Deleted.

Hello folks here,
We did some improvement on our 13g contra-rotating motor these days, one motor mount and one prop adapter was added, it will be easier for mounting the motor on the plane and installing the propellers.

Thanks and Best Regards!


Attached are the pictures:

The coaxial system, differential type , ready.
Weight system, with motor 22-2.5/37 is 14.2 grams.

So the O-rings are the gears in the differential? Brilliant!

Originally Posted by Lantsov Alexey

The coaxial system, differential type , ready.
Weight system, with motor 22-2.5/37 is 14.2 grams.

Alexey, congratulations!
Great idea and realization!

I believe that the presence of a electric rotating contacts in coaxial system completely kills the idea brushless motors.
You managed to get rid of it, but at the cost of the additional structural element-differential.
This element, though, and performs a necessary function of the opposite rotation, but from an energy point of view is the ballast.
That is, the extra weight does not give additional thrust.

In my opinion most promising idea is to system in Post # 107.
This idea is very simple, in a constructive sense.
The simplest design is usually the most reliable and efficient.
Here there is no unnecessary contact, no ballast by weight, no friction loss in differential.
But the problem is that for coaxial system with weight of about 14...15 grams, requires two motors with greater diameter of the rotor and stator with a lot of poles that can work with a 8...10-inch props and their weight should be about 6...7 grams.
This motor so far not, that's the problem.
But for a coaxial system with a weight of more than 22 grams is no this problem.

Alexey and David, great job both of you! Nice to see what started as a crazy idea being adopted by so many and in different variations!

Alexey, I did not quite understand what was the problem with the co-runner, can you explain further? In our first protos, there was a small issue that while hovering, the torque would most of the time be very close to zero, however sometimes the plane could torque to left or to the right. The this seemed to vary. We thought it could be just down to the manufacturing accuracy, which on ours was not that great. Is this what you experienced?

The friction drive differential is very interesting, should be very quiet. I did not really understand the first hand drawn picture, but the photos make it clear.

Is the rod with the ball bearings on the ends free to rotate on the carbon shaft? I did not see any ball bearings between that and the carbon shaft. If it’s fixed, both props will turn the same RPM in opposite directions. If it’s free to rotate, it should function as a differential, right? Anyway very interesting idea, looking forward to hearing how it works and seeing the video!

Hi Kimmo, and all guys.
Your idea to brush coaxial have a reduction of 1:2.
This is very good. you can put a large propeller.
But there is a loss of electricity and friction in the brushes.
In any case, my plane is flying 4 minutes at 120 mA acc.
It is more than necessary.
I hope the video of my system, make clear the work of a differential system.

Дифференциальная система (0 min 0 sec)

That's a fantastic piece of engineering; the gear box arrangement is just brilliant

Brilliant engineering guys, well done all.

I realise this question is a little off-topic, but why use two co-axial contra rotating props? Why not mount two conventional motor/props on the wings, rotating in opposite directions, like many full size twin motor lightplanes? This will solve the torque and P factor problems, and the greater swept prop area will probably result in a more efficient powertrain too.

Neil.

Originally Posted by Neil Stainton

Brilliant engineering guys, well done all.

I realise this question is a little off-topic, but why use two co-axial contra rotating props? Why not mount two conventional motor/props on the wings, rotating in opposite directions, like many full size twin motor lightplanes? This will solve the torque and P factor problems, and the greater swept prop area will probably result in a more efficient powertrain too.

Neil.

Tiny differences in each motors winding / efficiency and prop differences will result in unwanted yaw at different throttle settings. Also the added weight outboard of the centre line will give more unwanted roll inertia

Andy

Originally Posted by Andycap

Tiny differences in each motors winding / efficiency and prop differences will result in unwanted yaw at different throttle settings.

This is also true for all the dual motor co-axial solutions. The brushed single motor solutions have brush drag to contend with, so I think the only truly zero torque solution is Alexey's "differential" design.

Also the added weight outboard of the centre line will give more unwanted roll inertia

True. But with lightweight geared motors mounted only 10 cm (4") from the centre line, this may not be a big deal.

Neil.

Originally Posted by Neil Stainton

...
The brushed single motor solutions have brush drag to contend with, so I think the only truly zero torque solution is Alexey's "differential" design.

True. But with lightweight geared motors mounted only 10 cm (4") from the centre line, this may not be a big deal.

Neil.

Hi Neil,

I assume any effect from "brush drag" will be negligible.

The smallest difference in thrust on a twin model however will become very noticeable at low speeds, even with the prop axis just 8" apart. Considering a complete wing structure weighing only 20 to 25g, even light motors would increase wing inertia noticeably - the last thing you need on a vertical downline with two quarter rolls.

Jürgen

All that weight outboard on the wings would not only ruin the flight performance as Jurgen has mentioned but the added engineering to mount even the lightest of motors rigidly would add even more complexity & weight.

Dave

With the motors only 4" from the centreline we could probably only run 5" props too. Dont forget we have the horizontal fuselage still to deal with Even without the motor forces mounted on the nose it would till need to be around 2.5" at the L.E. of the wing to make the fuselage suitably strong

Нi Neil. Two engines on the wing be problems .
So as , to be weak flow to the rudder.