868/915 Mhz as a viable frequency for submarines.

Starting a new thread...

David and i have a few threads here now on using OpenLRS systems instead of the traditional PPM base frequencies, in an attempt to move submarines into the 21st century.

Both David and i have found great success in 433mhz in the USA, and 458mhz in the UK.

There is one small problem with 433mhz in the USA... it requires that you have a HAM radio license to be even close to "legal"...

There is, however, a different frequency that some OpenLRS makers/sellers have used in the past.  915mhz.  It does not require any additional licensing, and because of that I own a few receivers and one transmitter module that operate using the OpenLRS protocol in 915mhz, and they seem to work okay, as best as can be expected, giving me up to 3 feet of depth in the right circumstances...

The issue is that no-one now seems to be making these...   my last ebay source has told me that he has moved on to other items for sale, and he will require minimum quantities before he will make more...

so...

I have started looking around for other 915mhz equipment.

By shear luck, a very large Chinese radio manufacturer, FrSky, has started producing a range of products using 915mhz.  they sell it as a long range option for drone flyers... with quoted distances of up to 20km by some reviewers (air usage).   again, what i have discovered is that i can get anywhere from 18" to 36" below the surface and still have excellent control of the submarine using 915mhz.

I have spent the last 3 months testing both the 7 channel receivers that use OpenLRS on 915mhz, and two of the FrSky recievers that use the 915mhz frequency.

The modules i have tested are the OpenLRS TX module and a separate 7 channel RX that was sold by a russian ebay seller,

I have also been testing the FrSky R9M module, and both their R9 receiver, a full size 8 channel receiver, and their R9 Slim, a small 6 channel receiver designed for drones.  I also just recently picked up a brand new receiver they sell, the R9 mm/mini.  an ultra micro 4 channel receiver designed for tiny racing drones.

I have tested both the R9 and R9 slim in my Norbert Brüggen Delta submarine, and the R9 slim in my SWM blueback.  i have just recently put the R9 mm in to the blueback, and will be testing it as soon as possible.

to give you an idea of how big the R9 mm is, i have attached a photo.

the R9 slim and R9 mm are not designed to attach directly to servos without a little extra work, they are primarily designed to connect to flight controllers for drones with only 3 wires (positive, negative, signal) and they can operate on a single lipo cell (3.7v), but with a little work (soldering up connectors or a harness) they can be made to work with standard size or miniature servos.

more to come.

Impressively tiny equipment there, Tim!

Could be very handy for conversions of small kits.

The problem with all these developments is the continuing manufacture of equipment. 433Mhz seems to be reasonably robust in supply but I note the difficulties that you have in using 433 Mhz in the US and the supply problem with 915 Mhz.

To help anyone wanting to experiment with 915Mhz in the UK, I have just been having another look at potential UK radio frequencies. (Better than writing Christmas cards!) It seems that 886-906Mhz would be possible if you can tolerate some interference from industrial, scientific and medical apparatus (ISM).

This is the current basic document covering radio control:

https://www.ofcom.org.uk/spectrum/radio-spectrum-and-the-law/licence-exempt-radio-use/licence-exempt-devices/Radio-controlled-models

This document states the following:

"In addition to the frequencies above, radio control models may also share the frequency bands allocated to General Non-Specific Short Range Devices with all other such applications. Most of the Non-Specific Short Range Devices allocations remain impractical for model control, due to restrictions on channel capability or too little power to give sufficient range. Also, most General Non-Specific Short Range Devices allocations are located in bands also used for industrial, scientific and medical apparatus (ISM), so may suffer from interference in certain locations. Details of ISM bands are shown in annex A of the UK Frequency Allocation Table."

Annex A states:

https://www.ofcom.org.uk/__data/assets/pdf_file/0022/103297/fat-ism-frequencies.pdf

"83·996-84·004 MHz
167·992-168·008 MHz
886-906 MHz (My emphasis)

Radiocommunication services must
accept harmful interference from ISM
apparatus operating in accordance with
the WT (Control of Interference from
RF Heating Apparatus) Regulations
1971.

The WT (Control of Interference
from RF Heating Apparatus)
Regulations 1971 specify the limits
of levels of radiation permitted
outside the ISM bands."

So could be worth some experiments?!

David

David,

i have specifically standardized on this hardware because it is backed by one of the larger manufacturers... it is not open source DIY equipment. it is commercial equipment sold by FrSky to be used with FrSky radios, the target market is quad copter pilots. It is sold in the 915mhz range for US sales, and 868mhz range for European sales.

