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[Davy1]

Does anyone have experience of the FrSky R9M  900MHz Long Range System for model submarines?


It is normally used for drones but it is reported  that you can achieve control at depths down to about 2 feet.


Model submariners have the twin problems of  a growing shortage of r/c control equipment for model submarines and the use of higher and higher frequencies so that the signal is absorbed by water.  The FrSky system is easily available and can be used "out of the box" by relative newcomers to the hobby,


More background information here:


https://www.theassociationofmodelsubmariners.com/t83p150-openlrs-and-2-4-ghz-and-submarines#11450

[JimG]

One problem with it's use in the UL for submarines is that this is not a recognised frequency for radio control. Use is therefore illegal, if drones are using it then they are breaking the law. Of course if they are flying long range out of site then they are illegal anyway and don't bother about the laws. The 900MHz band is used for other legitimate purposes.

Jim

[Davy1]

Thanks Jim. I should perhaps have phrased the question as "approximately" 900MHz.
868/915MHz has been talked about as UK legal but I am not sure. I'm just hoping to find someone who has used this gear at these kind of frequencies and can comment on its use underwater. (Model submarine users are slowly being painted into a corner with respect to higher and higher frequencies by "air" users.)

David

[tsenecal]

I am using the following setup with limited success:

FrSky Taranis x9d
FrSky R9M module (2)

FrSky R9 receiver (1)
FrSky R9mm receiver (3)
FrSky R9 slim+ receiver (2)

they all work reasonably well, i use the word "limited", because the depth afforded by the system is less than two feet.  the "less" is dependent upon particulates in the water, like chlorine or minerals.   In all other respects it is just like using their 2.4ghz system, you get as many as 16 channels using s-bus based servos (or servo adapters) you get FrSky's x series telemetry, and of course you get all the "joys" of OpenTX.

there is one considerably large negative to the current system:

there have been about 7 updates to the firmware for these devices over the last year or so, and i myself basically am forced to run through all the devices every time i buy a new module or receiver.  updating firmware for the traditional "accst" based systems is not simple.  there is a three pin cable, unlike a standard servo cable, that you must use to connect the receiver to the back of the transmitter, so that the transmitter can send the firmware file to the receiver.  each receiver make requires a different cable.   there is no way of knowing what version of firmware a device has until you own it.

FrSky is in the midst of updating their protocol (new protocol is labelled "access") and the new protocol allows for updating receivers via "over the air" methods, meaning the firmware is transmitted to it as a giant data packet, so unlike what i am doing now, i would not have to figure out a way to attach a cable from the receiver to the transmitter to update each receiver.

all of the receivers but the original R9 are meant to be used with "drones" and their associate flight controllers, so they need to have a wiring harness made for them that will allow them to be used with traditional servos.  most of the receivers that require this will come with a short pigtail that can be used to build half of the harness, but the other half of the parts for the harness need to be bought, and the harness needs to be soldered together.

i will post pictures of my setup if you think they would be of help.


even with all these issues using the system, i find it more agreeable than using 2.4ghz with its necessity of rewiring the antenna so that it is protruding from some location high above the water.   several of the submarines i have built are "research subs", and they don't have a readily excusable periscope in which i could place the antenna, and i simply don't like the idea of having a 2 foot long antenna sticking out the top of my sub.

i have tried one other 915mhz system base on the OpenLRSng protocol, called ChipLRS, but they are no longer in production, as well as the 433mhz OpenLRSng setups from both hobbyking and others including DTF-UHF.   I abandoned 433mhz when all the major players left the market.  Hobbyking is the only remaining player making 433mhz equipment, and i consider their equipment one step above junk.

[Subculture]

Bob tried it and didn't seem too impressed.
https://www.youtube.com/watch?v=hGDxRDqIfdk

[JimG]

Thanks Jim. I should perhaps have phrased the question as "approximately" 900MHz.
868/915MHz has been talked about as UK legal but I am not sure. I'm just hoping to find someone who has used this gear at these kind of frequencies and can comment on its use underwater. (Model submarine users are slowly being painted into a corner with respect to higher and higher frequencies by "air" users.)

David

David the UK frequencies are from 433 to 459MHz in 3 separate bands, these would probably be better as they are at a lower frequency.
Jim

[Subculture]

868mhz is a legal frequency along with the 459/459mhz here in the UK. 433-458mhz is not permitted in other parts of Europe, but 868mhz is. This is probably why larger manufacturers have adopted the higher frequency for their long range systems. 900mhz is legal for the US, and probably some other countries too, but not is Europe or UK AFAIK.

[Davy1]

Thanks one and all for a brilliant response to the question. Plenty of food for thought.


 (Jim - some background information. 433 (458 in the UK) was pioneered by tsenecal himself. It does indeed work very well for subs but we believe that the only supplier (Hobbyking) may be stopping production and moving to higher frequencies, as indicated by Subculture.)


Thanks again,


David

[C-3PO]

Hello David,

I hope to be able to publish my experiment findings soon - the magic ingredient of time is in short supply - oh and other fun projects that grab my attention :)

The kit - 459 MHz packet radio / 459 Mhz LoRa / 459 Mhz openLRS / 868 Mhz packet radio - I have a homebrew 40 Mhz digital radio but it seems to have a mind of it's own so I have excluded it from this exercise.



C-3PO

[JimG]

868mhz is a legal frequency along with the 459/459mhz here in the UK. 433-458mhz is not permitted in other parts of Europe, but 868mhz is. This is probably why larger manufacturers have adopted the higher frequency for their long range systems. 900mhz is legal for the US, and probably some other countries too, but not is Europe or UK AFAIK.

