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Old Feb 03, 2004, 09:59 PM
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DIY bit gear gearboxes

Here's a homemade gearbox.

Specs
Current draw: 280ma. at 3.5V static measurement
Prop: 2.4x1.55
Gears: 6t pinion and 23t spur .4mod bitclone
Ratio:3.83:1.
Motor: 3.6 ohm bitclone motor with ytellow endcap I thought it was a 4 ohm but measured 4.2 ohm and .6ohm lead resistance.

Construction
1/8" balsa
thrust bearing - 3/32" OD al tube with 1/16" OD brass bushings
shaft: .031 music wire
washers from red spray tubes

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Old Feb 03, 2004, 10:00 PM
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Here is another view.

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Old Feb 03, 2004, 10:08 PM
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And one more view.
I used a 6t pinion to hold everything on.
On the gear and prop I used wire insulation to make a tight press on fit. This idea is credited to David Dewitt at least that is where I first seen it used.

These gearboxes should be good for 10g and under planes using the 90maH lipoly and bitclone motors. I guess if you used the didel 4.5ohm or greater motors then you might could use the 40maH cell. The Aeronutz and others have been flying 10g planes for quite sometime. It is new to me to be able to fly planes this small and lightweight but it is great fun.

I think this gearbox weighed around 1.7g with maple prop and plugNwires. That is from memory and it sems about right. I know it was compareable to Carl Martin's ply gearboxes. I used spacings that Carl suggested. The method I used to make the gearboxes was no where near accurate enough to take advantage of his spacing suggestions but the plans are with his spacings.

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Old Feb 03, 2004, 10:17 PM
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Here is another gearbox made with the shaft and bearings from a 6mm motor.
It is for 3:1 gearing with the 18t spur gear.
This gearbox as shown weighs about 0.23g.
The brass thing that makes up the space between gear and shaft also came from a 6mm motor. It was near the commutator.
The tube that the bearings are set in was removed from the magnet. It was the tube that the bearings were originially set in. This tube was cut in half to save weight. I think the tube is stainless steel. The walls are thin so I'm not sure if an aluminum tube would save weight here or not.


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Old Feb 03, 2004, 10:20 PM
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Here is another view.
I tried this gearbox with the above prop and it kept flying off till I had a really really tight press fit. It seemed to produce lots more thrust than the other gearbox but the current draw was too high on most bitclone low ohm motors for 90maH cell. Most of the motors would get hot but the ones that did not may have been on the borderline of being useable with the 90maH cell. I think it will take a smaller prop for this gearbox. Just have not figured out the optimum diameter and pitch yet. The 4.5 ohm didel motor or 8ohm might be a good match for this prop and gear ratio with the 90maH cell. I have yet to get my thrust test stand going yet. Maybe when I do get the new stand and balance I will post some thrust measurements.

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Old Feb 03, 2004, 10:22 PM
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Another view.
You can see iI used pinion shaved down to hold the shaft on. Washers again are from spray tubes.

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Old Feb 03, 2004, 10:32 PM
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One more view.
I start out with a sheet of 1/8" stiff balsa
about 7lb per cubic foot density. I guess les dense balsa could be used or even 2 peices of ply like Carl Martins gearboxes.On the 3.83:1 gearbox I have thought of adding a spacer between the aluminum tube and motor, toward the rear of the motor. The spacer would keep the thing more tru maybe but I'm not sure it is needed. I paste a printout that has the spacing marked with crosses and a 6mm circle. My printer is not that good of resolution so the spacing is not anywhere as accurate as a laser cutter would be. Regardless the meshing can be adjusted to run smoothly.

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Old Feb 03, 2004, 11:35 PM
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Here is a photo of the printout I paste on the balsa. Also in the photo is the tool I use to drill the 6mm hole. It is the key to making these gearboxes. I had tried drilling with drill bits but this tool works better. The tool is a 6mm motor which has been sharpened and magnet removed. Then a nozzle from a butane lighter is inserted in the shaft hole then soldered. A brass tube could be used in place of the nozzle it just happened to fit. The nozzle fits in my hand twist drill. I then score the edges of the can with either a needle file, corrundum , quartz, or some material that is harder than the metal can. The scoring allows the can to remove wood as it is pressed/turned in. You may have to file down your score marks a bit-if after you drill a hole, a 6mm motor does not fit "kind of tight". After the 6mm hole is driled I start the hole for the thrust bearing with a needle file. Then drill with progressively larger size bits till I get a good press fit with my thrust bearing outer tube. The press fit can not be too tight or the balsa will split. It is ok if the press fit is not really tight or if the hole is not perfectly true.

