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Jan 22, 2007, 03:22 AM
Sticky Shepherd
Graham Stabler's Avatar
John, the magnet is attached to a piece of balsa not rubber. It is a seperate piece with the grain runs the other way for strength.

Ralph uses tissue for his hinges IIRC in strips as drawn above.

Centering is not absoultely essential as you get aerodynamic centering from airflow.

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Jan 22, 2007, 08:49 AM
Registered User
Thanks for the info. Will give it a try.
Also since you didn't mention anything new in coils it looks like BalsaLock applied with the fingers and rubber grommets for a form will be the simplest way to go.
Jan 22, 2007, 01:49 PM
Registered User
Ralph B's Avatar

Graham is correct, the magnets are attached to a balsa piece with the grain at 90 degrees to the rudder. The hinges are tissue applied in the traditional over and under pattern or control line style. There is one pair of hinge strips at the top of the rudder and one pair at the bottom. I use a tan tissue that is very close to the balsa in color so the finished part is almost invisable and very free. Aero centering is good enough but I normally add a small centering magnet on the outside of the coil.
The coil winding technique I use is one I developed after destroying several good coils while trying to get them off the winding mandrel. I have access to a Shearline lathe so I machined some winding spools that have made coil winding painless. I start with a short length of poly or teflon tube that epoxy won't stick to and has an O.D. equal to the finished coil I. D. that I want. I machine a metal core to be inserted into the I. D. of the poly tube. The core insert is drilled to allow a screw to pass through it. After sliping the core into the poly tube the tube is cut so it is slightly longer than the metal insert inside it. About .010" in extra length is about right. The rest of the spool consists of the sides, a mandrell, and the screw to pull it all together. I use 1/16" plywood disks for the sides of the spool and to keep the epoxy from sticking to the wood I made some teflon washers the same size as the side disks with a center hole that will allow the secrw to pass through them and thread into the end of the mandrell. The first side with it's teflon face is placed on on the screw, then the metal core with it's poly tube, the second side and teflon washer and the stack which now forms a small spool is screwed to the end of the mandrell. As the screw is tightened the sides seat against the metal core and cause the poly tube to expand very slightly. The coil is wound and allowed to cure. When the screw holding the spool together is losened, the Poly tube relaxes back to it's original size and slides right out of the coil. The spool can be reused an unlimited number of times. I have built three spools for various size coils using a 2-56 screw down to an 00-90 screw for the smallest coils. The lenght of the core determines the width of the coil and the coil I.D. is determined by the poly or teflon tube O.D. From experience I have learned what coil O.D. for the various wires I use will get the desired resistance. I make a balsa feeler guage with a slot the same width as the desired coil O.D. I wind until the wire builds up to the size of the slot in my balsa feeler guage and it's done. It's simple to adjust the coil size by just making up a core and feeler guage for each coil desired.

Jan 22, 2007, 06:17 PM
Registered User

First coil

Thanks for the detailed description of your method.
It must be great to have a small day I hope.
After reading about your bobbin I found some round white plastic disk for small servos. Put two of them together with 2-56 bolt and nut. Then waxed the surfaces then wound the coil with the wire passing through two Q-Tips saturated with fingernail polish.
After a couple of hours curing the coil came off OK. Then decided to make a reusable test model with 1/64" ply. To my amazement it worked! Weight is .8g. Really was not too bad, but I can't believe how much I shake. Thank you Ralph, and everyone who posted coil info. I never could have done this alone.
Jan 23, 2007, 12:46 AM
Registered User

thank you !

Thanks for that pic John, and ralph's explanation ,,that looks like the perfect way to have the magnet and coil lined up and position fixed. I was worried about that part.

If you don't have a lathe, do you have a vertical drill press ? then you have a lathe.You just put a candle in it, run a sharpened object(correct width) into it sideways to the desired depth. take your homemade wax bobbin out and
insert a little threaded rod into screw gun,tighten,
run this into your homemade wax bobbin, alittle wobble wont hurt.
wind coil while apllying 30 minute epoxy, some use CA,
melt in boiling water, the wax dissapears, perfect coil !
thx to epilots post for was bobbin idea, he credits someone else for the wax bobbin idea, I think.
Last edited by skychaser53; Jan 23, 2007 at 05:21 AM. Reason: add thx
Jan 23, 2007, 05:15 AM
conversion's Avatar
John -

very nice indeed! how many ohms on your first coil ? and, have you any plans for "try-run" ? if its not intended for a specific model, try buyin a cheap AeroAce at your wallmart and do the actuator-mod on it for rudder

Jan 23, 2007, 08:48 AM
Registered User
Thanks for the comments. The lathe idea sounds definitely worth a try. Wonder if one of those small, cheap Harbor Freight drill presses could be mounted horizontal with a built point installed in the base would sub for most soft metal turning?

