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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 08-27-2012, 12:26 PM   #1
celticflyer
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Default 2.4 mhz low voltage problems

I have been in ongoing discussions of the reliability of 2.4
Some claim that they are susceptible to cell phones and/or suffer as many problems as 72 mhz. I think that (DUMB THUMBS) use TX/RX as a scapegoat.

HOWEVER, after a discussion with a MA columnist, much of the problem may be due to low voltage. He believes that 2.4 is susceptible to low voltage.
Digital servos and equipment demands, and a system that is just adequate.
What happens during a demand spike??
Any experience or opinions?
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Old 08-27-2012, 01:52 PM   #2
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Originally Posted by celticflyer View Post
I have been in ongoing discussions of the reliability of 2.4
Some claim that they are susceptible to cell phones and/or suffer as many problems as 72 mhz.
Absolutely 100% false. Cell phones in the US are NOWHERE near the 2.4GHz band. If they caused an issue for us - we would be causing an issue for them. How long do you think the RC industry would "get away" with messing with cell signals. Yea not one second of one minute....

Originally Posted by celticflyer View Post
I think that (DUMB THUMBS) use TX/RX as a scapegoat.
I think you are 100% correct. All pilot need something to "blame". Since it can't possibly their piloting skills - you need to blame something.

Originally Posted by celticflyer View Post
HOWEVER, after a discussion with a MA columnist, much of the problem may be due to low voltage. He believes that 2.4 is susceptible to low voltage.
Digital servos and equipment demands, and a system that is just adequate.
What happens during a demand spike??
Any experience or opinions?
That is a well known fact. As a matter of fact - all electronic equipment needs a minimum voltage to work. The servos do - the receivers do. The problem is the voltage floor for some 2.4GHz stuff is 3.5v - higher than where 72MHz used to crap out.

Some manufactures have dropped that low voltage floor to 2.8v (most servos don't work at this voltage). And others have added a quick connect feature so you get control when it "boots" much quicker.

No question we must power things properly and our radio gets the blame for poor BEC's and other poor power management for our models with high demand servos. It is sad to see the RX get the blame for the power supplies fault.

Originally Posted by celticflyer View Post
Any experience or opinions?
I did the first in print review of 2.4GHz air system. Horizon/Spektrum supplied me with a Pre-release version of the now world famous Spektrum DX6 radio system.

I knew within about 2 weeks of receiving that system the industry was going to COMPLETELY change. I mentioned that in my article too. So many were very skeptical. Well look at what we have now. I feel 100% confident in my statements in that review that the "future" was here now and I have been proven right.

2.4GHz has been the most reliable radio RF system to hit our market - period. It is better than the BEST 72MHz stuff - far better. No RF link is perfect but this is better than anything we have ever had. If it was not - people would have not left 72MHz in droves.

No we are on the 2nd and 3rd generation from most of the makers on 2.4GHz - it just keeps getting better!

Too many "old" farts throw around reasons not to go to 2.4GHz. Don't spend much energy on them. No RF link is perfect - but 2.4GHz is the best we have ever had in the hobby, period.

Life is good!

Mike
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Old 08-27-2012, 04:21 PM   #3
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Thanx Mike, More info than I expected this soon. I wonder if there have been studies or articles out there explaining just how to avoid this problem i.e. a proper setup and procedure for different systems.
I've been in the hobby for a while and find I'm still looking for answers. I can't imagine how it is for the newcomer. I know that there are plenty of answers within this forum but sometimes it is spread out and we get lost along the way with other distractions.

Life is good and never boring!!

John
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Old 08-27-2012, 10:11 PM   #4
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Originally Posted by celticflyer View Post
I have been in ongoing discussions of the reliability of 2.4
Some claim that they are susceptible to cell phones and/or suffer as many problems as 72 mhz. I think that (DUMB THUMBS) use TX/RX as a scapegoat.

