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Old 08-08-2013, 04:15 PM   #1
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Cool Are RC events getting too big to be safe?

I would like to ask for your thoughts on this topic.

This has to do with 2.4 GHz band saturation. In the beginning there was concerned as to whether we could have 40 2.4 GHz radios on at one time. Then we saw tests with 60 and I think I saw one all the way to 100. Are we now complacent?

This year at the International Radio Control Heli Assoc. there were 1100 registered pilots at the AMA site. As I understand it there was no frequency/band control. Should we be concerned? Should we consider capping these events over concern for RF band saturation? I don’t know.

A unique opportunity existed this year at the AMA home site during the IRCHA festival. There could have been hundreds of radios on at one time. Did AMA or one of the manufacturers monitor the 2.4 band? I would be interested to know. When we get this big we may, again, have to go back to some kind of frequency control, or more appropriately, RF band control.

With RC events getting larger and larger, and with no frequency control, do we have a potential safety issue around band saturation? If there were no problems, if someone actually monitored the air and all was good, I would like to see a report. If it did saturate, if there was evidence of RF saturation that could lead to safety problems, did we see problems? Safety should be everyone's top priority.

It might be that the band starts to saturate at 200 or ??? radios. Who would have thought that these events would get this big. I think we need to ask this question and to document the findings. Let us share that with the community, and especially the organizers of these big events, before some $50,000 6 engine jet or some giant scale heli with whirling blades goes out of control into a crowd and takes out some people and property. If there is a guideline to be developed, let the radio manufacturers, working with AMA, develop that guideline.

This is not a witch hunt or an alarmist post. This is not a brand concern as I think all the major brands, and most of the off brands, are pretty good. I am a concerned citizen of the RF community who might like to attend one of these big events. Is it safe? I would like to know if anyone is looking at this for large events.

If we have any RF wizards here, I would like to get your opinions on the question.

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Old 08-08-2013, 04:44 PM   #2
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I am shocked if they had no controls. While old "frequency" controls are not needed the number of "on" TX's matters.

I think we have shown in the past that the mega events cause issues. Spektrum DSM2 was especially hard hit, but ALL the major systems had some issues. This certainly makes sense as the noise floor on the band just gets higher and higher.

It would be interesting to see those systems than can log issues (like Spektrum) to see the fades and dropped packets.

I think most of the large events were talking about a system that would limit the number of "on" systems both on the flight line and in the pits.

It will be interesting to hear any issues at IRCHA, if any....

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Old 08-08-2013, 04:45 PM   #3
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Damn good question.... subscribed.

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Old 08-08-2013, 04:48 PM   #4
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I did some quick research - here is a copy of a post from Jeff Myers (SEFF).

SEFF will have some rules next year (2011) regarding 2.4 systems at SEFF.

1. Pilots will only be allowed to operate radios when located at a pilot station. There will be 26 pilot stations at SEFF 2011.....just like we had in 2010.

2. If a pilot needs to check their radio system when not at a pilot station they must hardwire their transmitters to their receivers with an appropriate cable.

3. For those that don't have the ability to do this, we will have a few designated locations behind the flightline boss EZ Ups for pilots to turn on a 2.4 radio to check something out.

4. My staff will need to discuss FPV and other 2.4 video and photo systems. They may not be allowed next year. I need to do some more research on the technology before we come up with any rules on this.

5. Above rules will be in effect from 7 am to 9 pm. We did not hear of any reported problems after hours. As long as we are not having problems at night, we so no need to impose the rule after hours.

Anyone found breaking these rules will face significant consequences. The penalty will be severe enough to deter those that are prone to breaking the rules.

It never fails....just when we think we have anticipated everything and have the event nailed....new things come up. We know all the major radio systems are solid products. We don't know how they all work together at a large event like SEFF. It is safe to assume that at times....well over 85 radios were on at one time. We did have enough people report "lock outs" / "complete loss of control" to where we know that it is prudent to make some changes before someone gets hurt.

We work very hard to make SEFF the best flight festival anyone could ever attend. We want to make sure we keep it that way. It is important that every pilot that attends SEFF feel comfortable to fly any electric aircraft they own. We have a year to plan 2011 and may come up with better solutions so understand that this may be fluid.
I thought most of the bigger events were doing something similar.

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Old 08-08-2013, 04:58 PM   #5
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Sorry to keep hogging the internet here with all my posts. One other interesting thing I found out - there was NO frequency control of any kind at IRCHA. Early reports show no real issues either!

But the flightline is over a MILE long at IRCHA (I can't even imagine that...). But that would likely help.

