Gemini Twirl

[rotorheid]

Hi Guys :)

The further adventures of the Twirl.

I thought I would make an even larger Twirl, it is such a versatile design and great flyer. I worked out that the best layout might be a twin motor, so after some scratching on paper I went ahead, It is still not proven, but there were interesting solutions to overcome on the way. I have to have a whole days clearing up now and get my other projects finished, so much to build!

http://www.rcgroups.com/forums/member.php?u=98579

regards Al(T)

[BragMan]

And rather neatly done, by the look of it. Your finger photo made me wince, been there, done that, bought the T-shirt and wore it out, as they say. ;)
Hope it's healing well.

PowerPoint output
There are some freeware (nagware?) PDF converters available - they work well enough in my experience - so much so that I bought one years back. It's called 'Jaws' PDF creator, and I bought the whole package with an editor, which was needed at the time and still comes in handy.

What one does after installing the software is use PowerPoint in the normal way, then click on 'File' then 'Print' and then select (in my case) 'Jaws PDF' as the printer, and it then creates a PDF file for you. Bingo! Then you can upload it.

The freeware ones do work, but some of them nag you to buy each time you use them. I can resist that, mind you! I'll try to look them up and report back, but I may take a while to get back.

I can't run up a copy of PowerPoint for you and see if it has any smart options - depends hugely on which version - since we switched to Star Office many years ago and then to Open Office (the free version) more recently. The latter includes export facilities from most of the modules. Worth a try, and free too.

Great model, can't wait to see the video!

All the best, Ben

[StephanB]

Hi Al,
yr. Gemini is beautifull. Thanks for sharing so far. Are there any news, maiden on the horizon?
Stephan

[rotorheid]

Hi Guys,
Weather was blowy but had two starts today, Will do small repairs and wait for calmer day. It is a real dragmaster! May shift up to 9x6 props for more thrust. Videos for your amusement,

http://media.putfile.com/Gemini-Twirl-1st-Flights

http://www.youtube.com/watch?v=qXKTtqMOwzo

[alfoot]

Hi Al,

Great to see her in the air - well done :) She looks really majestic in flight, and stable too.

Waiting for the next instalment.

Al

[David A Ramsey]

Man she really hangs on those props. A bit more power.

I really like your Gemini Twirl ... the shape, the framing ... NEAT!

[StephanB]

Yes, neat. More power and you have a winner.. :)
Stephan

[David A Ramsey]

Reminds me of an old fashioned Tinker-Toy Project. O brother Al, she's tempting. The kids in the neighborhood would love it.

[rotorheid]

Hi Guys :)

Thanks for the kind words, will try again tomorrow if Met ok, have re-propped @ 9x6, moved the two 1000mAh 3 cells forward and reglued the sprung joints. Overhauled the depron rotors, held them in the steam from boiling kettle for 30 secs or so, that takes out most of the creases and greased the bearings with some margarine, all high tech!

Aye Dave R, she reminds me of those sit and peddle wooden aeroplanes for wee bairns (kids) I'm having one of those when I get too old to drive! A two seater so I can take my wife shopping,

regards Al(T) :D

[JochenK]

Al (T9,

impressive appearance. Hope the 9x6 props will work for you,

Jochen

[rotorheid]

Hi Guys :)

Made a good test this morning, wind was only 5kt across the field, OAT +40c. I have to do so much manouvering with the goal posts in the way!
Any way nearly fully sorted now, c/g good enough and plenty of power too.

Vid for your enjoyment.

http://media.putfile.com/GeminiTwirl-test-II

http://uk.youtube.com/watch?v=dps6eMdnrQ8

regards
Al(T) :D

[David A Ramsey]

It's got that Flash Gordon look too. Al you are a true modeler!!!

You've gotta cut those goal posts down ..... unless you've been trying already. Tough to get a good cutting edge on those CF leading edges.

[StephanB]

Al,
fantastic! And filmed in "superautorotation"! :D I really like your contributions also for yr. sense of humour, whether there are poems or other small goodies. Thanks, mate.
Stephan

[David A Ramsey]

Al; Next time you're in New Jersey, how'bout stopping over and help me layout the Gemini fuselage on a 4' x 8' sheet of foam.

[alfoot]

Al,

Great achievement, and I bet Gerry Anderson would have loved to have such a machine in his shows :) . She looks nicely controllable against the cloudless sky and, from the movie, the rotors seem to be behaving themselves.

Are they still going left rotor CCW and right rotor CW?

Al



BTW, completely off topic so don't look if you only want to see autogyros, you can see the thing that goes with the music here :) :) :-

http://media.putfile.com/Fireball-XL5

[JochenK]

Al (F),

is this Harry Potter's new broomstick or is it Inter-Ex looming in the distance?

Jochen

[StephanB]

Jochen:
http://en.wikipedia.org/wiki/Fireball_XL5

Al(F):
very inter-exish! ;)

Al(T):
sorry for threadnapping..

