HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 04, 2005, 05:07 AM
Registered User
Dresden, Germany, europe, planet earth
Joined Aug 2003
800 Posts
JJ1,

it dosn't matter if you add a little more distance. With this close prop setup the aft prop have to cross the turbulence of the front one.
What gives the best result is measuring rpm vs. current one each motor separate. You will find a setup where at a given amp load the props turn faster; with a bit luck even faster as alone. They help each other. But it is only a small step, and all is lost. Be careful with the aligning of the aft-prop pitch. Mine is about an half inch higher than at front, but this can change. It may depend on pitch-speed, overall power, torque, etc.
The 10A range may be okay; when all is fine, the current may go down a bit.

Hope this helps,
Kuni
Kuni is offline Find More Posts by Kuni
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 10, 2005, 05:46 PM
Registered User
Stefan.s's Avatar
Sweden
Joined Jun 2002
159 Posts
GWS Contra rotating

Hi there

Just saw this thread, funny ! I have made a gws contra rotating system that works great,its easy to make and funny to fly with. Very easy to hover.
I am going to make one with Apache outrunner also, this was just an experiment .


Stefan
Stefan.s is offline Find More Posts by Stefan.s
Reply With Quote
Old Nov 10, 2005, 09:15 PM
Fidler & twidler
empeabee's Avatar
Cranfield U.K.
Joined Mar 2004
4,060 Posts
Quote:
Originally Posted by Stefan.s
Hi there

Just saw this thread, funny ! I have made a gws contra rotating system that works great,its easy to make and funny to fly with. Very easy to hover.
I am going to make one with Apache outrunner also, this was just an experiment .


Stefan
Very neat and interesting.
Can you post props/rpm/current/thrust figures?
Mike
empeabee is offline Find More Posts by empeabee
Reply With Quote
Old Nov 10, 2005, 10:08 PM
Registered User
USA, CA, Huntington Beach
Joined Mar 2005
4 Posts
for a given disk area, thrust goes with power^3/2, so comparisons to a single prop should be done at an equal total power or thrust (don't expect twice the thrust from two motors)

you might do a little better than the single by sharing the power between both motors equally using two ESC, where you should recover the swirl energy from the slipstream.

has anybody hovered with a contra-rotating setup? does canceling the gyro and swirl terms change the handling?
jimccd is offline Find More Posts by jimccd
Reply With Quote
Old Nov 11, 2005, 02:50 AM
jj1
Registered User
jj1's Avatar
Finland
Joined Oct 2004
234 Posts
@stefan, nice work.
Btw where did u get those props?

-JJ
jj1 is offline Find More Posts by jj1
Reply With Quote
Old Nov 11, 2005, 03:41 AM
Registered User
Stefan.s's Avatar
Sweden
Joined Jun 2002
159 Posts
Thanks , i have not checked the motors thrust, amps yet. I think it is really strong and im going to test with a gyro on one motor to se if it will stop rotation. It is very stable but i think the motors dont goes exactly the same, i try with one more ESC and test with a gyro today. The props comes from Todd`s modells and are quite cheep, i bought 15 sets for $ 3.99 each.
I am also going to build a 8 propeller heli,a sort of draganflyer but very big and perhaps with countra rotating props.Any one out there who have some advice how to program the radio, i have a Multiplex mc 4000.

/Stefan
Stefan.s is offline Find More Posts by Stefan.s
Last edited by Stefan.s; Nov 11, 2005 at 07:28 AM.
Reply With Quote
Old Dec 22, 2005, 08:28 PM
Registered User
Airboatflyingshp's Avatar
B'ham UK
Joined Oct 2005
2,990 Posts
Has anyone built a contra prop using a single motor?

I ask this because Ive thought up an idea very simple for a second stage bolt on gearbox for any pimary motor/gearbox combo brushed or brushless given size and wt. constraints ie its easier/suits Med to large sized models/motors better.

The beauty is you can swap around the primary set up given common input shaft sizes and with some engineering skill or luck possibly even build in a slight differential in propeller speeds sould you require that variable. Theres also no worry about two controllers as you only ever need one .............Im testing the water so can anyone see any problems with the basic concept of using one larger and hopefully efficient motor to drive two contra props ??
Airboatflyingshp is offline Find More Posts by Airboatflyingshp
Reply With Quote
Old Dec 22, 2005, 08:58 PM
Registered User
gmitano's Avatar
Newport Beach, CA
Joined Apr 2003
128 Posts
Mimic Contra Heli Design?

