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Old Aug 18, 2012, 01:55 AM
Mad on everything Swash
Joined Jan 2012
77 Posts
Heah Mike

I like it, very nice !
Seems to work good with one spar,but 2 will work better.... have you had it flying ?

Please can you describe what is stopping or preventing a force feedback from your pivoting hub through the slider to servo arm ?
I found this to be a real problem in water and only a screw on the thrusting slider will prevent it occurring. It may work fine with air....don't know, certainly gave me a headache !
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Old Aug 18, 2012, 04:04 AM
Registered User
Auckland.
Joined Jun 2010
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Hi, Craig...

Well Kjell and i had a few emails about that and my way forward / solution to obtain maximum rated servo power can be seen in the attached video.

Variable Wiggle Drive - Lifter. (0 min 11 sec)


The test bed in the previous video is exactly that - 'A test bed' and apart from the VWD's everything else is for test / evaluation, and yes you are quite correct twins spars are the way to go hence my VWD tops are configured for that set-up. Also not shown are a pair of tops i have made set at 15' to give a flapping offset, the ones in the video are 0' offset.!

I am currently working on my first flying attempt using VWD's
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Old Aug 18, 2012, 06:43 AM
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Joined Apr 2007
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Originally Posted by Snetzka View Post
Welcome Craig...

Good to see somebody else interested in the wiggle drive.

If i have managed to get this reply edited correctly, here is a video of my test set-up using my Mk2 VWD's. They are in my test frame, the real frame is destined to be a worm drive off a planetary gearbox, not spur gears and belts as here.. I just had them lying around.

My test frame is just placed on top of a solder reel, on our glass coffee table, and as you can see the vibration is not so bad even at full speed (See towards the end of the video.)

As mentioned elsewhere my Mk3 versions use the same spar holders (i have got those just about right now) but a subtle change to the slider and inner top part gives me 5-6mm less height (Read more compact) so they will be my final (flying) versions when i have made them.

Hope you enjoy the video....

http://youtu.be/beMOE9MCIfo
i am really loving this guys i cant wait to see this fly mike and i think it will work great for steering control in this manner .
I take my hat of to you all great work
regards Brian
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Old Aug 18, 2012, 06:54 PM
Mad on everything Swash
Joined Jan 2012
77 Posts
Heah Mike

Thanks for the video, thats the way i had understood,
Without being critical Mike, its not gonna work for long like that ! I have already been here to solved this problem five yrs ago, hence the headache !
What will happen is a force with travel from the wing back through the pivoting hub to the control link to the slider to the Sevo horn and move the sevo'd position or even worse, bust the gears in the servo....loosing control of that wing !
The answer is to put the servo on a thread or leads crew, ball screw, which will prevent this force feedback from occurring .
To do that is not an easy task, gotta remove the pot from the servo and attach it to a positioning arm and connect the servo to the lead screw, I ended up putting the slider on a thread and just adj it statically to find optimal deflection for water.
I really like you and Kjells prototypes, yeah mine are a lil' more elaborate being billet but in my eyes it the same thing "an experiment" to pioneer the way forward...its all good stuff
I will share with you a pic of my previous swashplate fin drive sitting on top, it has ur VWD or what i call a swashplate in it, (SWASH / Wiggle, same thing) anyway it is over 5 yrs old dude, and done a lot of swimming ! Just imagine were i am today !
But that is ok its your thread and ur VWD development...hope its some help going forward !
regards Craig
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Old Aug 18, 2012, 09:04 PM
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Auckland.
Joined Jun 2010
90 Posts
Indeed Craig, I fully understand the situation you are describing, durring early prototyping i gutted two servos and modified them just for that purpose - leadscrew and scissor jack type implementation. Oh and another direction lead me down the 'rotating ramp' (a-la servo saver) type implementation.

The ornithopter's whole weight is suspended basically on the two wing flap servos (50% each) and amplified to a larger than the static amount on the down beat of the wing.

But my Guru (Kjell) kept me on the straight and narrow with the words - Ornithopters fly when they are light.! and also words echo from my engineering days - KISS.

I have a target weight of 550 grams all up, so you see every little saving helps... including using ABS as part of the VWD (3D printing).

If my next prototype (correct motor / gearbox combination) fails as you describe, i have the fix up my sleeve - so to speak, but i have great faith in my 14 gram - MG90S's...

