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Corona DSSS problems

PostPosted: Fri Oct 15, 2010 8:31 am
by Bart Doets
In my club (G&E VVM, Holland) we recently had problems with transmitters that were modified with a DIY Corona module. While one member was flying, another one switched on his transmitter, started up his model and taxied with it before both planes went out of control. The first member saw his plane crash into a water surface.
A month earlier, I myself nearly lost a glider; it was launched piggyback, and I had checked the controls just before launch, but when it was released a minute later nothing worked. As there was one other member on the field with a Corona-modified transmitter, I later realized (after hearing about the recent incident) there might have been an interference issue. (My glider came down out of control and crashed into a tree, undamaged).
There has been a third incident too but it is less documented.

Yesterday evening, at a club night, three members brought their Corona-modified transmitters (one Futaba, one Graupner and one Multiplex) plus receivers, and we tried to duplicate the interference. But everything worked the way it should.

It is unlikely that if these incidents were really Corona-related, ours would be the only club where such things have happened. Which is where this forum comes in handy... has anybody here witnessed an incident where two Corona modules might have interfered?

Bart Doets

Re: Corona SSST problems

PostPosted: Fri Oct 15, 2010 8:47 am
by RCModelReviews
It is unlikely -- even if the modules were using exactly the same part of the band, they only transmit for about 10% of the time so the odds of them using exactly the same part of the band at exactly the same time are very, very low -- and even then, the GUID system should have meant they would reject the interfering transmitter's signal so the worst you'd get is a lockout.

Re: Corona SSST problems

PostPosted: Fri Oct 15, 2010 11:07 am
by Bart Doets
What I forgot to mention in the first place - in the first incident I described, after they picked the crashed model out of the water, they did some testing as well; and then, the transmitter of the crashed pilot (the Graupner TX) managed to completely lock out the other one. They did this several times and the effect could not be ignored.
Bart Doets

Re: Corona SSST problems

PostPosted: Fri Oct 15, 2010 8:13 pm
by RCModelReviews
Perhaps there was a fault in the transmitter board of that system.

Re: Corona SSST problems

PostPosted: Sat Oct 16, 2010 8:59 am
by Bart Doets
But two days ago at the club evening, that same transmitter (nor any other one) could cause any interference with any of the receivers...

The club got an answer from Corona:

--> Regarding your problem ,we felt very sorry about it .It maybe the ID overlap problem .
Here is our answer:
1.A turn on the power of the receiver then ,turn on the transmitter ,then start the binding the tx and rx.
2.B turn on the transmitter into to binding mode ,press the button of tx more than three seconds ,press the button of rx and power it.
3.Power B Rx, turn on B Tx. Establishing the Link of Tx and Rx.
4.You can try several times if there is still interference.
WE suggest you try the above steps for several times in order to separate the frequency of different corona users.
Pls check if it is ok. If not ,there must be the memorizer of MCU broken. That cause ID overlap.
By the way, If there is over 50 pilots flying 2.4ghz in the same field ,we suggest you not taking our 2.4ghz system. We can not guarantee the safety .
Thanks and best regards.
Corona RC Team

...But, if by now no interference can be observed, it seems irrelevant to follow this procedure.
By the way, before they sent the above advise, in another advise to another club member they made the remark to not use Corona when there were more then 100 people flying... so the next one who asks, probably gets the advise not to use Corona when more then 25 people are using the system...

Bart Doets

Re: Corona SSST problems

PostPosted: Sat Oct 16, 2010 7:42 pm
by RCModelReviews
I had forgotten about the Corona's ability to re-create a new GUID if the bind button was held down for an extended period of time -- that does rely on the EEPROM memory in the transmitter module being "good" -- but such memory failures are very rare.

The issue of "how many" 2.4GHz systems can fly concurrently is a vexing one and DSSS systems are generally not as good as FHSS ones in this regard.

This is why DSM2 is such a risky proposition at large events (despite what Horizon may say).

The reality is that DSSS systems work -- and then suddenly stop, as the noise level increases.

FHSS systems tend to degrade in performance far more gradually so when the noise starts getting too high (too many RC systems on at once), the latency increases. Pilots will notice that their model becomes more sluggish on the controls -- although they still have control. You'll definitely notice something is "not right" long before your system simply locks out.

None of this was an issue when Spektrum bought out their radios because 2.4GHz systems were the exception rather than the rule. Now however, at most clubs there are more 2.4GHz than FM/PCM systems so Spektrum's DSM2 system has passed its "best-by" date.

That's also why JR have opted to launch their own DMSS (FHSS) system rather than remain solely reliant on Spektrum's DSM2 or the slightly agile DSMJ.

Of course (yet again) Horizon deny all this -- because to admit the problem would harm sales.

I would say that Corona should be fine with 20-30 systems operating concurrently -- but 50, well that might be pushing it.

Corona (like Spektrum and Assan), really needs to stop resting on their laurels and get on with building improved systems that can better cope with the rapidly escalating noise levels on the 2.4GHz band. The more 2.4GHz fliers we have, the better their systems need to be in order to cope.

Re: Corona SSST problems

PostPosted: Sun Oct 17, 2010 6:24 am
by jeffie8696
OK well I have some concerns. In your opinion is the Corona system safe to be used with other 2.4 systems at the same field.
When I turn on my receiver then turn on the transmitter to establish the link will it scan the frequency to see if it is "safe". Or do I need to go through a special bind procedure for it to make certain it doesnt stomp on my fellow flyers each time?

Re: Corona SSST problems

PostPosted: Sun Oct 17, 2010 9:40 pm
by RCModelReviews
I didn't actually check but I think that the Corona establishes its operating frequencies during the bind process -- so it'll stick with those allocations until you rebind. This makes for faster-relink but does mean that it's not a silly idea to rebind if you fly from a new location.

I'll actually check this later this week because it is important.

We've had Corona systems flying here with half a dozen other 2.4GHz transmitters in operation without any issues at all.

Re: Corona SSST problems

PostPosted: Tue Oct 19, 2010 5:59 pm
by jeffie8696
I am sure that since the Corona uses 3 channels blind chance will allow it to operate safely but it would be great to know if it scans the frequency and chooses safe channels to operate on. Thanks Bruce.

Re: Corona SSST problems

PostPosted: Tue Oct 19, 2010 10:16 pm
by Bart Doets
RCModelReviews wrote:...This makes for faster-relink but does mean that it's not a silly idea to rebind if you fly from a new location.

Actually, I think you'd have to re-bind any time you come to your club. Because there just might be a member who was not present the last time you re-bound, so his TX could be on the same frewuency as yours.
Which makes me think... would I risk locking somebody else out when switching on my TX just to re-bind? As long as we are not sure what has happened, it's all quite risky.

Anyway, the board of my club has for now banned Corona SST systems, until we can be sure what exactly has happened, and what is safe and what not.