The coil came out at 46 ohms. Good question about what plane to try it in. Thought I'd laminate some very thin depron sandwiching the ply for rudder, then they could be easily removed when the plane romance dies. I'm so fickled I only stay with a plane for a few months. Must look up the Aero Ace. Heard the name but don't know what it looks like. Thanks much for the tip.
Jan 23, 2007, 10:14 AM
Registered User
Just a quick question: On the wake of the "lost wax" method, has anyone tried a "lost soap" method instead? the soap might be slightly harder to lathe to shape, but there should be less chances of the solvent attacking the wire's insulation.
Jan 23, 2007, 10:40 AM
hmmm, I've made tens of coils using the wax method and there was not a coil with insulation problems. The temperature of boiling water is just not enough to melt the lacquer (wire's insulation). On some wires the lacquer is so temperature resistant that even temperature of soldering iron could be not enough to melt it.
If you don't have the candles of the proper size (for up to 6 mm ID coils), you could make your own by using the tubes from semitransparent BIC brand pens. After you have made a candle put it in high speed electric drill and use a small file warmed up a little bit to make the bobbin of needed diameter, you may find it easier to make wax bobbins that way. Good luck !
Jan 23, 2007, 11:12 AM
Registered User
In a pinch, I've made my own wax cylinders from excess candle wax (globs, runs, and ends of used candles). I cut the top off a pop can and put the pieces of wax into the can. Then put a few cm of water into an old (in case you get wax all over it) frying pan and put the can into the pan on low heat. The water transfers heat to the wax and melts it (you'll need at least 1.5"). Then dip a small nail into the wax (holding it with a pair of pliers), let the wax harden (5-10 sec?), then repeat. It can take a while, but it works, and the nail in the center is perfect for gripping in a drill to "lathe" the groove with a small knife or chisel.

Don't rush the dipping. If the wax is still too warm, it'll dissolve back into the molten wax when you dip again.
You can speed up the wax hardening process by dipping it into a glass of cold water after every dip in the wax for a second. Just watch that you shake off any drops of water before dipping it back into the molten wax, as that can cause voids.
Use a larger nail, so you don't have to build up as many layers as wax (the nail has to be a bit smaller than the coil ID of course.
When you boil out the wax from the coil, make sure you get it all off the coil (absorb the water/wax with paper towel). Glue doesn't stick well to wax. :P
While you're making a coil (or more), make a spare...

Jan 23, 2007, 12:55 PM
Registered User
That is a very enlightening post Darkith!
Must give that a try.

BTW, do you guys use some kind of level-wind mechnism? I notice my first one would build up uneven and I had to back off and go slower. Don't want the coil to get too big.

Delighted to see this thread go two pages. Thanks guys.
Jan 23, 2007, 01:17 PM
Registered User
Originally Posted by John255
Thanks for the comments. The lathe idea sounds definitely worth a try. Wonder if one of those small, cheap Harbor Freight drill presses could be mounted horizontal with a built point installed in the base would sub for most soft metal turning?

I don't know about turning soft metal. I took a 1/4 in screwdriver ground it to 3/16(desired coil width) put a 45 degree edge on it clamped it in a small lathe vise, bolted on end of the vise down, and just slowly pulled the screwdriver into the candle, giving me the desired wax bobbin.
If you cant get 1/2 in or smaller candles just melt an and pour it into a 1/2 tube, brass ,copper water pipe. You could probably heat the copper with blow dryer and push the candle out.
Or use thick paper and peel it off..
As far as soap,My water was not roiling and the wax just goes away !! you are not going to hurt the coil.
Feb 16, 2007, 02:52 PM
Registered User

series or parallel

Hey, I hope this is not too off topic but this seems to be an actuator thread that is fairly active right now.

I am mounting two BIRD type actuators in the twin rudders on my A-10 project. Can anyone advise me as to wether they should be wired in series or parallel?

Feb 16, 2007, 03:43 PM
Only nerd in the village
Depends on the resistance of the coils and your receiver. More detail please.

Feb 16, 2007, 05:20 PM
Registered User

more details....

They are the dinky ones by plantraco. Should easily stay within tolerance for the plantraco Rx right? I need to get maximum torque.

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