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Old Jan 08, 2012, 12:54 PM
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United States, TX, Austin
Joined Dec 2011
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Originally Posted by Heli Pad View Post
I love my S107. I guess that's my problem. To be honest though, I'd never owned/flown a tandem helicopter. I wonder how it works? I think I have a pretty good understanding of how a 3ch coaxial helicopter works. Could you experts explain to me how a tandem helicopter achieves its 3ch functions? I have my theories, but I'd to hear it from you, especially the Yaw control. Then is there such a thing as a 4ch tandem? If so, how does it achieve aileron? AdThanksvance.
And for those of us noobs in the cheap seats, please include our audience in the answer...I've got my RC Helicopter Glossary standing by!

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Old Jan 08, 2012, 01:28 PM
We can rebuild it!
djdavies83's Avatar
United Kingdom, Wales, Swffryd
Joined Apr 2010
3,624 Posts
Well without going into how all helicopters work I can do the tandem explanation simply enough.....

Almost all "toy grade" (the things cheap enough for you and I to buy) are coaxial tandem, first up is how it turns left and right, the upper and lower set of blade spin in opposite directions (clockwise and counterclockwise) counteract each others Torque Effect, moving the throttle up increases the speed to both sets of blades by the same amount, when you move the rudder stick left/right it changes the power balance between the clockwise and counterclockwise, move the stick left and the clockwise blades will be given more power and the counterclockwise blades will be given less power so the torque of the clockwise blades will turn the body to the left. Forwards and backwards is done by having a bi-directional tail motor that pushes up or down on the tail, this changes the angle of both sets of blades by changing the above of the whole helicopter.

Now on to how the tandems work, imagine two coax helicopters with the tail motors removed and joined up tail to tail. Throttle/rudder (or yaw as it is also called with helicopters) is mixed in the same way, now remember how the balance of power between the upper and lower blades is mixed?

For pitch (forwards/backwards) on a tandem the power balance between the front and rear pair of blades is mixed, when you push forwards on the pitch stick this takes some of the power from the front pair of blades and moves it to the rear pair of blades, this lifts the back end up (tilts the angle of the while helicopter forwards) and just like the coaxial heli with a tail motor, make all the blades angle forwards.

I have attempted (currently on hold due to moving house) building my own tandem helicopter out of two S107 motor blocks, see below.....


This video should also explain the above, this is with 3 Vtail mixers used to send power to each motor. 
ORX214G Build log, 3x Vtail mixer test FULL LENGTH (5 min 21 sec)




This video is the building of my S240 airframe. Two S107 motor blocks controlled from a S026(nonG) PCB. 
DIY Syma S240 (0 min 44 sec)


this is a short test flight of the S240
S240 Build log - testing the airframe (0 min 26 sec)


Hope y'all get my explanation
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Old Jan 08, 2012, 02:49 PM
Against Helicopter Cruelty
Heli Pad's Avatar
Joined Aug 2011
6,120 Posts
So, Dave, if I understood you correctly, Rudder/Yaw is achieve by changing the relative power of the upper and lower blades on BOTH front and rear pairs? I was thinking that it would change one or the other. Both is twice as good then.

One of the biggest gripe about the 3ch is the forward/backward speed. So, what you're saying is the in the Tandem helicopter, the teeny tail rotor of a coaxial is now replaced by a set of main motors. That could be a very significant change to the pitch of the helicopter. Is the mix very limited by the Tx though, because I don't see tandem going super fast. I mean it should be able to, unless the mix is limited, right? So, if you built you own, and you have the control of the mix, you should be able to build a tandem that fly in some strong wind, right?
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Old Jan 08, 2012, 05:02 PM
We can rebuild it!
djdavies83's Avatar
United Kingdom, Wales, Swffryd
Joined Apr 2010
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Quote:
Originally Posted by Heli Pad View Post
So, Dave, if I understood you correctly, Rudder/Yaw is achieve by changing the relative power of the upper and lower blades on BOTH front and rear pairs? I was thinking that it would change one or the other. Both is twice as good then.
Sorry I forgot to say, yes the throttle/yaw mix is the the same for BOTH front and rear pairs. 

Quote:
Originally Posted by Heli Pad View Post
One of the biggest gripe about the 3ch is the forward/backward speed. So, what you're saying is the in the Tandem helicopter, the teeny tail rotor of a coaxial is now replaced by a set of main motors.
 
