Since there is a lot of interest on ccpm, I thought I would share this Mas Technique article published in our March 2002 Issue of Rotory

It's in two parts due to thread length

As one observes today’s helicopters, each model is somewhat unique when compared to others. One manufacturer might offer carbon frames, yet another offer aluminum. One machine might have an inline flybar, yet another has an underslung flybar. While manufacturers offer an array of hundreds of different features, all current models share a standard set of only three types of control systems.
1) Direct Type - this system has a fixed swashplate and uses a rod or wire connected to
a servo to control collective. This is a single servo collective system.
2) Elevator Control - This system is the most common. Collective control is achieved by linkages
that slide the entire swashplate up and down on the main shaft to achieve collective control.
This is a single servo collective system.
3) CCPM - This system uses two, three or four servos mounted close to the swashplate which
operate simultaneously to move the swashplate up and down to achieve collective and steering
control. CCPM systems offer less complex mechanical linkage.
There are five basic swashplate setups for model helicopters which are supported by mid to high-end radio control systems. They include a "Single Servo" system, and four different types of "CCPM." A Single Servo system uses one servo for each axis of the swashplate, such as; aileron, elevator, and collective. Single servo type systems may be found in the more popular "Elevator Type" helicopters which slide the swashplate up and down to achieve collective control. A single servo system is also used for the "Direct Type" collective system, where one servo moves the collective thru the use of a pitch change wire or rod. The "Direct Type" is the only system that uses a preferable fixed swashplate.
CCPM type helicopters utilize a combination of servos working together to achieve the 3 axes of control; aileron, elevator, and collective. There are a total of four CCPM types, however the "three servo type" is the most popular. The CCPM system offers far less mechanical complexity to move the swashplate of the helicopter. In addition, multiply servos working together increases the power of the system.
In one of my earlier Mas Technique articles, titled; "Helicopter Control Systems," (Jan/Feb ‘94) we examined helicopter control systems in detail. In a relatively short period of time, many helicopter manufacturers have re-tooled their equipment from the traditional "Elevator Type" sliding swashplate, and "Direct Type," to the now popular - CCPM system.
CCPM which stands for; "Cyclic Collective Pitch Mixing" has recently been promoted to be the greatest thing to happen to model helicopters in a long time. It promises a new control system that will allow you to achieve new levels of expertise in your flying, as well as offer amazing collective and cyclic control. Well . . . this is really not the case. Along with all the glamour and advantages of CCPM mixing, are a few downfalls as well. In this segment of the Mas Technique, we’ll take a close look at CCPM.
One has to ask - why has CCPM almost become standard equipment on model helicopters, and why did most manufacturers switch to it? For the most part, model helicopter mechanical design reached a plateau some 5 - 8 years ago. This was right after we went to, carbon this, and carbon that. There had to be something new with a bit of mystery to attract first time customers and entice the old ones. So along came CCPM.
CCPM evolved a bit differently than past heli evolution’s. Most all changes in helicopter design came from the users and competition - factory pilots who are always striving to improve their helicopter, thus improving their standings and performance. However, there were few competition pilots using CCPM. As a matter of fact, most competition and factory reps. dislike CCPM because of its bad habits. So the moral of this story is; CCPM was mostly introduced by the manufacturers themselves.
Not long ago - a major helicopter manufacturer offered a new model with CCPM as an incentive to market a machine that was unique when compared to other helis. Not surprisingly, the modeling public took interest in the proposed new system and purchased them. In a short period of time other manufactures, not wanting to be left out in the cold, offered the CCPM system as well. Within the last six months a few "diehard" manufacturers, who offer competition helis, reluctantly offered a CCPM machine, even though they vowed to never use CCPM on their equipment.
While CCPM has been promoted as a new and futuristic control system, in reality, it has been around almost as long as helicopters themselves. As modern helicopter radio systems evolved in the early 1980’s, so did CCPM. For the most part, CCPM mixing was developed and used extensively in German manufactured helicopters. My friend, Mr. Ewald Heim was instrumental in the early design and promotion of CCPM. As a matter of fact, CCPM has been standard equipment in past and present European helicopters such as Graupner, Heim, and Vario.
The truth of the matter is, CCPM is a manufacturers dream - gone are the complicated mixing trays, push-pull linkages, numerous bell cranks, ball joints, pushrods, links, etc. It’s a known fact that CCPM reduces 50% of the linkages on a model. Easy calculation, less parts = less cost! However, I have not witnessed this being passed to the customer.
Let’s take a look at some of the advantages of CCPM.
1) CCPM offers short coupled direct control from the servo to the control surface. Servos are mounted just below the swashplate, thereby eliminating the normal two or more pushrods and the use of bell cranks to change the direction of travel.
2) CCPM offers a powerful collective system, since three servos are now used for collective movement.
3) CCPM offers nearly 50% reduction of linkages, reducing the part count. This reduces cyclic/collective freeplay, as well as offer simpler construction when compared to elevator type collective systems.
4) CCPM offers a distinct advantage for scale helicopters since the main frame footprint is reduced. In addition, a forward mounted servo tray is no longer needed.
THE PRICE OF CHANGE
It’s a simple fact that it’s not easy to change model helicopter design. In most cases for every bit of good, there’s a little bad somewhere else. While CCPM offers some distinct advantages, it also has its share of problems. Let’s investigate where CCPM needs to be improved.
CYCLIC/COLLECTIVE COUPLING
With a CCPM system using 3 servos, all servos must move precisely at the same time as we add or subtract collective, otherwise we’ll end up with some unwanted aileron or elevator induced to the control. For example; as we quickly add pitch to perform a straight climb out, the servos tend to not travel at the same speed. This causes the swashplate to tilt slightly during the transition, causing the machine to veer off its straight climb out. This problem is more obvious during a roll. As we move the collective through its full range, from positive to negative, then back to positive, if any unwanted input is introduced during the roll, it results in a less than perfect maneuver.
Regardless of how slow or fast, or how powerful a servo is, most all servos travel at different speeds to reach a given point. This is caused by different tolerances of the servo’s motor, circuitry, and finally the gear train. I’m sure that when you bought your last radio, you wiggled the sticks to see if all the servos were spinning. You might have noticed something else - some servos seem to sound different, even though there is no load on them. This, in most cases, is caused by the differences of the gear train. Some are tight, some are loose. Different tolerances in plastic servo cases, bearings, gears, and their fit, make each servo unique. If you were lucky enough to find three servos alike, there’s another problem, the loads on the swashplate are different as well. This type of problem is only unique to CCPM systems, Elevator and Direct type systems are not affected, since only one servo controls the collective movement.
As CCPM became more popular, modelers moved to better and better servos that would work well with CCPM. The most common is the new digital servos with enormous power and the ability to achieve precise centering. The additional power helps to overcome many of the loads during servo travel, and the precise centering helps to maintain trim regardless of collective position. While digital servos do help - cyclic coupling still remains to a degree. During precision maneuvers such as FAI, where repeatability is crucial, CCPM can knock the edge off a maneuver which could mean winning or losing. This is the reason why few (unsponsored) pilots fly CCPM in competition.
One also has to be aware of the fact that digital servos are expensive. Four digital servos can cost more than the price of an entire sport radio system. Cost factor is important to our industry. Digital servos are not really an option for the new or sport pilot because of the initial cost. I can’t see a new pilot purchasing a $199 helicopter and the sales clerk tells him he now needs a $1000+ radio to make it work. Actually, beginner and sport pilots can still use standard servos in a CCPM machine, since at that level of training the coupling would hardly be noticeable.