868/915 Mhz as a viable frequency for submarines.

tsenecal wrote:Sadly,  the problems that you and i have had getting all these receivers to work has not helped my opinion of FrSky's work in the 900mhz area vs others like ExpressLRS (still my favorite) and TBS.


But it is nice to know that I know have an entire suite of 4 different protocols in the 900mhz frequency range to test and post my results on.

Because so many people have problems with frsky r9, I have been able to pick up modules for around £20 each because no one wants them.

I looked at Crossfire but its far more expensive, The mavlink telemetry implementation has a lot of problems and there is no way to have a 1W bidirectional link. ExpressLRS is all about low latency, there is a version for mavlink but its experimental at the moment.  The only other options for that are dragonlink and the RFD900 but you are still looking at over £200 for a set compared to £40 for a pair of R9M modules.

yep,

once i discovered the matek crsf pwm boards for the expresslrs receivers, i have basically standardized on expresslrs. the new v2 tbs crossfire stuff is considerably cheaper, but not as cheap as the expresslrs stuff.

and the betafpv 915mhz nano transmitter module fits perfectly on the tandem XE, as well as the radiomaster zorro. I just picked up two of the betafpv superd diversity receiver. i want to test that against a standard receiver and see if properly orientated antennas help any.


both tbs and elrs make r9 look like a much lesser 3rd place product. the only 900mhz product that is of less use to us is the jeti duplex stuff. that makes tbs v1 stuff look cheap, and 900mhz is only a secondary receiver. it can never be used as the primary receiver.

So...

I spent the 23rd and 24th of September running 7 submarines with 7 different radios.

The venue was the Fly Casting Ponds at the Golden Gate Park in San Francisco CA.



It is a cement "pond", with angled sides, 180' x 120', and about 4' deep.


The radios tested were:

Radiomaster Zorro
Radiomaster TX12
Radiomaster Pocket

Jumper T-20

TBS Tango 2

Frsky QX7
Frsky Tandem XE


The Radiomaster radios were used with ExpressLRS trasmitter modules, either Nano or Micro size, running at 250mw, with dynamic power on, and with 100hz, std telemetry, and wide switch mode.  firmware version is 3.3.0.  all Radiomaster radios were running EdgeTX version 2.9.0.  I used both a Happymodel TX module, and two different BetaFPV (nano and micro) transmitter modules.

The Jumper T-20 was also running the same version of EdgeTX, a branch of OpenTX, and the same version and configuration of ExpressLRS firmware on its internal RF deck.

The TBS Tango 2 is using its own "FreedomTX", a branch of OpenTX, and has its own built-in TBS crossfire RF deck, running at 250mw dynamic on, max power.

The QX7 is running OpenTX version 2.3.15, and was used with ExpressLRS micro tx module, TBS Crossfire micro tx module, and an FrSky access r9m module.

The Tandem XE uses its own Etheos firmware, and has a built-in r9m access rf deck.


The Submarines were as follows:

a 1/8 scale Norbert Bruggen Delta research submersible
a 1/96 scale Skipjack class USN nuclear fast attack submarine
a 1/96 scale Blueback class USN diesel electric submarine
a 1/35 bronco Type XXIII german ww2 u-boat, using an R&R model engineering wtc.
a 1/32 scale "Proteus" 16" long submarine from the movie "Fantastic Voyage"
a 1/32 scale "Nautilus" from the disney movie "20,000 Leagues under the Sea"
a 1/32 scale "Flying Sub" from the movie "Voyage to the Bottom of the Sea"





The receivers used were as follows:

TBS Crossfire 6ch PWM Nano RX
BetaFPV ExpressLRS Nano RX w/ Matek 6 channel PWM adapter
BetaFPV ExpressLRS Nano RX w/ Matek 8 channel PWM adapter
Happymodel ExpressLRS EPW6 PWM RX
Frsky R9 sx six channel PWM RX


There really is nothing odd to report here.  Of the 10 gentlemen and 29 submarines that were brought, myself and one other gentleman were using 915mhz.  The other 915mhz equipment was an FrSky horus x10s express, with an r9m module, and a r9 sx receiver (identical to what i used in the QX7).

Neither of us had any issues.  I tested the ExpressLRS, TBS Crossfire, and R9 systems in the same submarine (The Proteus) because it was easily configurable/modifiable, and could be easily seen anywhere in the pond.

