When JR decided with the Apex that it would be a good idea to let the customer have more throw than normal they actually cheated a bit. The standard pulse length per channel (throw) on just about every set had become established at 1 - 2 milliseconds, with a 1.5 millisecond neutral (some earlier sets used a slightly different neutral). With a trim throw of plus or minus 10%, this meant a total throw of 0.9 - 2.1 milliseconds. If you have much greater range than this the decoder design becomes very critical (actually, PCM could cope, but if you want PPM too...) and becomes even more tricky if you want a lot of channels.

So, what they did was to fix the maximum range of the throw, under all circumstances at 0.9 - 2.1 milliseconds (1.2 difference), while setting the standard throw at 1.1 - 1.9 milliseconds (0.8 difference). As 0.8 times 150% equals 1.2 - voila! 150% throw! This actually killed three birds with one stone (told you!) by allowing the new transmitters to work all existing receivers, allowing them to retain the existing PPM decoder on any new receivers and also ensuring that the servos would not be overdriven. Having said that, I believe that the latest servos sold with these sets do have a greater angular movement than early types to restore the original movement despite the reduced pulse length variation. If you are using your nice new PCM-10 to operate a model which has been set up on an old non-computer set, you will need to set all the throws to 125% in order to get normal movement.

On the Apex you could set the throw adjustment to 150% and the rate to 125%. Now even basic maths will tell you that this should give a maximum throw of 187.5%. Not so, because the absolute throw limitation of 150% came into effect. In some cases this could limit the throw in one direction, particularly when using the CCPM system.

As previously pointed out, the PCM-10 does not allow you to increase the throw beyond the amount set in FUNCTION 12. This is a swings and roundabouts situation, since it does remove the confusion which could arise when multiplying percentages, but is less versatile overall.

Now, for those who have not been paying attention, we have two limitations on the throw:
a) The amount set by FUNCTION 12 TRAVEL ADJUST which is the limit of normal travel including all trimmers. None of the trim levers, or rate switches, or pitch and throttle curves can exceed this amount of travel - see later.
b) An absolute limit of 150% throw which is the maximum which can be set on FUNCTION 12 and the maximum amount that any servo can move even when two or more inputs are being mixed via the programmable mixers.

These limitations can have interesting effects on the various trim levers. Taking the stick trims first; there are three(!) ways of using these:
1) Normal movement of the trim lever. These trims only effect the centre of the throw and do not move the end points of the servo travel. In situations where a very low travel has been set, or the rate switch is in the low position, the trim effect can be very powerful and this can seriously limit the stick throw in one direction.
2) FUNCTION 57 TRIM OFFSET. This duplicates the effect of the stick trim lever but can be used more than once to give greater trim offsets. It increases the dangers already described and should be used with caution. It cannot move the trim outside the limits set by FUNCTION 12, but if it is set to this limit there will be no stick throw in one direction.
3) FUNCTION 15 SUB TRIM. Unlike the stick trim this function does move the whole travel range, including the end points, in the manner we are accustomed to. However, it is still subject to the limitations set by FUNCTION 12 and overuse will limit the throw in one direction.

This is not as frightening as it all may sound and will only produce problems if used to extreme. If you are setting up a new model, my advice would be to set FUNCTION 12 to 125% and the rate switch to 80% (80% of 125% = 100%). Then use only FUNCTION 15 to sort out any gross trimming problems. This will move the whole throw range in the usual way without running into any limitation problems. You can also increase the throw via the rate switch if necessary.

There are also trim levers for high and low pitch end points. I personally do not normally use these since they work on all of the pitch 'curves'. The pitch curve is also limited by the throw set by FUNCTION 12. It can be reduced from this by using FUNCTION 68 PITCH CURVE, but you can only increase it by going back to FUNCTION 12. If FUNCTION 68 is set to the maximum (0 or 100), then the pitch trim levers will not be able to increase the throw either! However, the maximum throw corresponds to the centre of the trim lever, which means that the lower half of the 'high' lever and the upper half of the 'low' lever will still work! Confused?

If you want the trim levers to work normally, you must ensure that FUNCTION 12 is always set to give more throw than FUNCTION 68. In practical terms, this means that FUNCTION 68 should be set between limits of about 10 and 90. It is probably easier for most purposes to set the pitch channel to 150% via FUNCTION 12 and make all further adjustments via FUNCTION 68.

Before we leave FUNCTION 68, it has another little quirk. If you 'freeze' the throttle to make some adjustment, when you press ENTER you will be invited to MOVE STICK LOW POSITION. All very nice, but it does not invite you to move the 'flight mode switch' to the N position. So, if you were adjusting the pitch range on the 2 position (which normally has some idle-up added), when you move the stick to the low position it will BITE. You have been warned. The same thing applies when adjusting the throttle range via FUNCTION 18 so be careful!