I checked on the Ofcom site and 868MHz is not given as a frequency for radio control. The band this is in seems to be for international telecommunications although can be used for industrial, scientific or medical purposes. It can also be used in some circumstances by the military.
Jim

[chas]

Jim beat me to this, that frequency is not listed as a legal frequency, so can not be used. As in the bad old days of people miss using the old frequency bands, using it could endanger other legal users. Is it possible that someone has confused one of the 40 MHz band numbers with a frequency?
Chas

[HMS Invisible]

... Is it possible that someone has confused one of the 40 MHz band numbers with a frequency?
Chas

The IR2030 document previously specified rc, along with the power limit, at the same time as it was available for medical devices but no longer.
It was the first thing I checked when this subject came up.There is an email address for enquiries.

[Subculture]

868mhz is a general purpose band, used in domestic devices like fire alarms, smart meters and one of the purposes listed is 'remote control'. Radio control is a type of remote control. Not sure the exact protocol being used by Frsky for their R9, there are wattage limits and also duty cycle.

If you look down the bottom of the link, you'll see there is a statement that other bands can be used not stated in the table, but gives caveats.

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

[C-3PO]

IR 2030 Licence Exempt Short Range Devices(May 2020)

https://www.ofcom.org.uk/__data/assets/pdf_file/0028/84970/ir-2030.pdf

Non Specific Short Range Devices - IR2030/1/xx

Non-Specific Short-Range Device - The non-specific short-range device category covers all kinds of radio devices, regardless of the application or the purpose, which fulfil the technical conditions as specified for a given frequency band. Typical uses include telemetry, telecommand, alarms, data transmissions in general and other applications

Defined 5.11 Short Range Devices Information Sheet
This shows that the reference to telecommand and telemetry radio equipment applies to the control and movement of models

5.11 Model control devices are a specific kind of telecommand and telemetry radio equipment that is used to remotely control the movement of models (principally miniature representations of vehicles) in the air, on land or over or under the water surface


C-3PO _._

[tsenecal]

Bob tried it and didn't seem too impressed.
https://www.youtube.com/watch?v=hGDxRDqIfdk

I saw bob's video several months ago, and all i can say is is that i got better results than he did, i do not know what type of pool chemicals he uses, but i have run 433mhz and 915mhz equipment in swimming pools, and small ponds with performance as follows:

433mhz:  best case scenario was at 100mw output and i was able to reach 5 foot depth in a swimming pool and similar depths in a city pond used as a city water source (clean with very little mineral content), i was able to achieve 2 to 3 foot depths at a spring fed city pond where there was an extremely high mineral content

915mhz:  best case scenario was at 1000mw output at the same swimming pool used above, where i reached a depth of about 2 feet.  at the same city pond used as a city water source, this equipment regularly reached depths of less than 2 feet (perhaps 18 inches or so).

In all situations, i judged "full use" as total control of the vehicle, and no invocation of failsafe systems., however, proper configuration of failsafe systems allowed for swift retrieval/resumption of service and some of the equipment allowed for missing data packets, and until total loss of system control, failsafe would not be invoked, allowing for the appearance of total control, even though the standard 50hz data path may have degraded to as low as 1hz before failsafe was invoked.


in layman's terms, due to the protocol used by OpenLRSng, lost data packets were not immediately considered to be loss of control, and only when zero packets were transferred for a user selected period of time (i chose one second) did failsafe kick in.   this is very much in line with other stand-alone failsafe systems used by model submarines for the lower 27-75mhz classic setups which would allow for as much as a 5 second delay before the failsafe was invoked.


I will also say that David F and I have spent considerable time testing many different antennas both on the transmitter and receiver, and i have also found that antenna placement on the model can alter perceived range drastically.

[rhavrane]

Bonjour,
In France, model submariners regularly use 27 MHZ radios even if in theory, model boats frequencies for boats are 41.000 to 41.900 MHZ

A beautiful example : https://www.youtube.com/watch?v=-LVdjQhl0Bg

I was told that the lower the frequenvy is, the better it is under the water.

They often navigate in swimming pools and even launch torpedos :
https://www.youtube.com/watch?v=xiH5J5reBJA and https://www.youtube.com/watch?v=EJAdDqz3LxM

Other demonstrations : https://www.youtube.com/watch?v=e8ifCVlZ_iE&t=4s    https://www.youtube.com/watch?v=-LVdjQhl0Bg

[Subculture]

27mhz equipment tends to be even harder to find than 40mhz. Most manufacturers discontinued sets with greater than two channels in 27mhz very quickly once the 40mhz frequency was made available- hardly surprising as the frequency allocation was far more generous. Consequentially most 27mhz sets are over thirty years old, and getting a bit long in the tooth.

[Davy1]

Thanks to everyone for their most helpful replies, from which some picture is emerging.


The reason why I asked the question originally was just passing on a query from a newcomer to the hobby without any equipment. ( I have enough 433 and 40 Mhz  gear to last a lifetime!)


Based on your replies, I think my reply to them would be:


- Purchase the "900" Mhz gear if you can't obtain ANY OTHER r/c equipment and it's use will be legal in the country you are operating it in.


- Be prepared for the fail safes to operate (Don't forget to set them!)


David

[Subculture]

Must be the 966/868mhz version. 900mhz is for the States, but not Europe and UK.

Also Crossfire is a competitor to Frsky R9 system. Has a much higher approval amongst flyers, but is more expensive.

https://www.buildyourowndrone.co.uk/tbs-crossfire-micro-bundle