The Testing consisted of running the submarine in a tight figure 8 circle about 20 feet from the northwest corner of the pond, at a depth of 2 feet, with me walking backwards away from the submarine, toward the south end of the pond, until the "Telemetry Lost" notification was emitted by the transmitter (the 180' length of the pond).  I had a spotter watching the submarine at the north end of the pond, verifying that it was still under control.

IN ALL CASES,  I lost sight of the submarine before i heard any "Telemetry Lost" notifications.

The only difference between configurations was that which differed between protocols.

there is no way to set dynamic power on the FrSky system, so it was set to 250mw.
there is no way to set telemetry packet ration in FrSky or TBS, but i did have telemetry turned on in all cases, and i also had "vbatt" telemetry, and "Cells" telemetry available on the ExperssLRS and R9 receivers.

Edited on 3/12/24

Not saying this is "New", but i just found out that Futaba supports "CRSF" protocol output on a few of its radios.

a short list of known transmitters that allow you to connect either an expresslrs or tbs-crossfire module:

Futaba 12K
Futaba 16sz
Futaba 16iz
Futaba 18sz
Futaba 32mz
Futaba fx-36

however, this has one or two caveats depending on which model transmitter you are using:

none of the transmitters supports bidirectional (telementry) data transfer.  the protocol is outbound only, it is basically changing what was the s.bus output, and allowing it to support both s.bus and crsf.  there are only 3 wires on the connecter (gnd, vcc, tx) so the inbound (rx) pin does not exist.

on the 12k, 16sz, and 16iz, the power line is not available, so a secondary power input needs to be used to provide power for the module.


This was basically provided over 4 years ago as a firmware update for the radios that existed at that time, and all new radios out of the box since then.

Given the cost of these radios ($450-$3000) i would only recommend this option for someone that already owns one of these radios,
since any of the opentx/edgetx or ethos based radios fully support crsf/expresslrs (including telemetry) for considerably less money.

*it appears that the 12k was unofficially supported  in version 3 of the firmware.  it has since been updated to version 4 of the firmware, and at that time crsf support was removed.


-----  addendum as of 4/29/2024 -----

I went ahead and bought a Futaba 18sz, and verified that yes, it does support CRSF from the "S-I/F" port on the back of it.  this port is normally used to upgrade/configure devices that use futaba's s-bus protocol (servos, gyros, power boards) and when you have that port configured for CRSF output, it will work with either the TBS-Crossfire modules or the ExpressLRS modules that have advanced funtionality.  basically, the radio itself does not support any additional functionality, so anything that does not have its own capability of doing things like binding or configuring output power will not work on this radio.  I do own both the TBS Crossfire nano module and several ExpressLRS modules that have displays and controls to allow configuration and binding, and testing did show that all the functionality needed for bare minimum use is available.   As stated earlier, there is no two way communication, so telemetry is not supported.

Unlike my vintage futaba radios, there is nothing but a simple 3 wire connector needed to support ExpressLRS (no ppm to crsf converter needed), the "S-I/F" port is a standard 3 pin servo port, so a $3 servo extension wire and a 3 pin round 2.54mm pin header are all that is needed to connect a module.

-----  addendum as of 5/30/2024 -----

I got word from Futaba USA that firmware v4.1 has been released for the Futaba t12k, and it re-introduces the CRSF protocol on that radios S-I/F port. You now have a range of futaba radios from the $460 12k to the $3000 32mz if you want to run submarines with new futaba radios.

One more thing....


Futaba has its own 900mhz module & receiver.

Futaba TM-18 module & r9001sb receiver.

https://www.rc.futaba.co.jp/products/detail/I00000320

This works in conjunction with the CRSF update for their specific radios (you need to have the crsf protocol support to use this module)

I have seen different reports about its use, some reports indicate it is a backup system, to be used in conjunction with either the native fasst or fhss 2.4ghz protocol supported by the host transmitter.  At the very least, as with all CRSF modules on the futaba radios, this module does not support telemetry because there is no RX equivalent pin on the connector.


I have not found enough information regarding the actual hardware used, and do not know if the TM-18 module will work with other CRSF based receivers. (tbs-crossfire or expresslrs)

When I first started on this site, one of the very first pictures i posted was of a futaba 9c, with an OpenLRSng 433mhz module, from OrangeRX/hobbyking...

I want to post a new picture, of that same radio, with a new module on the back...






