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DigiFleet 'PCM-MX7' R/C System

Written for 'RCMW'.

What do you get? - What can it do? - Fixed wing - Helicopter - General - Conclusions

A relatively short time ago (well, about 15 years actually), there were more manufacturers of radio control equipment in the British Isles than there were in the rest of the world. Strangely enough, if we exclude the Far East, this may still be true, despite the fact that there are only a handful of survivors from that time. One of these is Fleet Control Systems, who manufacture 'Digifleet' R/C equipment, designed by Derek Olley. Fleet are probably the only surviving volume producer of R/C equipment in this country. If anyone wants to take issue with that, no doubt they will let us know!

Digifleet equipment was the first to offer a transmitter which could be switched between PPM and PCM, so that existing airborne equipment could be used. This feature has now been copied by all major manufacturers.

The latest equipment, the 'Digifleet PCM-MX7' incorporates the current trend of catering for all three of the basic types of R/C model - powered aircraft, gliders and helicopters - in one set. While the result will probably not satisfy the dedicated contest flyer in any of these types, it provides all that most modellers will ever need and is ideal for those who want to try their hand at more than one type.

What do you get?

Standard equipment includes the transmitter and a PCM receiver, four FPS-17 servos, a 500 mAH nickel cadmium battery, a separate switch harness (no charging socket), a dual charger, an aileron extension cable, four sets of servo arms and mounting grommets (including eyelets and screws), a set of servo trays (also including grommets and screws) and a well written 20 page A5 instruction booklet. All of the equipment is enclosed in the usual moulded foam container with the transmitter face down, which makes maximum use of the available depth.

The transmitter is the heart of the system and this is one of the neatest and most comfortable that I have seen or handled. It is small and slim, which means that you can reach both sticks with finger and thumb without having to use a tray, which is further helped by the fact that the sticks are mounted close to the outer edges of the case. Auxiliary switches are mounted on the outer edge of the top panel and operate from side to side, which means that you can operate them without having to change your hold on the transmitter. A stout carrying handle is mounted on the top panel and the aerial retracts half way into the case giving a compact unit.

Aileron and elevator dual rate switches are mounted on either side of the 'POWER' meter (actually, only a battery indicator) and, in common with many other systems, move down for 'Hi' rate and up for 'Lo'. The logic of this arrangement escapes me and I would much prefer things the other way around! Both settings are adjustable, as are all the main throws.

Stick mode can be changed by swapping the centring spring and arm and the ratchet plate and moving a switch from 'Throttle left' to 'right'. The ratchet can be changed to a friction device by reversing the ratchet plate. Stick trims are of the separate electrical type which allows the throttle and elevator trim levers to be mounted slightly below the main sticks for easy accessibility.

Two auxiliary proportional channels are operated by levers which are identical to the stick trims and mounted on either side of the 'On/Off' switch.

Frequency changing is effected by means of a plug-in crystal which is conveniently mounted immediately below the shielded 'On/Off' switch, which incorporates a red LED to show that it is switched on.

The case rear panel is retained by a rotating catch which is easily operated by a suitable coin. Removal discloses the control panel, which has 20 switches and 14 rotary trimmers. Many modellers dislike 'computer' sets, by which they usually mean equipment which has to be 'programmed' via pushbuttons and some form of display, but are quite happy with setting rotary controls or switches, as used in the 'Digifleet'. This is just one of the many reasons why there is lots of room in the world for this type of equipment.

Remembering that this is a seven channel PCM outfit, the receiver is commendably light and compact. All the servo sockets are at one end and the sockets themselves are a polarised, high quality type, with gold plated pins. They are not compatible with any other type of equipment. A plug-in crystal is fitted at the opposite end to the sockets. Both the transmitter and receiver crystal are fitted in plastic cases, which are plainly marked with the frequency number.

Servos are of average size and weight, are quite fast and appear to have adequate power, though they are a little noisy in operation. The output shafts are splined and a selection of output arms is included.

Receiver battery is a 500 mAH type and there is no separate charging socket on the switch harness so it has to be unplugged from the battery for charging.

What can it do?

Actually, quite a lot! The 20 switches already mentioned are in two banks of ten and can accomplish many things. The most obvious use of one of the banks being the reversal of six of the available seven channels (the 'retract' channel does not need reversing). That leaves four switches which select linear or exponential operation of the elevators and ailerons, together with PPM/PCM switching and throttle right/left switching.