HOWEVER, after a discussion with a MA columnist, much of the problem may be due to low voltage. He believes that 2.4 is susceptible to low voltage.
Digital servos and equipment demands, and a system that is just adequate.
What happens during a demand spike??
Any experience or opinions?
Yup
There is a major difference between these 2.4 Ghz receivers and the old 72 Mhz receivers. The 2.4 Ghz receivers REQUIRE a little microcontroller (microprocessor thing) to drive the microwave transceiver chip in the receiver. These microcontrollers have a minimum voltage feature, where if the receiver voltage drops below minimum, even for a fraction of a millisecond, the microcontroller is programmed to reboot.

The early Spektrum receivers took several seconds to re-lock in with the transmitter when they got hit by undervoltage. Spektrum reworked the software so the "reboot" time is now under a second. (Yes, I've checked it) My Spektrum AR7000 receivers all reboot at voltage under 3.2 Volts DC. (I've checked it)

So, what's to do?
Be danged careful on what is used for the receiver/servo power system in your models. A lot of the ESC's with BEC's (Battery Elimination Circuit) use a cheap LINEAR voltage regulator for the 5 volt output. IMHO, this type of setup should NEVER be used on any model with more than two LiPo cells for motor power.

If you are using those five cell "AA" type Nih cells, again be danged careful when working with high power servos. My giant scale models use seven Hitec 645MG analog servos. I've measured the peak current pulled by those seven servos at 14 Amperes. A current of 14 Amps placed on the typical "AA" nih battery pack will drop the battery pack voltage down below the reboot voltage of the 2.4 Ghz receiver.

This thread explains it all.
http://www.wattflyer.com/forums/showthread.php?t=63779

If you are working with giant scale models, IMHO, it's mandatory that dual receiver power supplies be used.
Giant Scale Battery Backup System
http://www.wattflyer.com/forums/showthread.php?t=63794

This is what I've been using in my two giant scale models now for two years, without a single glitch or issue.

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Old 08-28-2012, 09:06 AM   #5
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There are tywo main differences for me ...

Pro's :

The new sets generally 2.4Ghz are more programmable and have extra features due to the Chip than older sets.

Cons :

If you lose signal with 2.4Ghz - no matter how quick they make the reboot - it is still far longer than the instant re-control of older 35Mhz etc.

So like many things in life - there is always a trade-off.

I have to say this as well - I've observed more crashes / more unexplained mishaps with 2.4 than I ever witnessed with 35Mhz ...

Nigel

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Old 08-28-2012, 01:43 PM   #6
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Originally Posted by solentlife View Post
Cons :

If you lose signal with 2.4Ghz - no matter how quick they make the reboot - it is still far longer than the instant re-control of older 35Mhz etc.

So like many things in life - there is always a trade-off.

I have to say this as well - I've observed more crashes / more unexplained mishaps with 2.4 than I ever witnessed with 35Mhz ...

Nigel
That could not be further from my experience. While we use 72MHz here in the Colonies I have been at this a while. I have seen MANY more incidents with 72MHz.

Most relate to "stupid" like turning on when someone else is already on your "channel". That reason alone is enough reason to change IMHO.

But I have also had experiences with interference - to the point we had to ban the use of certain channels at the field. In fact pretty much every field I had - had one or two "bad" channels due to industrial (railroad switching was a big one) or TV use (audio for us here was pretty close - in some cases).

I have lost 2 planes to interference with issues over the years. I have had "lock outs" several other times but was able to recover. I have watched other pilots have planes go in - somewhat regularly over the years with unexplained lock-outs. To be honest I think many of those were power issues as well. All systems need power to work properly.

There is no question that we have seen issues with 2.4GHz mainly with the power issues we speak of here. Spektrum was especially venerable.

Futaba had issues with the GUID code being all zeros and that caused significant issues as when users who both had zeros would control each others' airplanes. They also had issues with receivers overheating and shutting down.

Hitec has the voltage issue - but has an SPC separate power port to help avoid the issues.

The RF link however has proven extremely reliable in all cases but one. That was when Spektrum (the only major system to select two channels and lock on to those) at HUGE events (more than 100 TX's on) causing lock outs. That was purely a factor of having too many TX's "On" at the same time. DSMX addresses that issue.

Futaba at these large events had issues with slowdowns (really slow response but not total lock outs) due to the sheer volume of traffic.

