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HomeRC & Power✈️Aircraft🚁HelicopterRadio - Spektrum DSM › DX8 and Swashplate Function.
04-25-2013 02:20 AM  7 years ago
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Indianapolis, IN - USA

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DX8 and Swashplate Function.
Good evening guys, I have the following question, when you select any swashplate type other the Normal 1 Servo the Swashplate function becomes available in the system set up screen. When you enter the swashplate function you can see that the values for Ail:, Ele: and Pit: all default to +60. Do we need to change these? I was fooling around with it the other day and could see that you can change the deflection of the servos for Aileron, Elevator and Pitch etc. In what cases would one need to change these and why? Thanks anticipated for your replies.
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04-25-2013 03:03 AM  7 years ago


Redondo Beach, CA

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The swashplate function values change the magnitude and direction of the swashplate motion relative to the respective stick inputs. You use those values to dial in how much aileron and elevator blade deflection you get as well as your maximum collective range.

If the swashplate moves the wrong direction for a given stick input, then you reverse the sign of that swashplate function value. For example, if left aileron stick input results in the swashplate deflecting to the right, you would turn the aileron +60 into -60.

The servo endpoints adjustments are used to level the swash at maximum and minimum collective.

- John
RR rules!
04-25-2013 03:42 AM  7 years ago


Cedar Rapids, IA

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Where to start? You haven't been around any form of RC helicopter, it appears.

The swashplate is what transfers control inputs from the servos in the non-moving part of the heli, to the rotating parts up on the rotor head so your control inputs move the rotor blades to allow you to direct the helicopter.

The swashplate is responsible for transferring CYCLIC pitch control to the the main rotor blades, and for transferring COLLECTIVE pitch control to the main rotor blades. In simple terms, CYCLIC is what allows you to move forward, backward, and sideways. Collective is what allows you to go up or down, vertically.

Most of the "serious" radio controlled helicopter kits on the market allow you to control both CYCLIC pitch and COLLECTIVE pitch. Again, all of these commands are transferred from the non-moving heli frame to the rotating rotor head by the swashplate.

You may notice that the swashplate can tilt forward, backward, and to either side (or any combination thereof) as it pivots on a spherical bearing that just happens to have the main rotor shaft going through its middle. The tilt is what translates your control inputs to the forward/backward, left/right cyclic commands.

The swashplate in most current helis with collective pitch is allowed to slide up and down on the main rotor shaft. This operation allows you to control the COLLECTIVE pitch of the main rotor blades to go up, or down.

If you find that after you connect everything up correctly that the swashplate tilts left when you command a right turn, this is corrected by using the REVERSE menu in you DX8 to reverse the sense of the left/right cyclic servo channel. If you find the swash tilts fore and aft backwards from correct stick movement, you use the reverse menu in the DX8 to reverse the function of the fore/aft servo channel in the DX8. If you find that the collective pitch function is backwards after setup, you use the transmitter reverse menu to reverse the collective pitch control channel.

The overall amount of fore/aft CYCLIC pitch is controlled by the TRAVEL ADJUST menu values for the fore/aft control channel. The overall amount of left/right CYCLIC pitch is controlled by the TRAVEL ADJUST menu values for the left/right control channel. The overall amount of positive and negative collective pitch is controlled by the TRAVEL ADJUST menu values for the Collective Pitch channel.


HOW the helicopter is designed to USE the tilt of the swashplate and the up/down motion of the swashplate determines WHAT you do with the SWASH menu in your DX8.

The default setting in your DX8 is "1 Servo". That is used with a helicopter design where one servo is connected to the swashplate to tilt it fore and aft (forward/backward cyclic control), one servo is connected to the swashplate to tilt it side to side (left/right cyclic control), and one servo is used to make the whole swashplate move up and down (collective pitch control).

In that case, you leave the SWASH setting at "1 Servo" and setup is relatively easy.

To move the heli forward or backward, only one servo needs to move. To move it left or right, only one servo needs to move. To gain or lose altitude, only one servo needs to move. The fore/aft input to the swashplate is connected to a control rod that is spaced 90 mechanical degrees (1/4 circle) from the left/right control rod.

In this setup, to go forward, you push the fore/aft cyclic stick away from you, only the fore/aft servo moves to tilt the swashplate down in front.

To go left, you move the left-right cyclic stick to the left, only the left/right cyclic servo moves to tilt the swashplate down on the left side.

To go UP, you move the COLLECTIVE pitch stick up. One servo then moves the swashplate up the main rotor shaft.

Collective pitch control remains independent of cyclic pitch control.

In the "1 Servo" swash control, those additional numbers you see as AILE, ELEV, and PITCH, that default to all +60 values are never, ever used and do not do anything at all. As a matter of fact, in "1 Servo" mode, you don't have access to that menu or its values. The amount of servo travel is solely controlled by each channel's Travel Adjust values, found in yet a different menu of your DX8.