After I get both holes drilled I cut out the gearbox to a cam type shape. You can make your gearbox any shape you want, square may be better for mounting I prefer the cam shape fro some reason. I then sand the thing down starting with 150 ending with 600 grit.

Note: You may want to skip this coating step and make the rest of the parts and test the fit first. Ecspedially if you deviate from any of the sizes.

I then coat the thing heavily on the outside and inside the holes with thinned Duco. You can use any nitro cellulose glue that can be thinned with acetone. Ambroid is another glue that could be used there are probably others. I guess thick nitrate dope could also be used. This gives the balsa more strength. It is like making it plastic.
You could probably make 2 of these with thinner balsa and put one in front and one in back sort of like the gearboxes on microplane solutions website.

Now you can make the thrust bearing and shaft while the duco is drying. I use .031" music wire for the shaft about 1" long. Cut the music wire to length then round off or bevel the ends about 1/32". Make sure the shaft is straight and true by rolling it on a peice of glass or flat surface.

The 23t spur gear will need an adapter for the .031" shaft. I used wire insulation (Thanks for the idea David Dewitt). once you find insulation that will allow a tight fit for the spur gear you can slide the spur gear so the back is about 15/16" from the front of the shaft, then cut and remove the extra wire insulation.

The aluminum tube is about 15/32" long and 3/32"OD and 1/16" ID, this fits the 1/16" brass bushings.

For the brass bushings start out with a length of 1/16" OD brass tubing. insert some scrap .031" music wire then place your hobby knife like you are going to cut it into - about 1/16" from edge. Roll the brass tube keeping the knife straight and applying pressure. It is good to not use much pressure at first till you have scored the tube straight-all the way around. After you have scored the tube straight you have a guide then can apply more pressure. This process is like cutting insulation without cutting wire.
The scrap music wire keeps the brass tubing ID from compressing while cutting. You may get a flange on one end so it may be a good idea to file each end off before starting a new bushing. I usually dont or only file it down a little - as it makes for a really tight press fit in the aluminum tube. Now that you have 2 bushings 1/16" wide insert them in either end of the aluminum tube.

Now cut some washers from some slick tubing. I usually use the red spray tubes. The same method can be used as cutting the bushings. A sharp thin blade helps to get thin washers. You will want an extremely as thin as you can get washer for the back as well as a spacer washer that goes between the spur gear and front bushing. The front spacer should be from 1/32" to 3/64" depending on how much insulation you leave on. This spacer keeps the spur gear from slipping off the pinion while the motor is idle.

A spare pinion can be cut in half and the teeth sanded or cut down to be used as a lock washer. If you don't have spare pinions then 1/16" tubing can be squeezed or glued on.

OK now you have your thrust bearing and shaft ready to go. Have a motor with wires soldered on and pinion pressed on ready.
The wires are tricky to solder make sure that you solder the wires on quick as too much heat can deform the plastic cap and misallign the brushes making the motor run poorly.

Now put the spacer washer on from the back , slide it up to the spur gear.


After the duco dries good about 5-15 minutes depending on how much is used I recoat the holes and apply a bit of glue to the motor and aluminum tube. Then I press in the motor and aluminum tube into the appropriate holes. Put the shaft in from the front and put on the back washer and the lock washer. You can now adjust the straightness of the tube and motor as well as adjust the meshing a bit. It will take a while for the glue to set so you have a little while for adjustment. You could even have a prop on the shaft, a power source and current meter hooked up to the motor to find the best mesh.

Now you should have a working lightweight gearbox ready. It is a whole lot easier to do than say.

Billy
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Old Feb 03, 2004, 11:39 PM
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The previous post explains how I make the gearboxes. You can use my drawings to make gearboxes using other size tubes and even other size motors like 1mm shafts and 4mm motors. Hopefully the explanation will spark some other ideas on how to make gearboxes.


brucej
yes they are press fit. The previous post should explain how to construct the bushings.