Stephan :)

[rotorheid]

Hi Guys, :)

Many of us "Cold war kids" were brought up on Gerry Anderson's fantastic TV programs in the '60's. It was the way of the future and we were going to make it, once/if we grew up, I was 7yrs old when I was exposed to this glimpse of what could be, many of Anderson's visions became reality, long before we had the technology or understanding. Notice in the opening clip (shortcut below) how once XL5 has gone supersonic in the climb, it clears the atmosphere to a black space with clear stars, eons before Mr Lucas and Star Wars switched on to special effects. Never mind that the Hover scooters sounded like your mum's vacuum cleaner, this was real enough for us.

http://uk.youtube.com/watch?v=E-1AMrSzN40

Stephan, No worries mate. :)

Al(F), Rotors are left cw and right ccw. They spin up pretty fast with the thrust from props. :cool: fireball XL5 video.

Dave R, Yes I'm a big fan of Flash too, those huge rivets and control wheels in the rocket are great! Aye, some one might put a rope on their car and haul those goal posts down? :rolleyes:

If the Met is kind I will try for ROG tomorrow, will have to use large carpark if it is quiet. ;)

regards
Al(T)

[newgirlintown]

Hi Guys, :)

Many of us "Cold war kids" were brought up on Gerry Anderson's fantastic TV programs in the '60's. It was the way of the future and we were going to make it, once/if we grew up, I was 7yrs old when I was exposed to this glimpse of what could be, many of Anderson's visions became reality, long before we had the technology or understanding. Notice in the opening clip (shortcut below) how once XL5 has gone supersonic in the climb, it clears the atmosphere to a black space with clear stars, eons before Mr Lucas and Star Wars switched on to special effects. Never mind that the Hover scooters sounded like your mum's vacuum cleaner, this was real enough for us.

http://uk.youtube.com/watch?v=E-1AMrSzN40

Stephan, No worries mate. :)

Al(F), Rotors are left cw and right ccw. They spin up pretty fast with the thrust from props. :cool: fireball XL5 video.

Dave R, Yes I'm a big fan of Flash too, those huge rivets and control wheels in the rocket are great! Aye, some one might put a rope on their car and haul those goal posts down? :rolleyes:

If the Met is kind I will try for ROG tomorrow, will have to use large carpark if it is quiet. ;)

regards
Al(T) What a real blast from the past!

[alfoot]

Al,

That's a great still from the movie, but come on - you've got the propellers in sync but you must try harder with the rotors :D .

I hope that it goes well for the ROG trials, looking forward to more great movies.

Keep 'em spinning,

Al

[rotorheid]

Hi Guys, :)

The Rise off Ground test went ok,
I made an error by not checking over the Gemini Twirl after the "heavy" landing, :o . Must have over stressed the hub on left hand side, I had to land out as I was having control response troubles :eek: !
All's well that ends well, got her back and very little damage, so we live to fly another day. Two vids for your pleasure.
regards

Al(T) :D

http://www.youtube.com/watch?v=ZIZZqHOqi0s

http://www.youtube.com/watch?v=OfBCjdehNbY

[alfoot]

Al,

The ROG take-offs look great, and I'm glad that the damage was not too bad. There are a lot of us on here enjoying your progress. Did you discover the cause of the control problems?

Al

[rotorheid]

Hi Al, :)

Glad you guys are enjoying this stuff, I learn a lot from others here on the forums. I get a lot of fun out of this too, makes my time here a little easier till I get back to the world.

Control response problems; I'll put down to a shoddy preflight check, after the arrival (wasn't a real landing) I must have weakened the phospher bronze bearing in the Left hub, it must have let go the bond to the hub after the second take off and I had a fully gimballed head on the left side :eek:

It was pitching back causing me to run out of left roll authority. Before I cut power, to emergency land, on the roof of our sports hall, I had full left rudder and trim. It didn't go with a bang, but snuck up on me as if the range of disc tilt was slowly getting greater.
On inspection after retrieving her, by very big ladder, I had 2 inch all round of free play! If it had tilted inboard I would have lost the blades.

Lesson one. Are all the bits of the aeroplane stuck together correctly?
I saw it in the video that the left rotor was not as free as the right during taxy test.
I will do some proper repairs over the next couple of days.
Cheers mates,

regards Al(T) :D

[David A Ramsey]

Well just hold up on the repairs for a bit OK? You've got Fans to look after!

I'd like to copy this Gemini Twirl thing of your's if you ain't got no problem with that. At least make up a drawing. You got a nifty photo with a ruller/scale type thingie shown. Now if your OS coffee mug has a diameter of 81mm, what is the length of that thare ruller? I get somewhere around 800mm. OH, and what's the Watts of them there blue thingies holden them thare props?

[rotorheid]

Hi Dave (R) :)

You are most welcome to build a GeminiTwirl and copy/use any of my stuff/ideas. I get my inspiration from others. It is just an adaptation of the Original Twirl, from the other Al. So I guess everyone should get the "mexican wave". But thanks anyway mate :o, glad you enjoy it.

