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Old Sep 09, 2013, 08:52 AM
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Ornithopter information needed

Hello,

I am Robbe Derks, and toghether with two people we are working on an ornithopter design as a school project. Our design will be around 1.5m from tip to tip, so it will be very close to the CarbonSail ornithopter for example.

As we can't find much information about ornithopters this size, we would like to receive some information about the specifications and dimensions of these ornithopters. What we would like to know for now:
- How strong do the servos which control the tail movement need to be?
- What size / power and KV of brushless motor should be used and with which gear ratio? We figured out that the ratio will probably be between 1:100 and 1:1000.
- Is there any type of special control strategy needed to keep a steady flight?

My part of the project is mainly focused on controlling the ornithopter in a smart way. I am currently working on a custom PCB which will intercept and override the servo and motor signals with a clever algorithm to keep the ornithopter steady during flight with sidewinds, etc. so it will be easier to controll.
The data needed will be coming from an accelerometer, gyroscope sensor and a magnetometer to keep the bird facing the right way during flight.

The controller will also put the wings into 'gliding position' (leveled) when the throttle is released. This will be acheived with the help of hall sensors checking for magnets incorporated in the gears.

Any information / suggestions will be greatly appreciated.

Robbe Derks
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Old Sep 10, 2013, 01:58 PM
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Tres Wright's Avatar
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Quote:
Originally Posted by DebboR View Post
- How strong do the servos which control the tail movement need to be?
Generally with the Kinkade ornis of that size we always recommend micro metal gear servos. Plastic-geared servos are adequate in the air, but when landing the heavy tail can snap down and strip the gears pretty easily.

Quote:
- Is there any type of special control strategy needed to keep a steady flight?
I'm not a orni designer, but I've flown a bunch of them and in many different sizes. They're all quite steady in flight in low wind conditions. When it's windy it's a lot like R/C planes- the higher the wing-loading the more solid they are flying in wind. My Parkhawk is the smallest of my Kinkade ornis and flies the best in wind by far (has the highest wing loading and fastest flap rate). My Slow Hawk is the biggest, flies the slowest (lowest wing loading) and is affected the most by wind.

Quote:
My part of the project is mainly focused on controlling the ornithopter in a smart way. I am currently working on a custom PCB which will intercept and override the servo and motor signals with a clever algorithm to keep the ornithopter steady during flight with sidewinds, etc. so it will be easier to controll.
Is this orni going to be R/C or free flight? I can see the need for this in free flight, but R/C ornis are already quite easy to control, they're a lot like flying trainer planes.

Quote:
The controller will also put the wings into 'gliding position' (leveled) when the throttle is released.
They glide better if there's a slight "V" to the wings in glide-lock rather than level. It acts like dihedral does on a free flight plane.

Quote:
This will be acheived with the help of hall sensors checking for magnets incorporated in the gears.
This has been done before, someone on here was offering such a device for a while but I have no idea if the schematics were made available. You might try the search engine to see if you can find more info here.
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Old Sep 11, 2013, 09:50 AM
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Originally Posted by Tres Wright View Post
Generally with the Kinkade ornis of that size we always recommend micro metal gear servos. Plastic-geared servos are adequate in the air, but when landing the heavy tail can snap down and strip the gears pretty easily.



I'm not a orni designer, but I've flown a bunch of them and in many different sizes. They're all quite steady in flight in low wind conditions. When it's windy it's a lot like R/C planes- the higher the wing-loading the more solid they are flying in wind. My Parkhawk is the smallest of my Kinkade ornis and flies the best in wind by far (has the highest wing loading and fastest flap rate). My Slow Hawk is the biggest, flies the slowest (lowest wing loading) and is affected the most by wind.



Is this orni going to be R/C or free flight? I can see the need for this in free flight, but R/C ornis are already quite easy to control, they're a lot like flying trainer planes.



They glide better if there's a slight "V" to the wings in glide-lock rather than level. It acts like dihedral does on a free flight plane.



This has been done before, someone on here was offering such a device for a while but I have no idea if the schematics were made available. You might try the search engine to see if you can find more info here.
Hello,

Thanks a lot for this information. The orni will be mostly R/C controlled, but as our studies are highly technical orientated, we have also been given the challenge to let the bird do a free flight you described. It will probably be possible to flick a lever on the controller, so the software knows it needs to keep it's heading, ... It's just to make the project a little more complicated

My main concern about the orni at the moment is the size / power / KV-ratio the main brushless outrunner should have. I have no idea at all how much watts are required. We have actually done some vary raw calculations, and we figured out it will require about 300W. Is this figure anywhere near correct?

In other orni designs, we have found that the motors have a very high KV-ratio (around 5000kv). Why is this better? With a gear ratio of 1:100, this would result in a way too fast flapping speed, no (50RPM / V)?

Thank you!
DebboR
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Old Sep 11, 2013, 10:33 AM
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Hi,
Have you looked at this site?
http://www.ornithopter.de/english/index_en.htm

Cheers,
Patricia
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Old Sep 11, 2013, 02:08 PM
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Originally Posted by Patricia J B View Post
Hi,
Have you looked at this site?
http://www.ornithopter.de/english/index_en.htm

Cheers,
Patricia
Yes, I already found this site, but I don't think it tells me what I'm looking for. The only thing I'm after at the moment is an approximation of the power needed to keep an orni of 1.5m tip to tip in the air. And if I should use a motor with low or high KV (800kv - 5000kv).

Thanks anyway for answering,
DebboR
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Old Sep 12, 2013, 09:58 AM
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Here's another link . This is a paper on the 1.8 m wingspan
'Phoenix' built for control research by Jackowski.

'Design And Construction Of An Autonomous Ornithopter'
By Jackowski
M.I.T

http://groups.csail.mit.edu/robotics...ackowski09.pdf

Cheers,
Patricia
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Old Sep 12, 2013, 12:39 PM
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Quote:
Originally Posted by DebboR View Post
Yes, I already found this site, but I don't think it tells me what I'm looking for. The only thing I'm after at the moment is an approximation of the power needed to keep an orni of 1.5m tip to tip in the air. And if I should use a motor with low or high KV (800kv - 5000kv).

Thanks anyway for answering,
DebboR
I don't have a Kincade type ornithopter but I have read posts that said they need around 100 watts for the larger models. Its not a difficult measurement to make or compute from battery recharging but power data is hardly ever discussed or shared, so I suspect the power used is higher than advertised. Its a good idea to first build a smaller model and see what works.

Once you know the power and the flaps/sec required, you chose a kv, motor size and gear ratio combination that results in the lightest weight and best efficiency.

Good Luck!
George
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Old Sep 18, 2013, 11:05 AM
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Quote:
Originally Posted by DebboR View Post
My main concern about the orni at the moment is the size / power / KV-ratio the main brushless outrunner should have. I have no idea at all how much watts are required. We have actually done some vary raw calculations, and we figured out it will require about 300W. Is this figure anywhere near correct?
No, it doesn't sound right unless the bird is going to be extremely heavy (and then you've got other problems). My Slow Hawk is around a 60" wingspan and at WOT pulls 91 watts, but in actual flying it rarely sees WOT.

Quote:
In other orni designs, we have found that the motors have a very high KV-ratio (around 5000kv). Why is this better? With a gear ratio of 1:100, this would result in a way too fast flapping speed, no (50RPM / V)?

I'm running an Axi 2208-26 on my Slow Hawk and Park Hawk, the KV is 1420. I run 3s on both.
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Old Sep 18, 2013, 11:45 AM
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The link I gave in post #6 gives details on how and
why they chose the motor, gear ratio etc
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