Compared to the first co-runners we built, the motor seems to be reversed which makes attaching it to the plane much simpler. Hard to see from the photo, but I'm guessing the stator is attached to the inner shaft driving the front prop and the rotor is driving the rear prop, opposite to any "normal" outrunner? It's a very interesting system, looking forward to seeing it in action.
About the brushes, since it's a constant connection, not intermittent like the commutator on a brushed motor, the lifetime of the brushes should be quite long.
Hey guys, here is Glavak system in use:
I will build new light plane and test Kimmo system in lighter application, then it will be fair to compare. In any case both systems give obvious advantages for F3P planes. I think in very near future it will become standart in hi level F3P competition.
Joined Sep 2012
At first we would like to introduce ourself. We are Sergej & Alex Glavak and come from Germany. The one or other pilot from the F3P scene know us.
Since we saw the first coaxial concepts for F3P from Kimmo and Fabien we decided to develop an own concept. We would like to introduce our coaxial system and share our knowledge/experience which we collect during the development. Maybe the one or other guy can use it (like us: we were also glad to found some first experience from Kimmo and Fabien). Thank you guys for that!!!
The idea was to create a coaxial system with following technical requirements:
1) low noise emission
2) high reliability
3) compact construction
4) enable a quick and easy exchange of propellers
5) enable a quick and easy exchange of the motor
6) low weight
The result of the requirements low noise emission/compact construction are the unusual propellers with a V-form.
We read the report from Kimmo about the optimal distance between contra rotating props and the optimum was: R(radius of prop)*0,35 = optimal distance between props. After a theoretical analysis "the formula says -> less radius = less distance" the idea of V-form propellers was born (and thus the first difficult part of this coaxial system ;-) ).
To develop a coaxial motor with low weight as possible the only opportunity was to choose the idea actio=reactio (rotating stator and rotor of a brushless engine). The result is that you have to use brushes to realize the electrical contact for the stator (and thus the second difficult part of the this coaxial system ;-) ). The next difficult point is to make a symmetrical and tidy motor winding to prevent unbalance of the stator. We also balancing the stator and rotor at the end to prevent unbalance of the rotating parts.
The result of the point high reliability/enable a quick and easy exchange of the motor was
1) the construction of a brush holder which is pivoted at the axle of the stator. This solution allows that the motor is autonomous from the plane. We are very proud of the solution with the brush holder because we have never seen something like that.
2) that we use silver-carbon brushes and slip rings of silver
Silver has very good electrical conductivity and is used for electric parts with low voltage and current. The second advantage of silver is that it does not oxidize in air so you are every time sure that the contact between slip ring and brush exist (it is not really a problem if you run the engine every day but if you do not use the engine for a longer time the slip rings can oxidize). We tried also bronze-carbon and carbon brushes and the difference (efficiency) to the silver-carbon is very high.
The diameter (4,3mm) of the slip rings was chosen as small as possible because to reduce mechanical wear of the slip rings and brushes.
3) that we made a cross mount to mount the motor at the plane.
The mounting of the engine is also standard (mounting diameter 30mm, like our normal engines, AXI .... ).
4) that both props have an prop saver
@ data of the coaxial system:
- weight: 16,5 g (only engine, without o-rings (0,3g))
- weight: 25,5g (engine, 2x o-ring, 2x prop=2x4,0g)
- prop size: 10"x3.8" (wide blade props, widest part 26,5mm)
- for planes less than 140g fly weight
- only on speed controller
- for 120mAh battery (for planes with 140 g flyweight better 180-240mAh)
- mounting size diameter 30mm (like the 12g engine)
- lifetime test at brushes 200 hours (100 hours without props and 100 hours with props) -> 4000 flights per 3 minutes (without problems)
- 900 Rpm/V
some test data: (120mA battery, 10" props)
thrust current voltage
100g 1,5A 7V
120g 2,0A 7V
160g 3,2A 7V
220g 5,0A 7V
diameter (mounting cross) 35mm
diameter (engine) 22,2mm
As you can see the weight of the motor is only 16,5g (thats not much we think). The big 10" props weight together 2x4g=8g. The result of the V-form it that you have side forces (centrifugal-forces) which reduce the distance between the props. There is no problem to make the props very light (3-3,3g like Kimmo´s) but because of the V-form I have to make them stiffer and that means additional weight of 2x1g=2g. However, we think this additional weight is worth if you can reduce the noise of the engine. The speed of the props is limited at 7000 1/min
The first small series was the first step of our development. We want to wait at first at the feedback of the pilots/ results after the EIAC 2012 in November (DMFV competition) and than decide if some design changes are necessary and make a decision of a bigger series.
As you see the motor has a lot of power. The decision to make a motor with more power was that the planes will be bigger (more weight) and that planes with a coaxial system have more weight.
We plan to develop a variant of this coaxial system for planes with a weight of 100g. This variant should be lighter more efficient (lower RPM/V value).
If there are more questions about details of the coaxial system feel free to ask us.
@ forum or personally @ email@example.com
Sergej & Alex Glavak
of course some pictures ;-)
Alex and Sergej; thanks for sharing the pics and info on the new set up, I will defiantly be getting the coax system as soon as you will sell me one.
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