Yep!

Quote:
Originally Posted by Heli Pad View Post
That could be a very significant change to the pitch of the helicopter. Is the mix very limited by the Tx though, because I don't see tandem going super fast. I mean it should be able to, unless the mix is limited, right?

Remember the Chinook is basically a flying truck, it's build for load capacity rather than all out speed, although the real Chinook is quite fast, ive seen youtube videos where it is almost vertical!

In the case of the Tandem Chinooks we're talking about they limited by two factors, they are coaxial (no coax heli likes going fast) and as you said, the Tx is limiting the amount of power shifted between front and rear blade sets. 

I have read from people who have decoded the protocols that Syma use in their helicopters, for example,

Unlike the trim on a traditional Tx where the little lever adjusts position of the POT that the stick is attached to (this changes the CENTRE value of the resistance reading of the channel going into the radio circuit) changing only one value. Say 0 is full left and 127 is full right it will change the centre value of about 63 to something not far from either side of that number. 

On the S107 Tx there are two POTs for Yaw, one on the stick and one for the trim, the trim POT does not adjust the value of the stick on the Yaw channel like the example above. 



The Yaw output is basically a window set inside the min and max possible Yaw, the trim POT moves the window to one side or the other here is a an example as best as I can show it.......


Min-max is 0-127
Left 0-------------[Yaw widow is 64 wide]-------------127 Right



Full Left trim. 
Left 0[0-63 yaw is min 0 max 63]----------------------127 Right

Centre trim
Left 0----------[31-93 yaw is min 31 max 93]---------127 Right

Full Right trim
Left 0----------------[63-127 yaw is min 63 max 127]127 Right

The Pitch trim of the S022 is done with button but it's done in the same way, a lot of S022 and S026 users will add a few extra forward trim clicks to get more speed and then trim back to centre when they want to hover.

The DSM2ir device I've been beta testing modifies the protocol as it transcodes it, this gives the S107 FULL min-max Yaw control....

Left 0[0-127      yaw      is      min 0 max 127]127 Right

Flying the S107 with this is great, it can turn a lot faster, it's like having a 3rd hand tweaking the trim knob each time I change direction!

I could be wrong but I believe the DSM2ir will also modify the S022 protocol as it transcodes so that FULL pitch forward on the stick will also shift the pitch TRIM value in the chosen direction then putting it back to centre when you want to hover, as soon as I have V2 of the DSM2ir I'll have video for you guys!



Quote:
Originally Posted by Heli Pad View Post
So, if you built you own, and you have the control of the mix, you should be able to build a tandem that fly in some strong wind, right?
 

Yes and No, just like "no coax (single or tandem) like to go fast", they also don't like wind, if I were to have better command of the mix so I could throw the balance even further to the rear so could have more forward pitch and go faster/fight the into the wind.... 
being a coax the wind would upset the flybar and the upper blades at the front and the rear and would probably just end up in a crash, I won't stop me from trying it one day though! 
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Old Jan 08, 2012, 08:21 PM
Against Helicopter Cruelty
Heli Pad's Avatar
Joined Aug 2011
6,120 Posts
Thanks, Dave. That was the most informative post I've ever read in this thread. Since I don't own a tandem, I don't even know why I'm lurking here, but I'm sure glad I did, because I learned a lot today.

So, instead of adjusting the yaw of one (front or rear) set of blades, kinda like turning a car with 2 turning wheels, the tandem helicopter would adjust the yaw of Both front and rear at the same time, kinda like turning a car with 4 wheel steering, or a long fire truck! And when you mix in the trim setting, this thing could turn on a dim!

I think the traditional 3 ch coaxial helicopter has no forward speed because the tail rotor is too small, and too under powered. I've seen modified 3ch coaxial that has quite impressive FFF, sometimes too fast and it ended up in blade strikes and fall out of the sky. But if we have proper separation between the blades, it should be okay. And we've seen that there are a small handful of coaxial that could achieve speed. So, I blame the weak tail rotor for speed. But in a tandem, there is nothing weak about the tail rotor. Just up the thrust in the rear and off you go!

IIRC, the front and rear rotors "overlap" each other? They are not striking each other because they have different height and out of phase? But I could see that in extreme speed/pitch, a strike could happen. But when you build your whole tandem, why couldn't you extend the distance between the front and rear, so no matter how hard they pitch, they could never touch each other?