Actually I remember the trouble of dealling with hydrodynamics when i raced tunnel hulls back in the UK with 10cc AMPS outboards. The pitch control on that 'ate' many expensive - high powered servos despite them all being well over spec'ed....

Craig - all input is welcome and we are all here to push forwards together, so I appreciate your input, as i do anybody's..... and I will now go and dust off the scissor jack raiser and ponder....

Mike..
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Old Aug 18, 2012, 09:51 PM
Mad on everything Swash
Joined Jan 2012
77 Posts
Heah Mike

I understand completely how weight is the underlying factor with an Orni, don't know if i have the spare time to get involved practically and start building ?
I also have some respect for the guru, he's been around a while ! I'm just not sure about the name wiggle, seems like ur trying to rename the swashplate, but heah if it floats you boat I'm ok with it ! I suppose the same could be said about swashdrive, so i suppose its me only being semantic, sorry.

The scissor lift sounds good and would only take half the turns using the same pitch, but still reaction will be slower than ur current method ! But the advantage in this method would move the screw perpendicular to the line of shaft rotation allow for more compact LIGHTER design !
I may just may have to get involve here (practically speaking), i think i just caught the Orni bug...bugger !
Craig...
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Old Aug 19, 2012, 12:22 AM
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australia
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beleave me Craig orni's are addictive my hobby i say wife says obsession hahahah started 6 or so years back
At one stage i was flying up to 6 or more hours a week even as much as 10 or more .As i work arvo's i could any how enjoy
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Old Aug 19, 2012, 09:40 AM
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just a question mike on vwd what will be the max up and down angle that you will be able to achievefrom 0 degrees each side
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Old Aug 19, 2012, 10:29 AM
Kjell Dahlberg
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In the beginning Mike was thinking to use 30+30 = 60 flapping angle. For mechanical reasons I reduced it to 25+25 = 50. In my Wiggle-drive, I am using 21+21 = 42.
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Old Aug 19, 2012, 02:34 PM
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Quote:
Originally Posted by KJELL View Post
In the beginning Mike was thinking to use 30+30 = 60 flapping angle. For mechanical reasons I reduced it to 25+25 = 50. In my Wiggle-drive, I am using 21+21 = 42.
Yep - As kjell rightly say's i now use 25+25 as my flapping angle in two different formats.
Head one gives me 25+25 about the horizontal axis, whilst head two gives me the 25+25 about a +15 axis (thats 40 up and 10 down about the horizontal axis). The offset being built into the head by drilling the two spar holes at the required angle.

The second is my prefered option due to the theoretical extra stability offered by the inbuilt dihedral.
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Old Aug 19, 2012, 02:40 PM
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Quote:
Originally Posted by KJELL View Post
In the beginning Mike was thinking to use 30+30 = 60 flapping angle. For mechanical reasons I reduced it to 25+25 = 50. In my Wiggle-drive, I am using 21+21 = 42.
That is one of the limitations of the Swash/Wobble plates drives they didn't like too much flapping amplitude but even 42 will be enough with some increasing of the flapping frequency .
Another problem that can't be solved completely by implementing variable flapping amplitude is the "Flapping angle - pitching angle dependance" which force the usage of very low flapping amplitudes in order to achieve proper pitching angles . Remember "Jharno Smeeths" machine it flap maximum with about 25-30 flapping amplitude.
Both mentioned problems above can be solved easily by adding condors and using of 4 wobble plates combined two by two in two "mechanical - phase shifting devices" like on the one ugly sketch that I already have posted in the past. The next reasonable question probably will be : If we add a conrods why to make this efforts of using wobble plates instead of simpler and contemporary cranks? My answer to this question is: Because I have found using of wobble plates is one easy way to create and control one "mechanical - phase shifting device"
I will re post the sketch for convenience. Sorry about the hand drawing
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Old Aug 19, 2012, 04:43 PM
Mad on everything Swash
Joined Jan 2012
77 Posts
Gday Seagull
I understand you completely with phase shifting....but think there might be some force feedback depicted in the drawing, but certainly a way to address pitching angle dependence. at first i thought the old law of physics how opposites attract or instead cancel, but i don't know about all the links ?

Really my stand point is from the hydro side of this devise, but i think absolutely relative... ironically its the same devise !

The way i read, is mike and kjell are using active wing twist, i would question the doubt of how well it would work for flight...certanly ideal for flight through water as the medium !