FUNCTION 18 does not affect the throttle trim in the same way that FUNCTION 68 affects the high and low pitch trims. In this case the low point set on FUNCTION 18 corresponds to the low point of the throttle trim, so the trim is always effective. If the throttle trim rate is set to 100% (FUNCTION 17), then high trim gives half throttle. However, this is modified by any extreme adjustment of the main throttle curve. Nonetheless, it is very useful for fast descents, since it gives an easily adjustable 'idle-up'.

Needless to say, the throttle hold (FUNCTION 16) is also limited by the overall travel already set. A nice touch here is that you can set the motor to a reliable idle by means of the throttle trim and then read the value from the display and transfer it to the throttle hold. Although, here too there is a little quirk.

When adjusting the throttle curve, you may notice that it sometimes takes two touches on the appropriate flag to increment the display by one. This is because the overall throw (0 to 150%) is actually incremented in 255 steps. If the throw is 100%, it takes 170 steps (this will make more sense to Apex owners). So, although the display goes from 0 to 100, you actually have to touch the flag 170 times.

It does not really matter whether you understand that or not, the real point is that the throttle hold only takes 100 touches of the flag (100 steps). Why this should be is a puzzle, but the effect is that the throttle hold adjustment is rather coarser than the main throttle curve adjustment. This is not really a problem, but if you have difficulty getting the right setting the answer is to go back to (yes, you guessed) FUNCTION 12 and increase the low throttle movement by 1% and try again. This should 'nudge' it enough to make the difference.

One of the nice features of the throttle 'hold switch' is that you can program the rudder to go to a set point. This is very useful if your clutch refuses to disengage, or if you have one of those fashionable 'driven tails'. It also switches off the ATS, which is thoughtful, but all the trims still work! Yes, it is very nice to be able to trim the tail on the way down (I should be so good), but you then upset your normal trim. If you should find it necessary to retrim the tail (by trim lever, FUNCTION 15, or FUNCTION 57), you will then need to reset the rudder position on 'hold'.

FUNCTION 44 GYRO SENS ADJ allows AUX 3 to be used with a proportional type gyro (JR or Quest) to set two gyro gains and switch between them at will. The AUX 3 switch is also the rudder dual rate switch and still works when AUX 3 is in use. This means that you can change both the rudder rate and the gyro gain with one switch. Note, however, that FUNCTION 23 AUTO D/R only changes the rudder rate and not the gyro gain too. Pity that.

I may be wrong, but I get the distinct impression that the 'invert switch' was added because people asked for it and, anyway, the PCM-10 was supposed to have everything. There are three main reasons for this conclusion:
a) While there is a fully adjustable inverted pitch curve, there is no corresponding throttle curve. The throttle curve stays as selected by the 'flight mode switch', which means that you must remember to put this in the right position before operating the 'invert switch'.
b) Whatever position the flight mode switch is in, the invert switch turns the ATS system 'on' to the N setting. As this is dependent on the N pitch curve and you are now using a totally different pitch set-up, there is no way in the world that this can be right! You will see a dramatic change of tail trim when you operate the 'invert switch'.
c) Both the 'flight mode switch' and the 'hold switch' can automatically call up the dual rates. The 'invert switch' can't!

Just how you handle the throttle curve situation is up to you. With careful adjustment - and a few compromises - you should be able to use all three of the curves available, which makes it a shame that you only have one pitch curve. If you are using the high and low pitch trimmers, these are effective on the inverted pitch curve, which could be useful.

The only answer to the ATS situation would appear to be to set all the N settings to 0 and do without it. Incidentally, the invert switch over-rides the throttle hold switch, so you can't do inverted auto's this way!

It is interesting here to compare the invert system with the PCM-9, which had an adjustable pitch offset when the switch was operated which effectively gave you three inverted pitch curves. There was also an easily accessible switch to turn the ATS system off!

Before we leave the invert system, we should consider its relationship to FUNCTION 23 AUTO D/R. This function allows you to set three different rates; two of which can be called up by the rate switch and all three of which can be called up by the 'flight mode switch', or the 'hold switch', in various ways. Not only is the invert switch incapable of doing this, but the 'flight mode switch' can still select dual rates while the 'invert switch' is in operation.

To summarise: The 'flight mode switch' can over-ride the 'invert switch', which can over-ride the 'hold switch', which can over-ride the 'flight mode switch', which can... Have you got that clear?

There are 5 programmable mixers available (FUNCTION 51-55) which can be used to do a vast number of interesting things; but although they are one of the most useful features of the equipment they are certainly the least understood - and least used - item. Let's see if we can summarise what they can do and then give some examples.

