The End of R/C

I would suggest a similar scheme to the 1991 issue. Give a 5 year grandfathering timeframe and then you just have to bite the bullet.

| I am with you. Moving us to higher frequencies might be a great idea, once | the agony of buying new R/C gear has been dealt with and put behind us. I | also like the idea of spread spectrum, but not at a loss of rapid update | times. I would think that this is the biggest problem to over come for such | a system.

There is no reason to lose rapid update times with a spread spectrum system. Make no mistake -- the biggest problems are political, not technical or economic. If 1 mHz of bandwidth somewhere could be dedicated to spread spectrum R/C, with 1 watt transmission power permitted, systems could be easily created that meet or exceed the update performance of current systems even with 20 planes in the air.

I tend to suspect that we could meet that level of performance with only part of a mHz hunk of spectrum, but I'd leave that determination to somebody with more experience designing these systems.

Of course, BPL is not likely to help that happen. What BPL is most likely to do to R/C is create a zone around power lines that you don't dare fly in. Exactly how big this zone is depends on how much intereference it actually emits and how far you are from that area. If the zone is small enough, it won't matter at all because flying mear (and into) power lines is bad anyways.

And if BPL is worse than I imagine for R/C, and it totally trashes our frequencies to the point that we can't fly more than 50 feet away, then the FCC is not likely to ride to our rescue and give us a new frequency band away from the BPL intereference. The AMA would certainly push for it, and maybe it would happen eventually -- maybe

-- but it wouldn't happen soon, and it wouldn't be a certainty. The FCC would probably be more interested in accomodating all the other things using the 2-80 mhz band that are asking for new spectrum ...

DSSS (Direct Sequence Spread Spectrum) is fully capable of updating our systems faster then ANYONE can move the sticks. This is being used with wireless networking right now at over 100mbps (US Robotics 802.11g systems). Even the older 802.11b (20 times faster than your average DSL connection) systems were fast enough for realtime video. And even at the low power they operate at, most are good for over 1000 feet outdoors unobstructed (average RC environment!)

| DSSS (Direct Sequence Spread Spectrum) is fully capable of updating our | systems faster then ANYONE can move the sticks.

Yes. I see 2 ms ping times on my 802.11b network -- that would be far faster than anybody's reaction time.

| This is being used with wireless networking right now at over | 100mbps (US Robotics 802.11g systems).

Those evil things also use almost the entire 2.4 gHz spectrum, and are part of the reason why we don't want to use it for RC -- being unlicensed, there's nothing stopping people from being downright rude about it and using the entire spectrum.

| Even the older 802.11b (20 times faster than your average DSL | connection)

Either your 802.11b is faster than everybody elses, or you've got really slow DSL over there. Most 802.11b setups get about half of the rated rate, or about 5 Mbps. And most DSL users around here get about

| systems were fast enough for realtime video.

You're confusing throughput and latency. 100 mbps and `20 times faster than your average DSL connection' are measures of throughput, not latency. The two are related, but only distantly.

But it's not hard to calculate how much throughput is needed. Suppose you have a maximum of 32 channels (since it's a new system, let's leave lots of room for future expansion), 16 bits of resolution per channel (giving you 65,536 possible stick positions) updated 50 times per second. That works out to 3.125 Kbytes/s -- a tad faster than the speed of your 28.8k modem. Not much throughput by today's standards. Of course, then you'll need to add some more for error correction (it would probably work like PCM does today, but faster), then multiply it by 30 or so (a theoretical maximum number of planes in the air at once) and then use that to determine how much radio spectrum will be needed. If you go over that 30 planes figure, then latency for everybody will decrease, but not by a large amount. Certainly, planes wouldn't fall out of the sky -- updates might just take 1/12th of a second rather than 1/25th of a second if you had 60 planes up in the air at once. All of the numbers I picked I just made educated guess at, so there's little point in stating that I chose poorly. :)

Of course, these figures could go way up if the capability was added to send telemetry back over the same network, and they would go through the roof if you could send video or something similar back. I think adding that would be a bad idea -- let another band be used for that. The current 2.4 gHz, 900 mHz or ham bands would work nicely.

| And even at the low power they operate at, most are good for over | 1000 feet outdoors unobstructed (average RC environment!)

I recall that there was a statement saying that they would not be allowed to cause HARMFULL interferance. That means that there would be a low level of interferance. This statement is used often in part

1. I don't think coax would work for powerline shielding, lines would get too hot for the insulation. In fact there would probably have to be an air gap and some sort of ventalation. Not sure but I wouldn't think it would have to almost completly get rid of interferance as coax does.

Most people I know use 500kbps DSL as any of the faster ones are far too expensive. My USR wireless system averages very near the 11mbps even in the harsh environment I live in (three block or plastered walls to go through. If I can get realtime audio and video through those, I can certainly control my plane with it.

