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

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Old 09-22-2012, 06:14 AM   #1
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Default myths about am servos.

I think it is time to dispell some of the myths that revolve around older planes, am radio's, and newer spectrum radio gear.

I have seen written many times, that am servo's are not compatable with spectrum receivers and other radio gear. Upon completion of my second am radio conversion, I would like to hear where this rumor comes from.

First plane I converted was an old 25ish sized phil craft ugly stick. I pulled an am radio out of it, replaced the battery pack, swapped in a newer parkflyer fm receiver off of my slowstick. I did several antenna down range check, and found everything on the model to work perfectly, farther then I can see it, with antennea down.

I used the fm receiver for two reasons. Plug and play with the origonal am receiver, and because I had doubts about if the spectrum receivers I upgraded to would work. After thinking about it, I went from a fm receiver to spectrum stuff on my slow stick. So I knew if the fm servo's would work, then so would am ones.

The old covering on my ugly stick was solarfilm. After a couple trips to different hobby shops, I decided that solarfilm is quite a bit thinner, and less heat resistive. I also could not find any trim sheets or stickers for it. I have had several holes open up on the wing in flight. My first patch I thought was caused by a level landing off feild when the motor cut out at low altitude. After inspecting the wing, it has many cracks and small holes in it already. The monocoat trim sheets I attempted to patch the wing with, work very well, but the solarfilm is too old and melts, even under the trim sheets.

This led me to another plane. We have three generations of airplanes in our garage. My grandfather. Was a silk and dope man. He also way overbuilt all of his planes. Making them very heavy, and many, the silk has rotted away. I found a foam wing and built up fuse with a newish looking .40 on it. We pulled it out, it fired right up, and the motor ran well. The biggest problem was the servo's. It used a pre 1991 am radio with the three prong futaba servo connevtors. I was getting ready to swap all of the servo's out when it hit me, I have about 5 bad servo's with good leads.

We had a 5channel "full range" receiver in my dads recently trashed trainer. I cut off all of the servo leads, removed radio and flight pack. Soldered on some "new" sevo leads, bound the receiver, and the plane is now ready to fly. After regluing the elevator stab, it should come out to be a very nice flying model. It is a high wing, symetrical foam wing covered in some sort of vynil meterial. Coming in at about 4lbs, this .40 fox motor should power it very nicely.


But back to the origonal question. Where did the am servo's not being compatable with spectrum receivers come from? I am guessing the radio gear to be somewhere between 1985-1991.
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Old 09-22-2012, 06:28 AM   #2
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Originally Posted by hayofstacks View Post
I think it is time to dispell some of the myths that revolve around older planes, am radio's, and newer spectrum radio gear.

I have seen written many times, that am servo's are not compatable with spectrum receivers and other radio gear. Upon completion of my second am radio conversion, I would like to hear where this rumor comes from.

First plane I converted was an old 25ish sized phil craft ugly stick. I pulled an am radio out of it, replaced the battery pack, swapped in a newer parkflyer fm receiver off of my slowstick. I did several antenna down range check, and found everything on the model to work perfectly, farther then I can see it, with antennea down.

I used the fm receiver for two reasons. Plug and play with the origonal am receiver, and because I had doubts about if the spectrum receivers I upgraded to would work. After thinking about it, I went from a fm receiver to spectrum stuff on my slow stick. So I knew if the fm servo's would work, then so would am ones.

The old covering on my ugly stick was solarfilm. After a couple trips to different hobby shops, I decided that solarfilm is quite a bit thinner, and less heat resistive. I also could not find any trim sheets or stickers for it. I have had several holes open up on the wing in flight. My first patch I thought was caused by a level landing off feild when the motor cut out at low altitude. After inspecting the wing, it has many cracks and small holes in it already. The monocoat trim sheets I attempted to patch the wing with, work very well, but the solarfilm is too old and melts, even under the trim sheets.

This led me to another plane. We have three generations of airplanes in our garage. My grandfather. Was a silk and dope man. He also way overbuilt all of his planes. Making them very heavy, and many, the silk has rotted away. I found a foam wing and built up fuse with a newish looking .40 on it. We pulled it out, it fired right up, and the motor ran well. The biggest problem was the servo's. It used a pre 1991 am radio with the three prong futaba servo connevtors. I was getting ready to swap all of the servo's out when it hit me, I have about 5 bad servo's with good leads.

