Setting up CCPM Helicopters

I have been asked numerous times as to how to set up ECCPM helicopters, and hopefully with this article it would help people who would like to know more about CCPM. First, I thought you might like to know that the term CCPM nowadays as we commonly referred to, should actually be addressed as ECCPM (Electronic Cyclic Collective Pitch Mixing). People into technical knowledge about helicopters would tell you that the term CCPM is actually the mixing and translation of controls by the swashplate to the rotor head, whether in the form of mixing by mechanical mixing arms, or electronically. As a result, all helicopter does some form of CCPM, whether electronically or mechanically.  The public now refers the term CCPM as equal to ECCPM, and I will use as such for ease of reference.

CCPM (Cyclic Collective Pitch Mixing) helicopters are gaining popularity nowadays, many thanks to manufacturers like JR who are actively promoting them and applying them to their helicopter designs.  Some top pilots even expressed that CCPM are their choice on control. Contrary to most belief, CCPM is not a new concept. Years ago when model helicopters were still in "cottage industry" era, a lot of helicopters use CCPM controls instead of mechanical mixing to save cost and time for design and production. This is understandable because manufacturers could do away with designing all the various mixing levers to speed up production. Back then, a lot of different CCPM methods are available, depending on the manufacturers' choice.  There are the two servo 180 degree CCPM, 3 servo 90 degree CCPM, 3 servo 120 degree CCPM and 4 servo 90 degree CCPM, without different servo and orientation combination. All CCPM method are to achieve the single form of mixing of controls from the swashplate to the rotor head.

In the past, most radio transmitters does not have computer software to control various mixing and settings like ours nowadays (I remembered my first multi-channel radio control was what we called the "Big eyes" from Futaba, where trim tabs for its four channels were a luxury feature, not to mention distinction of any between a plane or a helicopter version).  Due to the simplicity of radio back then, a "black box" would be used to connect between the swashplate control servos and receiver to perform some form of electronics mixing. These boxes were usually manufactured by the helicopter manufacturers themselves, required use of certain prescribed equipment (e.g. radio and servo), and were limited in functions (Forget ATV adjustment). This hindered the development of CCPM to its popularity.

In the recent years, there is a resurgence of interest about CCPM helicopters, thanks to the advancement of helicopter radio design, and efforts by manufacturers like JR. About 4 years ago, JR announced that they would start to support CCPM controls on their radios, and producing helicopters using CCPM controls. This was a "first of its kind" action by a major radio and helicopter manufacturer. To be fair, while other radio manufacturers like Futaba already had some forms of CCPM programs incorporated into their computer radios long before JR did, there was not a major helicopter manufacturer that vowed to produce CCPM helicopters in masse to support.  As a result, CCPM helicopter remained a rarity before JR's action.

Between all different CCPM methods, JR elected to use 3 servo 120 degree CCPM control as their choice of control, and not without reason (We hereby refers to it as 3X120). Basically, 3X120 is the most logical layout.  For our helicopters, it requires three channels of input for full swashplate controls (Collective pitch, aileron and elevator), so the use of three servos seemed the most logical, and putting the three control points at 120 degrees apart should even out the control distribution.   Owing to JR, being both a radio and helicopter manufacturer, and the seemly best logic of 3X120 amongst other CCPM method, 3X120 became the CCPM method of choice for most helicopter manufacturers.

Most CCPM helicopter kits now comes with detailed setup data for various radio and servo sets.  I recommend straight adherence to the data provided in the manual for a fool-proof start.  However, due to various reasons (Japanese language used in instruction is the most prominent), I check and found a lot of helicopter pilots that have incorrectly set up their CCPM helicopters.  In the following paragraphs, I will explain the setting of 3X120 CCPM, as it is the predominant CCPM configuration now used, but some setting procedures are also applicable to other CCPM methods with slight modifications.