I basically tied together four things:

1) BetaFPV makes a "micro to nano" adapter, for a JR style module socket, to use the newer nano/lite style modules.  This product includes two separate circuit boards as well as the plastic case (2 pieces) to make the conversion work.

2) found on ebay is a "CR1 PPM/SBUS to ELRS CRSF Protocol Adapter",  a very tiny circuit board that takes ppm, positive (5v dc to 12v dc), and ground as input, and outputs CRSF, positive (same as input) and ground.

3) I have a ton of old 72mhz (airplane frequency) futaba modules that i don't need anymore.

4)  The new Radiomaster Bandit series of ExpressLRS Transmitter modules.


I used this methodology simply because i did not want to alter a nano transmitter module in any way.

Sadly, the CR1 has no way of getting Telemetry back from the module... so no way to display any of that.


Perhaps the next version might use an arduino or similar instead of the CR1, allowing for more capabilities - decoding robbe multi function modules, PCM and telemetry come to mind. I am pretty sure the next module i make will also be a true "futaba" module, taking the guts of a bandit module and putting them into a new 3d printed case.

That looks very neat, Tim.
And i have 3 Futaba 9C's here. At last count!
Can we have a look "under the hood." or "under the bonnet" as we charmingly say here!

David

A link for the original micro to nano adapter:
https://www.racedayquads.com/products/betafpv-micro-bay-to-nano-module-adapter?variant=39721408397425

from that, you can see the new adapter's pedigree.

The "new" middle part that connects the existing nano sled to the futaba module was designed so that the bandit expresslrs module would not have to be modified in any way, and still fit within the constraints of the existing module bay on the transmitter, as well as the metal handle that exists on both the 9c and a couple 10c radios i now own.

You can also see from the adapter link that the two circuit boards that come with the case and a 6" servo extension gave their lives to work the new ppm to crsf converter into the existing futaba module. It was easier to use the micro to nano pcb than hack up the pcb from the futaba module.

Link to an ebay listing for the ppm to crsf converter:
https://www.ebay.com/itm/285318750917

the existing futaba module had its top chopped off, and a new 1/4" thick plate manufactured to both raise and shift the bandit module for proper fit between the bandit module's antenna and the metal handle on both 9c and 10c radios.

I will post another pic, as soon as i remember, of where the 3 wires are soldered to the bottom of the 5 pin female connector pcb. In addition a 1k ohm resistor is added to make sure the green LED illuminates, which is also mandatory for some robbe transmitters. They sense this pulled to ground pin to tell that an rf module is installed, and will only output ppm signal if it is present.

Two screws hold the 5 pin pcb to the bottom of the case, then two screws hold the bottom of the case to the middle, and the tab on the front of the nano sled, as well as two more screws at the back hold both the sled to the middle section of the case, and secure the 8 pin pcb in place. it is all quite sturdy, and will hopefully withstand several years of abuse.

I have a couple illustrations that also indicate what the pinouts for the nano module and the futaba module are, which will give more info for someone who wants to copy this.

tsenecal could you test the failsafe mechanism on your Radiomaster R900 receiver? I don't think it actually works but I'm not sure if its something on my TX module or the receiver thats the issue. no matter what I set the receiver to it just holds the last inputs.

geofrancis wrote:tsenecal could you test the failsafe mechanism on your Radiomaster R900 receiver? I don't think it actually works but I'm not sure if its something on my TX module or the receiver thats the issue. no matter what I set the receiver to it just holds the last inputs.

Sadly, it appears that the problems i had just getting them to work right was enough to make me get rid of them. i have searched for the 1+ that i had, and can not find them. all i have now are a bunch of r9 sx and r9 stab frsky access receivers, and even those have lost favor to the expresslrs.

I already have replaced the receiver with an 868 ELRS receiver running mLRS firmware. mLRS recently added support for msp telemetry that inav uses so I can have the same system on everything. I only kept the r9 on this because of the lack of telemetry support Inav had with anything else.

Two things to note about ExpressLRS equipment...

First, i took both a Futaba 10chp and a Futaba 9cap super with me with my "adapter" that allowed me to use them with ExpressLRS modules, and everything worked fine with my Proteus submarine test bed.


Second, when i got back, ExpressLRS firmware had been revved to version 3.5.x
One GIANT change that was made is that it can now take either the CRSF protocol or PPM as input. I quickly updated one of my transmitter modules to the latest version, and wired up a cable that basicaly just tied power, ground, and signal from the Futaba socket to the module... and it works! no more need for the tiny ppm->crsf converter board.