So the large events (IRCHA, Nall, SEFF etc) are now limiting the number of transmitters on at the same time. They require that you have a pin to transmit.

I stand by my statement - the 2.4GHz systems are the most reliable RF link we have had in the RC buz - period.

Even if you don't believe me - look at the everyone who has converted. The numbers speak to the reliability of the 2.4GHz RF link.

Let me guess - you have not converted yet. ??

Mike
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Old 08-28-2012, 01:52 PM   #7
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There is one almost foolproof way to keep your 2.4GHz system from having a brown out, power only the receiver with it's own battery, a low mah 4 cell will be very reliable. You then power ALL your servos and other electronics with their own power supply of whatever mah capacity is prudent. Not a difficult job and well worth it on any of your expensive planes. Of course for the majority of flyers with the small electrics, this is not very practicable.
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Old 08-28-2012, 02:47 PM   #8
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Originally Posted by rcers View Post
That could not be further from my experience. While we use 72MHz here in the Colonies I have been at this a while. I have seen MANY more incidents with 72MHz.
Never used 72 - as I was UK based and only 27 + 35Mhz was in use when I was there. 27 had issues with CB radio guys and their booster sets shooting down models ... which is part reason why UK adopted the European 35Mhz route.

Most relate to "stupid" like turning on when someone else is already on your "channel". That reason alone is enough reason to change IMHO.
I knew Kenny Binks - UK aerobatics champ .... he's guilty of that !! Beaulieu Scale Meet - I was flying, I had the peg cleared by Marshalls .. he fired up and my JR never missed a beat - but his radio went doo-ally !!

But I have also had experiences with interference - to the point we had to ban the use of certain channels at the field. In fact pretty much every field I had - had one or two "bad" channels due to industrial (railroad switching was a big one) or TV use (audio for us here was pretty close - in some cases).
I assume on 72Mhz ... i respectfully repeat that I am a flyer from 27 and 35Mhz days ... never had 40 or 72.

I have lost 2 planes to interference with issues over the years.
That's 2 more than I've had over 40+ years.

I have had "lock outs" several other times but was able to recover. I have watched other pilots have planes go in - somewhat regularly over the years with unexplained lock-outs. To be honest I think many of those were power issues as well. All systems need power to work properly.
Now I feel that - too many claims of radio this ... radio that I reckon are often due to the hands on the sticks ... I've watched so many pile in and you know they were waving those sticks about and basically lost it ! But wo betide anyone who tells the guy !!

There is no question that we have seen issues with 2.4GHz mainly with the power issues we speak of here. Spektrum was especially venerable.
My comment was the reboot vs re-control of the two mediums ... 2.4Ghz - lets be honest unless you are way up high - you've lost her ! 35Mhz - instant re-control - I reckon a better chance of saving the model.

The RF link however has proven extremely reliable in all cases but one. That was when Spektrum (the only major system to select two channels and lock on to those) at HUGE events (more than 100 TX's on) causing lock outs. That was purely a factor of having too many TX's "On" at the same time.
You do live dangerously !! no=ones supposed to knock Spekies !!

So the large events (IRCHA, Nall, SEFF etc) are now limiting the number of transmitters on at the same time. They require that you have a pin to transmit.
Nice one !

I stand by my statement - the 2.4GHz systems are the most reliable RF link we have had in the RC buz - period.
I don't argue that point - I agree with you ... it's the reboot of a chip I am commenting on.

Even if you don't believe me - look at the everyone who has converted. The numbers speak to the reliability of the 2.4GHz RF link.
If lots of people tread in cows muck - does that change the fact you're treading in **** ? Just because millions buy Ford - doesn't make Ford best. I am not saying 2.4 is crap .. far from it ... but it's a weak argument because basically at end of day ... look on the shelf of any LHS and what radio do you see ? 2.4Ghz ... is that because buyers demand 2.4 ? No sorry - I don't follow that road - I am a staunch believer that designers / manufacturers THINK they produce what people want - but in fact build and convince Us this is what we want. Sublimal has never stopped !

