Why so many Ch on Transmitters?

[Argonaut]

What do each of the channels do on a RC heli ?
I have read that Digital servos are the best choice, and one single digital signal can send servo either way ..... so I'm guessing a Ch for Cyclic, one for collective, one for throttle, on for tail rotor pitch ?

That makes 4

Read that 6 Ch is minimum, and 8 being preferred, I must be lacking in basic understanding, can someone educate me ?

[Guest]

I don't normally answer in techy threads as I am still a newbie but hear goes:

1x throttle, then the cyclic has 3 servos..1x elevator, 1x aileron and 1x pitch. Then there is the rudder, this servo needs a channel as does the gain control for the gyro so it can be controlled from the tx...the 7th channel might be used for a governer on a nitro heli..and for an 8th...it may be used for retracting gears on a scale model - I think that is all correct.

[andylinney]

makes perfect sense Jack...

3 for the Head,
1 for the Power,
1 for the Tail.

That's the barest minimum....


Ideally,

3 for the head,
2 for the power (throttle and govenor)
2 for the Tail (Directional control and Gain)

(then any other functions you want to control from the Tx: Gear, lights, mixture, daft scale bits like winches etc)

Then you get into programming flybarless etc

[Biggles]

What do each of the channels do on a RC heli ?
I have read that Digital servos are the best choice, and one single digital signal can send servo either way ..... so I'm guessing a Ch for Cyclic, one for collective, one for throttle, on for tail rotor pitch ?

That makes 4

Read that 6 Ch is minimum, and 8 being preferred, I must be lacking in basic understanding, can someone educate me ?

You have said 'a' channel for cyclic....cyclic is aileron and elevator which like a plank are seperate channels....thus 2 channels.

[moyesboy]

3 servos control the head. this is in effect 1 for forwards and backwards (elevator) one for left and right (aileron) and one for up and down (collective).
On modern helis these three channels work together to tilt and move the swashplate using special mixing in the transmitter called ccpm. All modern heli transmitters have this.

The next channel is throttle which controls the speed of the main rotor.

Rudder controls which way the heli points.

Gyro gain controls the sensitivity of the gyro on the tail rotor and switches it from rate mode (which allows the heli to weathercock into wind) or heading lock (which holds the heli direction still whichever way the wind blows).

That adds up to 6 channels. All you need for an electric helicopter to do every manoevre you can think of.

The popular 7th channel is to control the governor on a nitro heli. This device controls the motor throttle to keep the head speed constant. The extra channel sets the head speed and allows you to have a slow speed for hovering and a high speed for flying aerobatics. Throttle is still needed as a separate channel to control the motor after it starts and to get it up to the governor speed.

Thats all you need to do any manoevres with a pod and boom helicopter.
some people use extra channels to adjust the engine needle in flight, and then to do scale stuff.

The most popular tx for helis in the UK is the spektrum dx7 with the AR6200 for electric helis and AR7000 for nitro.

On your shoppng list when choosing a heli transmitter should be:

Ccpm mixing (thats for the swashplate) there are a few variants but 120 degrees is the essential one.

5 point pitch and throttle curves (3 point will do, but 5 is better).

3 flight modes plus throttle hold. known as normal, idle up 1 and idle up 2.
When you first spin the heli up the throttle stick stops the motor when it is fully down. to fly upside down you switch to the next flight mode (idle up) and then the throtle stays open with the stick down and you get negative pitch to fly upside down.


Oh dear I've gone on and on and on again....

[Brian Gifford]

That's an excellent answer, tho.

[Argonaut]

Thanks ... lots of good information.
Which always raises questions :-)

OK I now understand that the cyclic needs 3 servos? - 2 servos on x & y axis should give full cyclic response, with a 3rd for collective.

Does that mean that Transmitters have a 'combined' 3 servo control joystick ?

(starting to get my head together so I make right purchase for 1st Heli)


I thought the Gyro took care of it's self once set up ? .... do you have to make changes to it from Transmitter frequently ?

With all the servos required do you buy a matched set pack, or do you need to pick & choose each servo for function ?

For example my Heli choice is Raptor Titan 50SE ... would I get 5 identical servos, or is there a 'family set of 5 different but matched units' ?

Sorry if this is way too basic questions.

Not found anybody local yet to go and talk to so t'internet is my eductaor.

