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Old Jun 06, 2012, 11:14 PM
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mrexcel's Avatar
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15" RC Ornithopter

Greetings,

I have couple of following rubber powered ornithopters..

http://tanjongbunga.olx.com.my/pictu...-iid-162280275

I also have some micro motors and gear boxes like..

GP-6, GP-7, GP-8, KP-00, 7mm motors, 2gram motor and 5gram motors.

I have also got Plantraco and micro DSM2 Rxs.

All these time I was building micro planes and now I feels like convert the above rubber powered ornithopter to electric.

I would like to build a gearbox on my own using an old servo.

Where should I start?

Please note that, I am aware there is an ornithopter forum. But I prefer posting it here, since I always get good response from Indoor section.
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Old Jun 07, 2012, 05:31 AM
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I also have some of those ornithopters.(10 actually!) I have been considering converting one to RC and I think the best power system that could move the wings is the motor and gearbox from a flytech dragonfly. But I also have a smaller 4 winged RC ornithopter which has a pretty powerful setup and has a wingspan of almost half this rubber powered Orni. Considering that power system as well... but the only problem is how I'll setup the turning system... actuator or motor?
Will be following this conversion...

SS
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Old Jun 07, 2012, 05:37 AM
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Ah. I just did that. I also had 2 of those small four winged birds. What I did was changed the motor to 7mm super slick, then fitted to the rubber powered bird. It can fly. But little under-powered. Now I am thinking of replacing the motor with 5 gram HK brushless.

Experts, please comment!
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Old Jun 07, 2012, 06:35 AM
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5gram brushless? you sure the gearbox can take it? I've yet to change the motor on mine to a 7mm...

SS
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Old Jun 07, 2012, 06:42 AM
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Should be able to find a way to get the 5g motor fitted to the gearbox. Even the 7mm will not slide in, you just have to find your own way.

Other option I am considering is using 2x 7mm motor to produce enough thrust!
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Old Jun 07, 2012, 01:33 PM
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nice you guys, good luck! I did an ornithopter bird with a r6400 brick and 5gram DD to the geared orni mechanics - it didn't work very well b/c the torque needed to drive heavy gears was too much for the BL motor to handle, connected BL efficiently but drive was clunky and not smooth through entire range.

BL motor geared then applied to ornithopter mechanics could work but the weight gain sucks and is difficult because my motor was behind the wing gears and made for tough c.g.

torque needed and weight gains are major limitations to micro ornithopter imo
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Old Jun 07, 2012, 02:04 PM
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thank you for your suggestions.

My main goal is not to build a micro ornithopter. Its just build something with stuff I have. For eg. 5g brushless motor and 180mah 2S battery means some decent power setup for me. Also its very easy to handle.
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Old Jun 07, 2012, 02:55 PM
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Quote:
Originally Posted by mrexcel View Post
lectric.

I would like to build a gearbox on my own using an old servo.

Where should I start?
Its easiest to do a few tests on your models while they still are rubber powered and use that info to get close to the correct motor and gearbox you will need.

Weigh the rubber used. Its unlikely that there is a motor,battery,servo setup that will weigh less than the rubber band so the wings will have to flap faster. Try using 2 rubber bands to see if the wings can take the strain. Its better to risk breaking the wings now before you invest a lot of time and money.

Lock the wings to have a little dihedral and trim for best glide by adjusting the tail. see where it balances. Add some clay to the balance point and note how its glide and balance point changes. The wing trailing edges will deform as weight is added, so the glide will likely degrade as weight is added and the balance point will change but you need to know where to place the batt,motor and servo. Make a graph of where the balance point goes as you add weight.
Try to find how much torque the rubber band has at max winds by taping a long wood dowel to the crank and hanging clay or pennies on the rod or place the free end of the rod on a scale, then convert to ft-lbs or kg-meters or what ever units you use. Use that data to select a motor-gear ratio that is LIGHTEST. Try to estimate how fast the wings flap with rubber power; use a digital video camera with slo-mo if you have one or use a tach. The wings will have to flap faster after you add weight.
Your motor torque times the gear ratio should be at least as large as the max rubber torque at a higher flap rate.
Hope this helps,
GB
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Old Jun 07, 2012, 03:18 PM
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you might try to build the control surfaces before the power system. that way you can run it as rc on the rubber band power before extensive mods. give you and idea of what is involved and how it will handle.
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Old Jun 11, 2012, 05:10 AM
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I created a test gearbox using 2 units of GPS-7 gearboxes from HK . Now the flapping works fine using the same flapping mechanism which came with the rubber powered bird. It seems like the flap rate is too slow now.
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Old Jun 11, 2012, 05:12 AM
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My next option would be to use a 5g brushless motor in place of the 7mm coreless and see
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Old Jun 11, 2012, 04:06 PM
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you might try a worm gear and a spur gear. very high reduction, means lots of torque and lower rpms.
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Old Jun 11, 2012, 07:05 PM
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does it seem like the flap rate is low because the gearing is too low, or because the wings are too much load on the motor?
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Old Jun 11, 2012, 08:18 PM
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Yes. It was slow not due to the gear ratio. I found it was due to the lose pinion gear. I changed it and now the flap rates are fine. Now I have a new issue. The 7mm motor gets too hot which makes the gearbox to melt!
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Old Jun 11, 2012, 08:30 PM
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it does sound like its working a little hard, you might try some smaller wings, either span or chord and see if you can get the current down.
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