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Old 07-27-2016, 01:15 PM   #1
HeliXXL
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Default Rc flettner rotors

Hello all,

Not sure if this is the correct place for this post but I wasn't sure where else to post. I am working on a rc flettner rotor heli but I don't know how to control yaw using standard rc tx/rx. Collective and cyclic should be relatively simple since servos (ccpm) on both rotors should be doing the same actions. My thought for collective and cyclic was to put both sets of servos on a y because each side should mirror the other. That is until you introduce differential collective where each set of ccpm servos will work as independent sets in collective but in unison for cyclic. Does anyone know if it is possible to get all six servos to work this way using channel mixing or anything like that? Is it possible to use a fbl unit? I have heard of people using fbl units and or channel mixing to control yaw, collective, and cyclic on coax machines but I can't find any info on controlling a flettner style rotor. I hope my description wasn't too confusing.
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Old 07-27-2016, 05:27 PM   #2
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AFAIK if you need differential pitch for yaw commands you will need to buy/build a mixer board.

A basic micro can do this pretty easily, but I doubt any FBL manufacturer has it built in.
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Old 07-28-2016, 06:55 AM   #3
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Thanks for the info desert stalker, do you know where I can get one or how to program the mixer?
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Old 07-28-2016, 10:56 AM   #4
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If I understand this correctly, it is two intermeshing rotors mounted side-by-side with no tail rotor.

Like the Karmen K-Max.



I think I'd take a look at the Skookum SK-720 FBL.
The developer has added a "tandem rotor" function (for a Chinook CH-47) and some other neat features.

Skookum is based in Canada and Art may be able to offer suggestions on how to set it up for a "Flettner" rotor heli (AKA: synchropter).
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Old 07-28-2016, 12:37 PM   #5
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Exactly like the kaman k-max or husky or the flettner 282. Thanks for the tip I'll look into the skookum. If you have any info or if you find anything out let me know, I appreciate all the help I can get!
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Old 07-31-2016, 12:17 AM   #6
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Here's another question for everyone. When determining the area and disc loading of a flenter type rotor how to you figure the area? Do you consider both rotors as one, basically radius of one rotor squared times pi? Or do you add the area of both discs together, or do you add the non overlapping area of each disc to the single disc area? And would solidity be figured considering it as basically one 4 blade rotor? I have also read that when the US conducted tests of the flettner 282 after ww2 they tested a 282 with two 3 bladed heads and it was described and being very stable and much smoother than a traditional style rotor layout. Why would that be? Stability I assume might have to do with the auto torque cancelation and the rotors providing some opposing force but bein smother with less vibration? Thanks!
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Old 07-31-2016, 12:45 AM   #7
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For dual rotor, the disc area is generally considered to be that which is not overlapped. Solidity is per disc. The disc area is used to define the cross section of the outflow (stream tube)- where for given thrust level, less disc area requires higher flow speed.

These layouts are not efficient, which is why 95%+ of working helis are of a conventional layout. Flettner layouts are typically quite slow, where drag is a real problem. Weight can be also- so they are typically built using very low mass blades with absolutely minimal complexity as regards cyclic control (ie. servo tabs to twist the blades- which is less possible with robust/stiff blades- this doesn’t scale up well with size or speed).

But, they can be very stable- as a function of some very complex aero/rotary dynamics. And that helps for something like the Kmax- where you throw a massive turbine in the thing, keep its mass very low, live with low speed and no internal payload- but achieve stable hovers and a high payload to gross weight ratio.
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Old 08-15-2016, 04:51 PM   #8
Corne
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@ HeliXXL

I am Building a K-max 700 size (scale 1:8.5)
You defenitly need a Mixer to achieve differential collective and/or differential nick.
Channel mixing on a TX is possible but this depends on a lot of things. I didn't even consider it.

In my first flights I used a Heltronix mixer of cad-jung-shop.de

With this mixer you can only use differential collective.
The problem is when you flare off your horizontal speed the tail goes all over the place.

I am almost sure this is a property of the intermeshing rotor config.
I know that the K-max has something like a rudder reverser with the treshold around hoverpitch.
"Extrapilot" would be the one to tell something about this fenomona.

Now I use a Flip 32+ board with integrated FBL system and something similar to the rudder reverser.
The software is written by Anton T. (thtexpert : www.rc-heli.de)
At the hover treshold point the differential collective reduces and differential nick is mixed in.

I tested this on my K-max 450 and it works like a charm.

Its now already build in in my K-max 700 but not tested due to lack of time.

Kaman K-max-700 Test 05 with mini auto (7 min 40 sec)


Good luck with your build.