Interesting...
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Old 08-08-2013, 05:44 PM   #6
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Originally Posted by AEAJR View Post
I would like to ask for your thoughts on this topic.

This has to do with 2.4 GHz band saturation. In the beginning there was concerned as to whether we could have 40 2.4 GHz radios on at one time. Then we saw tests with 60 and I think I saw one all the way to 100. Are we now complacent?

This year at the International Radio Control Heli Assoc. there were 1100 registered pilots at the AMA site. As I understand it there was no frequency/band control. Should we be concerned? Should we consider capping these events over concern for RF band saturation? I don’t know.

It might be that the band starts to saturate at 200 or ??? radios. Who would have thought that these events would get this big. I think we need to ask this question and to document the findings. Let us share that with the community, and especially the organizers of these big events, before some $50,000 6 engine jet or some giant scale heli with whirling blades goes out of control into a crowd and takes out some people and property. If there is a guideline to be developed, let the radio manufacturers, working with AMA, develop that guideline.

This is not a witch hunt or an alarmist post. This is not a brand concern as I think all the major brands, and most of the off brands, are pretty good. I am a concerned citizen of the RF community who might like to attend one of these big events. Is it safe? I would like to know if anyone is looking at this for large events.

If we have any RF wizards here, I would like to get your opinions on the question.
Yeah, as RCERs points out in posting #5.

There is another issue here. That is the relative signal strength of the transmitter signal at your receiver, versus the signal strength of a transmitter much closer to the model then yours.

That was a big problem back in the 72 Mhz days while flying sailplanes in an area where there was no specified pilots location. Flying your sailplane 100 feet over the head of another transmitter 500 or a 1000 feet away, and you could get hit, even when you were on different channels. That happened to me several times in the mid 1980's.

And, with the spread out flight lines that might exist at some of those giant fun flies, this could be something to consider. It isn't hard to fly one of those giant scale models 500 or 1000 feet from the transmitter at the speeds they are flying. And, those giant models will still be quite visible. Anyone that doesn't believe this has never had to find a model that crashed in a farmers field, a long distance from the pilot area.

What is happening here is the relative signal strength and how it varies with distance. Double the distance, four times less signal. Ten times the distance, 100 times less signal. So, if you're flying on that mile long flying field, and fly to far in one direction, your poor receiver has to pick out your transmitter from a bunch of closer transmitters with perhaps 100 times more signal strength. I don't know if anyone has ever tested for this issue on the 2.4 Ghz frequencies.

This falls into the area at the IRCHA where the flight line is a "Mile Long".

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Old 08-08-2013, 06:20 PM   #7
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The Heli events have an advantage in the signal strength area in that they tend to fly their helis relatively close, so I would not expect that to be a major factor here.

Sailplanes go to the other extreme where it is common to fly them very high and far away. 1/2 mile up and 1/2 mile out is not out of the question with wing spans in excess of 4 meters. Now signal strength, in the middle of a very busy 2.4 environment could be an issue.

Is a 1 mile span enough to diminish signal strength concerns? Most of our radios typically have a range of more than a mile.

But distance related signal strength aside, there is only so much bandwidth. At some point it saturates and even if your system is hopping, if enough of the band is fully saturated you could lose contact with the bird. Or is that not likely?

Is it statistically impossible to completely saturate the band to the point that a hopping protocol would be locked out?

Maybe a fixed channel pair implementation, like DSM2, would be easier to blank/jam out, but are the hoppers really immune to this if there are 200, 300, 400 hoppers?

I have no idea.

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Old 08-08-2013, 06:38 PM   #8
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Originally Posted by AEAJR View Post
The Heli events have an advantage in the signal strength area in that they tend to fly their helis relatively close, so I would not expect that to be a major factor here.
100% correct -an excellent observation. The heli guys at our field all do a "close in" routine part of what makes it fun for them. So they are not spanning large left and right of TX center areas as we plank fliers that go from one end of the field to another, all while crossing 3,4,5 or more TX's.

Close is a big factor I suspect.

Originally Posted by AEAJR View Post
Is a 1 mile span enough to diminish signal strength concerns? Most of our radios typically have a range of more than a mile.
O yea... no question this is a factor. But also no question that range for our stuff (primarily a component of the RX) is well over 2 miles (for the most part).

Originally Posted by AEAJR View Post
But distance related signal strength aside, there is only so much bandwidth. At some point it saturates and even if your system is hopping, if enough of the band is fully saturated you could lose contact with the bird. Or is that not likely?
Not that is likely - that is the noise floor I talk about. Just like a water pipe the more water (in this case signal) the less space for new signals in the pipe. As you start to get really busy some traffic just does not make it in the pipe.

