes hard to fit into the available space. This one mounts well on two elongated tubes, but the tubes have an unusual cross-section, which is hard to come by.
A custom mowing deck, which allows the rover to be shorter and more manoeverable.
This is the same as the circuit diagram for the Davrover.
Doesn't show the voltmeter to check voltages, or the red flashing strobe light.
Flashing red light - this is always on when the 24V components are powered.
Two way momentary switch to activate Voltmeter - one way to measure 24V, other way to measure 5V
Voltmeter measures 24V from battery and 5V out from transformer
Small switch 24V, but powering the 24V to 5V transformer
Big on/off keyed switch - high current 24V. This is both a safety switch (with a removable key), and an emergency stop.
Switch-mode transformer 24V to 5V (this has a built-in voltmeter which is not visible when the box is closed). Note that this powers the Raspberry Pi directly through the GPIO. The Raspberry Pi has no over-voltage protection in this mode.
Socket mount for Arduino Nano (not yet actually fitted). This will handle collision detection sensor switches, RPM motor measure, current sensor for electric mower.
Raspberry Pi B Version 3
The Sabertooth 2x25 motor controller. This has been mounted on some flat aluminium with thermally conductive paste to help cooling.
Raspian - Linux for Raspberry Pi
RTKLIB - for the differential GPS
i2c-tools - Raspberry Pi I2C Library
Arduino - for software development on the Nano
Pi4J - Java I2C libraries
RXTX - to let Java talk to the serial ports (and pseudo serial ports)
Java - for software development.
A truckload of software to make this do anything sensible.