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Oct 30, 2016, 01:56 AM
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therealthing691's Avatar
i wish you the greatest success and cant wait to see it fly regards Brian
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Oct 31, 2016, 01:26 AM
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It's nearly finished now. I've got a few details to complete and then I'll try gliding and flying it. It's not as heavy as it looks, probably less than 1 lb.

Steve
Oct 31, 2016, 10:19 AM
Woof

What type of fabric did you use?


It looks like ripstop, what weight did you use? Your project looks AWESOME BTW!
Oct 31, 2016, 10:33 AM
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It's Coverlite:
http://www3.towerhobbies.com/cgi-bin...?&I=LXWK09&P=M

I glue it down with this:
http://www.loctiteproducts.com/p/cnt...e-Adhesive.htm

Thanks,

Steve
Oct 31, 2016, 11:58 AM
Woof
Thanks Steve: Interesting specs on the coverlight - "Extremely light weight of only .89 ounce per square yard" . So this material is lighter than ripstop nylon (the lightest I have seen is 1.0 ounce rip stop) but heavier than the nylon membrane fabrics I have been looking at. I guess with a full profile wing you covered the top and the bottom.

Can't wait to hear more!

Thanks
-BigSabu
Oct 31, 2016, 07:31 PM
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I made an initial test flight this evening. I needed to add 5 #32 rubber bands to pull downward on the wings before the model could even begin to fly. These rubber bands even out the loads between up and downstroke and are essential on this type of model. After I got it trimmed I managed a non-climbing flight shown in the video below. The servos were not even warm, I'll need to experiment and hopefully get more power from them.

Steve

Servo-Flap Ornithopter Flight #1 (0 min 27 sec)
Nov 01, 2016, 07:25 PM
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I added a 3 cell 450mah Li-Po pack running through a Castle Creations 10A BEC set to 9V output. This delivers more electrical power to the wing flapping servos and even though 9V is above spec, I haven't seen any issues so far.

With the increased power I was able to fly a couple 360 loops around myself and then glide to a landing. The model still doesn't really climb, but it appears to sustain altitude now. I weighed it today and it's much heavier than I had guessed, 1.6lbs total weight!

Steve

Servo-Flap Ornithopter Flight#2 (0 min 41 sec)
Nov 01, 2016, 11:33 PM
There's magic in those wings !
khaled_abobakr's Avatar
Amazing ... flaps really slowly .... majestic flight
Nov 02, 2016, 12:51 PM
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Quote:
Originally Posted by mlbco
I added a 3 cell 450mah Li-Po pack running through a Castle Creations 10A BEC set to 9V output. This delivers more electrical power to the wing flapping servos and even though 9V is above spec, I haven't seen any issues so far.

With the increased power I was able to fly a couple 360 loops around myself and then glide to a landing. The model still doesn't really climb, but it appears to sustain altitude now. I weighed it today and it's much heavier than I had guessed, 1.6lbs total weight!

Steve

https://www.youtube.com/watch?v=Yts0sKnhx0Q
Just counted the flapping cycles and they are 67 - during 36 seconds flapping flight duration it's 1.86 Hz flapping frequency.Probably on 2.5 Hz it will be abble of climbing.
Here are the servos specs:http://www.mksservosusa.com/product.php?productid=145
According to specs on the higher voltage rating they are abble of 60 degree /0.10seconds without load which mean 0.20 seconds on flapping cycle or 5 Hz flapping frequency without load.