Quote:
Originally Posted by Airboatflyingshp
Im testing the water so can anyone see any problems with the basic concept of using one larger and hopefully efficient motor to drive two contra props ??
Do you know if any of the contra helis that are becoming popular (Megatech, etc.) use one or two motors? If any use just one, they may yield some design ideas. - Gary
gmitano is offline Find More Posts by gmitano
Reply With Quote
Old Dec 22, 2005, 11:18 PM
Suspended Account
ni'ihau
Joined Nov 2003
3,241 Posts
In full scale the Griffon (Rollsroyce) motor does it with just a gearbox.
also there was a much smaller scale version used in a "target drone" aircraft
made by the company where Maryln Monroe worked... (and was subsequently discovered at)
jimbo
Eljimb0 is offline Find More Posts by Eljimb0
Reply With Quote  (Disabled)
Old Dec 22, 2005, 11:31 PM
CD-ROM Junkie
Art Newland's Avatar
United States, WA, Bellingham
Joined Apr 2001
13,962 Posts
I had a Blade-runner coaxial heli and it used to motors very much like the pictures in Stefan's post.
Art Newland is online now Find More Posts by Art Newland
Reply With Quote
Old Dec 23, 2005, 03:46 AM
Tech freak
Sundsvall Midlanda, Sweden
Joined Aug 2002
502 Posts
Still no good source for left rotating prop right?
I want to se some different alternatives.

/Wheaz
Wheazel is offline Find More Posts by Wheazel
Reply With Quote
Old Dec 23, 2005, 04:34 AM
Registered User
Stefan.s's Avatar
Sweden
Joined Jun 2002
159 Posts
Quote:
Originally Posted by Wheazel
Still no good source for left rotating prop right?
I want to se some different alternatives.

/Wheaz
Todd´s modells sells them, 10 x 4,7.

Finns säkert fler sorter ,läs igenom hela tråden så kanske du finner.

/Stefan
Stefan.s is offline Find More Posts by Stefan.s
Reply With Quote
Old Dec 23, 2005, 08:45 AM
Registered User
Airboatflyingshp's Avatar
B'ham UK
Joined Oct 2005
2,990 Posts
third time lucky...jimbo knows something

Quote:
Originally Posted by Eljimb0
In full scale the Griffon (Rollsroyce) motor does it with just a gearbox.
also there was a much smaller scale version used in a "target drone" aircraft
made by the company where Maryln Monroe worked... (and was subsequently discovered at)
jimbo
Ive been asking jim questions because of that motor
I bought the Supermarine Seagull 381 plan from Traplet 60" span and powered by a motor Im not familliar with and it looks like its no longer made a MEC Tubo10plus mated to a 3:1 graupner off set gearbox driving a .10x6 Grish Tornado..
I did some reseach and from the bits I picked up it sounds quite powerfull any suggestions???? Jim would yours do it???...because of the layout and being scale Im limmited to 3 bladed prop diameters of 10 possibly 11inch........unless I grow it all by 10-20% -72" span at the latter.


Im told that Im going to need to generate 300 watts plus.....NiMhs 8-12 cells no lipos.....so Im looking for motors that can deliver and doesn't cost a an arm and a leg and will fit in that tapering cowl There's another complication the space for the motor has to be no more than 3 1/2" front to back at original scale unless I start modifying the center section.
Airboatflyingshp is offline Find More Posts by Airboatflyingshp
Last edited by Airboatflyingshp; Dec 24, 2005 at 11:19 AM.
Reply With Quote
Old Dec 23, 2005, 01:49 PM
Suspended Account
ni'ihau
Joined Nov 2003
3,241 Posts
Airboatflyingship,
My motor does 500 watts with no noticeable heat buildup, I am not sure if all 500 watts are going towards forward motion... at least 100 seem to be going towards making noise. I like the idea of a bigger diameter prop. The master airscrew props I am using are suited for what I did.. 60" wings I think would like an 11" diameter pair... That is just intuition not engineering. The "colorado" stator that Kuni used (see superdittos site) would be good.

It is tough to find enough of them.
jimbo
Eljimb0 is offline Find More Posts by Eljimb0
Reply With Quote  (Disabled)
Old Dec 23, 2005, 06:55 PM
Registered User
Nobert's Avatar
Tucson Avra Valley, Arizona, United States
Joined Jul 2002
1,475 Posts
Wheaz
Jeff at eflightline has them(www.e-flightline.com).
Neal
Nobert is offline Find More Posts by Nobert
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Contra-rotating vs. single prop? stangrob Power Systems 7 Nov 21, 2006 09:44 PM
Contra-rotating prop units? Angelo Scale Kit/Scratch Built 2 Feb 19, 2005 07:35 PM
Counter-rotating prop? f2racer Electric Plane Talk 1 Sep 01, 2002 09:00 AM
Rotating Can Brushless Motors bps Electric Heli Talk 4 May 30, 2002 07:31 PM
contra rotating blades help........pls! Devilfreak Electric Heli Talk 5 May 13, 2002 02:01 AM