Here are the pics with a 36 inch tape measure stuck on a balsa sheet.The image will be slightly distorted, but if you go in a "ish" way, I'm sure it will fly, if you stick to the empirical angles of the Twirl. 5-7 degrees down thrust, both motors have 3 degrees ish right thrust. Mast angle 7-10 degrees. tailplane is neutral and the datum. C/G, whole thing hangs level by horizontal tubes. Blades 3mm depron with carbon Le reinforced with doculam foil/film/parcel tape. set @ -7/-10 degrees. AUW 700-800g.

Motors turn 9x6 @ 6000 rpm for 12.5 A and 11 volts, ish. so thats close to 137-140 W a side, say 270 Watts on a good day. Motors weigh 58g. and are 28.8mm diameter by 29mm long 1060 Kv. < 80% efficient. I run two 16A ESC with both bec in operation, never flown it long enough to worry about what happens as the packs voltages diminish. I have 5 mins set on my timer untill I get some good recharge information.The remaining info is in my blog, or PM me if you need more gen.
I am building a new set of blades now, easier to do than glue in hub bearings again.
Good luck if you make one, would like to see some pics sometime.
regards
Al(T) :D

EPS Bloody good guess on ruler. it is 750mm.

[JochenK]

Al (T),

be careful with those motors. If you're using them at 6000 rpms full speed, you've got an efficiency of roughly 50%. That means you're using half of your power input to heat them up.

Jochen

[rotorheid]

Jochen,
Thanks mate, I didn't know that :eek: Heat is the last thing they will need as they never go below 35c with the ambient. I got my figures from my mate Wolf's power gizmo, same prop and motor but on a 2100mAh 3 cell lipo, I am using a 1000mAh 3 cell per motor, hopefuly it is not too bad?
Any way I fly it with minimum power from now on.
regards
Al(T)

[JochenK]

Al (T),

the motors are mounted uncovered and directly in the prop wash, getting optimal cooling. Just take your favourite finger and check the temperature after a flght.

Jochen

[David A Ramsey]

750 on the first scale??? I first got 749mm based on the OS coffee mug. I get my inspiration from the same source. Just once I like to have an original idea but have tremendous pleasure to see the effort of others.
Usually a twinn anything means doubling the cost of the most expensive items. Here in the US, www.bphobbies.com has some small CD ROM brushless motors selling for US$12.50 each. I think Randalll1959 used them in his Slo G Pico F. Hopefull a pair of these were made for the Gemini Twirl.

Thanks Al, for taking the time to provide all the info. May take awile to build, but will be fun to draw up and plan out. Hope to capture the flavor of your's.

[rotorheid]

Jochen,
Aye, I will try that, usually with inside of my wrist for the battery pack temp, better not abuse my fingers anymore for a bit, hahaha!

Dave (R),
Have a look at these guys in HK for keen prices, they only deal with paypal and delivery can be somewhat protracted. They get good recomendations in RC G Vendors. We have a team order, in progress, so hopefuly it will arrive here without too much trouble.

https://www.unitedhobbies.com

One set of blades done, the other tomorrow.
regards
Al(T)

[JochenK]

Al (T),

after having a look at some data from a drive calculator program, I think it may be worth a try to use 10x3.8 props instead of the 9x6s. I'd estimate the speed of the 10x3.8s to be about 500 rpms higher, which means less current draw. At the same time the static thrust will go up and the optimal flying speed for the prop will go down from roughly 15 m/s to about 10 m/s.

Jochen

[rotorheid]

Hi Jochen, :)

Thanks for taking the time and effort to do some research, I appreciate it.
Yes I have plenty of 10x4.7 and 9x3.8 props and only one well used 10x3.8. I am home in 4 weeks for vacation, I will pick some up then. I just have to go easy on the gas. What program do you use for motor calculation?

Al(T) :D

eps; What do you think about cliping down a 9x6 to 8x6 ?

[JochenK]

Al (T),

it's a German program called 'Elektroantrieb' written by Wilhelm Geck:
http://www.geck-elektroantrieb.de

I think instead of decreasing the diameter and keeping the pitch constant, you should increase the diameter and lower the pitch. A 6" pitch is far to fast for a plane like the Gemini Trirl. 'Elektroantrieb' tells me that even a 10x4.7 APC SlowFly prop would be better than a 9x6, though the reduction in input power is not as good as with a 10x3.8. Worth a try anyway.

Jochen

[David A Ramsey]

Al; Appreciate the link & rotor photos.

[rotorheid]

Jochen,
Thanks, I'll give it a whizz with the 10x4.7 later today, I do it without video as it makes me work too hard flying and video at the same time. (too hot with the camera hat)
The 'Elektroantrieb' program looks very comprehensive, I try it for the 30 day free period and see how it goes.
Cheers mate,
regards
Al(T)

Later that day... :(

Not to good I'm afraid, big left roll all the time, pushed the front in a bit on landing, so I have some work to do, will check the rotors and motors later, down one 10x4.7 as I wacked a blade off on the last one....rat's poop!
Tomorrow is another week for me so have to get up at stupid o'clock in the morning for the work thing, more broken aeroplanes to fix.
Have a good weekend lads, hope all your troubles have rotors.
regards
Al(T) :D

[alfoot]

Al,

There is also a free motor performance calculator at the following link:-

http://www.drivecalc.de/

I don't know if it covers your motors but I've found it reasonably useful.

