Multiple Robots over Long and varying Ranges

Other Hardware Robotics
1

Hi Everyone,

This is a question about:
A) best comms for multiple commands between a (travelling) user and (3) robots over 1-5km.
B) best comms for images (but not live video, talking 4mb images every 10 seconds perhaps) also over 1-5km.

Here is the use-case for background:

I have 3 lawn mowers. But I have, say, 20-30 big lawns spread over a large countryside region. So this is not urban.

Attached image is of a golf course, blue circles show a 2km range.

I want to be as efficient as possible, so I drop 1 robotic lawn mower off at one field, where it'll work autonomously for, say 10 minutes.

During which time I travel to other fields and deploy those and pick up the earlier robots as they finish their tasks. So I can keep shuffling between robots.

Great because of efficiency - but I want to know where my robot lawn mowers finish. So I'm going to get them to send me their GPS.

But I also want them to send me pictures every 10-30 seconds so I can check on how things are going. There is an rpi writing to an SD file, but the Arduino is handling the comms. (it can access the SD).

Hence, between myself (in a car) and each robot I am constantly travelling between 1-10km as I deploy one, and go to another field to drop another off.

I see FPV kits that can do 1-5km. Is this wifi or radio? Surely if someone can do video over 2km, I can do intermittent images over 5km.

So I want the best comms or combos to tackle this (Not Urban)

Here are my approaches ranked best

  1. Long range Wifi seems to work, put a directional antenna on the car/van, and get the arduinos at fields 5km away to log into the wifi. This is periodic as my directions will change but thats fine. Gives me the bandwidth for both commands and images no problem. Wifi at 2.4Ghz

  2. Lora + wiif combo. Perhaps Wifi can't do more than 2km. Lora for longer range e.g. 2-10km but commands only. Wifi for image transmission as it gets to 2km.

  3. Lora but also on 2.4Ghz gives max bandwith for lora. If I use something like GitHub - StuartsProjects/SX12XX-LoRa: Library for SX12XX LoRa devices I can maybe get 1 image every 30 seconds? Not very clear how his 2.4Ghz FLRC mode works at 1-10km vs the test he did at a few feet. Can certainly do commands though.

  4. Other radio options - I'm not knowledgeable about these.

What do you all think?

And thanks for any input.

Update with some LTE-M pricing:
Best estimates for 2GB per month ( or 1000 8mp images per month, 30 a day) is $12 per month per device. Not terrible. And will work.

WiFi ofc would do much higher amounts of images for free. But need a likely rotating directional antenna. And not be obstructed.

Golf Mowing Robots
Golf Mowing Robots1735×1185 281 KB

2

WiFi is radio, as are FPV transmissions.

All transmissions in license-free high frequency radio bands are limited by law in transmission power and to line of sight range, so 5 km range is very, very unlikely for images. No hills, buildings or forests between you and the rigs.

3

Welcome!
I think it can be done. I do not know your resources or skill set so at this point I cannot say with confidence you can do it.

I do not know your laws regarding radio transmissions or what bands are for what, you will need to find that out as doing this on a wrong frequency can get expensive.

You may be able to use the internet but from the sounds of what you are saying it is not available.

4

Theres a guy on youtube reviewing Long range WIfi. He sets it in his house, drives 5km away then logs onto youtube in his car (5km away).

What do you think about this?

5

It is line of sight only. If he claims otherwise, he is lying.

Climb a hill to overcome line of sight obstacles.

6

Yes, agree. And some fine tuning can be done with directional antennas, supposedly to get slightly longer ranges.

7

A great deal can be done with directional (high gain) antennas, but you have to point them in the right direction. Still line of sight only, though.

Cell phone networks would work for your project, if there are towers in the vicinity.

8

The wifi option, if I'm correct, should be easy (?) - e.g. imagine ESP32 on those robots and I'm pointing my long range wifi in their general area. I have them to set up to scan and log into my long range wifi upon detection and send me something.

Sounds feasible?

9

Okay.

Cell phone, like an LTE module for the arduino? Possible, its just cost if I make 3,000 lawn mowers instead of 3.

Does the wifi option generally sound best to you?

I've been looking into Lora and I'm 50/50. For general commands and a few bytes it can constantly send. But the images, even sporadically, I'm not so sure about.

10

What about tweeting a photo from an old phone? I have a device called a OneSheeld that I think may be obsolete but it connected via BT to an android phone (Galaxy S3 iirc, yep, pretty old) and allowed Arduino access to the sensors and devices on a phone.
https://youtu.be/Pv6MCJgPjbc?feature=shared

11

Since this is obviously a business, I hope you have a very large liability policy. At NO TIME did you describe any feedback from your mowers so you can know how many dead bodies the mowers have left behind.

12

Haha, yes I might need to look into that. (if it scales!)

13

You need to carry out some range tests.

Its unlikely someone has already carried out a survey of you Golf course for 2.4Ghz LoRa comms, so the only reasonable way anyone could predict what will work is to carry out tests yourself.

There are ready built, battery powered, modules with SX1280s on them made by Lilygo for one.

Only with practical tests will you know what the maximum data rate you can reliably get with LoRa. If the environment is good and clear then you would likely be able to run FLRC\LoRa at a fast rate, for quicker image transfer times. If the environement is not so clear then you would need to slow down the FLRC\LoRa to get longer range capability.

If during a range test with a particular set of FLRC\LoRa modem settings you are reliably receiving 90% plus of the packets, then its likely that you can do image transfers at that rate.

You talk about using directional antennas to improve range, and whilst that does work you need to check whether its legal to do so, both for FLRC\LoRa and WiFi.

14

Ok.

Re: directional antenna - I can't find anything regarding law except for using frequencies.

What should I watch out for ?

And If both Wifi and Lora worked - which one would you go for? Is there any upside to one over the other?

15

Most all places in the World will have power limits for the frequency bands.

Take the UHF ISM bands, in a lot of places in the World the power limit for the 434Mhz band has a effective radiated (ERP) power limit of 10mW, normally assuming a 2dBi antenna.

If you then add a directional antenna, yagi say, with a gain of an extra 10dB, your ERP would then be 100mW and thus illegal. So in a lot of places in the World adding directional antennas is pointless for transmitting as you need to reduce the transmit power so there is no net gain for distance. You can use it to improve reception range however.

WiFi, it has much higher bandwidth capability.

16

Okay.

I'm thinking to go for the 2.4Ghz band. From what I've read most out of the box antenna with this should be fine - since this band has less restrictions?

P.S - https://www.youtube.com/watch?v=yCLb2eItDyE
This guy has an ESP32 + Directional antenna hitting 10km.

regarding law on this set up: He has a directional antenna on the receiving end.

From the video this is saying, by having the TX at normal EIRP, this is actually legal. He is receiving a video link (band quality) at 10km. Clear line of sight for sure.

My lawn mowers will transmit constantly and my car will twirl around the directional antenna to pick up their sporadic emissions. I think it should be out of the box legal....

17

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