A second, more popular way to move the swashplate around to make your heli fly is more complicated. In the most common setup, the swashplate is directly supported by three pushrods, each going to a separate servo. The three control inputs to the swashplate are equally spaced around the circle, 120 mechanical degrees apart.

To properly position this swashplate requires that all three servos work simultaneously together.

This configuration is known as 3-servo, 120 degree, CCPM control. It takes three servos, operating together, the servo inputs are spaced 120 degrees apart, and your transmitter (again, keeping it simple) must electronically mix the servo controls to make the swashplate move correctly.

In this case, when you push the fore/aft cyclic stick away from you, it will cause two servos to move downward (usually in front of the main rotor shaft, one on either side of it), while the third servo (mounted behind the main rotor shaft, and on the centerline of the heli)moves upwards. When all three servos move correctly, the front of the swashplate tilts down, the rear tilts up, the heli goes forward.

To go left, when you push the cyclic sitck to the left, one of the servos in front of the main rotor shaft, to the left of center will move down. The other servo in front of the main rotor shaft, to the right of center will move up. The rear-mounted servo on the heli's centerline does not move at all. The swashplate tilts to the left, the heli goes to the left.

To go up, when you push the COLLECTIVE stick UP, all three servos move upwards, in unison, to slide the swashplate UP the main rotor shaft.

In this kind of control, the transmitter must have the proper MIXING built into it to make the three servos move correctly, together, at the same time.

The CYCLIC and COLLECTIVE PITCH controls are MIXED to make the swash do its thing. This is the basis of what is known as Cyclic-Collective Pitch Mixing, or CCPM.

There are many variations of CCPM out there, the 3-servo, 120 degree version is by far the most common, 3-servo, 140 degree version is somewhat common, then you get into some more obscure variants with two, three, or four servo CCPM. What they ALL have in common, however, is that the transmitter must be responsible for mixing together your stick control inputs properly to simultaneously control the swash. Cyclic-Collective Pitch Mixing must be enabled in your transmitter.

The need to enable and use CCPM control is defined by the type of swashplate control the heli uses.


When you DO have to use a CCPM swashplate control method, the SWASH MIX menu becomes available.

Since all three servos must move correctly to make the heli fly as it should, a different method is introduced to allow you to reverse the sense of a control input, and to control how much of a control input that function sees.


If, after you set everything up correctly, and your transmitter has those default values for AILE, ELEV, and PITCH all set to + 60, you may find that foward stick causes the swashplate to tilt backwards, instead of forward. To fix that, you would change the "+60" value in the SWASH MIX menu so that it reads "-60". If you find that left cyclic input makes the right side of the swashplate tilt down, you reverse that function by changing the the AILE value in the SWASH MIX menu from "+60" to "-60". And, if you find that the swash moves UP when you want it to move down, you fix THAT by changing the PITCH value in the SWASH MIX menu from "+60" to "-60".


In the single servo control system you reversed just that channel using its setting in the transmitter reverse menu. In the CCPM world, you simply change the sign of the number in the SWASH MIX menu from "+" to "-", or "-" to "+".

If you find that you need more fore/aft cyclic pitch in a CCPM system, you INCREASE the magnitude of the value for that function in the SWASH MIX menu. If you find that you need less cyclic pitch in a CCPM system, you decrease the magnitude of the value for that function in the SWASH MIX menu.

Not enough fore/aft cyclic? Increase the ELEV number from that 60 setting, to something like 75 (keeping the sign properly set). Too much left/right cyclic? Decrease the AILE number from that 60 number to something like 50. If you need more overall collective pitch, make the pitch number greater than the default of 60.

The individual channel reversing function is ONLY used initially at set up to get all three servos moving correctly with respect to each other when you move the stick. Getting all three to move correctly with respect to the stick movement is controlled by the sign of the associated value in the SWASH MIX menu.

That is different from the 1 Servo control setup.


In the CCPM control method, the individual channel TRAVEL ADJUST values are ONLY used to make sure that the swashplate remains level at full negative collective pitch, zero collective pitch, and full positive collective pitch.


Hope this helps...

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
04-25-2013 03:24 PM  7 years ago


Central California

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Very good Dave.
04-26-2013 01:55 AM  7 years ago


Indianapolis, IN - USA

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Wow...!, thanks guys, excellent explanation Dave. I was kind of under that impression as I was able to level my Gaui Hurricane 425 Swashplate by changing the aileron value. I got my DX8 just last year and before that I had a DX6i for two years so I was not familiar with this screen. The DX6i screen is different and I had not done the programming on it as I had my neighbor do that for me. But I'm learning and your excellent explanation of this screen certainly helped me understand it better, Thanks again.Carlos
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