Again, back to large events, most describe their systems as getting "slow" or sluggish. This means that frames are dropping, fades are occurring and you have a BIG problem.

Our equipment is good though and it just keeps trying.

Originally Posted by AEAJR View Post
Is it statistically impossible to completely saturate the band to the point that a hopping protocol would be locked out?
I think it is - again at the mega events all systems have reported issues with crashes. The problem is, and this is a problem we always face, did you crash (dumb thumbs) did you have another issue, or did you really get locked out. I think there were enough incidents with enough pilots that would fess up if they just crashed. But it is super hard to document.

Originally Posted by AEAJR View Post
Maybe a fixed channel pair implementation, like DSM2, would be easier to blank/jam out, but are the hoppers really immune to this if there are 200, 300, 400 hoppers?
DSM2 had a very hard time coping with the 200+ TX on situations. Really that is well past design so still pretty darn impressive. Originally folks speculated that 40 was max, but Spektrum showed good performance even with 100 TX's on.

Due to this - I think these large events need to limit the TX's "on" to around 100, including both the flight line and pit area. But that is hard to do. Can you imagine running an impound with 1135 pilots. That is over 2k transmitters. No thanks.
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Old 08-08-2013, 06:40 PM   #9
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Originally Posted by kyleservicetech View Post
That was a big problem back in the 72 Mhz days while flying sailplanes in an area where there was no specified pilots location. Flying your sailplane 100 feet over the head of another transmitter 500 or a 1000 feet away, and you could get hit, even when you were on different channels. That happened to me several times in the mid 1980's.
+1 - agree with you.

I also remember in my 72MHz days - I was on CH14 and those low frequencies had conflicts with other channels in the band! O yea.... It was good to have really good receivers with good filtering.

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Old 08-08-2013, 07:25 PM   #10
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How many people know how to hardwire from their TX to their RX?
(How many systems even have that capability?)

Imposing a rule that is impossible to follow is not bright.
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Old 08-08-2013, 08:01 PM   #11
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If my 9C Super can hard wire to my receiver, assuming I can get to the receiver, I don't know how to do it.


As for enforcement of a transmitter max, I don't think you can do it. BUT I think you can monitor the RF spectrum and put out an appeal for people turn off to open up the airwaves.

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Old 08-08-2013, 08:05 PM   #12
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Originally Posted by rcers View Post
100% correct -an excellent observation. The heli guys at our field all do a "close in" routine part of what makes it fun for them. So they are not spanning large left and right of TX center areas as we plank fliers that go from one end of the field to another, all while crossing 3,4,5 or more TX's.

Close is a big factor I suspect.


O yea... no question this is a factor. But also no question that range for our stuff (primarily a component of the RX) is well over 2 miles (for the most part).



Not that is likely - that is the noise floor I talk about. Just like a water pipe the more water (in this case signal) the less space for new signals in the pipe. As you start to get really busy some traffic just does not make it in the pipe.

Again, back to large events, most describe their systems as getting "slow" or sluggish. This means that frames are dropping, fades are occurring and you have a BIG problem.

Our equipment is good though and it just keeps trying.



I think it is - again at the mega events all systems have reported issues with crashes. The problem is, and this is a problem we always face, did you crash (dumb thumbs) did you have another issue, or did you really get locked out. I think there were enough incidents with enough pilots that would fess up if they just crashed. But it is super hard to document.



DSM2 had a very hard time coping with the 200+ TX on situations. Really that is well past design so still pretty darn impressive. Originally folks speculated that 40 was max, but Spektrum showed good performance even with 100 TX's on.

Due to this - I think these large events need to limit the TX's "on" to around 100, including both the flight line and pit area. But that is hard to do. Can you imagine running an impound with 1135 pilots. That is over 2k transmitters. No thanks.
If you are flying something fast, a 3D routine or a heli, sluggish could be enough to cause a crash or an out of control aircraft. You might never lose signal but the response be too slow to be able to keep the aircraft under control.


Do our transmitters Ack and Nak? Do they retransmit position changes or does the packet go out and, if not received, just drop?

Does the transmitter send the position of all controls in every frame or just the changes?

I don't know. The first could be bad in a highly saturated environment.

The second would give you the sluggish response but at least you get current position for all controls on every received packet.

