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Old Oct 21, 2010, 09:41 AM
Storm Runner guy
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USA, OK, Muskogee
Joined Nov 2008
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Easy 4mm servo gearbox

This is a micro gearbox, made last night, from a servo on a Parkzone Cessna receiver.

A common report is of people experiencing stripped servo's, bind broken receivers or smoked bricks. Many same folks also have an interest in building small aircraft. As far as I know, people often throw the receivers out...this idea is something I haven't seen mentioned and may be of use.
Gearboxes are generally quite the expense within the hobby, so here's a potential answer and reuse of components from such receivers...two potentially gearboxed motors are on every brick !

I took the screws from a linear servo and snipped the motor wires.
Removed the end cog from the servo's shaft and removed the track itself.
A sewing pin was used as the replacement shaft (see Notes).
The pin was secured from forward movement at the rear.
The cog was put back on the new shaft and secured with epoxy.
That's it for a functioning gearbox
Next step, to cut away the plastics at the top middle and the screw tabs on the bottom under the motor, to lighten.

The gear ratio is 1:4, the motor cog having 8 teeth and the shaft cog having 32 teeth. Sewing pins have very good strength and should see little in the way of bends, with the forces at these sizes.
This first one has the wrong propeller on at the moment, it being realised that with reduction, the prop won't spin to full efficiency and is most likely too heavy in any case. But it serves as an example. Idea is to make some different ones of different types, in keeping with 4mm gearboxed aircraft.


Notes: The little piece of plastic that normally goes behind the shaft, to stop the cog moving off the end of the motor can be reused to secure as it always did, but mine was found to be loose on the pin. So, I used a piece of clear covering that comes from those twisty pieces of metal that secure store bought clear fronted boxed items.

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Old Oct 21, 2010, 11:20 AM
TheyreComingToTakeMeAway!
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interesting indeed. however, i think the motors that come on the board are higher Ohm than what you would use for flight. and for more power you could switch to the long can 4mm motor
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Old Oct 21, 2010, 11:33 AM
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Elmhurst, NY (Queens in NYC)
Joined Apr 2004
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I can hardly wait to break one of my rx's. . . .

I really love small stuff. If this idea takes off (sorry about the pun) maybe someone will make a smaller rx to fly these planes with. Then we can make still smaller motors etc.

A reverse of Johnathan Swift's pre fractal poem:
...
"So nat'ralists observe, a flea
Hath smaller fleas that on him prey,
And these have smaller fleas that bite 'em,
And so proceed ad infinitum."
...

Time to go out and crash something so I can help start the revolution.

Pete (who will remember the concept)
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Old Oct 21, 2010, 06:17 PM
Storm Runner guy
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Hehe thanks Pete...i'm rather shooting myself in the foot with my public domain mind, was going to post an ad for dead Rx's !

I agree Derk about the probable motor strength as stock. The two holders on such servos readily allow changing out one for another though
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Old Oct 21, 2010, 08:06 PM
Lawn dart pilot/builder
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N.L. Canada
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now .. slider.. you will have 4 pico z tail rotor motors comming ..
and they are the same can dia. as the motors on my AR6400 board.

but ! they are as long as the servo rails . well 2x what that wee motor is .. but
in length .. soo you wee GB coudl become very usefull to your RTP fleet . LOL
( ps i will be in town friday , and will drop by post office with package , hope it;s cheap . LOL )
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Old Oct 21, 2010, 08:07 PM
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Slider,
you're stoopid creative! big compliment And I love the way you think.

Keep up the good work
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Old Oct 21, 2010, 09:22 PM
Way to many airplanes!
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Is the propeller kind of home made from a larger one, or is it something you picked up from the shelf?

Definitively a good idea....
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Old Oct 21, 2010, 09:47 PM
Storm Runner guy
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Thanks for the update Prime_8 and the words elvill and RealGambler

The prop on it in the pic is a standard 'Air-Hogs' type. They need direct drive really and are made for 6mm (heavy in comparison) so aren't a good choice. Anything of the type that normally go on 4mm gearbox's would be a lot better idea...the Ptero Scout one on Derk's biplane would probably be about right (that's presuming the Ptero uses a 4mm ?).

