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Old Mar 29, 2011, 11:11 AM
Fly lower!
aerolite's Avatar
West Texas
Joined Jan 2005
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Quote:
Originally Posted by Kimmo Kaukoranta View Post
A few interesting questions arise from this:
-If both parts of the motor rotate, is it an inrunner, outrunner or both?
.
It's a co-runner.........

aerolite
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Old Mar 29, 2011, 02:53 PM
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Sverige, Östergötlands Län, Linköping
Joined Mar 2011
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Kimmo thanks for explaining. I really like this idea and the potential it has. I wish I had more time for experiments. How did you do your slip rings? You should really patent this idea

Quote:
Originally Posted by Kimmo Kaukoranta View Post
Actually I have first built several single prop geared systems before the geared coaxial due to those benefits. The latest one, which also Janne Lappi was using in Lithuania weights <11g and provides 210g static with 7.4V 3.4A 25W input power using a 10" prop. I do not think there is an direct drive motor which can match that. If anyone is interested on that I can write a bit more on that in a separate thread when I have the time.
I agree. To give you a comparison. I made a 14g motor wound for high torque. With a 10 inch prop I got 182g of thrust at 3,96A from a 2s batt. Efficiency in terms of gram/watt was decent, but motor efficiency is as low as 38%. Regular F3P motors of the same weight, turning GWS 8x4.3, usually are in the range of 40-50% and 250g thrust. We tend to over prop for the preferable flying characteristics a large prop offers, so theoretically geared motors in F3P should be beneficial. Please share your experience.
…Although I must say that I don’t fancy the “kyosho minimum” sound a geared motor produces. Could belt drive be an option?


Donatas (aka DaveL). Good luck at Etoc! A symmetric with contra prop must be as optimal as it can be.

/David
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Old Mar 30, 2011, 01:50 AM
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Kimmo Kaukoranta's Avatar
Tampere, Finland
Joined Apr 2004
82 Posts
I do not think the idea is totally new. Although it is not very common, something like his has been used on some applications before. So I do not think it could be patented.

We did the slip rings from some brass tubing, soldered a wire inside and had some insulator pieces cut between the rings from fiberglass board using a CNC mill. The carbon brushess came from some brushed motors (speed 300 I think).

Yes a geared motor does have some noise, but the good thing is You get a better audible feedback when you increase or decrease the throttle. Our planes are getting lighter and lighter every year, the amount of power, and thus also the noise will decrease. The noise is not as bad in reality as it seems on some of the videos.

There are things that can be done to suppress the noise, like building a totally enclosed gearbox. I have not explored those options further (yet). With the open gearbox, it is better not to build any of those 45-degree depron pieces on the nose, those will amplify the noise a lot

Also the proper mesh of the gears, the modulus (size of the teeth) etc affect the amount of noise. The geard ratio and the RPM affect the base frequency, I try to stay away of very high ratios because the pitch of the noise becomes very annoying. Try a >10.000 kv motor on 2 cells in a 15:1 gearbox and you know what I mean

With a belt drive you would need a very small toothed belt to prevent it from slipping (that is actually available). Other problem is getting large enough reduction from one stage. But certainly it could be done.
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Old Mar 31, 2011, 08:04 PM
Eric Johnson
United States, NY, Northport
Joined Mar 2011
36 Posts
where can i purchase this setup?
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Old Apr 01, 2011, 01:34 AM
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Kimmo Kaukoranta's Avatar
Tampere, Finland
Joined Apr 2004
82 Posts
I can offer a few units for sale. I do not have them ready, but I can make them to order. Please email me at kimmo.kaukoranta@gmail.com for details.

My current way of making them is not really optimized for mass production, but requires quite a lot of manual work on my part. I was thinking I could also offer a kit if there is enough interest, that would leave most of the very time consuming steps like finishing and balancing the props to the builder. If someone is interested on a kit, please contact me privately and we will discuss the details.

Also if there is someone out there with the manufacturing capability and interest in actually productizing this system for bigger volumes, I'm all open to suggestions on co-operation. I would gladly have someone else producing them and I could concentrate on prototyping and developing it further. There are a few details that could be improved on a commercial version, mainly to reduce the time to make them.
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Old Apr 02, 2011, 07:43 AM
f5b-uk
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United Kingdom, Dorset
Joined May 2002
3,066 Posts
Painting mylar

A quick question about your mylar covering. Do you paint it first to have the paint on the inside?

Oh, and what paint are you using that sticks well to mylar?