Good luck with the bigger props.

Cheers,

Al

[David A Ramsey]

Later that day... :(

Not to good I'm afraid, big left roll all the time,
Al(T) :D

Is this the prop-wash effect on the rotors I've read about? From you, Ari and others.

Real pain when work gets in the way of the fun stuff!

[rotorheid]

Dave (R), :)

Have to think about that one, hmmm....could be as it will be intensified by,
a) Propwash very close to rotor inflow.
b) Counter rotating rotors but not counter rotating props.
c) Murphy's law.

I have been changing the props up an inch in diameter too.

Will sleep on it.
regards
AlT) :D

[StephanB]

Hi,
drivecalc is very helpfull. Jochen, give it a try.

Al (T),
good luck with yr. next steps, you will succeed, no doubt.. :)

Stephan

[JochenK]

Al (T),

if you have problems with 'Elektroantrieb', don't hesitate to ask me.


David, Al (T),

I don't think this is prop wash, I think it's simple motor torque. Al, do you know varioPROP (http://www.varioprop.de/home_e/varioprop_e/varioprop_e.html)? They make pitch-adjustable props and have got 10.4" cw and ccw blades. The hubs are a bit expensive, but the blades are o.k. And you can just replace a single blade.

Jochen

[StephanB]

Propellerheid,


a) Propwash very close to rotor inflow.
b) Counter rotating rotors but not counter rotating props.
c) Murphy's law.


This should help against b): http://www.pyreneesmodeles.fr/catalog/product_info.php?cPath=55_56&products_id=2154
These 10x4,5 props are available in cw and ccw.

Found here: http://www.rcgroups.com/forums/showthread.php?t=716870&page=2 (post22).

Stephan :)

[rotorheid]

Hi Stephan, :)

Thanks for the information, that will be the best solution to have normal and reversed rotation props on either motor. Meanwhile I will remake the front to include new motor mounts that are aligned on a transverse plywood beam, this will give me a new Datum for motor offset, that can be adjusted more acurately. Also this makes the whole autogyro more rigid with respect to the motors and rotors alignement.
I'm just back from work so will get cracking on this modification after I have some tea, after all it's past 4 'o clock, and everything stops for tea.

Cheers mate,
regards,
Al(T)

[David A Ramsey]

I see Dr. Al has opened up the patient. Another photo, and it's a big one, for my file. Thanks.

[rotorheid]

Hi Guys, :)
Some pretty drastic surgery carried out, :eek:
New motor mounts in progress, should be ready for tomorrow, hopefuly.
Some scary pics for fun.
regards
Al(T) :D

[rotorheid]

Hi Guys, :)

Weather was far too nice this evening NOT to fly, so I only got a little bit further with Gemini Twirl's repairs.
See pics for realigned motors. A wee bit more downthrust and both motors have 2 deg right thrust.
See links for this evenings flying, very busy car park, walking man and fittness bloke just came barreling through, sort of fitted in with music though, so left them in.
For your entertainment.
regards
Al(T)

http://uk.youtube.com/watch?v=U6bvzmoc0yA

http://media.putfile.com/Sunset-flying

[David A Ramsey]

Nice!

[rotorheid]

Hi guys, :)

All major mods done,
increased mast angle to reduce nose up attitude,
increased dihedral, hopefully to increase stability.
Will carry out a :cool: "Jochen" tethered anti torque test before I fly again with those props and see the results.
regards
Al(T) :D

[rotorheid]

Hi Guys, :)

I got the test to check my motor side thrust done tonight, looks to be OK!
Thanks Jochen, good idea mate.
So If weather ok tomorrow after work I'll give her a go, all those mods at once will make her new beastie! :eek:

http://media.putfile.com/Torque-test

http://uk.youtube.com/watch?v=uNFDJeEx2xU

Cheers mates,
regards
Al(T) :D

[leadfeather]

Looks really good mate, good luck! :)

Those first flights are always exciting. Trying to fly while hunting for the trim buttons is always good for an increase in heart rate! ;) :D

[JochenK]

Al (T),

glad to have helped. Now, if she's still leaning to the left, you can safely assume that it's due the torque of those 10" props turning in the same direction.