I am at a R/C regatta/fun-run this weekend where i had hoped to be testing the receiver shown in the original posting, but the speed control for that submarine died 15 minutes into the first day of the fun-run, and i wasn't able to do any real testing. It's getting too cold where i live to be running anything (water is now solid) so i am going to have to pick this testing up in a few months when the ice melts.

beyond that, i have tested standard size receivers and mid size receivers and they are performing nicely.

Thanks Tim. I had rather missed the point that the gear is being offered by a major manufacture (FrSky) so hence better reliability of supply?

It must have been something to do with Santa Claus but just before Christmas, Hobbyking were offering this combo below at the bargain price of £3.95

ORANGE RX OPENLRSNG 915MHZ WITH BLUETOOTH TX MODULE AND RECEIVER COMBO (JR PIN CONFIGURATION)

SKU: 9171000872-0


I duly ordered one and when (and if?) it arrives I will give some feedback on how it is. (I am particularly interested in the use of Bluetooth for setup and whether the frequency can be changed to UK frequencies.)

David

David,

so sad to see that last post...

2 huge problems:

1) I bought that when it was brand new... at the time i think it was a package deal for $50 or so... but it was a total bust. it is running (like all things OrangeRX) an outdated rev of the firmware... but it is a SPECIAL version of the firmware designed to work in conjunction with a mavlink drone flight controller. it requires a special version of the Chrome Configurator, and even then, there are no binaries available for the 915mhz chipset. i actually destroyed a receiver trying to update it with the standard configurator and original 915mhz binaries. when i got the second receiver in, i was able to get it working (only with the special 915mhz bluetooth module) but even then, i had to buy a ppm to pwm converter to get standard servos to work with the receiver. as i said, the receiver is designed to work with a flight controller, not servos, so it literally has a 3 pin connector to go directly into one of those, and the decoder allows you to revert back to servos.

link to sbus/ppm decoder:
https://alofthobbies.com/frsky-sbus-decoder.html

link to sbus/ppm decoder programmer:
https://alofthobbies.com/frsky-servo-channel-changer-sbus-cppm.html

if you need more than four servos, then you will need to have 2 or more decoders, in parallel, up to a total of four decoders for 16 servos.

then i had to wire up a wiring harness that fed 6 volts to both the receiver, and the decoders, to drive the servos. it was a dreadful mess of wires.


2) 915mhz is not legal in Britain, 868mhz is... and for the openlrs/openlrsng devices, the 915mhz chips are pushed a little too far to work right, so a different set of chips specifically for 868mhz need to be supstituted 90% of the time.


put lets hope you have better luck... right?


all in all, even with the 915mhz being legal, it still ended up being a total bust.

Fortunately it only cost £3.95 - not too many dollars even with current exchange rates!

Your experiences, Tim, maybe show that they were offloading the stuff. (I was getting worried that Hobbyking were deliberately targeting me with special offers!)

Did your version of the combo have Bluetooth?

Many thanks for the advice.

David

David,

my combo had the bluetooth, but i had to remove it... the bluetooth board connects to the exact same pins the FTDI adapter connects to when connecting the TX module to the PC when running the Configurator chrome app... I didn't want or need the bluetooth, so it was removed as soon as i discovered that i needed to. of course, i then promptly fubar-ed everything trying to update the firmware, and the bluetooth was irrelevant at that time.

I have no idea how/what/when the bluetooth is used in the originally intended mavlink scenario.

one other "advantage" i neglected to mention in the first thread... because the new FrSky 915mhz R9 equipment is made by FrSky... I don't have to build my own telemetry devices (unless i want to) all the OEM X series sensors plug directly into the receiver, and the transmitter knows how to display the data with no futzing.

Well the good news is that Hobbyking delivered the previously discussed equipment very quickly. The bad news is that it is exactly as you say, Tim!

No servo sockets etc.

I had a little play with the Bluetooth and this did pair with my Samsung Mobile which had"Mission Planner" installed but for any serious configuration I would need a laptop with Bluetooth.

My experiments were conducted quickly because I had no way to change frequency.

So I don't suggest anyone else repeats the experience although I now have an interesting £3.95 paper weight!



David

Sorry late to the post, this could be old news by now,
I have the same thing and the 433MHz one too. Banch tested with this encoder got all the servo working.

Sorry for digging up this Thread...

Did you get any usable results with the FrSky R9 stuff ?

I am also looking at the LoRa DIY in the other thread but would prefer an of the shelf solution.

BG Max

maxx78 wrote:Sorry for digging up this Thread...

Did you get any usable results with the FrSky R9 stuff ?

I am also looking at the LoRa DIY in the other thread but would prefer an of the shelf solution.

