GWS r-4p mod for palm size heli - RC Groups
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Dec 04, 2003, 10:40 AM
Registered User

GWS r-4p mod for palm size heli


I want to mod a cut down gws receiver for a magnetic swash and two esc onboard decoder.

I will do this by re-using the reciever part of the circuit and replacing the decoder with a PIC micro and a couple of fets. Hopefully I can lighten the receiver in the process (I wrote the code for this about 7 years ago but back then the technology wasn't really readily available to implement it).

Has anyone scoped the circuit and determined useful info such as where the multiplexed signal is accesible from?

Also, has anyone substituted an air cored coil for the aerial. I mean a copper coil round a short drinking straw type of thing?

Finally what sort of power can I expect from magnetic actuators driven directly from a pic? If I remember right they can sink about 20mA per pin.

Looking to build a 5" rotor heli much like the french one. Going to cnc cut all the hardware since I cannot work that small with my hands ;-)


Last edited by devmonkey; Dec 04, 2003 at 10:43 AM.
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Dec 04, 2003, 03:40 PM
Registered User
Actually looks like Andy B has already done all this for a 3 channel setup. Can anyone help me on making an aircored aerial for 3MHz?
Dec 05, 2003, 03:42 AM
Registered User
JVBAV8's Avatar
they make one that plugs into the rffs 100
think it was called
Dec 05, 2003, 05:28 AM
Registered User
billystiltner's Avatar
I seen aan aircoil on Gordon Johnson's Quick Junior site. I didnt know what it was till I read this post.

Check out Todd Woodhous's plane. Maybe Gordon can get you in contact with him.

I have found the 200 ohm coils are quite powerful driven directly from a PIC.

You could make some Fet Hbridges if you need more power. Look at Koichi Tanaka's new IR RX in the DIYIR thread it is a few posts back. I will try to get my website caught up with some of Koichi's latest stuff translated in the meantime you can visit his site and translate with babelfish. I think the way he done the Hbridges would probably be the best way to go if you need more torque from the actuators.

Koichi's site

Link in thread with N/P mosfets part numbers

Dec 05, 2003, 08:46 AM
Sticky Shepherd
Graham Stabler's Avatar
The 20mA max from a pic is correct however remember that the push pull outputs drop volts so if you were running at say 5v then although 5/200 gives 20mA the acutator would probably only see 3v. What this means it you can drive say a 150ohm actuator from a PIC output possibly less. To find out for sure you would need to run the PIC at the max voltage it will see and add a variable resister to the output. CAREFULLY lower the resistance while checking the current. When it is 20mA then remove power and measure the resisters resistance. Add a bit for good luck and this is the min resistance the set up can handle.

However 4 dual mosfets will not weigh much at all and may be required for positive control.

Dec 05, 2003, 10:01 AM
Gambler-AG DLG Designer
Allan Wright's Avatar
I believe Gordon's antenna on his Quick Jr. is the Azarr antenna for the RFFS. They're very good and light. I use them too. A bargain at $10 each.
Dec 05, 2003, 01:47 PM
Just an average RC'er
Jim McPherson's Avatar
The Lightenna72SF is perfect for this application at only .2-.3 grams it's very light and will have far more range than you can use. It's only $6.00 at .

Dec 05, 2003, 02:07 PM
"Simplify, then add lightness"
Since Joe is in London, I doubt a 72mhz antenna would work for him. A quick internet search turned up these for 35mhz.
I am flying several models with 72mhz antennas made from 39" of litz wire wound on soda straws, and they seem to work fine. I have built them from 2" to 8" long. How long is a 35mhz wire antenna? I would just take that much fine wire, and wind it on a straw and try it out.

Dec 05, 2003, 03:25 PM
Just an average RC'er
Jim McPherson's Avatar
Good call Jeff, I didn't catch that. Most (if not all) 35Mhz antennas are also 39-41'' long.


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