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pb_guy
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Re: Possible inexpensive contra-rotating prop gearing
Reply #6 - Sep 21st, 2020 at 10:12am
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Yes, Mike it is strict 1:1 gearing using the 2 smaller white gears to transfer power from inner shaft to outer tube. The only difficulty of the setup is that there is no room for a bearing for the motor tension inside the case, so it will be plastic on plastic. I wonder if a bit of lube would make any difference? or if it would just gum up the works.

ian
  
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MKelly
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Re: Possible inexpensive contra-rotating prop gearing
Reply #5 - Sep 21st, 2020 at 9:17am
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Interesting work Ian.  With the direct drive do both shafts have the same gearing (1:1 rubber turns to prop turns)?

Mike
  
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pb_guy
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Re: Possible inexpensive contra-rotating prop gearing
Reply #4 - Sep 20th, 2020 at 5:44pm
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Update.
  The easiest thing to do seems to be to take the center shaft out and replace it with a piece of music wire. The case has a convenient hole already at that spot. The inner shaft is 0.049 inch. When I removed it, I found that it was knurled, so it was hard to remove. I drilled a 1/16 hole in a piece of wood and drove it out with light taps with a hammer. I searched around my old supplies in an out-of-the-way storage spot and found a used piece from an old C/L model that was 0.047 inch. If I manage to knurl the shaft in the right spot, a drop of epoxy should hold it in place. This way the outermost prop would be direct driven and the back prop would be gear driven.

ian
  
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pb_guy
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Re: Possible inexpensive contra-rotating prop gearing
Reply #3 - Sep 16th, 2020 at 10:08am
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What a surprise! The gearbox is NOT glued together. It can be taken apart by spreading two catches on either side! This is what the interior looks like. I should be able to drill through the case with a pin drill and insert the motor shaft through either of two white gears.
ian
  

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gears.jpg
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pb_guy
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Re: Possible inexpensive contra-rotating prop gearing
Reply #2 - Sep 15th, 2020 at 9:33pm
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I am disappointed. I should have expected it, but I was a little dense. The gearing on this setup is about 13:1, which is fine for an electric motor, but no good for rubber. I did do a conversion before I twigged on to the problem, and the pictures are the setup I used before I figured that it wouldn't work.

  I am going to take the gearbox apart and see if the setup can be salvaged in some way.

ian
  

( 55 KB | 9 Downloads )
fig_1.jpg
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fig_2.jpg
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fig_3.jpg
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Sky9pilot
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Re: Possible inexpensive contra-rotating prop gearing
Reply #1 - Sep 1st, 2020 at 8:46pm
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Looks interesting. Will have to check the Dollar store near me!
  

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pb_guy
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Possible inexpensive contra-rotating prop gearing
Sep 1st, 2020 at 6:26pm
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  I happened across a toy helicopter in the dollar store yesterday. It cost $4 (yes, 4 dollars Canadian), so I bought 2 of them. It is by Montoy. Others have posted some pics of using it or similar on Youtube ( here and here ). I took it apart and sliced the blade supports off with a craft razor blade. The unit contra rotates, driven by a single electric motor. If you can use the gear on the motor with a rubber motor attached to it somehow (that is where most of the work will be), you have a relatively inexpensive contra rotating gearbox setup, The gearbox, excluding the motor weighs in at 3.4 grams! and some of that weight could be trimmed off, starting with reducing the length of the shafts and shaving off some extra plastic extrusions.

ian
  

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Montoy_helicopter.jpg
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gear_case_side_view.jpg
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interior_gear_view.jpg
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interior_gear_view_with_motor.jpg
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