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Old 08-08-2013, 08:31 PM   #13
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I would have to say the only way to prevent any problems with saturation is to limit the number of transmitters on.
I have never been to any event where there were more than 6 aircraft in the air at any one time,but I imagine if you have 1100+ registrations,you would have to increase the number allowed up.
But I still have a problem with 100 transmitters switched on at the same time.Or,actually ,to have 100 aircraft in the air at the same time.Say that 20 of those are yellow Piper Cubs,and you're flying a yellow Piper Cub,it takes only a fraction of a second's distraction to lose your own aircraft in the air.
The local Maa limits the number of aircraft to 5 in the air,even at large events.However,large meaning more than 50 pilots registering.At the larger US meetings,perhaps there should be a limit of 20 or so.This would solve the saturation issue and overcrowding in the air in one go.
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Old 08-08-2013, 08:37 PM   #14
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Getting back to the original question, I am hopeful that someone was monitoring the RF band during this event.

I have sent a note to AMA since this was at the AMA home field to see what they might be able to tell me.

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Old 08-08-2013, 09:12 PM   #15
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Originally Posted by DHC Beaver View Post
The local Maa limits the number of aircraft to 5 in the air,even at large events.However,large meaning more than 50 pilots registering.At the larger US meetings,perhaps there should be a limit of 20 or so.This would solve the saturation issue and overcrowding in the air in one go.
That is pretty standard for regular events. The events we are talking about are MEGA events with over 300 pilots. In the case of IRCHA they had 1135 pilots! That is the largest RC event in the world.

One thing that these events have - is multiple, or in the case of IRCHA a single giant long flight lines. At SEFF another huge event they have each area mapped out at the big venue. So there is a fast area, a heli area, a slow/light area etc.

But you certainly could not have a 5 pilot limit on the flight line or few would have the chance to fly.

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Old 08-08-2013, 09:17 PM   #16
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Originally Posted by AEAJR View Post

As for enforcement of a transmitter max, I don't think you can do it. BUT I think you can monitor the RF spectrum and put out an appeal for people turn off to open up the airwaves.
Good question.

I don't know if monitoring the 2.4 Ghz radio frequencies would work. The reason is the different modulations of the transmitted signals that are involved.

The "Frequency Hopping" types of transmitters are transmitting all over the 2.4 Ghz band with narrow band transmission, kind of like the narrow band transmission we had with the 72 Mhz narrow band radios.

The DSSS (Direct Sequence Spread Spectrum) radios such as Spektrum and JR units are transmitting wide band signals. You could put perhaps a dozen or more frequency hopping signals right in the middle of one Spektrum wide band transmitted signal. Its the nature of this wide band transmission that it pretty much ignores signals right in the middle of it. How it does this is pretty involved. And, it wasn't possible without the high powered computer chips we have in the transmitters and receivers. Just google "Direct Sequence Spread Spectrum"! I'd guess this stuff was designed with people with PHD's in computer science behind their name. Now, Spektrum has their DSMX which is a combination of both DSSS wide band signals AND frequency hopping signals. (What DSSS is doing, is modulating the "Simple" servo signals pulse train with a second modulation pulse train frequency much higher than the servo signals. The process of doing this creates the wide band signal transmission.)

FYI, the Frequency Hopping design goes back to World War II, and is pretty easy to design with the computer control stuff we have now days. This DSSS stuff is new technology. It is by no means simple to design, or simple to understand. And, methinks the Spektrum DSMX system is the best combination of both Frequency Hopping Spread Spectrum, and Direct Sequence Spread Spectrum.

Here is what some of this 2.4 Ghz stuff looks like:
http://www.wattflyer.com/forums/showthread.php?t=63497

I've looked at the transmitted signal from my Spektrum DX8 transmitter with its DSMX technology on this spectrum analyzer. That DSMX signal pretty much covers the entire 2.4 Ghz frequency band, as it operates over a period of perhaps seconds or minutes or so.

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Old 08-09-2013, 05:52 PM   #17
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Originally Posted by AEAJR View Post
Getting back to the original question, I am hopeful that someone was monitoring the RF band during this event.

I have sent a note to AMA since this was at the AMA home field to see what they might be able to tell me.
They probably won't know. Nobody except us knew at past events when we did it either.

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Old 08-09-2013, 11:06 PM   #18
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Originally Posted by AEAJR View Post
Sailplanes go to the other extreme where it is common to fly them very high and far away. 1/2 mile up and 1/2 mile out is not out of the question with wing spans in excess of 4 meters. Now signal strength, in the middle of a very busy 2.4 environment could be an issue.
For what it's worth, I just came back from putting four flights on my giant Big Stick model. Those flights had one of those keychain video cameras mounted on the wing.

Our field pit area is located 2100 feet from the railroad tracks located east of our field. And, I've got video showing my giant big stick model is flying directly over those railroad tracks. The model was still quite easy to see.

