2.4Ghz radio control

[storm]

Leo, the testing/statement should come from the manufacturer. I could get someone here to draw up a testing methodology that we could go through but I would rather see a statement from the manufacturer.

All Im saying is that before we all charge ahead and buy new TXs we should check that how they behave when large numbers of them come together is understood - that seems an obvious thing to do to me ?

One option may be to run TX control and simply not allow more than 10 802.11 transmitters out at any given time to avoid the problem from occurring ?

Id certainly be wary of allowing them at an XFM event (where no disrespect the risk is taken by me the event organiser) without understanding some simple fundamentals as outlined above.

Ed

[leorcc]

I understand where your concern as a event organiser is coming from Ed, but I dont see the higher risk in allowing a frequency to be used if the maximum risk afaik is that a robot goes into failsafe because it cant find a free channel.

On 27/40 MHz where the robot might be taken over by a different TX i would be more worried. As people may have seen when Hammerhead was powered up a couple of years ago in the UK, that is a serious safety issue.

Turning in your TX to transmitter control with the link is something I support anyway, no matter what frequency.


(Message edited by leo-rcc on August 30, 2006)

(Message edited by leo-rcc on August 30, 2006)

[Mouldy]

Ed, Two quetions:

1) Have you personaly e-mailed the manufacturer with the information you have heard?

2) Can i use my DX6 set at your next event?

[james...venom]

Here are some details from Spektrum (the manufacturer).
The Spekturm system uses DIRECT SEQUENCING SPREAD SPECTRUM (DSSS).
The DSSS standard is unique in that it hunts for and locks into a single channel; there isn€™t any channel-hopping. When the transmitter is turned on, the module scans and locks on to any channel that is not in use. Because of the 2.4GHz spectrum€™s collision avoidance requirements, locking into one channel requires different anti-interference measures than those implemented in FHSS systems. A DSSS-based system spreads the RC data over a wide bandwidth using a pseudo-random noise code. The receiver knows its transmitter€™s spreading code and can distinguish its intended radio signal. Spreading has the additional benefit of digitally increasing the range of the system for the same power. A further security method particular to the DSM is the use of a globally unique identifier code (GUID). This code is encoded into every RC data packet. The GUID is one of 4.2 billion potential codes; there aren€™t even 7 billion people on the planet.

WHAT ABOUT CELL PHONES, CORDLESS PHONES, WIRELESS ROUTERS, ETC.?
All wireless devices on the 2.4GHz have to include collision-avoidance technology €”no exceptions. There could be 20 cordless phones, as many wireless routers and a multitude of other devices, and the result would be the same: no interference.

In the US model nitro car racing clubs have been using Spektrum for a period of time now, running over 20 radios at the same time. This has been so successful that some organizations are almost insisting that they are used.




(Message edited by james...venom on August 30, 2006)

[storm]

Dave in answer to your questions

1) Yes I have

2) Until I get a response from the manufacturer I cant really answer that can I Dave ?

James : Im not questioning the problem of interference as we know it in 40Mhz systems. Im wanting assurance on how it deals with collision avoidance. Also if 20 units can run together this suggests theyre doing something othat than blocking out 6 frequencies for themselves each as there just wouldnt be enough frequencies left.

... I dont like unanswered questions !

Ed
http://www.teamstorm.comhttp://www.teamstorm.com

[babeth]

Was there any robot who did have a problem with it during the past event ? And what exactly happened ?
So far, from hearing some of the proud owners, it seems to work like a charm. But before people start robbing banks in order to pay for the new sets we should know about every little glitch or major jam that could happen.
After all, safety must at all times be utmost prominent in what we do.

[storm]

Guys there are a number of issues that need to be ironed out before 2.4Ghz can be accepted into the FRAs rules.

Most of these will be around process and procedure when using the units. Ensuring that the BIND process is controlled, understanding what happens with multiple units and dealing with a TX check in/out process (which may remain as is for example).

My concern is that we are all rushing out an buying the kit before the FRA has approved the hardware and surrounding process and procedure for use at FRA events.

Until that time use of these units would be down to the event organiser in question and it would be their responsibility to come up with their own process and procedure to ensure safe use of the technology.