Well, now that you benchmarked a possible system, let's explore it a little more.

Do we NEED 16bit res? I doubt it. 8bit would be just fine as no one I know posseses the fine motor skills to command 65,000 unique positions of the stick. Given a WAG of 2" total stick travel, that means you would have to be able to move the stick 1/32500 of an inch. Probably an order of magnitude greater than we need.

Assume we keep the same frame rate as the current systems, these are updated about 50 times a second. Cutting that in half wouldn't be discernable to about 99% of fliers.

I was making reference to the very low power levels the current WLANs operate at. With the approx 1/2 watt we use for RC, the distance would be much greater.

WLANS are low range - even with clear line of sight at best 2-300meters without directional antennae.

Part of the problem is teh 2.4Ghz is very much absorbed by water - in leaves, in the air - anything.

Also ahe data rate is so much higher that a broader spectrum is needed, This increases noise levels.

Digital encoding for spread spectrum should enable much higher ranges as would a shift to another frequency as well as higher power.

Like most, I see no fundamental problem. Just a huge learning curve and technology development one.

| I recall that there was a statement saying that they would not be | allowed to cause HARMFULL interferance. That means that there would | be a low level of interferance.

`Harmful interference' is a bit too vague. So the law has defined a specific amount of power that you cannot exceed. And yes, it's pretty small.

However, with BPL, every powerline everywhere (at least near the houses) would be emitting at at this low power. It probably won't affect R/C too much, but it'll be a disaster for ham radio DXing, shortwave listening and radio astronomy. Which will be louder -- a

Also, the power companies are attempting to have the lower power figure increased, so that they can spew even more noise.

And then there's the question of exceptions. If a certain stretch of power line is exceeding the legal limit, how long will it take to find it and get them to fix it?

| This statement is used often in part 15.

Yes, but they also define harmful interference more carefully.

| I don't think coax would work for powerline shielding, lines would | get too hot for the insulation.

Power lines don't really get too hot. Power lost to heat is money lost, so the power companies really try to avoid it. So the power companies increase the voltage and decrease the amperage, decreasing the power lost to resistive heating.

Alas, having a 100,000 volt line would make running it through coax difficult -- you'd need some serious insulation. In fact, most high voltage lines don't have any signifigant insulation on them at all (perhaps some paint, but that doesn't insulate very well.) Which is why birds get often get fried when they fly through them just right. It's just not cost effective to put the massive amount of insunation needed on, when a large gap of air will work nicely.

There's no practical way to shield power lines, especially the existing power lines that they want to run BPL over. If you need the ability to send a shielded signal, you should just run coax (or something similar) next to the power line and leave the power line alone. Of course, this isn't BPL -- it's cable, a well proven and reliable technology.

| In fact there would probably have to be an air gap and some sort of | ventalation. Not sure but I wouldn't think it would have to almost | completly get rid of interferance as coax does.

Merely putting the power lines closer together will reduce the interference, but once they get close enough, air isn't a good enough insulator anymore and you need to add something better, adding cost and maintenance requirements. And of course, the power companies aren't going to change any power systems just for BPL -- the advantage of BPL is that they don't have to.

"aerobat" wrote

No, Larry. I'm still in Georgia.

Ed Cregger

You'd better believe that HV lines get hot!

I used to work for Electric Power Research Institute (EPRI) at site here in north Texas. For research into power line sag with elevating temperature, we put up a pair of conductors 6 feet apart stretched the length of our 375 foot shop. We instrumented the conductors with thermocouples to monitor temperatures and linear transducers to measure sag. We recorded ~2 foot sag increase caused by 450 amps thru

That's why we were doing the research - how much more power could be pushed thru the lines before heat induced sag became a problem.

BTW, 100kv lines are puny these days.... think more like 1mv for long distance lines.

BTW, we also inadvertedly visually demonstrated the basic electronic law that conducters with current flowing in opposite directions will attract each other - our test conductors would move ~8 inches toward each other at max current. I set up a video camera that monitored the conductors at the time that current went to 0 amps during the test and have a clip that shows the conductors swinging apart when the current is cut!

David

SNIP>

| You'd better believe that HV lines get hot!

Ok, I stand corrected. However ... | We recorded ~2 foot sag increase caused by 450 amps thru | 2 inch ACSR (Aluminum conductor steel reinforced). The temp rose to | ~115 deg C IIRC. You might say "only 450 amps?". Multiply that by | the possible 1Mv on the lines..... Power=amps x volts.

How many amps does your typical HV cable carry? (I do not know.) Knowing the voltage and the power transmitted, it's a pretty simple calculation. Is 450 amps typical?

As for the power lost (to heat), it doesn't actually depend on the voltage *at all*. Instead, it's based only the amperage and the resistance.