What i see as a real advantage would be the ability to vary pitching angle dependence and there has to be a solution out there ?

I have observed there is one really important law that requires a disipline when considering design of this mechanism. All constraints attached or working on the swashplate needs to have its line of symmetry fall through the origin of the swashplate, which in this case is the point were the centre line of pivoting hub axis falls through the centreline axis of the rotating shaft.
One might suggest this is the zero point transition from rotating to reciprocation or vise versa.
Once mass is constrained off the origin it will run out and cause excess vibration ! In an idea situation the wing centre of sym and twist should fall through this origin, or is this already widely known here ?
The one way to get around this is by having a equal and opposite force acting with it !
regards
craig
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Old Aug 20, 2012, 01:37 AM
Kjell Dahlberg
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Mallorca Spain
Joined Nov 2005
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In the beguinning Mike didnt know about the importanse to have the wiggle centre point in the proper position. After altering his design, now it is in the rignt position. In his video it is possible to see the good balance in his VWD.
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Old Aug 20, 2012, 05:49 PM
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Quote:
Originally Posted by Lil aus View Post
Gday Seagull
I understand you completely with phase shifting....but think there might be some force feedback depicted in the drawing, but certainly a way to address pitching angle dependence. at first i thought the old law of physics how opposites attract or instead cancel, but i don't know about all the links ?


-Hi Craig,
You are right about force feedback but in this case servo will have to fight against only the forces caused by reversing of the wing pitch on the end of up and down strokes which are relatively smaller than forces caused by wing flapping.During all other parts of the wings beating cycle the forces on both ends of servo horns are balanced.
I don't like conrods and ball links as well but I haven't found another way to solve this problem.



Really my stand point is from the hydro side of this devise, but i think absolutely relative... ironically its the same devise !

- Agree just combination of wobble and swash plates arranged in different ways.
The water is about 800 times thicker than air but still fluid.


The way i read, is mike and kjell are using active wing twist, i would question the doubt of how well it would work for flight...certanly ideal for flight through water as the medium !

-Here disagree. They use active pitching of whole wing thru the wings' base the twisting is lived on the wings elasticity, aerodynamic and inertial forces so it's passive.
This is an insect type of wing which is good for thrust generation and is common for all flying creatures in the low Reinold's numbers range .For efficient low energy demanding flight the bird type wings are better and more universal .Birds can hoover for a while too.

What i see as a real advantage would be the ability to vary pitching angle dependence and there has to be a solution out there ?

-Yes this important that's why I am trying to find some decisions.Next time will post another one.

I have observed there is one really important law that requires a disipline when considering design of this mechanism. All constraints attached or working on the swashplate needs to have its line of symmetry fall through the origin of the swashplate, which in this case is the point were the centre line of pivoting hub axis falls through the centreline axis of the rotating shaft.
One might suggest this is the zero point transition from rotating to reciprocation or vise versa.
Once mass is constrained off the origin it will run out and cause excess vibration ! In an idea situation the wing centre of sym and twist should fall through this origin, or is this already widely known here ?
The one way to get around this is by having a equal and opposite force acting with it !
regards
craig
Agree and I like your designs and especially the ways you use to prevent the free rotation of the swash plates .Kjell - Mike way cause a slight cyclical forward/backward motions of the spars.
Also supporting of swash/wobble heads' shafts on both ends is always better and especially in the VWD case where flapping generated forces act on shaft supporting bearings through very long arm.
I am maybe too critical about Mike-Kjell design but this is because I hope somehow to help them to improve it .I am very impressed from Mike-Kjell results to the moment as well.

Otto
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Old Aug 20, 2012, 07:52 PM
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Otto.

Interesting comment as it was only friday last week that Kjell and i shared an email / drawings about supporting the VWD from both the top and bottom, have you been reading my mail.?

From the begining we have talked about the multiplication of force transfered from the (long) wing spar, through the VWD and ending at the top mounting point (top bearing) in my prototype. That is reason behind my quest to shorten the height of the VWD above the mounting bearing. On the grounds of less height = less force multiplication.

The drive shafts i am using are hardened steel and for this prototype adequate (although weighty.!) and i do not know if it was visible in the video, but my mounting bearings area's were doubled up (3mm G/F) in an attempt to stop flexing of the base.

So many ideas, so little time.....

Mike...
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