Jochen

[rotorheid]

Hi Guys, :)

Well the forecast for today is ok,
Thursday
Clear. High: 114° F. / 46° C. Wind NE 8 mph. / 14 km/h.
Humidity: 36%
Dew Point: 77 °F / 25 °C
Wind: 7 mph / 11 km/h / from the SW
Wind Gust: -
Pressure: 29.49 in / 998 hPa
Visibility: 3.0 miles / 5.0 kilometers

So I,m off out for a try with the modified Gemini, report and video to follow.
They do say it's "mad dogs and Englishmen" that go out in the midday sun,
I should be ok as a Scotsman and it's just after 10 o'clock :rolleyes:
regards,Al(T) :D

[StephanB]

114° F. / 46° C. :eek:
Good luck for your maiden. :)
Stephan

[rotorheid]

Hi Stephan, :)

Aye it was very sticky, I am soaked with condensate, my radio might get rusty?
Test flight went very well, far more stability, no uncontrollable roll to left, thanks to Jochen's idea :) Fluffed the landing again, need to keep power on untill the round out/flare.
Just uploading video now so it will be an hour before posting, I'm off for a cuppa and a shower.
cheers mates,
regards Al. :D :D

[rotorheid]

Hi guys, :)

Sorry for the delay in uploading this "Cassic" video, the sattelite must have had a long lunch break....... anyway, for your entertainment.


http://media.putfile.com/Gemini-Twirl-1st-Modified

http://uk.youtube.com/watch?v=CFN60yo6BHE

I made a naff landing, power to low and flaired too soon, :o
(Could do better 3/10 see me later!) ;)

regards
Al(T) :D

[David A Ramsey]

Now that's a video worth hearing! Finally, some good music!!!

With the sun setting amidst a lightly clouded blue sky, I like backing my Van up to the flight line, open up the back doors to get full volume from the speakers playing "Out of Africa", Tract 1 & 7 in repeat ... and fly.

[leadfeather]

Nice flight and video Al! She looks smooth and graceful in the air. :)

My bare bones smaller gyro is really hard to keep orientated. With your larger full fuse design, it looks like you can actuallly tell which way it is pointed pretty easily. ;)

[rotorheid]

Hi Dave (R) :)
Glad you like the classical music, but there's some great Rock, punk, reggae and all sorts out there that fits the scene too. I like the thought of flying to music from the van/car, one day, in the real world maybe.

Hi Dan :)
I did go to half speed during editing, but only from the turn onto finals till the end, I wanted to show the approach, warts and all, also it made the music easier to fit in, hehe. The remainder is copied at 1/1 speed. I like colour on my rotors for the smaller gyro's, easier to see and not lose the orientation.
cheers mates
regards
Al :D

[StephanB]

Now that's a video worth hearing! Finally, some good music!!! ()

David,
if you like classic music, try this. You should like it.
http://www.rcgroups.com/forums/showthread.php?t=636806#post6855650

Videoheid,
you really have a beauty of an autogyro there, nice video. :)

Stephan :)

[JochenK]

Al (T),

well done, mate.

Jochen

[rotorheid]

Hi Guys, :)
I flew the Gemini Twirl this evening and had my mate Rab video it for me.
There was only a zephyr of wind, so to get my landing sorted had to make long approaches, over the wire, over the lights and past the goal posts. I nearly slotted my camera man as he was right behind me! :eek: Still it's the closest airborne video I've ever seen. ;)
Gentlemen, for your entertainment.
regards

Al(T) :D

http://media.putfile.com/gemini-Twirl-landing

http://uk.youtube.com/watch?v=p2H10Ok7chw

[alfoot]

Hi Al,

Great movie :D I'm glad that "mindmaheid" did!!!

She looks nicely sorted now, perhaps still a bit of rotor speed asymmetry from the movie?

It will be interesting to see if she will do steep, high power approaches (starting up high first, of course.......)

Al

[rotorheid]

Hi Al,

I don't get that speed disymetry on my video, I got a 60 hz vdu and I'm on 110V over here.....must be the UK's 50hz power system.... ;) haha, yes it seems that they are rotating close to a video frequency in image capture, one seems to be still and the other just speeds up or slows down a wee bit, must have been when I glued up the hub, had the jig slack on some blades.
Cheers mate
Al(T) :D

[JochenK]

Al (T),

this is the first time you could see what a big bird she is. And it's nice to get some good close-ups that let you see all the details.

Jochen

[David A Ramsey]

David,
if you like classic music...

Impressive and delightful. Thanks

[David A Ramsey]

Gentlemen, for your entertainment.


Well move over Cecil B. DeMille! That was a goose bumper!

[rotorheid]

Hi Guys, :)

A different landing.
During the last flight of my GT earlier this morning she became progressively more unstable, I decided to throttle down and land immeadiatly. On the turn to finals she was handling like a burst water bed in the fast lane.
There was a rotor strike, one blade came off and she just came verticaly down for a perfect mains only impact on to the pavement! Ouch! Damage was light considering the jarring she got.
I found the R/H mast some 2" out of it's carbon holder, but due to the "dihedral" angle it hadn't come straight out, eventualy this caused the two discs to merge and wallop off the one blade on the L/H side.
Possibly the stability loss was due to the extra leverage the now taller rotor, put on the restraining system (kite string) and during flight manouveriing, it developed into a phugoid wobble that my opposable thumb skills couldn't match.
It is repairable, but I think I will re-build her as there are certain areas for improvement... GT mkII to come later.
Cheers mates,
regards.
Al(T) :D

[David A Ramsey]

The certification process on your Gemini Twirl is taking a toll.