I was testing the setup just now and unfortunately the pic off the webcam is naff, but shows the cut downs for lightening the unit. I took the redundant side off and the little screw holes.
The finely dextrous amongst us could probably reuse those tiny screw holes though, to fit to a balsa firewall, which would reduce any glue useage.
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Last edited by Slider2732; Oct 21, 2010 at 09:57 PM.
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Old Oct 22, 2010, 04:40 PM
Storm Runner guy
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I've always been one for authentic engine sounds and a mistake today produced something of one.
It was quickly realised, that the piece on the back end of the gearbox shaft isn't needed, a flat head pin can perform the forward limit function of the propeller thrust.
So, taking a flat head pin, I redid the gearbox..what I didn't realise was that this pin is a slightly lesser diameter than the other one. It has given a loose fit within the housing. Nothing of a concern really, the gears still mesh.
A cut down and reshaped ITC propeller was fitted (similar to Air-Hogs type above).
When fitted to a piece of foam (with hotglue) the sound produced at low revs, from the loose fit, has been something similar to an old engine at tick over
Might be worth installing this one in a desk based small model, running off USB.

Power in the vid, is from my PC USB rig. Diode protected and with actuator wire wiring, the voltage is about the same as a fresh 1S lipo.
The top end revs have been surprising, as you can hear and I daren't run the thing for very long like that, no matter if the motor isn't really strong enough for flight models. Might need speakers turning up a bit:

4mm servo prop run (1 min 7 sec)
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Old Oct 22, 2010, 06:16 PM
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Argentina, Corrientes
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very nice!!!! I will try this gear in my aichi val 4:1 instead of 8:1 that is running now... good idea...
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Old Oct 26, 2010, 03:52 AM
TheyreComingToTakeMeAway!
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ok so i made one of these gear drives from a dead rx servo. a little different without the pin-shaft, but it works. so i threw together a micro thrust stand and installed a 4*11mm tail motor and an aeroace prop. on 1s around 3.6 - 3,7 volts it was putting out 4.0-3.8 grams thrust
so its not bad but i think an optimized prop would be a bit better so maybe 4.5 grams isn't impossible
but with this higher rpm ratio, the planes will need to be higher flying speed to make it work at its best.
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Old Oct 26, 2010, 01:36 PM
Lawn dart pilot/builder
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that woudl be why i want to do printable props . LOL
laminated paper coudl let us tweek our props . lol
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Old Oct 26, 2010, 02:02 PM
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San Diego, CA
Joined Oct 2005
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slider I love the sound of that video! now the 4mm doesn't sound like a buzzy little bee!

with that 1:4 gear ratio derk you may need a slightly larger prop than a direct drive aero ace. A cut down 3222 prop would probably give you about 4.5, maybe 5 grams. The carbon butterfly with a full 3222 prop puts out about 6 grams thrust with a 6:1 gearbox.
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Old Oct 26, 2010, 02:12 PM
Storm Runner guy
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Yeah, the sound on the video isn't really doing justice to the actual effect, it sounds really very nice indeed...for what it's coming from. It's still sat like that and I power it up goofily every now and then.
The thrust out of that version is quite wild, but that's why i'm not running it at such speeds now. It needs to be redone with such a prop as you describe Baratacus.

The aero-ace and ITC props are just too thick and strongly made for this system I reckon. The Carbon Butterfly type are where it's all at, light, thin, able to be spun quickly without deforming. 4 grams is good from the off the shelf props, but I do hope we find the completely ideal props for different servo gearboxes..AR6400, etc included.
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Old Oct 26, 2010, 09:06 PM
TheyreComingToTakeMeAway!
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ok i tried another larger lighter prop and got over 5 grams of thrust from it this time
its a prop from the Ptero Scout plane, similar to the old airhogs IR living room fliers.
it was around 5.8 grams to 5.5 grams on 3.9 volts
i think i will drop it into my next micro and see how it does in the air
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Last edited by derk; Oct 26, 2010 at 10:18 PM. Reason: re-tested
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