Corné
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Old 08-16-2016, 02:27 PM   #9
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Corné,

Thanks for the info I really appreciate it! Did you build your models from a kit or from scratch? Do you have a build thread? I'd love to see some pictures of your build and finished machine if you have them. I will look into the mixer, I appreciate the links and tips. Thanks again.

Jonathan
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Old 08-16-2016, 04:51 PM   #10
Corne
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Jonathan,

I build the model from scratch.
Some components are from standard heli parts like rotor head, swashplate and some modified gears. I have no build thread.

Specs.

Kaman K-Max 700:
Semi-scale 1:8,5
Rotordiameter: 2x 1525mm
Take Off Weight : 7,8 kg
Rotorblades : Align 690D (HD690BT)
Motor: Helidrive SK3 Competition 4962 - 480 kV
Speedcontroller : Kontronik Heli Jive 120HV
Servos: 6x Savox-SC-1256TG (•Speed (sec/60°): 0.15sec @ 6.0V •Torque (kg-cm): 18.0 @ 6.0V)
Receiver : Spektrum AR8000 + 2 Spektrum DSMX satellites
Powersupply: 6V (from internal Kontronic BEC)
Flettner Mixer : Flip32 with software developed by Anton T.
Flybarless controller : Integrated in Flip32
Lipos: 12S, 2x6S, 5Ah Turnigy
Gear ratio Total : 1:15,5
Stage 1: inclined gear ratio 4,133 (pinion1 Z=15 steel, Maingear1 Z=62 POM)
Stage 2: Straight gear ratio 2,5 (Pinion2 Z=18 POM , Maingear2 Z= 45 POM)
Stage 3: Bevel Gears Spiral Tooth System, ratio 1:5 (Pinion3 Z=16 Hardened steel , Maingear3 Z= 24 Hardened steel)
Headspeed : 1300-1500 rpm

I will try to post some pictures.

Corné
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Old 08-17-2016, 10:30 PM   #12
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Corné you are amazing! I really appreciate all the info and photos of your K-max, beautiful work! Was you transmission gear train off the shelf parts or did you design those yourself? Really awesome looking machine! My progress will be slow, I'm in the info gathering and design phase and I'm in no way fluent with CAD but I'll try to keep you updated as I go. What cad software did you design all your components and assemblies in? Thanks again!
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Old 08-18-2016, 05:14 PM   #13
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Jonathan,

With some effort anyone can achieve a similar result.
I spent more time in gathering all the info I needed, then the actual design phase. I looked up every possible info regarding the K-max including pictures.

So also my progress was very slow.

I got some help from a nice man from Germany.
https://www.rc-heli.de/board/showthr...=242992&page=3
This man has build many nice machines. Unfortunately its all in German langue.

I found a lot of usefull info in the KAMAN MODEL K-1200 K-MAX
Maintenance and Servicing Instructions.

I used Autocad only to find out if my design fits in the scaled overlay drawing in the Kaman K-1200 K-max manual.
The machine is so small in the bottom that you can hardly squeeze in the drivetrain.
Thats why I choose scale 1:8.5 and it still does not fit perfectly....thats why I call it Semiscale.
I did not even try to scale the nice bladeflap design.

For the design I use Inventor.
I think its a good Idea to spend time to learn a 3D design programm. I have no idea how I would get the gearmeshes fit without a 3D programm.

Some parts are off the shelf but all are somehow modified.
The alumium frame parts where lasercut, The carbon frameparts where CNC milled. All other parts where made with conventional milling and a lath.

In the attachment you find the (semi) off the shelf parts.
No secrets here.

PM me if you need more info.


Good luck with your build.

Corné
Attached Files
File Type: pdf Kamax-700-02X-1-components.pdf (486.3 KB, 72 views)
File Type: pdf Schema-K-max-700-03.pdf (110.5 KB, 62 views)
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Old 09-12-2016, 10:16 AM   #14
Block137
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Hi
Sorry for a bump

I've just finished my Synchropter as well.

And also having problem finding mixer
My radio is powerful enough to do the mixing. But without stabilization, I don't want to fly it (again).
Tandem mixer on Skookum almost worked. Only problem with rudder.
I'm going to try open source flight controllers like APM or Pixhawk. Any suggestions?

Since you showed yours, I'll show mine
It use 325-380mm blades and famous 450 helis
-WARP360 style swash anti rotation
-GAUI X3 swashplates and spindles
-Forza 450 DFC link
Design focused on simplest but difficult-to-make drive train having only 4 gears
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Old 09-12-2016, 04:51 PM   #15
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Very nice work guys. Respect.
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