Rhilluk

Been trying for a while to get my head round how this would work. I'm wondering if he is using a differential gearbox similar to the one that drives a cars wheel and then taking this to the props and reversing one of the feeds to spin the other way.

Anyone actually know how its been done?

Velco

I have to say that it is a very interesting concept. I did some research my self some time ago and all I could find is this:

http://en.wikipedia.org/wiki/Planetary_gear

where the red part is where the rear prop is attached to and the front prop is on the yellow axle as usual. The central gear and the planetary gears should be of the same size to keep the rpm equal.

Here is something a bit more complex, and patent protected:

http://www.wikipatents.com/5795200.htm

and here you have the info about the manufacturer whose system Seba is flying:

http://www.f3a-e-factor.de/

From the photo where Seba is holding the plane and knowing the spinner size I have calculated that the props are size 19, while the pitch is probably size 12. What should be remembered is also that one of the props is a pusher prop and 19x12 pusher is not easy to find, probably only at F3A E Factor.

Barye

My Feedback: (27)

Himax makes contra-rotating motors.
http://www.maxxprod.com/mpi/mpi-266.html

Rhilluk

Hi There,

what I find interesting about the design is that it is all run off of one motor and equal torque is sent to both the propellors, if one comes under load the other will spin faster to equal the torque. Apparently when the plane was at standstill the propellers were freely spinning.

The only way I can see is that there is a form of differential gearing in there.

I drew up some plans on paper last night and I believe the concept would work. But the engineering involved in making it is beyond me.

Velco

Actually not. Contra rotating props are exclusively on one axle, when there are 2 axles, hence 2 motors, they are called counter rotating props as you can see here http://en.wikipedia.org/wiki/Contra-rotating_propellers

This system would require 2 ESC with 2 independent batteries

ssatoru

There are a few Miss Wind Pro with contra prop flying here and I had a chance to see them. Michael Ramel at E-Factor wrote an article in local magazine and he mentioned prop size is 22x18, swinging at around 6,000 rpm. That gear and prop is state of art, driven by single Hacker C50 motor. I guess gearbox uses planetary which Velco explained.

Sorry to point to other forum but I posted photos and more info here.
http://www.rcgroups.com/forums/showp...postcount=1133

Satoru

Rhilluk

This is the bit that interests me as just planetary gears would not do this. Its the torque distribution which most interests me.

Velco

One link I posted is not working so here is the one that hopefully is OK. It is US patent 5795200

ssatoru

I have no idea for gearbox design and arrangement. No, it is not simple planetary and should be more complex than the design Velco has posted. (it reduces rpm and rotates 2 props.)

The gearbox is not much larger than standard planetary. There are a few unit photos in below linked page. (texts in Japanese, local distributor's blog page.)
http://rctips.jp/archives/51412117.html

It is from my observation how it sounds during flight, it seems it has similar function as car differential as you mentioned, not tightly coupled. Both props are consuming the same torque and are rotating at the same rpm (almost always..)

I saw several pilots flew them. Flights were great at very constant speed, looked and sounded very different from regular electrics.

Satoru

Rhilluk

thats very interesting ssatoru, also the use of an 8XL motor. I was assuming the gearing was all in the spinner somewhere but it is where the usual gearbox goes.