BG Max

Maxx,

Covid did a real number on my testing of this equipment.  basically didn't get anything done in 2020.

I did finally get to a submarine regatta with this equipment in the summer of 2021, and it did work well enough, but it doesn't have the range that one of the other 915mhz products i have used has, and FrSky has really screwed up their product line, now selling equipment that uses a completely new protocol  (old stuff called accst, new stuff called access).   to get any of the older accst stuff working, i had to go through more firmware upgrade headaches than i originally went through with the OpenLRSng DIY equipment.

I have not yet purchased any of FrSky's new access based equipment to see if it works any better.

So far, the best 915mhz equipment i have used is a now out of production OpenLRSng product made by a russian guy who sold his stuff on ebay.  It went by the name of "ChipLRS".  it was nice, good stuff.  I still have several of his receivers and a transmitter module.  if the transmitter module stops working i am dead, but i have about 8 of his receivers, so hopefully, if i drop back to using his equipment, i have enough parts to keep myself working for a while.

I have since (in the last 12 months) purchased two more 915mhz products.   The first is the "Crossfire TBS" family of products that are all 915mhz.  I have one TX module and two different RXs (both standard PPM servo output)  The Crossfire products are primarily meant for Drones, but in the last couple of years they have both dropped their prices, and come out with receivers that work with standard servos.  their equipment is more sophisticated than the FrSky r9 equipment, so it may not have the weird range issues i was getting with the FrSky stuff.

TBS Crossfire is in a weird position of not really being a big corporation, but it has been around for years, long enough that it has a lot of clout in the drone community, it seems to have some respect for building good hardware, and it is big enough now that it is diversifying its product lineup, making cheaper versions, as well as stuff not targeted directly at drones.

Due to the testing being done by a gentleman on RCGroups.com, the second set of hardware i have picked up is a new family of products for Drones based on OpenLRSng, called "ExpressLRS".  products are both 2.4ghz and 915mhz, so i picked up a chinese 915mhz matched set of TX module and receiver.  I hope to be testing both the Crossfire and ExpressLRS equipment this summer, in two different subs.   the ExpressLRS looks very promising, having almost identical features to the ChipLRS equipment i like so much.

Of course the ExpressLRS stuff still suffers from the DIY type of low level support and no backing from a large company, so we have no idea how long it will stick around.  If i find that it "works" for me, i plan on buying a ton of those parts so that i have enough equipment to last me for the foreseeable future (20 - 30 years)

a link to the RCGroups discussion:
https://www.rcgroups.com/forums/showthread.php?4103101-RC-systems-for-submarines

chinese expressLRS:
https://www.getfpv.com/catalogsearch/result/index/?frequency_group=905&q=happymodel
https://www.getfpv.com/happymodel-expresslrs-pwm-rx-6ch-epw6-900mhz.html

expressLRS to servo adapter (for RX in first getfpv link above)
https://www.getfpv.com/mateksys-crossfire-to-pwm-converter-crsf-pwm-c.html



tbs crossfire products i purchased:
https://www.team-blacksheep.com/products/prod:crossfire_micro_tx
https://www.team-blacksheep.com/products/prod:xf_nano_div_rx
https://www.team-blacksheep.com/products/prod:nano_divrx_adptr

Thanks for this detailed explaination.

FrSky really drives everybody nuts. My Taranis & X7 are still using pre-LBT firmware. But at some point there is no avoiding the update nightmare for my boats, planes and Drones.

And i completely forgot about the TBS Crossfire, they do some clever tricks with reducing the number of channels and refresh rate to get more range.

And i really like the idea to have telemetry.

I got my hands on a EHZUHF set working on 433Mhz but that stuff is no longer sold for years.

And i will read up on the RCgroups thread.

tsenecal wrote:....
chinese expressLRS:
[link]
expressLRS to servo adapter (for RX in first getfpv link above)
[link]

.....

I was browsing around yesterday and also found a 6Ch Receiver for the ExpressLRS, so you would not need the Servo adapter:

HappyModel ExpressLRS ELRS EPW6

i found it at Aliexpress, but i am not allowed to post links (yet)

maxx78 wrote:

tsenecal wrote:....
chinese expressLRS:
[link]
expressLRS to servo adapter (for RX in first getfpv link above)
[link]

.....

I was browsing around yesterday and also found a 6Ch Receiver for the ExpressLRS, so you would not need the Servo adapter:

HappyModel ExpressLRS ELRS EPW6

i found it at Aliexpress, but i am not allowed to post links (yet)

Yep, i saw that, but the TX/RX combo i bought has a tiny little RX that needs the servo adapter, that was why i gave the link for it, but GetFPV also has the 6ch pwm receiver as well:

https://www.getfpv.com/happymodel-expresslrs-pwm-rx-6ch-epw6-900mhz.html

Just a heads up on this topic.

