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Nov 03, 2016, 11:44 AM
Woof
Thank you Steve, I guess to go with a passive tail feather, two "modes" of steering would need to be implemented in the servo control code. Mode one is "throttle on" and varies flapping amplitude. Mode two is throttle off, this would vary the wing position when gliding to achieve steering/ roll. Since I am building an S1 now (much slower than you!) I will ask Nathan C about this. If it does not exist I will code it up as my object is to not have an active tail feather just a horizontal stab.
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Nov 03, 2016, 02:17 PM
Registered User
Nathan have ready to use (programmed) servo controler so no need to learn the basics of programming and aerodinamics to be able to make your own
http://www.birdkit.com/robotics.axon1.html
Here is the video , the tail is absolutely passive .
New Type Ornithopter - S1 Robotic Bird Flies! (1 min 9 sec)
Nov 03, 2016, 04:08 PM
Woof
Thank You, ZTEX - I am building his kit now. (but I am slow lol)
Nov 03, 2016, 04:46 PM
Registered User
Thread OP
It just occurred to me that if you trim your model with a large download on the horizontal tail, you can get rudder effect by changing the dihedral angles of each wing when gliding. This effectively "rolls" the fuselage and tilts the loaded horizontal stabilizer, just like a Park Hawk did for rudder control.

Steve
Nov 03, 2016, 06:14 PM
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Quote:
Originally Posted by mlbco View Post
It just occurred to me that if you trim your model with a large download on the horizontal tail, you can get rudder effect by changing the dihedral angles of each wing when gliding. This effectively "rolls" the fuselage and tilts the loaded horizontal stabilizer, just like a Park Hawk did for rudder control.

Steve
Yes, this work with V tail too .When you try to change the wings/fuselage angles assimetricaly actualy you tilt the fuselage , this tilt the V tail and one of the fins become more "horizontal" another one more" vertical" . Since they are set on negative angles of attack the more horizontal one produce most of the tail down force and try to roll the model in the proper for the turn direction the motre "vertical"one produce
more outside of the turning radius pointed force and point the nose in the turning direction.
I was thought befor for turning with V tail by only rotating of the" tail boom".
Nov 03, 2016, 06:38 PM
Registered User
This toy ornithopter called CyberDactyl turns this way.
Rolling is initiated by assimetric flapping and the rest is done by the tilted Vtail. The tail is firmly connected to the fuselage and don't have any active surfaces.
I explained this way of turning here when this toy come first time on the market .
http://t.toysrus.com/product/index.j...uctId=33799406
Nov 03, 2016, 07:57 PM
Registered User
This ornithopter from Robert Korobelnik use similar way of turning .On the next wideo turning only by assimetric wings angles.
Ornithopter wings differential ABIRK System (1 min 21 sec)
Nov 05, 2016, 01:24 AM
Registered User
An article by Nathan about servo powered ornithopters. There is his an old design from 2005 year which actualy is better solution for independent wings driving.
He use two sets of absolutely separate (mechanically)motor- reductors which are sinchronized or desinchronized (for turning ) only electronically by the micro controller. Feedback potentiometers are coupled to the wings'sholders hinges shafts. This ensure closed loop feedback which prevent any desinchronizations because micro controler knows permanently where wings are , opposite on the open loop control when use non modified servos (servo potentiometer middle point is not connected to the micro controller ) . The effect of decreasing the amplitude with increasing of flapping frequency and the load is result of the open loop control used.
http://www.the-nref.org/content/building-robotic-bird
This way you can't vary the flapping amplitude but since converting the rotational to reciprocational motion happens in the last posible moment and the motor -reductor turns only in one direction ,the efficiency is much better.
Nov 05, 2016, 02:03 AM
Registered User
BTW I invented an method for improving the efficiency of pure reciprocating servos powered ornithopters.

The idea is to use so called final point stroke springs and to switch off the servo motor a bit earlier before to reach the end of the stroke. This way the inertia of the servo motor reductor and the wing just will load the spring. When the micro controler detect stopping of the whole sistem only than it will generate controll signals for moving the servo arms in reverse and the loaded spring will help to the servo motor to accelerate the wing backward much more easely .This system is better than using energy recovering servos because the efficiency of energy recovering is higher this way and the motors load is reduced significantly . In energy recovering servos actualy when stopping the servo arm ,the motor works as an generator so it's still loaded and produce heat.The above Is possible if you use constant amplitude of flapping. Also final point stroke springs have to be used on the both ends of stroke. To complitely switch off the servo motor a litle electronic modification of servo motor controller bridge will be required and one more signal wire will come off the servo and will go to the micro controller .
Will make sketch and post it tommorow for illustration of the idea. And sudgest schematics for servo bridge modification.
Nov 05, 2016, 12:15 PM
Woof

ZTEX - I believe that your idea could be achieved with just software programming


The code could be changed such that as the servo reaches the end of its travel range, its slows down via code before reversing direction.
Nov 05, 2016, 04:04 PM
Registered User
Quote:
Originally Posted by CosmicDog View Post
The code could be changed such that as the servo reaches the end of its travel range, its slows down via code before reversing direction.
I don't think so.

If somebody understand what I'm explaining and is interested in I will continue .
If not, then it will be nonsense to continue further.

Thanks

Z
Nov 05, 2016, 07:03 PM
Woof

Please continue


would love to see your design.
Nov 05, 2016, 07:26 PM
Registered User
Quote:
Originally Posted by CosmicDog View Post
would love to see your design.
It's not a design, it's idea only .I do not going to design and build servo powered ornithopter, because I know what the result will be in advance.
Just trying to help to you ,Steve and others who think that this option is viable in order to soften the problems a litle bit.
Will have to draw sketches first ,they still only in my head yet
Nov 08, 2016, 01:23 AM
Registered User
Thread OP
Z,

I thought Horst Rabiger propose a system with springs at both ends of the stroke, but I couldn't find it on his website. I use large springs to resist the upstroke and add force to the downstroke, they are essential for efficient flapping flight. I have not studied the optimal means to implement servos and springs, but if you have a closed loop RPM control system on the drive motor it should reduce the need for springs a bit. One day I will write a complete simulation of the motor, drive train, aeroelastic wings and multiple wing spar joints and run an optimizer on it to see what I get. This is the only way to make progress from theory but I haven't had time to write this simulation, it has been easier to just build the model for me!

Controlling the ornithopter with the wing servos will come later for me, it's not something I'm very interested in now. I'm more interested in the design of efficient wings and prefer to use separate servos for control. It's great to see that Nathan has figured something out for this application.

Thanks,

Steve
Nov 08, 2016, 01:40 AM
Registered User
Thread OP
I now have 30 flights on my model and I was tuning it for climb performance when I noticed it was flying a bit worse each flight. I found that one of the servos was failing and when I disassembled it I noticed that one gear was partially seized to the support shaft. I removed the gears and cleaned all the pieces and will re-assemble with plenty of fresh lithium grease. The motor looks good and only the gears were having issues. I've had some fun flights with the model and here are some recent photos.

Steve


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