the reason robots and especially small weed picking robots
are so expensive is they are not mass produced.
In part. But robots are also fantastically complex, which adds to the price. Keep in mind, complex objects like cars and planes are mass produced, and yet they are quite pricey.
how much does it cost to build and deploy a communications satelight?
yet I can get tv , internet , telephone for apx $80.00 a month.
Yeah, but your not buying the satellite, nor are they mass produced. What you are paying for is permission to intercept the signals from one. Hardly a relevant comparison.
just like the farming robots , but in mass production the small weed picking robots will be made of plastic , have photo comparison software in something like a cell phone sized computer
that takes a picture of the ground then determines the weeds position , then moves to that position and plucks up the weed.
I think you underestimate the complexity of IDing a 3D object, separating it from the background, and identifying what it is. As part of my day-to-day job I write software which automatically analyzes 2D microscope images (which have a only a single colour, btw), identifies and classifies objects within those images, and preforms various forms of analysis and processing.
Despite the "simplicity" of the image processing I engage in, it requires a large distributed network of computers to preform that analysis. We're talking a total of 32 computers cores (plus an additional 8 that preprocess and oversee the whole process). These processes are far simpler than what would be needed to ID a weed verses a crop (which would require colour analysis, morphology analysis, the ability to ID a 3D shape given multiple possible viewpoints, be able to ID different developmental states, etc), and even given the massive computing power we have still takes hours to run. And you think a cell phone-level computer is going to be able to preform a far more complex tasks in seconds?
Also, keep in mind that the robot you propose isn't going to offer farmers much - its simply taking care of one task that a laborer could otherwise do while engaged into other tasks. If you're going to have a guy/gal walking down the rows of your crops planting, picking, running watering lines, tasseling, etc, you may as well have him/her pull weeds at the same time. Why spend hundreds (I'd argue thousands to tens of thousands) for a robot that does one task, when you're going to have to hire humans anyways, and they could do the same task as part of their day-to-day duties?