Let me guess - you have not converted yet. ??
You are far far wrong on that ....... I have 2 x 2.4Ghz sets right next to me right now. 1 is my Heli radio - other is my general fly all radio.
I have my old JR 35Mhz there as well - but it's not installed in anything at present. I have an old Futaba M 35Mhz as well - but that's just a Shelf item now.
The rest are RTF and rubbish supplied with models that I use indoors ..

I am a convert - but I am waiting for the real answer to all our prayers ...

Nigel

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Old 08-28-2012, 03:13 PM   #9
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It is really close to the real answer to all our RC prayers.

I am at 34 years so you have me. My two losses were I have been shot down once and the jerk didn't pay up GRRRR but as you point out even the big names and the smart among us make mistakes. The other was a cheap 72MHz RX and flying on a "low" channel that actually can get hit from higher channels (another issue with 72MHz). It just was not rejecting the other signal well and I went haywire it was a small electric - so it too may have had ESC interference, yet another 72MHz issue!

Sad story - Several years ago we had a really bad situation. We had a local field here in DFW and a guy that got kicked out the club over a safety tiff. He was told to never come back. Sadly he did come back. The bad news is he had a spectra module in his system. He would go out to the field - hide in his van and change the channel on his system to purposely shoot down the other pilots. As you would imagine it was NOT a pretty scene. They had many members who lost high dollar models in this criminal act. Obviously it was a huge safety issue too. I think they actually caught and prosecuted they guy.

I know you don't fly 72MHz but that is what the bulk of users here in the US used. But several of these items are an issue on 35&27Mhz as well.

At any rate - I am a Spekky, Hitec, Futaba and Airtronics guy so I can gripe about em all...and praise them too! LOL!

Mike
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Old 08-28-2012, 05:52 PM   #10
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Losing models .... (sorry for drift here ....)

I had a really nice Royal Kit P51D Mustang, HB50 up front .. proper spinner etc. Flaps ... it was really a cracking model and always got admiring looks from others when I put on flight line.
One day - flying along and in she went ... no warning, no big show ... just pitched down and into the tarmac. All built up construction and tarmac do not agree.
Why ? Previous week I had my radio gear in for service. Guy didn't like my home-made NiCD Rx packs ... pushed me to replace with factory welded pack. During that flight - one cell contact came adrift ... no power to Rx. I went back to making my own packs !!

Another was my Mig DF model ... 20 glow powered ... I watched the wing fold in flight when the main spar gave out.

I've had various crashed models - but none due to Radio failure ...

My 20 Pylon racer had a midair with a mates aerobatic machine when he stupidly tried following me into a tight pylon turn ! I sliced his wing of !!

My display biplane was launched into a hedge one day !!

My WOT4 display machine had a 61 with tuned pipe and in a vertical WOT dive - the motor shattered and she never pulled out !

But back to radios ... for me I have a old-time comfort feeling with my JR Propo 35 set .. it took me through competitions, displays, all sorts and it's still there today. Only change is I matched a Corona syn Rx to it after the old modular Rx failed.

I put all crashes of mine down to ME !! or other failures.

Nigel

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Old 08-28-2012, 08:28 PM   #11
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Originally Posted by rcers View Post
But I have also had experiences with interference - to the point we had to ban the use of certain channels at the field. In fact pretty much every field I had - had one or two "bad" channels due to industrial (railroad switching was a big one) or TV use (audio for us here was pretty close - in some cases).

I have lost 2 planes to interference with issues over the years. I have had "lock outs" several other times but was able to recover. I have watched other pilots have planes go in - somewhat regularly over the years with unexplained lock-outs. To be honest I think many of those were power issues as well. All systems need power to work properly.
Ah yes
Interference. I've also played that game on the old 72 Mhz frequencies. Seems when you get above 20 Nicad cells or so on those Astroflight geared 40 motors, the resulting interference really starts hitting the 72 Mhz receivers.

In fact, I had an Astroflight geared 90 motor on 38 Nicad cells. The range test on that thing was about 20 feet. With the transmitter antenna fully extended.

Took a long while to figure that one out. What worked was a pair of toroid ferrite chokes directly around the wires between the motor and ESC.

It's very difficult to generate 2.4 Ghz on purpose. Far more difficult to generate 2.4 Ghz frequencies by accident, like brush noise, and similar stuff.