I just now got to a point where i can start playing with the ExpressLRS equipment. I am getting two of my submarines ready for a local regatta on 8/13-8/14, and a california fun run the weekend of 9/3-9/4.

I finally have all the hardware set up and working on those two submarines.

they are the same two submarines i tested the FrSky r9 equipment on, so i should get a good idea of the differences.

I have already found two big differences... the ExpressLRS (ELRS for short) equipment i bought.... some of it was dead on arrival, so i went ahead and ordered two of the 6 channel PWM receivers that were pointed at in an earlier post.

Those are definitely recommended as items you will want to get if you want to use servos, they offer fail safe settings directly via a setup page.

Other important info: there is a configurator tool much like the configurator for the OpenLRSng equipment that David and I have used, but it is used differently.

the configurator's sole purpose is to build firmware for the devices, since each device (TX module or receiver) has a 2.4ghz wifi chip as well as the RF chip for 868/915mhz. specific configuration options for the device are set using the wifi page.

again, all of this is primarily designed for Drones, so the assumption is that you will set any additional features like failsafe from the Drone's flight controller. The PWM servo receivers don't need flight controllers, and they have more options (mainly the failsafe settings). the use of the PWM servo receiver's is almost mandatory for us, otherwise a failsafe device for a specific servo output will need to be used.

i have also picked up two different brands of equipment. From a company called "Happymodel" and a company called "BetaFPV". the betafpv equipment seems more polished, and will work with any radio that uses the JR style socket, or the new "nano" style frsky socket. the Happymodel equipment works with JR style socket radios, but it also requires the use of a "Lua" script to initiate binding, therefore it basically only works with radios that run Open-TX.

more to come after the testing this weekend.

Last weekend i finally got to try out my ExpressLRS at 868 MHz.

I was at a RC event in an outdoor pool (Freibad ). on the final weekend of the season they open it for RC Boats.

It worked not so well as i hoped but on the second day there where some other Subdrivers and they also had issues on 40MHz.
One of them mentioned that the operator increased the chlorine content in the water for some reason.

We all had issues after 5m @ 1m deep.

But what was really great is the telemetry, it had issues while being submerged but connected often enough, so i felt comfortable to run my battery quite low

My conclusion is that it work at least as well as 40 MHz but with the benefit a digital link and telemetry data.

This was with a Happymodel Transmitter and ES900 receiver

I spent this past weekend at a sub fun run, i ran 3 different boats (Delta, Holland, Blueback), all using the ELRS hardware.

all ELRS hardware was updated to identical version 2.0.0 firmware so all devices could bind to one another.

Delta = Happymodel epw6
Blueback = Happymodel epw6
Holland = BetaFPV ExpressLRS Nano 915MHz Receiver connected to a Matek CRSF PWM 6

all three subs theoretically had a 6 channel receiver capable of driving six standard servos.

for the transmitters:
both transmitters were upgraded to the latest Open-TX so they could output CRSF protocol, and run LUA scripts for the TX module binding operation.

FrSky x9d with a Happymodel ES900TX module

FrSky Q x7 with a BetaFPV ELRS Micro 915MHz TX module.


here is a rather non eventful youtube link for a 2 minute run of the Blueback:
https://www.youtube.com/watch?v=kovN-EEkJu8

as you can see, it runs perfectly fine.

that specific run was using the FrSky Q x7 with BetaFPV module.

there are other videos taken that weekend of other submarines running on 75mhz equipment, the 915mhz and 75mhz usage at that venue was indestinguishable.

as to my personal preferences from the weekend of use:

RX:
i prefer the happymodel epw6, it can be configured with channel "swapping" and specific failsafe values for each individual servo output.   this is not possible with the matek CRSF pwm boards, they set their failsafe values based on their "startup" settings, ie, whatever the switch on the TX is set to when you first link up with the RX, that is your failsafe value.  i prefer setting it specifically, there is no possibility of stupid mistakes.

TX module:
i prefer the BetaFPV module, because it has a nifty little tiny lcd display and tiny 5 position joystick right on the back of the module, allowing you to configure it and bind using only the module.  no need to install or use LUA scripts on the radio.

both TX modules were also set the "WideHybrid" mode, and 100mw output max.  widehybrid mode allows the TX module to send 4 proportional and a single on/off 5 channel packet each time, and an additional 7 proportional channels one at a time, allowing the epw6 to actually use 6 servos fully proportionally.