We had a 5channel "full range" receiver in my dads recently trashed trainer. I cut off all of the servo leads, removed radio and flight pack. Soldered on some "new" sevo leads, bound the receiver, and the plane is now ready to fly. After regluing the elevator stab, it should come out to be a very nice flying model. It is a high wing, symetrical foam wing covered in some sort of vynil meterial. Coming in at about 4lbs, this .40 fox motor should power it very nicely.


But back to the origonal question. Where did the am servo's not being compatable with spectrum receivers come from? I am guessing the radio gear to be somewhere between 1985-1991.
That's interesting. I just wrote an article on this very subject as the editor of the RRCC (Racine Radio Control Club) September newsletter. A copy of that article is attached.

The conclusion of the tests on my oscilloscope show that the servo's I tested worked OK with a receiver servo signal that ranged from zero volts to a minimum of about 1.7 volts DC at the pulse voltage peak.

Most newer receivers use what's called "CMOS" integrated circuits for driving the servo signals. These CMOS chips have an output voltage that swings from zero volts to what ever the receiver uses for its operation. And that voltage swing is well within the requirements to drive the servos that I tested.

Some integrated circuits are known as "TTL", that have very different output voltage swings, usually from 0.7 Volts as a low signal, and about 2.5 Volt as a high signal. Using this type of TTL circuit would be very risky on a servo. It could work, only marginally. That said, TTL stuff dates back to perhaps the 1970's or so, and were replaced with the CMOS stuff.

Take a look at the attached PDF file.


Attached Files
File Type: pdf Servo Compatibility - WF.pdf (546.0 KB, 86 views)

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Old 09-22-2012, 11:59 AM   #3
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Denny, I'm glad you jumped in. My dad is an electorics guru and was half the reason I tried it. He has an osciliscope, and told me that even newer digital servo's work the same. We have a couple of am servos and radio's from 1976 that we could try out on it.

I'll consult with him and see what he has to add.
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Old 09-22-2012, 06:59 PM   #4
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Originally Posted by hayofstacks View Post
Denny, I'm glad you jumped in. My dad is an electorics guru and was half the reason I tried it. He has an osciliscope, and told me that even newer digital servo's work the same. We have a couple of am servos and radio's from 1976 that we could try out on it.

I'll consult with him and see what he has to add.
Sounds good.
FYI, my testing of the servos in my stuff were connected to a circuit that allowed varying the voltage output from the receivers signal wire with a simple 1K potentiometer. That way, the driving signal can be varied from zero volts to the full output voltage of the receiver.

I used a PicChip to generate the servo signal. If your dad ever played with these PicChips, let me know, I can send the assembly file used for the project. What's needed is a Microchip Pickit3 and a PicChip Pic12F675 computer chip, both from www.digikey.com. The circuit for the servo driver consists of the 12F675, a resistor, a capacitor for the 5 volt source and nothing else except connectors. You can program and reprogram these chips some 10,000 times with the PicKit3 programmer, and run it right from your computer.

Take a look:
http://www.digikey.com/product-detai...130-ND/2171224

The Pic12F675's go for about a buck each. You will also require a Radio Shack perf board, #276-150. Let me know if you are interested, I can send photos and wiring diagrams, what little wiring is involved that is.

The whole thing was monitored with my scope. The only thing not tested was whether the servo had a minimum required voltage. But since some of the servo's I tested only required 0.7 volts pulse voltage, I assumed that the low signal level would always be zero volts.

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Old 09-22-2012, 11:09 PM   #5
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After talking with my dad, he said that he had a toy usb controlled robot, called a "bo bot". It used a basic stamp controller, and had warnings on it saying to only use digital servo's for required operation. He said that knew the digital servo's were exactly the same, but tested them at that time with an old futaba receiver and found no differance in form, or function between digital and regular servo's. He used some old servo's he found in a am receiver box he got from his dad, shortly aftter he died.

At the time I remember it functioning with an old mxpc controller he had when they were fairly new.

My dad is big into pic controllers, has and adrunio, and plays around with his reprap a lot. He is getting ready to build his second one. The thing I find funny, he has no idea how to size electric motors. I think you would get along well with him.
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Old 09-23-2012, 02:08 AM   #6
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Originally Posted by hayofstacks View Post
After talking with my dad, he said that he had a toy usb controlled robot, called a "bo bot". It used a basic stamp controller, and had warnings on it saying to only use digital servo's for required operation. He said that knew the digital servo's were exactly the same, but tested them at that time with an old futaba receiver and found no differance in form, or function between digital and regular servo's. He used some old servo's he found in a am receiver box he got from his dad, shortly aftter he died.

