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Sep 21, 2014, 02:40 PM
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Interesting ideas potentially applicable for the ornithopters

The next idea is applicable for wings actuation and controls actuation as well .

Writhing Thread Actuator Demo (5 min 49 sec)
Last edited by ZTEX; Sep 21, 2014 at 03:22 PM.
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Sep 22, 2014, 06:57 AM
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Tying Fishing Line For Powerful Artificial Muscles (1 min 50 sec)
Sep 22, 2014, 08:27 AM
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Another MIT project using the same actuators:
Sep 22, 2014, 06:55 PM
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Originally Posted by pteronaut
Another MIT project using the same actuators:
Not the same things !
MIT use SMA wire for actuator .
In first video twisted strings play role of RPM reducing gearbox which increase the motor torque in direction parallel to strings and motor shaft. This solution provide very high torque/weight ratio but the motor must to be reverced on the end of the strokes . Also it's capable of variable stroke amplitude.
In second video is demonstrated artificial muskle made by fishing line and powered by heating it. Very high force/weight ratio , variable amplitude they claimed 100 times stronger if compair to humans muskles . My doubt is only response times and not sure about the efficiency.
By the way SMA wire isn't fast as well.
Last edited by ZTEX; Sep 22, 2014 at 07:03 PM.
Sep 22, 2014, 09:25 PM
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Here is the speed comparison betwin SMA(shape memory alloy ) wire (muskle wire) and fishing line artificial muskle.
I think that fishing line is faster .
Muscle wire actuator (1 min 12 sec)

Artificial Muscles from Fishing Line and Sewing Thread # 4 (0 min 19 sec)

Power Fabric from Fishing Line Artificial Muscle (1 min 20 sec)
Sep 24, 2014, 04:25 PM
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New material , light as a foam but strong as plastic and commercially available .
Strong, Machinable Aerogels Now Commercially Available (3 min 52 sec)
Sep 24, 2014, 04:28 PM
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3D printing of CF parts
Meet the Mark One: the world's first Carbon Fiber 3D printer (3 min 24 sec)
Sep 26, 2014, 04:22 AM
XXXmags's Avatar
The twisted string idea is really good, In essence, a low friction worm drive. What a simple and light way of creating a transmission. Thank you for posting this.

One of the problems that plague ornithopter drives are the huge loads (and hence torques) involved. Many times one is limited by the power the drive system can absorb and not what the motor can deliver. I've had shafts bend and break under the huge pulses of force they have to receive.

Since the twisted string can bypass all torques except that needed to flap the wings, the power it can transfer can be much higher than with gears ( for the same weight ). This is especially true if the string is made out of a strong fiber like nylon. That could achieve extremely good power to weight ratios, something ornithopters are in dire need of.

Although the twisted string system won't work for a continuous system, using it for a servo would still be worth the effort. The motor reversal is still an issue though.

In a crankshaft-conrod drive system, the kinetic energy imparted to a wing at the start of a stroke is lost once it reaches the extreme of it's motion. The conrod must expand to decelerate the wing, and as it has internal resistance ( damping ), the kinetic energy is not conserved in elastic potential, but lost as heat. Most ornithopters loose a lot of energy needlessly expanding and contracting the drive mechanism.

If this energy could be stored by means of a generator slowing down a wing, and recharging a battery with it, then a servo drive might be a viable power plant.

Consider this cycle:

- Motor starts from rest to accelerate the wing. it continues to deliver power at as the wing passes through the middle of it's stroke ( where the drag loads are highest).

- As the wing reaches it's point of reversal, the generator slows it down to a halt, storing that energy in a battery.

- The energy in this battery is fed into the motor, accelerating the wing once again.

- After this sequence, previously stored energy (which was not regained in the deceleration of the wing ) is drained from the battery to counteract drag.

From here the cycle just continues.

Even though the motor has still started from rest under load (and hence very high startup currents ). Some of the energy used for this can be conserved.

If the whole mechanism could be forced to start moving, say by means of a high torque actuator, to get the motor spinning, and deliver it's power to counteract drag, and not in accelerating the wing, major efficiency grains can be made.
Last edited by XXXmags; Sep 26, 2014 at 10:01 AM.
Sep 26, 2014, 03:19 PM
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@ pteronaut - I forgot to say thank you for posting about SMA actuator , so I'm sorry and thank you pteronaut!

@ XXXmags - Glad you liked the idea and thank you about your comments . Will post some solutions of the mentioned problems during the weekend.

PVC_Gel_Artificial_Muscle (2 min 6 sec)
Oct 06, 2014, 06:55 AM
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Wing design idea
DR at SOFIC 2011: Prioria Robotics Maveric UAS Throwable SUAV with Flexible/Bendable Wing (2 min 32 sec)

Folding Wing UAV Mechanical Test 2 (0 min 7 sec)
Oct 15, 2014, 02:17 PM
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RC Bird tail (0 min 27 sec)
Oct 15, 2014, 02:49 PM
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Marcialtech's Avatar
Originally Posted by ZTEX

I have a similar tail control on my 1st and 2nd generation Orni design , i even tried using pushrod inside the shaft instead of strings or belt drive ... works well on small lighter tail but abit more difficult to use on larger heavy tail without causing excess weight when making it stronger , maybe a 3d printed parts would work cuz it can be design lighter and stronger.

Fred M.
Oct 15, 2014, 03:53 PM
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Here is how good is only by the wings control. Tails fixed!
Whole wings pitching / differential pitching
Multiplex Fox glider power conversion wingeron & a P-51 crash in the background (4 min 5 sec)

Only by the wing tips controll .fixed tail!

RC Herring Gull Maiden Flight. Loops and Rolls (2 min 53 sec)
Last edited by ZTEX; Oct 15, 2014 at 04:05 PM.
Oct 15, 2014, 10:13 PM
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Love it. Nice work.

Originally Posted by ZTEX
Oct 16, 2014, 02:56 AM
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Velko Velkov's Avatar
Originally Posted by ZTEX
Here is how good is only by the wings control. Tails fixed!
Whole wings pitching / differential pitching

Only by the wing tips controll .fixed tail!

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