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Old Feb 04, 2004, 12:14 AM
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This drawing should print to scale with a graphics program. It will not print out to the accuracy of which the numbers it was based on but if you follow the directions in the previous post you should get a smooth running gearbox using these drawings. I would like to thank Carl Martin for providing me with the spacing recomendations. soon I might clean up my cad drawings of this and put together some construction drawings and post the files here. I am interested in other techniques for making gearboxes with these gears. I know Nick Leichty uses these gears with Gasparin props If I remember correctly he uses the high pitch props 1.5" with 3:1 and 2" with 3.83:1. Hopefully with these instructions you can make a really small plane. I have seen some interesting gearboxes posted here and Aeronutz Mark makes some nice gearboxes. I was inspired to make these after reading the DIY gearbox thread where Gordon Johnson, Ralph Bradley, and others made simple gearboxes for the N20 or M20.

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Old Feb 04, 2004, 12:22 AM
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I forgot to mention you might want to use some sort of lubricant with the brass bushings.
I used WD40 but 3in1 oil or machine oil may be a better choice. I am not sure the best method to apply the lubricant without getting it on the other parts. I sprayed some on a shop towel then applied to shaft.

Another thing I forgot to mention is that you might think that the balsa would be to soft of wood for this. It probably is but after adding DUCO it is like plastic and stiff. Thinner spruce or ply cold probably be used in place of balsa.

One more thing I have seen gearboxes like Koichi Tanaka(very nice gearboxes) and others make with only a balsa spacer between the thrust bearing tube and motor.
The drawings could be used to get the spacing close with these type gearboxes as well. That is the lightest weight solution for a gearrbox I think. The type gearboxes in the photos are more for trying out different motors easiliy. All it takes to change the motor is a squirt of acetone then remove the old motor and put in the new. Then a few drops of thinned duco on either side around the motor/balsa joint will secure the new motor in place. Once you get a motor you like you can always bond it permanently with epoxy or CA.

Any and all comments, suggestinos, questions, etc.. as well as other techniques/materials/etc.. for making gearboxes are all welcome here.

Billy
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Old Feb 04, 2004, 01:12 AM
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Carl Martin uses plastic or silicon bushings instead of brass bushings. One advantage of using plastic bushings is that you do not have to lubricate them. I have used silicon spray tubes for making bushings for 3/64" shafts.


If you accidently split the balsa while pressing in the motor. The wood can still be used if you wrap some thread around the whole thing. 3 or 4 loops around ought to be enough and ithe thread will help in mounting the gearbox. Must be that the fibers make for some very porous material.

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Old Feb 05, 2004, 12:00 AM
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I crashed my plane on landing this morning. A breeze blew it into a truck and the balsa gearbox broke. So I made this ply gearbox. I wanted to try out the drawings I posted here. Well the lines are a bit too big on the drawing I posted so I'll try and hurry to get the cad drawings cleaned up and posted. As you can see in the photo the gears are not meshed good. It was dificult to get the al tube holes started directly in the center with the big center cross lines. It is easier to get the holes started with thinner lines like from a cad printout. I think the pdf printout may print smaler lines as well. Anyways the ply gearbox works like this and the motor does not get hot. I don't see much difference in climbing so it must be putting out the same mount of thrust as the balsa gearbox. I'll have to measure current draw to see for sure. My RX did start glitching for some reason. I think that could be from the 9V battery becoming discharged. I left it in the TX overnight so I am guessing that is why I am having glitches.

Billy

[edit]
I forgot to mention that this gearbox was broken during construction and held up to many trimming flights and landing crashes where the wind blew the little plane off balance while landing. It made quite a few prop first landings , the wind would throw it off balance(landing downwind) I would try to pull it back up with the throttle and sometimes the angle was too steep and it would just crash quicker. Sometimes I was able to pull it back up. The final crash that done the gearbox in was a side swipe crash. I could have glued it back together but it was getting too heavy from glue fuse/gearbox glue buildup.

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Old Feb 05, 2004, 12:05 AM
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With the ply gearbox you can skip the duco coating step. I used 1/64"ply. The motor and tube fit is tight with this gearbox. I only added minimum glue after everything was put together. I used thinned duco about 65%duco and 35%acetone. The thin glue seeped into the joints. I did push the al tube forard a bit and coated all the way arounfd then pushed it back into position and put a spot or 2 on the other side.

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Old Feb 05, 2004, 12:10 AM
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It is much easier to get these gears meshed when using a drawing. I had tried to make gearboxes like this before by drilling the motor hole then installing motor and then putting a short shaft on the spur gear and lining it up with the pinion. I would press the shaft in the wood to mark where the hole for al tube would be drilled. Well I would always end up with too mush or little distance between spur and pinion. With the drawings(printed from Cad program) I can get the space right a whole lot easier.

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