Before setting up a CCPM helicopter, remember that we have to set up the controls to achieve the proper mixing of movements of the swashplate control servos to reflect desired controls to the swashplate.  i.e. Increase or decrease collective pitch will move the swashplate up or down, left cyclic or right cyclic will tilt the swashplate left or right, fore and aft cyclic will tilt the swashplate fore or aft.  These three channels of output are independently exist, and should not be mixed together.  A very good identification point is by looking at the swashplate, cause its it that our servos are going to control.  The swashplate is going to tell you whether you have done it right or wrong.

Assuming I have the helicopter assembled, with servos in place, swashplate control ball links made to the lengths as specified in the manual, and radio control hooked up according to the manual. To ease identification, I will refer to each servo and swashplate control points using the names as below:

Most 3X120 setup in the market have the above control point orientation.  For some helicopters (e.g. JR Superio Katsuyuki CCPM), the swashplate would be layout to the reverse of the above (Swashplate control points at 2, 6, 10 o'clock position).  If that's the case with you, then refer to the 6 o'clock position as Servo A, and clockwise for Servos B and C.  For your information, one radio manufacturer once proposed layouts of 1, 5, 9 o'clock position and 3, 7, 11 o'clock position, but there is only a few helicopters that I know of have options to choose to use these types of control point orientation. For other CCPM configurations, there should have control points at 90 degrees apart (Either controlled by 2, 3 or 4 servos), you could name the 12 o'clock position Servo A, and clockwise B, C and D.

Elevator Movement Check

The objective this test is to achieve the right elevator control movement of the swashplate.

Put the elevator stick to full down, note the swashplate.  There are two possible movements of the swashplate

Case 1 - swashplate tilt fore

If the swashplate tilt fore, move on to Aileron Check.

Case 2 - swashplate tilt aft

Go to the swash mix menu of the transmitter and adjust the mixing value (Where it read Pit 60% at default) to a negative value of the same amount (i.e. if at Pit 60% in the swash mix menu the swashplate lowers when the throttle stick is at top, adjust the Pit value to -60%), move on to Aileron Check.

Aileron Movement Check

The objective this test is to achieve the right aileron control movement of the swashplate.

Put the elevator stick to full right, note the swashplate.  There are two possible movements of the swashplate

Case 1 - swashplate tilt to the right

OK.

Case 2 - swashplate tilt to the left

Go to the swash mix menu of the transmitter and adjust the mixing value (Where it read Ail 60% at default) to a negative value of the same amount (i.e. if at Ail 60% in the swash mix menu the swashplate lowers when the throttle stick is at top, adjust the Ail value to -60%).

This is a personal opinion.  It all depends on the flying style of each pilot.  If you as me, as a F3C pilot, I would say "No". CCPM, in my opinion, have very sensitive cyclic controls, especially with collective pitch.  However, for F3C contest where very minute adjustment are needed for hovering maneuvers CCPM is just too sensitive for my taste. I remembered Curtis Youngblood brought two Vigors to Poland for the World Championship, one regular mixing, and another CCPM.  He used the regular mixing one for the whole contest, and the CCPM one remained on the ground.  I think Curtis made his choice when it comes to the control of choice for contest.

CCPM does not need high torque and better servos

Absolutely NO!  CCPM requires high precision servos that would result a balanced system. While differential travel for each servo will not affect much with regular mixing helicopters, differential travel on just one of the CCPM servo kills the whole system. Since CCPM would use at least 2 servos together to control swashplate movement, the required force to move the swashplate is distributed between the servos that control it. However, on the same token, any pressure being transferred back to the servos will be shared between all servos.  So, if one servo in the whole system have differential travel, chances are at some point of control the one servo that over travels would bind the other servos and slowly push them to burnouts. While with regular mixing helicopter if a cyclic control servo burnout happen in flight the helicopter would still have cyclic controls on the remaining channels, but with a CCPM helicopter only one servo in the whole cyclic control system fail would render the whole cyclic system uncontrollable.  CCPM is not a way to use low torque servos on 60 size helicopters.

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