As for the reliability of 2.4 Ghz around our club, probably 99% of the 2.4 Ghz radios in our club are Spektrum/JR types. After more than a few years of flying with these systems, crashes caused by the 2.4 Ghz frequencies are very rare. And the two foamie crashes I'm aware of were caused by using linear BEC's on the ESC's where the linear bec simply overheated and shut everything down.

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Old 08-28-2012, 09:01 PM   #12
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As an interesting corollary to all this on the TX side, if the power glitches fast enough (due to a bad switch is one way) the TX can show no signs of a power problem but the microprocessor can lock up, if the reset/low-voltage circuitry was robust this wouldn't be the case but I've seen my DX5e do it (and have seen it happen to other processor-controlled equipment).

Ask me why your DX5e is doomed... and how to fix it.
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Old 08-29-2012, 01:49 AM   #13
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I never had one radio related problem when I was learning to fly on fm. I switched to spectrum, and now I wonder why. A nice fm computer radio is cheap, and can do everything a 2.4 ghz system can, until you get a lot of models or fly with a bunch of others.

However, fm receivers are now more expensive then spectrum knock offs.

I also fly out on the salt flats, and I almost never see anyone else on the feild, and there is nothing to create interferance. I have had 3 planes on spectrum and 3 on fm. Never beleived to have had a glitch on fm, had several different problems on 2.4ghz. Just last weekend, we popped an am radio out of one of my grandpa's planes, hooked up a battery pack and fm receiver, and went flying.
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Old 08-29-2012, 02:51 AM   #14
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Originally Posted by CNY_Dave View Post
As an interesting corollary to all this on the TX side, if the power glitches fast enough (due to a bad switch is one way) the TX can show no signs of a power problem but the microprocessor can lock up, if the reset/low-voltage circuitry was robust this wouldn't be the case but I've seen my DX5e do it (and have seen it happen to other processor-controlled equipment).
The company I worked for manufactured computer controlled high voltage circuit breakers. These controls absolutely have to work 24 hours a day for decades without ever locking up, even while getting a hit by lightning.

The low voltage reset, and software programming to identify and reboot during a run-away computer program were major issues during the control hardware and software design stage.

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Old 08-29-2012, 02:54 AM   #15
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Originally Posted by rcers View Post
Futaba had issues with the GUID code being all zeros and that caused significant issues as when users who both had zeros would control each others' airplanes. They also had issues with receivers overheating and shutting down.
Did Futaba ever resolve their problem with their receivers overheating? Their web site still has a warning on over temperature for the receiver.

Take a look:
http://www.futaba-rc.com/faq/faq-fasst-q1064.html

It's interesting that several years ago, Spektrum had an advertisement where they put one of their receivers into an enviromental chamber that could vary the temperature. They then proceeded to heat the chamber and the receiver inside up until the receiver quit. That Spektrum receiver finally quit at high temperature, AFTER the receiver's plastic case melted!

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Old 08-29-2012, 03:45 AM   #16
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I suspect they did some work to help with that issue but not sure. I have never had it here in hot TX and my Futaba stuff. Not sure though - they tend to be the least communicative of the mainstream bunch.

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Old 08-29-2012, 03:54 AM   #17
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Originally Posted by rcers View Post
I suspect they did some work to help with that issue but not sure. I have never had it here in hot TX and my Futaba stuff. Not sure though - they tend to be the least communicative of the mainstream bunch.

Mike
Hi Mike
Good info, thanks

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Old 08-29-2012, 06:15 PM   #18
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Originally Posted by hayofstacks View Post
.............Just last weekend, we popped an am radio out of one of my grandpa's planes, hooked up a battery pack and fm receiver, and went flying.
??

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Old 08-29-2012, 06:59 PM   #19
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We pulled am receiver gear out of my grandpa's ugly stick, then threw a fm receiver back in. My grandpa passed a while ago. We figure the plane had been sitting for about 20 years. His health left him way before he died.