Dave, between this tandem design and the DSM2ir beta testing, you are doing some interesting great work. I admire you and I envy you. I'm looking forward to seeing you change the world in this flying game. If you ever need another beta tester... I'm just saying...
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Old Jan 08, 2012, 08:58 PM
S107, S026
TSquare123's Avatar
Nashville, TN
Joined Aug 2010
140 Posts
Quote:
Originally Posted by Heli Pad View Post
Since I don't own a tandem, I don't even know why I'm lurking here, but I'm sure glad I did, because I learned a lot today.
Hey Heli Pad,
You really need to get you a S026. It is like a S107 on steroids. It will definitely move across a room faster than you want it to. I have the non-gyro version and it is a challenge to fly because when you want to straighten up out of a turn you can't just center the stick you have cancel the turn by going the other way briefly. I understand that the S026G is a lot easier to fly though.
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Old Jan 08, 2012, 09:23 PM
Against Helicopter Cruelty
Heli Pad's Avatar
Joined Aug 2011
6,120 Posts
T2, Perhaps you're right. I never own a tandem helicopter because the shape of a "flying truck or hotdog" (I've heard worse) does not appeal to me. But after reading its flying merits, I'm gonna look for one to try. Is S026 the way to go then? Does the S022 offer any advantage besides size?
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Old Jan 08, 2012, 10:23 PM
S107, S026
TSquare123's Avatar
Nashville, TN
Joined Aug 2010
140 Posts
Quote:
Originally Posted by Heli Pad View Post
T2, Perhaps you're right. I never own a tandem helicopter because the shape of a "flying truck or hotdog" (I've heard worse) does not appeal to me. But after reading its flying merits, I'm gonna look for one to try. Is S026 the way to go then? Does the S022 offer any advantage besides size?
I have not tried the S022, always wanted to, but I don't think it will do well outside in the wind, (it is RF not IR control), and I don't have an indoor area big enough for the S022. I felt the same way about the flying truck back when I first got my S107, but I kept reading the S026 thread on this forum along with the S107 thread as I was trying to decide whether to get a second 107 or something different. I finally decided to pull the trigger on the 026. As another comparison, the S107 is like flying a kid's balloon where the S026 takes more concentration and you must pay attention to what you are doing. No hands off hovering.
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Old Jan 09, 2012, 01:25 AM
Different fly 4 different guy
gordonzo's Avatar
Canada, BC, Salmon Arm
Joined Jan 2011
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I had both the S026G and the S022. I sold them to a friend that collects more than he flys and mostly just keeps them on his shelf!

My experiences:

S026G:

The S026G has decent speed and fast turns, needs to be moving. Looks very .

Mine had short flight times and required frequent trimming.

S022:

The S022 is an impressive machine in the air, especially flying overhead, looks awesome and sounds even more awesome. It actually handles a light breeze very well, better than a regular coax, as long as you don't get sideways to it, then the 3 channels become limiting.

With no gyro, you need to keep it moving and it can be a bit of a handfull indoors.

I had my S022 facing into a decent breeze and with full fwd trim it just hung in the air not moving. I wish I had my video camera ready. I did not have my anemometer at the time but based on the weather station I believe the winds were close to 6-8 km/h (3-5 mph) at the time.

This a video from shortly after I got it.
ChinookApr2011 (6 min 3 sec)
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Old Jan 09, 2012, 12:03 PM
Master Of My Universe
scotsoft's Avatar
Newcastle, UK
Joined Jul 2010
2,699 Posts
Quote:
Originally Posted by Heli Pad View Post
T2, Perhaps you're right. I never own a tandem helicopter because the shape of a "flying truck or hotdog" (I've heard worse) does not appeal to me. But after reading its flying merits, I'm gonna look for one to try. Is S026 the way to go then? Does the S022 offer any advantage besides size?
I was checking out the Syma site a few days ago and they have the S022 now with a gyro, that is one beast I would like to have a fly with.

The S026G is a great little heli to throw about, here is a video I did with one of my mini Chinooks

S026G (6 min 36 sec)
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Old Jan 09, 2012, 12:14 PM
me, right now.
hooligan russ's Avatar
United States, NC, Clayton
Joined Nov 2009
498 Posts
Got my chinook stuck about 40ft. up in a tree. I hit the throttle and it fell, bounced and started to fly again. I got it on tape with an on-board video.

