outdoor ultra sound positioning system robotic lawn mower [duplicate]

Question

I have a dream to build robotic lawn mower that uses a positioning system, so that can cut grass once and effective. Building the robotic lawn mower is not a problem, but the navigation system is, so I came up with an ultrasound idea to locate the lawn mower on a field.

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Basically the lawn mower will have mic mounted on it and will be listening for a signal from the speakers. There will be four ultrasound speakers in each corner emitting sound. At a start lawn mower will send by RF signal to first speaker to send sound and then will measure time and calculate distance. Then will do this process with second speaker and so on. When it will come to the end it will take all distance and calculate where exactly is it on field.

Now I have some questions will this system work outside and in greater distances like 100 meters X 100 meters? Which ultrasound speaker/mic is best for this job? Is there a better way to control position of lawn mower? Will this system ever work?

Answer 1

Things you might need to consider:

• Ultrasonic frequency can be heard by dogs and other animals and insects. It might affect them.
• This approach will work best in open areas with no obstructions such as walls in between or trees because they will affect the received signal in a weird way.
• You will have to use at least three different frequency speakers for a proper triangulation. Most probably three separate mics as well for easy implementation.
• Accuracy will depend on the quality of hardware as well as weather conditions which might be difficult to compensate easily.

Here is what I suggest:

Use GPS modules for positioning. You can easily get GPS modules with 2-3 meters of accuracy. Program the mower in such a way that it stays at a safe distance from any structure/tree. Once it does it's job, someone can manually cut the remaining grass near the structures.

GPS will also save you from the trouble of putting 3-4 speakers in the corners of field and laying wires for them. These days drones are equipped with GPS and they are working well so I believe it might work for you as well.

Modification for lawn mower:

I haven't used one but I feel that small stones or pebbles might damage the blade if they get into it. If someone is manually mowing, then they can tackle the situation but when it's running automatically then I guess you need to take precautions.

You can modify the mower to use a rotating wire similar to this machine:

It uses a plastic wire attached to the rotating head to cut down grass.