[rotorheid]

Hi Dave (R), :)

Yes it's a bit of uphill learning, but great fun. Once you get all the bugs out of it and becomes more predictable you can relax more. Still if everything was too easy it would be very boring I think. I may go down a few % in size with the next one to reduce weight and use only one power source, I was getting strange recharge rates. The battery that I connected first seemed to be supplying the motor and the servos, like a latched in supply, the other, just the motor. If I go that way again I will ensure that I alternate the first connection, maybe some one has experience of this?
regards
Al(T) :D

[rchopper56]

Al(T)

I have several 30 size electric coaxial models, all scratch built in an attempt to come up with alternate yaw controls and hopefully resolve the outdoor forward flight issue. They range from tilting vertical fins to full cycle control.

One of them uses two 05 size electric motors. I had a similar problem to what your having. I resolved it by installing a stand alone BEC and installing one battery set. The positive supply to the both speed controllers are disconnected. At first I tried disconnecting the positive from just one of them, the ESC built in BEC could not handel the current.

I think a solution of a seperate stand alone BEC may solve your battery issues for you will only need one battery pack.

Gene

[rotorheid]

Gene, :)

Thanks mate, that makes sense to me, I never thought of the stand alone BEC :rolleyes:
1. Do you have : battery pack > BEC> two esc > two motors, with the BEC lead to RX and servo's ?
2. Can you point me to a supplier please, I will search any way, but a brand name or secifications would certainly help, thanks again.
regards
Al(T) :D

eps, Would be interested in seeing your scratch built projects if you can spare the time to post some pics, thanks.

[JochenK]

Al (T),

there are some ESCs with BEC that will use both BECs if you connect them to the battery at the same time, with a V-connection, for instance. Others won't work in parallel at all, unless you put a diode each between the ESCs and the point were you connect them together. If you want to use diodes, take Schottky diodes with a low voltage drop.

Jochen

[rchopper56]

Al(T)

Do a search for Ultimate BEC. The 5 to 35VDC should do fine. <http://www.hobby-lobby.com/ubec.htm>

Yes; one battery pack, one Ultimate BEC, two ESC's - Castle Phoenix 45's , two HiMax HA2825 brushless motors, and the two ESC's and BEC are powered by the battery and the BEC output pluged into the battery slot of the receiver but could be pluged into any channel if using a y-harness.

As far as scratch built projects go, I very seldom post unless the project is debugged. I am more of a builder then I am a flyer or writer. I learned a long time ago not to publish for I was plumented with questions from an artical in the early 70's. I would rather spend my time building.

I have thought about posting, but if I did, it would be in the dual rotor section.

Jochen, It never occured to me to use diodes and I was unaware that Schotty diodes had a low enough voltage drop and still leave enough voltage to power the receiver and servos.

Gene

[David A Ramsey]

Al; Have decided on using 2 HC2812-0850 motors and 2 Castle Phoenix 25 ESCs:

http://www.maxxprod.com/pdf/HC2812-xxxx.pdf

Single battery will be 3S, 2100mAh @ 20C.

Y-connectors for ESC battery and RX connection.

Will be adding +2 degrees to stab leading edge.

Can't see why you would need a seperate BEC for only two servos.

Note: Castle does not recommend Thunderbird ESCs for twin motor applications.

[rchopper56]

David,
The BEC onboard voltage regulators fight each other if connected in parrallel and will fail if no BEC is used.
Gene

[David A Ramsey]

David,
The BEC onboard voltage regulators fight each other if connected in parallel and will fail if no BEC is used.
Gene

Thanks Gene;
I've wondered about that. I Just read some Castle info on using 2 motors and ESCs. Castle does not recommend their Thunderbird controllers for 2 motor applications, but to use their Pheonix line without disabling any RX wiring for BEC operation.

http://www.castlecreations.com/media/castle_scribe_archives/Castle%20Scribe%20CE-03-Mar2006.pdf

Any thoughts on that Gene, based on your Pheonix 45s?

[rchopper56]

David,

All I can say is that I have had to send back to Castle for repair at least three Phnonix 45's. At over $100 each, it was a very expensive lesson. Your comment at to not having to disable the Pheonic line makes me question the onboard BEC current capability. I do know that most voltage regulators cannot be used in parallel to increace current capability. This info comes from National handbooks.

Gene

[rchopper56]

David,

Just read some of Castle info on paralleling Phoenixs and that has not been my experience with them. My ESC's were not purchased all at the same time and that may have been why I burned out so many. I also burned out several Griffen 55H's before I learned my lesson. It is my opinion that a stand alone BEC is the better solution.

Gene

[David A Ramsey]

Fair enough Gene. Your hands on experience means a lot. Even so I think I'll press Castle on the subject. Appreciate your info on additional BEC as a solution.

[David A Ramsey]

David,

Just read some of Castle info on paralleling Phoenixs and that has not been my experience with them. My ESC's were not purchased all at the same time and that may have been why I burned out so many. I also burned out several Griffen 55H's before I learned my lesson. It is my opinion that a stand alone BEC is the better solution.

Gene

Well at least you know what I read. Thanks again.