If there is a good guide I should read please point me there - looked at this web site and Heliguy, raptortechnique.com & littlerotors.com (which was great for background)

[moyesboy]

Most newer design helis use eccpm where the three swash servos move the swash together and they have to move in a team to tip or raise and lower the swash appropriately. The electrickery to do that is done in the transmitter, or with an onboard mixer (such as CSM CL1).
with that system the three swash servos need to be identical and are best bought together (ie don't use an old worn out one and two new ones).

The raptor has mechanical mixing, so it has separate aileron, elevator and collective servos. The mixing in the transmitter is not used.
In the case of the raptor the load on the collective servo is more than on the aileron and elevator, so it is common to use a more expensive and more powerfull servo for collective and std servos for the other two.

The servo for the tail is usually a very fast one - the gyro is driving it faster than your hand ever could. This is usually a digital servo costing at least £50 (eg FUTaba 9254 or align DS620 are ideal for a raptor). The servo is designed to be fast rather than powerful.

The throttle servo has little load on it so a std spektrum ds921 or fut 3001 is fine there (under £20 worth).

You might find an align 600n is cheaper to run than a Raptor - raptors are fine though. The aligns are now more popular than the raptors.

[Rotorhead]

It can be even more than 3 channels for the head, you can have up to 4 servos on some eCCPM setups, separated by 90 degrees rather than 120/140

[Dedcalm]

2 servos on x & y axis should give full cyclic response, with a 3rd for collective.

Indeed on the Raptor (mCCPM) the x and y axis or pitch (elevator) and roll (aileron) is 2 channels and 2 servo's. The collective is the 3rd servo to control the pitch on the rotor blades. I use Futaba 9252 digitals on my cyclic and collective.

Does that mean that Transmitters have a 'combined' 3 servo control joystick ?

No, the left stick (mode 2) looks after rudder (yaw) in the x axis and combined throttle and collective in the Y axis. The right stick (mode 2) looks after the roll (aileron) on the x axis and pitch (elevator) on the y axis

(starting to get my head together so I make right purchase for 1st Heli)

good news

I thought the Gyro took care of it's self once set up ? .... do you have to make changes to it from Transmitter frequently ?

Once setup the gyro wont need to be touched generally. I haven't adjusted mine for years.

With all the servos required do you buy a matched set pack, or do you need to pick & choose each servo for function ?For example my Heli choice is Raptor Titan 50SE ... would I get 5 identical servos, or is there a 'family set of 5 different but matched units' ?

I would choose the servo for the job, i.e. I have 9252's on collective and cyclic, a fast 9254 on rudder, a fast 9254 on throttle via a governor (you could use a 3001 or other basic servo if you wish but my governor supports a 'super' servo and I had a 9254

Matched servos would be required if the heli used eCCPM, such as a T-Rex 600 as the swash plate is positioned by 3 servos (or 4 in some other 90 degree eCCPM systems). You need all 3 servos to move the same amount to ensure the collective movement keeps the swash level or you get what is known as interaction. Of course this is all irrelevant to the Raptor and as such is far simpler to set up.

Sorry if this is way too basic questions.

There is no such thing as a 'too basic' question

Not found anybody local yet to go and talk to so t'internet is my eductaor.

Let me know (PM if you like) if you have any more questions you need answering

[snapshot]

Just to correct a misconception.

CCPM (Collective Cyclic Pitch Mixing) is present on all modern heli's

But they are either mechanical or electronic. The raptor has mechanical and the Align's have electronic.

[Dedcalm]

Indeed you are absolutely correct. I have argued this point in the past so no idea why I wrote it down in this thread... I have corrected it now.
My ancient Kyosho Nexus (yeah I know!) was not CCPM, similarly the old Concept wasn't. I believe Kalt heli's might also have not been CCPM but these days all heli's are as far as I know in either mCCPM or eCCPM

[unwind-protect]

I believe the Falcon 3D is non-ccpm (last tiem I looked there was a pushrod that went up the mast seperate from the swashplate that controlled collective pitchlike, much like the Kyoshos and Kalts)

[Mart61]

Lots of really good answers here guys. I'm sure Argonaut is now considerably better informed than when he began.

[Argonaut]

Good answers indeed ... and giving rise to some new questions, great for me

Thnx to all