With all the hassle i have had to deal with using the FrSky r9 equipment and the FrSky move to 'access' protocol from 'accstd', i do think that the ExpressLRS is a better product, for both the easier setup and compatibility (you can upgrade firmware much easier, you can tell what version of firmware you are using much easier, and there is no confusion about what will work with what)

both systems (r9 and ELRS) do require more setup than either the older 35/40/75 mhz equipment, or the 2.4ghz equipment.  i do think that the ELRS is slightly easier to setup than the OpenLRSng, only because there are fewer options to decide on.


I will now decide which sub gets to be refit with the TBS crossfire module and receiver to see whether it is better than the ELRS or not.

tsenecal wrote:.....
RX:
i prefer the happymodel epw6, it can be configured with channel "swapping" and specific failsafe values for each individual servo output.   this is not possible with the matek CRSF pwm boards, they set their failsafe values based on their "startup" settings, ie, whatever the switch on the TX is set to when you first link up with the RX, that is your failsafe value.  i prefer setting it specifically, there is no possibility of stupid mistakes.

....

i use the RX with a flightcontroller for drones (Matek F411) so i set the failsafes in the FC. The FC also works to keep the Sub level (don't know the english term for "Lageregler")
The nice benefit is that i get telemetry so i know battery voltage and used capacity.
Telemetry does not seem to work well while submerged but i get updates when surfaced.

Side note: the FC has a pressure sensor normally used for altitude on planes/drones. This actually can be used to see if the sub is watertight. The dive system creates an overpressure inside the WTC which reads as altitude in the FC. So no or small change in altitude = no leak.

maxx78 wrote:

i use the RX with a flightcontroller for drones (Matek F411) so i set the failsafes in the FC. The FC also works to keep the Sub level (don't know the english term for  "Lageregler")

"leveler" would be the best term...

however... looking at the Matek series of products, there seems to be several F411 FCs made by them... i looked at the "F411 wing" model, since it technically has 6 servo outputs (2 of those designed specifically for ESCs)

there is also a larger "F405 wing", which appears to have 8 servo outputs... (2 for ESCs)

i guess its time for me to look at FCs and their setup software.


thanks maxx for posting your findings as well.

I used the "MATEK F411-WTE"

it took me a while to figure out how to setup a failsafe that works like i intended.

But now it works great.

I just set it up as a plane so the outputs ar correct for the use on a Sub.
An i remapped the outputs to the 4 Pin headers. Unfortunately INAV locks output 1 & 2 for motors and i didn't like to solder the ESCs directly to the FC.
I also treid to use Betaflight for the Fc but could not get the airplane mode to work. Beta flight is more designed for Multirotors.

I also had the idea to connect the barometer to the outside and use the "altitude hold" function of the FC for depth control. But it will only work to around 80cm depth as the baro measures max 1100 hpa absolut pressure.

maxx78 wrote:I used the "MATEK F411-WTE"

it took me a while to figure out how to setup a failsafe that works like i intended.

But now it works great.

I just set it up as a plane so the outputs ar correct for the use on a Sub.
An i remapped the outputs to the 4 Pin headers. Unfortunately INAV locks output 1 & 2 for motors and i didn't like to solder the ESCs directly to the FC.
I also treid to use Betaflight for the Fc but could not get the airplane mode to work. Beta flight is more designed for Multirotors.

I did see that the Matek f411 wte (or its predecessor the wse) seems to be popular in the youtube videos... figured i would get one of those.

so... are you using INAV or beta flight for your FC? i understand your concern for outputs 1 & 2, although i figured for those to be used by me, i would wire up a couple female servo pigtails so i could use whatever i want.

looks like i get to order a wte

personally i use INAV for my Planes and Betaflight for the Quads.

As far as i know Betaflight is a little bit ahead in development and features (which are almost irrelevant for Submanrines), while INAV is more geared towards planes.

I first tried Betaflight but couldnot get the servo to work so after an Hour or two i flashed INAV and everything worked.

Side note: i my old Sub i used an Arduino Mini and the accelerometer from a Wii Nanchuck, running o a modified version of Multiwii (the grandfather of Betaflight) and it worked well.


Maybe we should move this to a new Thread ?

hmm... we are still talking about using 915mhz/868mhz equipment in submarines, so this is another aspect of the topic... to properly use equipment originally intended for drones, some new equipment might be needed.

we already incorporate the new sensor telemetry that we have access to. now we get to include flight controllers.

however, i do like the fact that the tiny happymodel epw6 is about 3/4" square, and it provides everything that a basic 2.4ghz receiver would provide.

Let me know if you would like another thread created and a suggested name? (Admin Note.)
(Personally speaking frequency seems a good basis.)

David