It seems like the rear blades are either out of balance or the the shaft may be bent. I'm losing forward power and I wonder if its because this imbalance is killing the rear motors.
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Old Jan 09, 2012, 12:39 PM
Against Helicopter Cruelty
Heli Pad's Avatar
Joined Aug 2011
6,120 Posts
Well, guys, thank you for sharing the videos. That looks like a lot of fun. And flying that many motors for 6 mins+ from a single charge was very impressive. It appears that the S026 flies even faster than the S1xxG in your other video, would you agree, John?

For the price, I'm considering adding a S026 to my fleet. Let me ask a few more questions. I am under the impression that the S026 has an extra trim button? Does it mean that the Tx is not compatible with my S107G Tx? There are many S107G clones out there. Do I have to worry about buying a fake S026G? A quick search on Amazon brings up many different pages for S026G, different seller, different prices. Any recommendations? Do you guys lose orientation flying this thing? As I'm watching the video, I couldn't tell when it's going forward and when it's going backward, cause the front looks like the rear and the rear looks like the front! LOL The lights in the bottom just didn't help with orientation.
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Old Jan 09, 2012, 12:57 PM
Master Of My Universe
scotsoft's Avatar
Newcastle, UK
Joined Jul 2010
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Quote:
Originally Posted by Heli Pad View Post
Well, guys, thank you for sharing the videos. That looks like a lot of fun. And flying that many motors for 6 mins+ from a single charge was very impressive. It appears that the S026 flies even faster than the S1xxG in your other video, would you agree, John?

For the price, I'm considering adding a S026 to my fleet. Let me ask a few more questions. I am under the impression that the S026 has an extra trim button? Does it mean that the Tx is not compatible with my S107G Tx? There are many S107G clones out there. Do I have to worry about buying a fake S026G? A quick search on Amazon brings up many different pages for S026G, different seller, different prices. Any recommendations? Do you guys lose orientation flying this thing? As I'm watching the video, I couldn't tell when it's going forward and when it's going backward, cause the front looks like the rear and the rear looks like the front! LOL The lights in the bottom just didn't help with orientation.
The S026G will fly faster than the S1**G lol as you can adjust its forward trim from sedate to suicidal and I usually fly at the suicidal end

I love these little Chinooks and the back is higher than the front so it's easy to tell which way you are going, the position of your right thumb will give a big clue as well

The Tx is different, the two "horns" on either side of the i/r array are the trim buttons. You can fly the S108G Cobra with the same Tx.

I am not aware of clones as such, there are other mini Chinooks but they have different paint jobs.

The Tx is the same as the S107 except it has a gold front instead of silver.
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Old Jan 09, 2012, 01:02 PM
Against Helicopter Cruelty
Heli Pad's Avatar
Joined Aug 2011
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So, regarding to the Tx, it sounds to me that if I get a S026G I could use it to fly my Syma fleet, but not the other way around because of the extra trims. But that's okay. I'm just trying to avoid having two many dedicated Tx, with too many AAs. Sedated to Suicidal, huh, I like the sound of that. I now wish that they have the same feature built into all the Symas.
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Old Jan 09, 2012, 01:17 PM
Master Of My Universe
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Newcastle, UK
Joined Jul 2010
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Originally Posted by Heli Pad View Post
So, regarding to the Tx, it sounds to me that if I get a S026G I could use it to fly my Syma fleet, but not the other way around because of the extra trims. But that's okay. I'm just trying to avoid having two many dedicated Tx, with too many AAs. Sedated to Suicidal, huh, I like the sound of that. I now wish that they have the same feature built into all the Symas.
You will not be able to fly your Syma fleet by getting the S026G.
You will only be able to fly the S108G Cobra with the S026G Tx.

The S102G Blackhawk, S107G, S109G Apache and S111G Coastguard will all fly from the same Tx.

I use rechargeable AA batteries in my Tx and they last a long time

Of course once DJDavies and myself have completed our test flights with the 2.4Ghz system you will be able to fly all your 3ch helis with one Tx

p.s. It is brilliant
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Last edited by scotsoft; Jan 09, 2012 at 01:19 PM. Reason: 2.4 info added
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