We broke a prop on takeoff, threw a 9X9 on it and flew it around for a bit. Too much prop for the .15 motor though. I am going to pick up some more 8X5's this weekend and see if we can get back out.Pplane flew pretty well. If it fly's well enough when we get it going well, I want to throw some smaller servo's and fix some of the small things.
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Old 08-30-2012, 01:12 AM   #20
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Originally Posted by hayofstacks View Post
We pulled am receiver gear out of my grandpa's ugly stick, then threw a fm receiver back in. My grandpa passed a while ago. We figure the plane had been sitting for about 20 years. His health left him way before he died.

We broke a prop on takeoff, threw a 9X9 on it and flew it around for a bit. Too much prop for the .15 motor though. I am going to pick up some more 8X5's this weekend and see if we can get back out.Pplane flew pretty well. If it fly's well enough when we get it going well, I want to throw some smaller servo's and fix some of the small things.
Yeah
I've got an old Controlaire Mule II transmitter and receiver running on 27 Mhz. This rig dates back to the mid 1960's. It's a single channel with the only control being a pushbutton.

That transmitter and receiver still works.

I converted one of these transmitters to work with the Rand Galloping Ghost servos back in the mid 1960's. The GG servo's worked fairly well, but that transmitter running on the 27.195 Mhz frequency was the most unreliable radio I ever had. Any CB operator transmitting within 5 miles could and did shoot my model out of the air, no matter what channel they were transmitting on. BTW, that receiver is a superhetrodyne.

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Old 08-30-2012, 10:57 AM   #21
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Originally Posted by hayofstacks View Post
We pulled am receiver gear out of my grandpa's ugly stick, then threw a fm receiver back in. My grandpa passed a while ago. We figure the plane had been sitting for about 20 years. His health left him way before he died.

We broke a prop on takeoff, threw a 9X9 on it and flew it around for a bit. Too much prop for the .15 motor though. I am going to pick up some more 8X5's this weekend and see if we can get back out.Pplane flew pretty well. If it fly's well enough when we get it going well, I want to throw some smaller servo's and fix some of the small things.
Makes more sense now ... first reading looked like you were saying you flew FM Rx on AM gear !!

...

I have my old JR Propo - 35Mhx Fm - still works, has a Corona Synth Rx with it now ... I'm thinking to install it in the next depron job I'm throwing together ... a profile Me109 ...

Kyle - please stop talking about those old radios ... I can still remember and they give me the shivers !! UGH !! Just to think what we tried to do with them ...

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Old 08-30-2012, 04:49 PM   #22
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Originally Posted by solentlife View Post
Kyle - please stop talking about those old radios ... I can still remember and they give me the shivers !! UGH !! Just to think what we tried to do with them ...

Nigel

LOL
I've still got a MicroAvionics Servo from a four channel radio system with that square four lead connector. That radio cost me the equivalent of four months rent, and this radio was two years old when I bought it.

It's reliability was not much better than that old single channel thing.

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Old 08-31-2012, 08:07 AM   #23
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Ii quit counting our old am radio's at 12. When we go out flying, I give my kid an old 4 channel am radio to play around with. He's 3 years old, but he alrady knows not to point the antennea and hasn't broken an antenna yet. I don't think he has figured out that the transmitter contols the plane yet though...
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Old 08-31-2012, 11:29 AM   #24
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Originally Posted by kyleservicetech View Post
LOL
I've still got a MicroAvionics Servo from a four channel radio system with that square four lead connector. That radio cost me the equivalent of four months rent, and this radio was two years old when I bought it.

It's reliability was not much better than that old single channel thing.
I gave away my **** and invested in the NEW fantastic Futaba !! I coulodn't believe it - PROPORTIONAL control !! AND IT WORKED every time I switched on !
Then I progressed to Futaba M series .... working my way up through the 3ch .. 4ch .. then finally one of the last M's they made - the 6ch :



Now all these had a 6 pin DIN socket to allow Buddy Box Traning ... amazing !

But Oh what a price !!

Nostalgia ... !

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Old 09-04-2012, 10:39 AM   #25
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OK group, I have Spektrum DX7, what should the min. cutoff voltage be on my esc be set? CC ICE 50 (5 amp bec) preset to 3volt per cell.
I guess the real question would be, what is the min. power for Spektrum RX
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