At the time I remember it functioning with an old mxpc controller he had when they were fairly new.

My dad is big into pic controllers, has and adrunio, and plays around with his reprap a lot. He is getting ready to build his second one. The thing I find funny, he has no idea how to size electric motors. I think you would get along well with him.
I've done a lot of stuff with those PicChips, from simple servo drivers, to a PicChip controlled A123 charger that charges a 4S, 5S or 6S2P pack at 10 Amps. The PicChip also operated an LCD display that shows total time, total Amp Hours, current amps, and a few other things. The assembly program for that project was some 30 pages.

Still got two of them, still use them on occasion. They were obsoleted by a Cellpro Powerlab 8 charger.

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Old 09-25-2012, 09:43 AM   #7
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I used old NES501, 101 JR servos from 1980's in my big Gas powered biplane ... FrSky 2.4Ghz Rx etc.

No problem apart from one servo became intermittent ... checking back my old stuff - I'd forgotten about that servo and should have left it in the bin !
Only thing I found was they were slow compared to todays similar sized large servos.

I spoke to ex JR Service Manager (UK) and he reckoned no problem to use ... even had same plugs.

I also have Futaba 1980's servos ... but they have the old 3 pin style plugs ... I'm told is not simple matter to change over.

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Old 09-25-2012, 12:35 PM   #8
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Originally Posted by solentlife View Post
I also have Futaba 1980's servos ... but they have the old 3 pin style plugs ... I'm told is not simple matter to change over.

Nigel
This is exactly what I just did. I just cut the leads off of a couple of cheap broken servo's we had laying around, cut the old 3 pin connector off, did a quick solder job, and its considered to be ready to fly. Red to red, white to white, and black to black. Done deal.

One thing I have noticed.

Holding even a large "newer" style servo next to on from the am days, the am servo's were almost twice as deep, and weigh quite a bit more. They also seem to have less travel. If you look at the control thows for our lighter electric models, they are probably twice the size, and twice the throw of a similar sized nitro model. They also fly much slower, and have quite a bit less weight.

Because of this, the older nitro planes I have been playing with, there take off speed is probably what some of my electrics are, wot in a dive. The control surfaces are much smaller, have less throw, and the servo horns are thicker and stronger, but smaller. With the higher speed, I just simply don't think that you need the throw.

One thing I have noticed that seems to be a trend, the rudders on planes have gottten bigger and have more throw. Some of the planes I have dug out, the rudder is almost in-effective at full throw. My dad said they never really used rudders much back in the day. Don't know if that is just his planes, or the way it was back then.
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Old 09-25-2012, 06:17 PM   #9
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Just curious about the last statement "My dad said they never really used rudders much back in the day. Don't know if that is just his planes, or the way it was back then."..........

I've been a round a few old school pilots and their re-vamped glow plug set-ups......nearly all of them are three channel, rudder controlled.

A couple of interesting artilcles can be found on the these links.....seems three channel was the preferred choice as far back as 1937...

http://www.rc-airplane-world.com/vin...airplanes.html

http://www.vintagercsociety.org/vrcs_app/eligible.php

http://www.indoorflyingmodel.com/AntiquePlanePlans.html
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Old 09-26-2012, 02:18 AM   #10
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I can't go back as far as some - but Rudder was on nearly all my models in 70 .. 80 ... 90's. But I was only the owner of 3 - 3 channel rudder machine. All but those used ailerons and were 4 channel at least. The 3 were 2 gliders and 3rd a basic trainer.
Ineffective rudders ? No I would disagree - all mine were similar to what we have today ... being glow powered meant no difference as I see it. Yes the models were heavier ... but that's all.

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Old 09-26-2012, 09:35 AM   #11
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My dad and grandpa had a couple of "pattern" planes. All of them have very small rudders and were setup for very little throw.

Most of my grandp's planes were free flight converted to 2 channels, and some of my dads earlier planes were single and 3 channel. Some with rudder, some without.

My dad is really proud of all his .049 with exhaust throttles. Said back in the day, they had no throttles on most motors andjust ran them till gas ran out.

My granpa built basically freeflight models but wanted to be able to trim them in on the fly. He lost feeling in his hands from cancer treatments, and hated to fly infront of other people.
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