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        Watch gear gearboxes

#1 billystiltner Nov 18, 2004 12:05 PM

Watch gear gearboxes
I have started on a gearbox for some watch gears.
The watch gears I have look like the watch gear drive on Ralph Bradley's firefly.
The spur looks like the spur on Bob Bailey's Room flyer. The pinion has 10teeth and fits over a 4mm pager shaft with some reaming. The spur gear has 60 teeth. The best I can measure with a vernier caliper I get 7.7mm for the spur and 1.5mm for the pinion. Has anyone else measured these little watch gears with a dial caliper? I would like to get the measurements right before I design a gearbox.


#2 LSB Nov 18, 2004 12:34 PM

1 Attachment(s)
Clockmakers use a simple tool for marking the centers of the gears, called "depthing tool"
attached (I hope ) are two relatively easy to make versions i use.

#3 GIFLYRC Nov 18, 2004 12:47 PM

LSBThanks for passing along the info on a center finding/ marking tool

I have beat my brains out trying to measure and lay out the holes when building GB's

Sure will make my life easier, thanks;

Roger aka GIFLYRC

#4 billystiltner Nov 18, 2004 02:10 PM

That ought to help get a gearbox made.


#5 Graham Stabler Nov 18, 2004 02:38 PM

3 Attachment(s)
Billy, with these tiny gears it is nice to have some adjustability. Peter Frostick recommended this gear box style to me and I tried it out last night. The diagram is by Peter and shows a box he made for an M20 motor. The mesh can be adjusted with a tiny wedge or if you keep the pinion loose till the last minute by bending the wire (needs to be well attached) in the relevant direction until the mesh is good.

Mine is for a 4mm pager and is slightly different. Firstly my spur gear has a long tube in the middle that could be used directly as a bush, this however meant I had to use slightly thicker wire. Also because the 4mm pagers are delicate I opted to mount the motor in a small tube made from carbon braid. The wire was bent roughly to size, glued and then wrapped with a few tows for extra security. Teflon tube is used for bearings and pvc wire insulation for retainers. The new prop was just glued to the brass tube. There is a small plastic spacer behind it made by heating an pulling some plastic tube.

The box weighs 0.1g so I think it is a little heavy however I think it will pay for itself in efficiency and I want to see if this is so.


#6 billystiltner Nov 18, 2004 03:17 PM


Thanks. I might try that on my next one. Your pinion looks to be the same one I'm using but you've trimmed it down. I've allready fitted a spur to a 0.25" shaft.
Thought about using 1/64" shaft but gosh thats small. I guess I'll try one like Dave W posted to begin with. I'm wanting to be able to change out motors initially and use the gearbox with the 20maH as well as 40maH on small and large(pistachio)planes. Wonder if 6:1 will have to have too big of prop for a 4" plane at the weight they(4"span planes) are currently made? Seems like Matt said there was not much diference in flying time with the different motors and ratios but is flying for longer now. With the higher ratio I will most definately use your(Peter's technique you posted) technique as theres no room for the bush tube with that small of ratio. Nice gearbox. I think it will pay for itself with the added efficiency plus you wont notice if you change your mains to Litz wire. On the Litz wire thing I found I could fold the end over a pin, hold both ends, and twist(same direction as Litz was made) so I have an eylet then apply flux with toothpick. Apply solder to iron tip, push iron tip into eylet, hold till smoke disapears, pull iron out and have an eylet filled with solder. The eylet then solders to anything with a touch of the iron and the ends do not fray.


#7 Graham Stabler Nov 18, 2004 03:54 PM

Actually I think Matt also used this style of gearbox in his SE5, I could be wrong. The secret may be thin prop of low weight, certainly if you consider your prop to be a scaled down version of larger props the weight and thickness should also scale. There is not really much info (scientific or modeller based) on such small models but most I have seen do LAR (from the TLAR principle). Apart from anything else I think Lipoly's let us get away with a lot.


#8 Dave Wulff Nov 18, 2004 04:05 PM

1 Attachment(s)
This is how I have done it:


Oops, a bit large...sorry.

#9 brucej Nov 18, 2004 10:11 PM

thats neat dave

#10 peter frostick Nov 19, 2004 11:18 AM

Nice gearbox. Hard to believe it's that small utill you start scaling the photo!!

Good luck with flight tests.


#11 Graham Stabler Nov 20, 2004 05:03 AM

Prop is too small, cynoed bearing mounting new prop, will try again :)

#12 Joe P Nov 20, 2004 09:16 AM

Where do you find watch gears other than junking old watches?

thanks Joe

#13 Dave Wulff Nov 20, 2004 10:13 AM

Are watch gears really that much lighter than plastic (nylon, delron, etc.)? I know Ralph has been fond of them for years and I wonder what I am missing.


#14 Raj Quest Nov 20, 2004 08:01 PM


Junk old watches might be the best and the cheapest source, but you could also try cassette player/recorder (including walkman) spares suppliers and repairers........
But these will be mostly nylon gears.


#15 RC_AV8R_181 Nov 20, 2004 09:21 PM

Look here-
A load of watch gears and pinions for $6. Also, if you look under "American watch parts/ movt parts" you can get 100 pinions for $7 (I think these are larger mod than the gears though).

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