[JochenK]

Gene,

I just had a look at the data sheet of a 3 A Schottky diode (first one I found) and the manufacturer specified a forward voltage value 0f 0.3 V a 1 A current. No higher values given.

I definitely know that Schulze ESCs with BEC can be operated in parallel with both BECs providing their full current, because I talked to Schulze about this kind of use. The only provision is, that the BECs already have to be connected in parallel when you supply power to the ESCs, and that the power to the ESCs has to be applied at the same time.

Jochen

[David A Ramsey]

Quote from previously posted Castle link:
"The absolute most important thing to remember is to run ALL of the controllers
off a single battery pack, no matter how many motors are in the setup."

[rchopper56]

David and Jochen,

You each have offered alternative solutions to mine as to how to solve controlling multi motors using a single battery source. I hope all of this encourages Al(T) to keep the Gemini Twirl a twin motor design.

Gene

[rotorheid]

Gene,
Aye mate, she will be the twin. thanks for all the good gen guys, that has been very enlightning. Just need to make up some Y power leads now and give it a whizz.
regards,
Al(T)

[rotorheid]

Dave (R),
Re your post #73, I think that proposed set up will do admirably, those are quite perky motors. One question,
1. Are you changing the tailplane/horizontal stab incidence to fly a more nose down attitude?
regards,
Al(T)

[JochenK]

Al (T),

there's another possibility of connecting two ESCs to two batteries that will work as well as Y cables. Just make a connection - 0.5 mm² wire will suffice - that will put the two ESC connectors in parallel. If you plug in one ESC to its battery, the other ESC will be powered up, too. Then plug in the other ESC and make the real power-carrying connection. When the two motors are running, each will draw its main current from the respective battery, the interconnection serving as an 'equalizer' for the batteries. This may save you lenghty power leads.

Jochen

[David A Ramsey]

Dave (R),
Re your post #73, I think that proposed set up will do admirably, those are quite perky motors. One question,
1. Are you changing the tailplane/horizontal stab incidence to fly a more nose down attitude?
regards,
Al(T)

I feel that +2 degrees at the stab leading edge would help the nose down attitude at increased flying speeds.

I think I got a bit pricy on the motor/ESC combo. Good to know you think it will work.

Gemini Twirl has to be a twin. Darn thing has character!

[XE521]

@ Al(T)

Hi Laddie,

I've notice a glaring discrepancy on your Geminitwirl. It concerns the duster located on the tail, the whyte and reid croces a nay reit mon. Here's me thinking you were The Flying Scotsman, you're letting the Clans down. :( They should be as shown below. Please have them corrected and submit the result to the Lord Lyon King of Arms before your next video. :D

Regards. Karl.

[rotorheid]

Karl, Michty me! :)

Aye mannie, yer richt enuff mun!
Whit a scunner! Ah wis jist thinking ah'd done nae bad wi yon arial hurlie, like ye ken!
Ah'm awa to skite ma heid aff the wa noo! It gies ye the boke! Ah'm richt gled ah'm soon gang hame fur a wee brake!
Here's yon proper Flying Scotsman fur yie tae hae a keek at, so it is. :eek:

Cheeriebyeranoo!

Aye Al :D

[David A Ramsey]

Hello Al;

I made some head way, but work has interrupted further progress till the end of September.
I changed the truss so it's raked forward from the top cross rod by 20 degrees. The rotor masts have a rearward 10 degree tilt. Was wondering where your balance point was? How does yours hang relative to the truss?

[rotorheid]

Hi Dave, :) :cool:

As the weans say at home, "Man that's pure dead brilliant!" looking really good mate. :cool: I like your longer and more angled drag brace, that will give more support than mine. Have you got anything, as well as the depron nacelle to tie the motor mounts to the truss? I had a 1/16 ply side plate.
I balanced her , without rotors, on the horizontal part of the truss, just get everything on apart from the battery/s and lift her by your finger tips under the main spar, mid span, or hold by the top of the rotor shafts about 2-5 degrees nose down. I am impressed with that build Dave, love the cabin windows being cut out. What size did you go for in the end? I have been real busy with other stuff and maxed out at work, so I know how you can't throw yourself into the stuff you want to get on with. I bet she will be a looker when finished, have you thought of a colour scheme/ theme yet?
regards
Al(T) :D

[David A Ramsey]

As I can't get 3mm Depron that actually measures 3mm, not 2.5 or 2.75, I made the whole airframe from 6mm. Will still make the rotor blades from covered 3mm Depron and 3mm carbon rod.
Wasn't too sure about Depron nacelles. Photo shows section. The nacelle is notched to fit over the 6mm carbon rod cross point and glued on with a mixture of laminating epoxy and micro ballons. The rear section of the nacelle is glued with CA. It's feels quite sturdy. The carbon cross rod between the fuse and nacelle adds to rigidity. Motor mount is 3mm lite ply.
Except for lengthening the nose about an inch, she's built to your dimensions.

As of now, with the battery in front and against the truss bulkhead, the rotor masts are verticle when suspended by the cross carbon tube. Thanks for your hang angle. Without top and bottom 3mm sheeting and only the motors attached, I've got about 2 degrees nose down.