As mentioned before, our models can be a lot further away than one might think.

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Old 08-16-2013, 04:04 PM   #19
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Sharing what I have learned from people who seem to know what they are talking about.


Total lock out - not likely with hopping protocols. When some of the 2.4 systems were on one or two channels and Spektrum was on DSM2, there were lock out reports that might have been related to a busy RF band, but it is hard to be sure of the cause without someone doing RF correlation to time in the air for the model. Apparently DSM2 was great when we had 200 pilot events and half were on 72 MHz but, as Spektrum said, as the events got bigger, they saw the need for DSMX. Now Spektrum hops too. And many of the off brand systems hop, at least to some extent.

What about Increased latency? - This seems to be the most likely problem. I remember seeing reports of this when the first hopping protocols came out. As the band got busy the response time went up. I have seen this demonstrated on the RCModelReviews videos. And I seem to recall seeing reports of this at past big events. But it is hard to prove or to to pin down the cause without someone doing a correlation between the model in the air and the state of the RF band.

Decreased range - General opinion is that this is also very likely in a busy environment. However this is not something you would notice at a heli event or most airplane events. If your system has a 1 mile (5,280 feet) working range and you are less than 1000 feet from your model you are unlikely to notice a range reduction. This would be of primary concern to glider pilots who fly high and far. So far, none of the glider events have gotten anywhere near big enough to likely cause band saturation.

I presume if you were to host a glider event while the IRCHA event was going on you could see a problem. But that is not likely to happen.


So the consensus is that latency creep is the most likely thing we would see. Unless someone is watching the RF band and doing time correlation of band state to model in the air time, there would be no way to peg the issue to band saturation.

Would it be enough to cause a crash or a mishap? Would a latency jump from 10 ms to 100 ms be enough to case a problem on a 3D heli flight or a high speed pass of a jet? Again, hard to say with no one monitoring the situation.

So that is what I have learned so far, but would be very open to other thoughts or opinions.

In my opinion, large event organizers should consider setting up some kind of band monitor/recorder to see what is going on. I would like to see AMA do this next year at the IRCHA event. The low cost versions may not have the absolute precision desired but they might be good enough to see if further study would be merited. There are probably less than 10 events in the USA that are large enough to merit this, but it might still be worthwhile.

Thoughts and opinions welcome.

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Old 08-16-2013, 04:18 PM   #20
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Honestly, I think you're trying to create a mountain where there isn't even an anthill.

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Old 08-16-2013, 04:20 PM   #21
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So you say Andy, and I respect your opinion. But no one has published anything on this so I am seeking information in an information vacuum.

I have gotten some good feedback and feel I understand the possibilities much better now than I did before and that was my objective.

Will someone run with this? I don't know.

On a personal note, since I don't typically attend the IRCHA event or events of this size I have no real personal concern or vested interest. Primarily I fly gliders. I was just wondering.

However I did take this into account when I was going to 2.4. I had started to move to Spektrum DSM2, but as the events got larger and 72 MHz was being fazed out of the big events, I became concerned. Then Spektrum announced DSMX and explained why. Made total sense to me.

If I could have gotten a DSMX module for my Futaba radios I would have continued with Spektrum DSMX. But I could not get a DSMX module for my Futaba 9C radio, so I switched over to Futaba FASST before I went to the NATs last year. Never a problem. And I am sure DSMX would have worked just as well.

But this is not about brands, and it is not about me, it is about "what if". And "what if" is always a valid thing to ask.

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Old 08-16-2013, 04:26 PM   #22
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Like a lot of things in life, or in court, it takes a law suite to bring change. When someone gets hurt, sues AMA and they pay they will change the rules after it cost them money.

You want to bring about change or punish someone, organization, government, or company? All you have to do is get into their pockets.
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Old 08-16-2013, 04:29 PM   #23
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Hopefully it does not come to that.

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Old 08-16-2013, 04:33 PM   #24
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Well, you can continue to speculate, but it isn't going to make anybody publish their data. Data is expensive and helps us beat the competition. Why should anybody share that?

It isn't about brands, I agree - all the big-name brands work; we have to, or we would end up dying.

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Old 08-16-2013, 04:46 PM   #25
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Originally Posted by AEAJR View Post
Hopefully it does not come to that.
Me to, but just about every law, policy, building code, or rule made was a result of death, injury, or property damage.

Want hot coffee to go? Not anymore someone sued McDonalds to make sure coffee is not hot any more.

On the other hand the world is full of stupid people. Just remove warning labels and the problem solves itself.
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