The other 10 switches are used to configure the equipment for a variety of model types and variations within each type as follows:

Fixed Wing

Most of the generally accepted features of fixed wing models, both powered and gliders are included, as follows:
Aileron rudder mix. The aileron stick operates both ailerons and rudder, while the rudder stick remains fully operational. Rudder movement variable via separate knob. Switched in or out by 'Mix Sw 1'. Crow Flaps. Using a separate servo for each aileron and one or two servos for the flaps (three or four servos total), the ailerons can be set to go 'up' when the flaps go 'down'. Can be switched in or out by the 'CROW' switch.
Differential Ailerons. Using a separate servo for each aileron, each can be set to give more 'up' than 'down'. Cannot be used with flapperons.
Elevator 3-position Trim Switch. This is an optional extra and gives three separate elevator trim positions operated by a 3 position switch. Does not effect elevator trim lever.
Elevons. Using one servo for each elevon, they can be used differentially for ailerons and together for elevators (Delta wing models).
Fail-Safe. All servos can go to a preset position or hold the last position. When a preset position is used, the information is held in the receiver and will be lost if the battery is disconnected for more than 1 hour. Flap-Elevator mix. Gives an elevator trim change with flap (or flapperon) movement. Trim variable via separate knob. Switched in or out by 'Mix Sw 2'.
Flapperons. Using a separate servo for each aileron, they can be used differentially for aileron, or together for use as flaps. Cannot be used with Differential Ailerons or Crow Flaps.
Flap/Throttle lever. If preferred, Flaps or Crow can be operated from the throttle stick.
Throttle Hold. Throttle can be frozen at a preset point by operating the 'TH-CROW' switch.
Twin Engine. Using a separate servo for each engine, both are operated by the throttle stick and have individual throw and trim settings. 'Throttle hold' can be used to allow one engine to be 'frozen' while the other is adjusted. Cannot be used with Differential Aileron or Crow Flap.
V-Tail. Using one servo to each half of a V-tail control surface, they can be used differentially for rudder and together for elevators.

In many of the above mixing options, some experimentation with servo reversal and the order that the servos are plugged into the receiver may be needed to obtain correct operation.


All of the basic helicopter features are included and are more than adequate for the beginner and average flyer. Specific features include:
ATC Mixer. Applies an automatic correction to the tail trim to compensate for torque variations. Can be operated from either the throttle channel (fixed pitch models) or the collective pitch channel (collective pitch models). Can be switched in or out via 'Mix Sw 1'.
CCPM 90 degree. Allows the use of a three servo Cyclic/Collective mixing system with the servos spaced 90 degrees apart around the swashplate.
CCPM 120 degree. Allows the use of a three servo Cyclic/Collective mixing system with the servos spaced 120 degrees apart around the swashplate.
Collective Pitch Curve. Changes the collective pitch about the mid position without effecting the end points (hovering pitch).
Idle-Up. Raises the engine speed at the lower end of the throttle stick travel. Can be switched in or out via 'Mix Sw 2'.
Invert Switch. Reverses the direction of elevator, rudder and collective pitch operation for inverted flight. It also puts an adjustable offset into the collective pitch angle (set by 'INVERT CPO').
Throttle Hold. 'Freezes' the throttle at a preset point for autorotation practice.

Note that there is only one throw adjustment for the collective pitch channel. However, the provision of a 'hovering pitch' control allows for the incorporation of differential throw, if needed.

When used with a tail rotor gyro which has two switched gains, the easiest option is to use the 'retract' switch for this ('Ch Sw 2'). Gyros having a proportional gain control can use one of the auxiliary proportional channels.


All of the various throws and mixing ratios are set by one or other of the 14 rotary trimmers, which automatically change their function as required by the operation of the various switches. The aileron, elevator and throttle throws can have different values for each direction, while the others have a single adjustment.

In PPM operation, any existing 'Digifleet' FM receiver can be used, but the fail-safe facility will not work.

Two transmitters can be coupled together for 'Buddy box' operation. The two transmitters must be on the same frequency and be set up in the same way. Control is transferred by the 'Master' transmitter being switched 'on' or 'off'.

The instruction manual is well written and tells you how to set up a model, rather than the more usual 'how to set up the transmitter' type. With each of the above functions, an explanation is given on how to obtain and adjust it, together with what it is used for. Also included are notes on installation, maintenance and even user repairs! Probably unique is the instruction not to cycle nickel cadmium batteries, which I heartily applaud! Unfortunately, the scope of this article does not allow me to explain why.


A neat and practical system which should appeal to the average flyer who wants to try more than one type of model. It incorporates all of the features that such a modeller will ever want, and more.

I liked the provision of eyelets and suitable screws with the servos - a thoughtful point that is frequently overlooked. The screws are particularly useful in that they are a self tapping type with full thread, rather than the useless wood screw type which is often seen. Servo trays are another useful item that seem to be going out of fashion.

It does seem a little odd that there is no separate charging lead incorporated in the switch harness, when disconnection will lose the failsafe memory in the receiver. This may possibly be to prevent the charging current from being applied to the memory circuits, in which case some specific warning should be included to prevent the owner making his own modification.

Another point is the provision of two ways of warning that the transmitter is switched on - an LED and a battery meter - and no means of noting that RF is actually being transmitted. Likewise, the operation of the buddy box system is, perhaps, a little clumsy - particularly when the main switch is shielded.

In the final analysis, though, this system has a lot to offer. If you are one of those who dislike 'computer' systems, this may soon be your only choice.

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