Not sure about livery yet. Perhaps leave fuse white with big window up front, red nacelles, white stab, red fins and yellow and red striped rudders. Rotor blades red. Hummm, what airline? Was thinking Al-air.

Thanks Al.

[rotorheid]

Hi Dave, :)

That is real neat building, I like your set up for the rudder with the ply reinforcement, carbon cross tube, also better than my after thought bracer, very inovative! How about "Twirl Air" or "Depron Air", mind you, the last one sounds like a '50's dance band, Dave and the Depron Aires? As my old boss used to say "Call me what you like, just don't call me late for dinner!" Colour scheme sounds good, plenty of contrast for good orientation. I must get some proper carbon when next home. Keep up the good work, cheers mate.
regards
Al(T) :D

[David A Ramsey]

Gemini Twirl is like a Siren ... Keeps calling out: "Please don't leave me ... finish me, please finish me!" Well OK, I'll just install 2 servos and that's it!

Logo will have a bit more flair, but Airline is:

Al-air

[David A Ramsey]

Took her out this morning (5 mph wind, or so). Thinking about all my autogyro first flight mishaps ... Damn I wish I had some antacid tablets. Well she was off the ground at 1/2 power and climbing with a strong tendency to bank left. Under power, rudder response offered good correction. Approach to landing was a challenge as the left bank was harder to correct with the reduced forward speed and airflow to keep the rudder and elevator active. Not a pretty landing. Second flight was the same, only this time I let her slow down too much and meet the ground with the left rotor tip and left gear at the same time and popped off a rotor blade. That carbon truss is incredably strong.

I think the left bank tendency is due to the right rotor working better than the left rotor. Both rotors are ball bearing supported. I did notice that the faster she flew, less right rudder was needed. I never got much over 3/4 power as the climb rate was incredible.

So first thing will be to switch rotors. CW on right side and CCW on left side.

I can't see motor torque as a problem as asymmetrical lift is more noticable without power ... As in rudder and elevator loose effectiveness to correct.

If I can get things balanced out and flying level, she will be fun to fly.

Flying weight is 900 grams - 32 ounces.

[JochenK]

David,

congratulations on your maiden flight. That's a nice looking gyro you've got there.

Your remarks about asymmetrical lift being strongest without power made me raise my eyebrows and caused some wrinkles to appear on my forehead. Very unusual. Please let us know about the results of the rotor switch.

Jochen

[David A Ramsey]

David,
Your remarks about asymmetrical lift being strongest without power
Jochen


Rather than "STRONGEST", I should have said - More noticeable.

You got some thoughts ??? while my epoxy cures.

My landings looked like Al's next to last video.

http://uk.youtube.com/watch?v=CFN60yo6BHE

[alfoot]

Hi David,

Nice Gemini :) and congratulations on the first flight.

This is my first post since Inter-Ex (still going through the backlog of work from the vacation) and, like Jochen, I'm scratching my head on the characteristics you describe.

I've found that small changes in the tilt angle of the rotors can result in unwanted yawing and rolling moments. As the effect dininished with speed, one reason might be that the rotors were both being tilted back by air loads to a more similar tilt angle when at the higher speeds?

It might be worth looking at this before changing the rotors around.

Al

[David A Ramsey]

Hi David,


I've found that small changes in the tilt angle of the rotors can result in unwanted yawing and rolling moments. As the effect dininished with speed, one reason might be that the rotors were both being tilted back by air loads to a more similar tilt angle when at the higher speeds?

It might be worth looking at this before changing the rotors around.

Al

Aaah, wish I could provide a video. Both rotors are mechanically the same rearward tilt, plus both rotors tilt inward by 5 degrees.
In your "TWIRL" Article you mentioned rotor placement on left or right for direction didn't seem to matter, so I'm going to try that first. If my bank angle now rolls to the right then I might assume I have a single rotor problem. Then again if I still have the left roll bank, then I should look at changing the right or left mast tilt ... Lots of choice.

Yesterday was very gusty so I did my range check and some taxing. I noticed then that the right rotor (CCW) always seemed to be turning faster, although holding the gyro into the wind showed both rotors, seemingly, turning the same speed.

Not sure how to judge or mechanically correct for different air loads. I don't feel this left bank effect diminishes with speed, but as speed builds up I have stronger rudder response to correct.

Thanks Al.

Epoxy is pretty well cured .....................

[JochenK]

David,

another thought. I've been looking through Al's photo gallery of his Gemini, and it looks as if the rear inside quadrants of both rotor disks might be influenced by prop wash. If, after exchanging both rotors, your gyro banks to the right, maybe you should try an autorotation to see if she's flying straight without any 'outside' interference.

Jochen

[StephanB]

David,
your Gemini Twirl looks beautiful.
I had a similar problem with Whopper, when one of the supporting struts came loose from the left rotormast. Angle of left rotor went up on the left side at higher loads, leading to a strange banking to the left "slip"-manoeuvre including nose-up. But, your pictures show outstanding building skills, so that i do not really believe in such a simple answer to your problem.
Stephan