Power (watts) = Amps x Volts, true, but when you're talking about the heat generated, you're talking about the voltage drop, not the total voltage. And Voltage Drop = Current * Resistance.

So power lost to resistive heating = (current)^2 * resistance -- there's no voltage variable at all in there. That's why the voltages used are so high -- if you double the voltage, you halve the current (for the same power) and therefore decrease the energy lost to heat by a factor of 4.

| That's why we were doing the research - how much more power could be | pushed thru the lines before heat induced sag became a problem.

Seems to me the way would be to go to two million volts, or four, or as high as you could go ... of course, at some point, the insulators available won't be good enough, you'd need huge gaps between the wires, and you'd have a hard time coming up with transformers that could handle that much voltage. I'm guessing that that point isn't much more than the highest voltages commonly used.

(But I'm sure y'all are already aware of all that. For maximum power, you want maximum current and maximum voltage. And 1 million volts may be close to the maximum voltage ...) | BTW, 100kv lines are puny these days.... think more like 1mv for long | distance lines.

Ok, one million volts. But it's the amps and resistance of the wire that determines how much power is lost to heat, not the voltage. Still, 100 C isn't that hot. But that's with no insulation whatsoever

-- so obviously, adding anything would make it much hotter. So again, as mentioned before, shielding the wires for BPL is not practical.

Not that any of this has anything to do with R/C anymore, and I'm just going to let it drop here :) Though I could point out how bad 1 million volts would be if you happened to fly your plane in just the wrong place ...

Really? Doesn't depend on voltage at all? OK! Then drop it to zero volts and problem solved!

Yep. Zero volts would need infinite current.

Does this moron actually have a vote?

What you were trying to say, before you accidentally put your 'X my vote marks the spot' vote on the local communist candidate, was 'so lets use infinite volts and zero current'

Which is, as far as is practicable, what power engineers try to do. Unfortunately infinite volts means infinite sparks, and they also draw power...

You know, I doubt any HV lines will be used for BPL, just the medium voltage lines. I envision round insulators holding spiral's of wire sheathing existing lines for shields. This doesn't completly cover the lines and allows airflow to cool them. Have no idea how much it would reduce RF.

I will be charitable and say you misunderstood. He was correct in saying power loss is a function of amperage, not voltage.

Guess what? 1,000 amps at 12 volts will heat a wire at EXACTLY the same rate as 1,000 amps at 100,000 volts.

-- Dave Thompson

| You know, I doubt any HV lines will be used for BPL, just the medium | voltage lines.

Probably not. It's really only the last mile (to the house) that they're after.

| I envision round insulators holding spiral's of wire sheathing | existing lines for shields. This doesn't completly cover the lines | and allows airflow to cool them. Have no idea how much it would | reduce RF.

Yes, that could be somewhat effective -- a faraday cage. But it's not going to happen.

Let me see if I can make this as clear as possible, as to stop any further speculation about what kind of shielding could be used.

The reason that BPL is attactive is that it allows one to get fast Internet access without any additional wiring being added to each house. It's an economic thing -- it's cheap. You'll need to add some hardware to each neighborhood, to put the signal into and read it out of the power lines, but you don't need to run cable to each house.

Adding *any* sort of shielding to the existing wiring going to each house would remove the economic advantage of BPL. It would be much cheaper to just run coax to each house rather than add *any* sort of shielding, so if shielding is required, they'll just ditch BPL and go with standard cable (or fiber, or whatever.)

So quit talking about how power lines could be shielded -- yes, they could, but it's not going to happen. :)

This thread needs to die. If you want to reply, email me rather than posting. Unless your post is related to R/C planes, that is :)

Ob R/C: I slapped a 3 cell 2200 mAh iRate Li-Poly battery into my Combat Wings XE2 with an Astroflight 020 motor ($75 for the battery -- ouch.) It will now go vertical and pulls 21,000 RPM (on the ground) with a 6x4 prop, screaming like a banshee in the process. Wheee! Alas, I needed to add a 1/2 oz. of weight to the nose to make it balance properly -- I hate doing that with electrics, but this battery is so much lighter ...

flexibility.

You are certainly welcome to stop posting, Doug, but really don't think that it is up to you whether the thread dies or not. After all, it's MY THREAD.

Paul McIntosh

How about this Doug.....put a Graupner 480 speed direct drive with a 6 by 5 Carbon Electric prop in a Koyosho Spree....not only will it go vertical but it roll over and......well alas it needs some mending :-( I wanted to upgrade it but I think I went overboard I guess the better upgrade would have been a 400 geared to the recomended ratio then the stock geared 380???? Here is a question for you and anyone else who reads this. I have a Herr Enginering Piper J-3 Cub ( I just love those planes :-) ) the kit calls for a direct drive 280 class motor that spins a Paul Gunther No. 302 125mm by 110mm prop. Wing span = 35.25 Wing Load =

TY Mike