Watch gear gearboxes - Page 4 - RC Groups
 Nov 24, 2004, 08:13 AM Registered User Graham That thread is some very good reading. I read it again and picked up some things I had forgot. I seen I was having trouble with the wire insulation glue then as well. I remember I had good results with Duco and CA later with the wire insulation. I must have some grease or sweat on the insulation now. However I did not find the post that Robert mentioned using the calipers to mark the ply for center distance. I think someone else actually posted the technique and Robert explained to me how to do it. JMP I will try to explain in babelfish freindly terms. (I know you know english very well though) Example: center to center distance is 5.15mm 1. On a sheet of paper draw a line 2. Mark 51.5mm points on line. 3. Set divider close to 5.15mm(use magnifier and caliper) 4. Step out the divider 10 paces on the line to check distance. 5. If too wide - close divider 6. If too narrow - open divider 7. Repeat steps 4 to 6 For more accuracy mark out 515 mm and step the divider 100 times. Divider may open or close with 100 steps if you are not careful. Billy Billy Last edited by billystiltner; Nov 25, 2004 at 06:26 AM.
 Nov 25, 2004, 03:33 AM www.jmquetin.com Thanks Billy for your efforts ! I almost got it but I am still a little bit confused as my English (dictionnary) does not make a difference between a divider and a caliper ! I think the method you mention is based on the same principle as a calliper square (pied à coulisse in French). So I think I can get the same result just using a calliper square, a compasses and a magnifier, right ? Jean-Michel. Last edited by jmquetin; Nov 25, 2004 at 03:38 AM.
Nov 25, 2004, 04:41 AM
Registered User
Jean-Michel

Divider: device that divides a line
Looks like a compass with 2 needle like points.

Caliper: device to measure distance
Has a scale on it.

I used to call a divider a caliper for some reason.

I looked up pied à coulisse , the picture showed what appeared to be what I am refering to as a caliper.

Maybe this diagram will help.
Billy

### Images

Last edited by billystiltner; Nov 25, 2004 at 06:24 AM.
Nov 25, 2004, 05:26 AM
www.jmquetin.com
Quote:
 Originally Posted by billystiltner ...Example: center to center distance is 5.15mm 1. On a sheet of paper draw a line 2. Mark 51.5mm points on line. 3. Set divider close to 51.5mm(use magnifier and caliper) 4. Step out the divider 10 paces on the line to check distance. 5. If too wide - close divider 6. If too narrow - open divider 7. Repeat steps 4 to 6
Billy, I think I got it if I read your step 3 as "Set divider close to 5.15mm" (and not 51.5 mm). Right ?

Thanks again.

J.M.
 Nov 25, 2004, 06:25 AM Registered User JM Yes Thanks for pointing that out. I uploaded a diagram that may be more clear. Billy
 Nov 25, 2004, 06:33 AM www.jmquetin.com Billy, it cannot be clearer . Thanks. J.M.
Nov 25, 2004, 07:12 PM
Registered User
Here's a new gearbox.
Without prop or wires it weigherd in at .64g.
The motor is the long 4mm Electronics Goldmine cored pager about 14 ohms.
I tested with a 3.5" x 2" prop at around 3.7V 190ma. The gears do not run as smooth as the previous drive. May have reamed the spur coencentric trying to match it up to a tiny plug for a spacer. I ended up reaming too far and had to use wire insulation again. I modeled this gearbox from the one on David Dewitt's 1.48g plane. I did add an extra ply disk to the back of the upright for a bit more sturdiness. It seems that teflon glues to ply with duco I would have never imagined. Maybe it's just a tight fit. Dave D what did you use as a bushing and bushing tube on your gearbox if there is a bushing tube? Again I'm not sure what this thing will fly have not done any thrust measurements. 190ma is quite a bit of curent draw for this motor/gear/prop I think. I did connect it up to a 40maH lipoly which was charged to 4V and curent draw was only 140ma with reduced rpm and thrust of course. Not sure if it would pull a little 5 or 6g plane around with the 40maH cell.

Billy

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 Nov 25, 2004, 10:00 PM Registered User I was sitting here spinning the prop on the new gearbox and started spinning smooth. I think I may have had some glue get in the gears from previous glueing and squirting with acetone. The prop will spin freely now but not as freely as the dual upright gearbox. There are 2 other non apparent differences that may cause the single upright box not to spin as freely as the dual upright box - 1) The bushing is a tighter fit 2) The bushing was sanded instead of cut for true alignment with the retainer. (there is also a teflon washer on the single upright box). Reasons: 1) I thought the wobbling of the first gearbox may have been caused by: (a) poor alignment of retainer and bushing. (b) loose fit of the bushing and axle 2) No matter what kind of jig I have used, have I been able to cut teflon tubing perfectly straight. I can get them close sometimes by eye. Anyways the sanded teflon tube may cause a bit more friction than a cut tube even if the sanded tube is straight as can be. I did polish with 600 grit testors sand paper. Technique was same as that of polishing fiber optic cable - figure 8s. I ran the new gearbox in front of my monitor and did not notice any wobble. Allthough When I first ran the new gearbox the prop was not secure and it made the weirdest wobbling sound which repeated at about 0.5Hz then sped up to maybe 4Hz then slowed back down to 0.5 Hz for a bit then stopped. I could see the prop tilting in proportion to the wobbling sound. I imagine the small helis do something similar. Dave W You asked earlier on in the thread about the weight of the watch gears. Well my new gearbox with the long 4mm motor weighs the same as my gearbox with Didel .2mod thinned gears and 4mm short motor. It is not a good comparison though as different materials were used. Plus the wires are still on the short pager motor. Jean-Michel The divider/caliper/magnifier thing is great for marking out gear centers. I used to draw plans and print them out then paste the plans to ply. With 600DPI printer lines can be 0.00167" but the program I use to draw the gearbox plans makes much thicker lines when printing small scale drawings at 1:1( I have overcome this for drawing small masks by scaling the drawing up and exporting the image then increasing DPI to get back to correct scale ). I would have never thought to use dividers and step out 10 paces to check. It is a neat idea wonder where it comes from? Billy Last edited by billystiltner; Nov 25, 2004 at 10:05 PM.
Nov 25, 2004, 11:30 PM
Registered User
I think my bushing is too long. I reckon a shorter one would produce less friction and the extra bushing sticking out the back of the ply spacer is not necesarry to hold the axle steady correct?

Well I came up with a new gearbox idea.
It is a conglomeration of other ideas I have seen.
Spured from what Ralph and Jochen said about drag and friction.
As well as Dave W''s idea for adjustable mesh.
Now that I think about Dave's idea it would not be that fiddly if the ply spacers were a tight fit on the bushings or bushing tube.

Heres the idea.
Make a ply upright that fits on the front of the motor.
On ply upright drill hole a tad larger dia than shaft for shaft to go through.
Cut 2 ply discs with hole larger dia than shaft.
Cut out 2 brass sheet squares or discs if you can cut circles that small.
Brass squares need to be larger than hole in ply discs.
Start hole in brass with nedle file.
Ream out to perfect fit for shaft.
Glue brass bushes to ply disks.
Put upright on motor.
Put shaft(with gear attached) through first bushing/ply disc then through upright then slide remaining bushing/ ply disc over end of shaft. Adjust for good mesh with condensor paper or by eye then glue.

Attached is a drawing for clarity.

Billy