Here are some sudgestions what to do.
1. Lighten it as much as possible:
1.1 Use smaller possible capacity battery. Calculate it in the way just to meet max servos current requirement and don't worry about flight duration.
1.2 Remouve tail servos ( just for the experiment ) fix the tail control surfaces for very large radius turn and try it this way. In the future you can write new programm which to turn the ornithopter by assimetry of flapping or assimetric wings/ fuselage angles when glide. Variable average dihedral for pitching up and down etc.
1.3 Cut openings in the fuselage after the wings and cover with thermo stretching film.
Lightening will allow faster down stroke and then remove some of the elastic strings for faster up stroke.
2. Electrical measures :
2.1 Shorten the servos wires as much as possible.
2.2 Soldering ultra capacitors as close to the servo as better on servo powering wires will help with voltage sag too .
2.3 Better power the servos straight from the battery 7.4V because the BEC dinamic output voltage reaction is unknown ,for saving weight by eliminating the BEC and one of the battery cells and for higher efficiency.
3 Aerodinamics:
3.1 The glide ratio is excellent but if the negative tail angle can be further flattened this will help for sure.
3.2 Use the cover for betwin the wings space and shape it as aero foil like ,since the upper wing surface produce about 2/3 of the lift and this will reduce the drag too.
3.3 Remouving the tail servos will help with reducing the drag too or at least move them inside.
4. If all above doesn't work choose different servos faster and more powerful on 7.4 V without using BEC and 3S battery.
Not sure if the brushless will be better because coreless motors probably have lower momentum of inertia and this is very important when you will have to reverse the motor periodically .

That's all that comes to my mind for your case Steve
Whish you success
Z
Last edited by ZTEX; Nov 02, 2016 at 01:24 PM.
Nov 02, 2016, 03:02 PM
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Thread OP
Here's a video after lightening it up by an ounce or two plus a few other adjustments. It now has a small rate of climb and has even caught a thermal.

Steve

Servo-Flap Ornithopter Flight#3 (1 min 11 sec)
Nov 02, 2016, 07:28 PM
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Thread OP
Quote:
Originally Posted by ZTEX
...Here are some sudgestions what to do.
1. Lighten it as much as possible:...
Z,
Those are all good ideas, some of them have already been incorporated. Many would best be attempted on a new model although I'm not planning on building another one anytime soon. Yesterday I was able to reduce the weight by a couple of ounces by replacing the switch, receiver, and some wiring with lighter components. The servos are running happily on 9V and the battery is a 3S 450mah pack which is about as small as I dare to go. I have a small positive rate of climb now and I might look for an adjustable DC-DC regulator that would let me drive the servos at 9.5V.

Unlike my previous model which used the Futaba S9352HV servos, the MKS HV777 servos are not heating up and seem relatively "happy" flapping these wings. The Futaba's were lower torque and higher speed, not a good match for this size and weight model. I can increase the flapping frequency with software to the point that the flap amplitude decreases due to lack of servo torque, but the model does not fly better there. More voltage is the best way to get more power, so long as I don't burn up the servos!

Thanks,

Steve
Nov 03, 2016, 09:12 AM
Woof

AWESOME BIRD - Can you share the specifics of your build?


Can you share the specifics of your build? Things like wingspan, chord and the shape of your wing "struts" ?
Nov 03, 2016, 09:17 AM
Woof

One more Question


Had you considered a static tail feather and using variable flapping amplitude to achieve turning ? This is the design of Nathan C. S1 Robotic Bird (servo driven)
Nov 03, 2016, 11:23 AM
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Quote:
Originally Posted by CosmicDog
Had you considered a static tail feather and using variable flapping amplitude to achieve turning ? This is the design of Nathan C. S1 Robotic Bird (servo driven)
I've considered it but what would you do to control the model when gliding? Unless the wings are flapping you have no roll control with this approach and I need to maneuver in the glide.

I might try experimenting with this type of control but if I can't ditch the tail servos and wiring to save weight, why bother?

Steve
Nov 03, 2016, 11:25 AM
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Thread OP
Quote:
Originally Posted by CosmicDog
Can you share the specifics of your build? Things like wingspan, chord and the shape of your wing "struts" ?
Wing span = 69"
Root chord = 12"
Tip Chord = 7"

Rib shape is shown in the photo, I only cover the wing upper surface however.

Steve


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