Mike
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Old Apr 03, 2011, 03:26 AM
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Kimmo Kaukoranta's Avatar
Tampere, Finland
Joined Apr 2004
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I cover first, then paint. I used some cheap acrylic paints, nothing special and they seem to stick very well to mylar. The 5 micron mylar I'm using came from Freeflight supplies in the UK.
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Old Apr 03, 2011, 03:42 AM
f5b-uk
Mike Seale's Avatar
United Kingdom, Dorset
Joined May 2002
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Thank you. Looks like my next project is to make a mylar frame!

Mike
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Old Apr 16, 2011, 06:23 PM
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Basingstoke Roy's Avatar
United Kingdom, England, Basingstoke
Joined Oct 2005
450 Posts
Hi Mike

I thought you may like this photo I took, it's the machine Donatas was sporting at this years ETOC.

Cant help thinking that an contra with a gearbox is more complicated than needed.
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Old Apr 17, 2011, 03:00 PM
WBE
Las Vegas Circle Burners
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United States, NV, Henderson
Joined Aug 2005
592 Posts
Quote:
Originally Posted by Basingstoke Roy View Post
Cant help thinking that an contra with a gearbox is more complicated than needed.

There was a gentleman that used a fluid driven contra-prop on his f2b plane about 20 years ago. The second props sole purpose was to straighten the airflow over the airframe. The idea worked but, apparently, the extra effort in the form of a special machined hub, free spinning, left-hand prop wasn't worth the trouble. Other things that must be considered are the extra weight and power it extracted from the driven prop/drive train.

Driving the rear prop with thrust from the forward prop is a much simpler system, but it fell short. Kimmo's solution may seem more complicated than necessary but his approach, execution and operation are brilliant.
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Old Apr 19, 2011, 05:05 AM
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Kimmo Kaukoranta's Avatar
Tampere, Finland
Joined Apr 2004
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Co-runner video

Roy, I do not think the two motors + two gearboxes system is very complicated. And like I have explained earlier, I think the geared solution has some benefits on it's own. Like being able to swing a much bigger prop for the same weight as an direct drive outrunner, which in turn gives you better braking. But there are many ways of building a coaxial.

If you like simple solutions, here's a video of our "co-runner" system (thanks for the name aerolite). It does not get much simpler than this:
F3P Coaxial "co-runner" prototype (3 min 31 sec)


The system on the video is the first prototype. Since that we have built 2 more, but a bit lighter ones.
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Last edited by Kimmo Kaukoranta; Apr 19, 2011 at 05:13 AM.
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Old Apr 19, 2011, 05:17 AM
f5b-uk
Mike Seale's Avatar
United Kingdom, Dorset
Joined May 2002
3,066 Posts
Quote:
Originally Posted by Basingstoke Roy View Post
Cant help thinking that an contra with a gearbox is more complicated than needed.
For me and my flying skills, yes...the contra-rotating system is more complicated than needed. But at the very top level (and for anyone aspiring to that level) it could be the way to go. Not having to compensate for torque could be a real bonus and bigger props are always going to be better for slowing the down-lines.

Would be nice to see (hear!) one which uses helical gears to try and reduce that whine though.

Mike
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Old Apr 19, 2011, 12:39 PM
Eric Johnson
United States, NY, Northport
Joined Mar 2011
36 Posts
kimmo,
can u post a pick of the slip-ring co-runner setup?
eric
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Old Apr 23, 2011, 01:59 PM
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Kimmo Kaukoranta's Avatar
Tampere, Finland
Joined Apr 2004
82 Posts
Here's a few close ups on the second version of the co-runner (first version on the video). This is based on the Turnigy 2204-14T Axi copy.

If I were to build a third version, I would use a bit smaller and much higher kv motor. There is a built in 2:1 reduction in the system since both props are turning about half the motor RPM, so a motor normally designed for single 7-8" prop can easily swing a pair of 10" props with same current.
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Old Apr 25, 2011, 09:22 PM
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Oregon USA
Joined Aug 2010
165 Posts
Hi daveL322 thank you for the Donatas video ! HE IS SOOO AWESOME!!!
He bought my RcSuperhero.com plans and then I got to repay the favor and I bought his ARROW V3 PDF plans. I found you here because I was researching the micron films and came across you comments and WOW -was I happy to see Donatas flying!

Thank you RC friend I'm still trying to find the place that sells the micron film to cover the milled out 3mm foam planes _perhaps you can e-mail me at gregtanouslasering@yahoo.com GT thank you!
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