I should also point out that currently the use of a 100mW transmitter for the use of radio controlled models (which we would fall under) is not permitted in the UK. Ofcom are currently looking at changing this.

The reason for the restriction is to deal with congestion in the 2.4Ghz band. Its all very well having a 3000ft range, but if a group of 20 of us can saturate the WiFi spectrum for 3000ft around us that annoyes a lot of DECT, Bluetooth, WiFi etc users ! So currently the technology isnt licenced for use in the UK for model control.

-------------------------------

Copy and Paste from the Ofcom site

http://www.ofcom.org.uk/radiocomms/ifi/licensing/classes/rlans/technical/ofw311/http://www.ofcom.org.uk/radiocomms/i...hnical/ofw311/

4. What frequencies are available?
The specific frequency bands available for the use of radio controlled models are shown below, with the maximum effective radiated power output of the transmitter measured in milliwatts. Within these bands, specific channel arrangements apply. Please refer to the UKRCC website http://www.ukrcc.org/ for full details.

26.96 to 27.28 - 100mw
34.945 to 35.305 - 100mw
40.66 to 41.00 - 100mw
458.5 to 459.5 - 100mw

However, radio control models may also share the frequency bands allocated to General Telemetry and Telecommand with all other such applications. Most of the Telemetry and Telecommand allocations remain impractical for model control, due to restrictions on channel capability or too little power to give sufficient range. Also, most General Telemetry and Telecommand allocations are located in the international Industrial, Scientific and Medical (ISM) frequency bands, so may well suffer interference from commonplace machinery. Details of ISM bands are shown in annex A of the UK Frequency Allocation Table [UK FAT]

One ISM band that has been identified by model control manufacturers, in the General Telemetry and Telecommand allocations, is 2400 - 2483.5 MHz. The power output is low at 10 mW e.i.r.p, however the wide bandwidth can be used to give acceptable operability for surface use only.

Frequency (MHz)

2400 to 2483.5 - 10mw

----------------------------------

Again further information from the UKRCC website states

2.4GHz band - covers the frequencies from 2.400 to 2.4835GHz providing 80 channels with a maximum transmitter power of 10mW erp. Automatic frequency selection (no crystals required).

Until OFCom approve the 100mw control solution for use in the UK I wouldnt advise any event organiser to reccomend its use as should there be an issue (Safety or otherwise) they would be liable for endorsing it. Ditto the FRA.

And you can state all the blah blah but the manufacturer says all you want, it doesnt change the law !

Surley thats common sense ?

Ed
http://www.teamstorm.comhttp://www.teamstorm.com

[ewan]

It did seem almost too perfect. It will be interesting to see what (if anything) Spektrum have to say about how the transmitters actually handle packed Wi-fi and bluetooth bands - as Ed says each Tx couldnt possibly saturate six channels completely if twenty sets really can run together.

Has anyone yet turned on their Tx for it to say that there are no free channels available, or does it just seemingly butt its head into a smaller space in the band?

[kane]

Sorry Ive not been able to post for a while due to the championships and work commitments. Since I last posted, Paul Cooper emailed me regarding the power output of the DX6 which he had been assured was 100mW. Having phoned Spektrum again, I have been told that it is indeed 100mW output which means that its use in the UK for radio controlled models is not currently legal.

Ofcom currently have a consultation out which includes the use of 2.4GHz at 100mW for radio controlled models. This consultation is due to be implemented in November/ December.

People may draw their own conclusions from that.

My personnal experience with the DX6 has been great. The reception is flawless and completely glitch free. Failsafing works perfectly even without the transmitter on.

But the system is yet to be tested thoughly. One works perfectly. Weve had possibly three or four running together. But if everyone had one would it still work perfectly. Ed has some very valid points that do need to be discussed.

That said, the safety aspect alone is enough to switch to Spektrum. Anyone whos had their robot glitch during arming/ disarming will know what I mean.

[james...venom]

its use in the UK for radio controlled models is not currently legal.

thats exactly what ive been saying scince the beggining lol

Ed with all the tx sets haveing a unique GUID they cannot possibly interefere with each other. They also have 2 recivers built in 1, completely separete systems so if one some how has traffic the other will search for a new frequency.