186Views7Replies

### Author Options:

So I have a pipe dream of building an extremely long range remote controlled boat (100's of kilometers). from my research it seems as if I would need to broadcast my control signal at less than 30 MHz so that the waves travel along the ground and less power is used for longer range. I am up to my ears in designs for the vehicle itself, but I am struggling as to how I would communicate data for such long distances. I have considered adapting Ham radios, and making a sound controlled robot. but this seems unreliable. So... any ideas?

-Cheeseboy

Tags:

## Discussions

If you mean ULF, I think you mean 30 kHz, not MHz. You're going to be dealing with very low bandwidth (think 300-baud modem, not WiFi), and you'll need pretty strong error correction codes. Google Scholar is a good resource to find real scientific and engineering publications, patent results, etc.

There may be commercial products available.

I'm not set as to the frequency as yet, due to the bandwidth issues associated with these lower frequencies, but I got the number 30MHz as the maximum frequency at which radio waves will travel along the earths surface.

Google scholar is really helpful, thanks! it's much better than the Wikipedia and yahoo answers results that a normal Google search turns up (not that I don't love Wikipedia)

Error correction is going to be a major issue, I figure that because no precise movements are required, a few drop outs and lost data is no big issue, the robot will simply turn a bit while it moves, or stop and start. is this a valid assumption to be making?

Regarding error correction -- it depends on what you plan to transmit. The basic thing to consider is, "what happens if a bit gets flipped?"

Let's suppose that your rotation servo works in two-degree steps, so you can code any direction in just a single byte (180 < 255). Now, you transmit the code to turn your robot 45 (really, 46) degrees. You transmit 23 (= 00010111 binary). But the transmission is corrupted along the way, and what the robot receives is "01010111". That's just one bit difference, but now the robot is going off at 174 degrees, not 46. Oops.

Error correction protocols (like Gray coding) include a few extra bits with each byte in order to either detect, or even better, fix, errors like that.

You do not have to come up with something like this yourself. There has been a tremendous amount of research on this (think about space probes), and you can find plenty of solutions in the literature, let alone commercial products. My point is more that this is the sort of thing you need to keep in mind when designing a remote system with a lossy control channel.

Look up LORAN. You should get some ideas there.

Qa

If you were keen enough I guess you could - get the boat to call via a mobile satellite phone once a day or what ever and then upload position & other data and down load new instructions.

If you can't see it - How do you control it?

i don't think your going to pass video back via ground wave radio .

Perhaps an autonomous vehicle is more like what your needing - Send it out on a pre programmed mission and then return. Not too impossible with a boat.

Yeah Water seems to be the best option, by far.

I was thinking of a GPS tracking system, and controlling it via its position on a map, well that's the dream!

But your Idea is far more practical, and there would surely be commercial products for this sort of thing... Thanks for the suggestion!