Mixing takes place on a master/slave basis. That is, a part of one channel (the master) is mixed into another (the slave). The 'part' is variable between 0 and 100%, which means that the slave can move only a fraction as far as the master or exactly as far. This movement can be in the same direction or in the opposite direction. Note that the slave cannot move the master, another mixer would be needed to do that.

If the master has a trim facility, you can choose whether or not to pass this on to the slave. Similarly, if the master is itself a slave to another master channel, you can decide whether to pass this first masters movement on to the second slave.

You can also arrange things so that the slaves neutral has some offset from the masters neutral. This is not at all easy to set, since you have to offset the masters control by the required amount and then touch the appropriate STORE flag. You usually then find that the effect is the opposite of what you required and you have to start again!

Lets assume that your helicopter has some interaction between lateral and fore/aft cyclic (swashplate phase-lag). When you apply a 'right' command, it drops its nose, while a 'left' command makes it nose up. Here you make lateral cyclic the master and fore/aft cyclic the slave, so that 'right' adds a little bit of 'back' and vice versa. You would probably include the trim so that a little 'right' trim gave a little 'back' trim.

If your model loses height when you move slowly away from the hover, you could use another mixer and adjust the mixing directions so that 'right' or 'left' would both add a little power. A third mixer could give the same result for 'forward' or 'back'. Here you would leave out the trim since this is to adjust the static trim and you don't want to change the power.

Carry things a stage further and imagine that any tail rotor input now causes the model to bank, as well as yaw. You can use a fourth mixer to sort this out as in the first case, but we are only considering large inputs so you don't include the trim. In this case you would not 'include' the tail rotor signal in the lateral cyclic's signal to it's slave, the fore/aft cyclic.

We now have a situation where the tail is a master to the lateral cyclic's slave, which is itself a master to both the throttle slave and the fore/aft cyclic slave. Meanwhile, the throttle is also a slave to the fore/aft cyclic master. In this situation, the tail rotor trim only trims the tail rotor, the throttle trim only trims the throttle, the elevator trim only trims the elevator, while the aileron trim controls both aileron and elevator. Forgive the lapse into aircraft terms - its simpler that way!

The situation described is an extreme case - and probably a nightmare to sort out - but I hope it makes things clearer.

Note that the actual percentage of the mix can be different for each direction and the actual direction is set by the positive and negative signs in front of the percentage on the display. Getting the directions right is purely a matter of trial and error.

You have a wide choice regarding just when mixing is to take place. It can be permanently on, or switched on by the 'mix switch'. It can also be switched on by the 'flight mode switch' in the N position, or the 1 and 2 positions, or just the 2 position. Thus, the above system could be arranged so that it was only effective with the 'flight mode switch' in the N position and is automatically switched out in all other positions. A minor snag here is that operation of the 'hold' switch would not switch the mixing off.

We have already mentioned that there is an absolute limit on the servo movement of 150% throw. When mixing is used you should ensure that the total of the mixed signals does not exceed this amount. If channel A is a slave to channel B and both have 100% throw, then the mix ratio should not exceed 50%. If the mix ratio is, say 100%, then a situation can occur where A is required to move 200% - and it can't! The result is that the servo will reach its limit before the input reaches it's limit and will not move any further. In extreme cases this can produce a situation where there is no movement at all in one direction - as previously described.

In any mixing situation (especially CCPM) you should run the system through all possible combinations to check that this does not happen. Finding out with the model airborne could be disastrous.

Before we move on to CCPM, there is one other little peculiarity of the mixing system which should be mentioned. You can mix any channel with itself. This may seem like a rather pointless exercise but, if you mix a channel with itself in the reverse direction, the result is to render that channels control stick, knob or switch inoperative. The channel concerned can then be used as a slave to another channel without the result being affected by accidental operation of its own control. This can be quite useful. Incidentally, you cannot mix channels 9 and 10, which is a little unfortunate since they are both proportional channels, while all the other auxiliary channels are switched.

In keeping with the basic premise of 'having the lot', the PCM-10 also includes a CCPM system. It does seem, however, that having both CCPM and an invert system in one transmitter has meant that both systems have suffered, since the CCPM system only caters for set-ups having 3 servos. Or, in other words, three inputs to the swashplate. These may be spaced at 90 degrees or 120 degrees and are selected via FUNCTION 65 SWASH TYPE.

When you select CCPM, you will find that the mixers involved have a default value of 60% to avoid overdriving the servos, as previously described. It is not at all clear whether this 60% is the actual mix ratio or the overall throw of the servo after mixing. The overall result is that the collective and cyclic channels (2) are mixed to produce a moving swashplate system which should be fairly easy to adjust when used on a new model. However, if you try to match it to an existing model which was set-up on an Apex, you may have fun. More on that anon.

The idea of letting you adjust both the mix ratio and the throw of each channel is really too much of a good thing. With the amount of adjustment (0 to 150%) which is available for each channel, the mix ratio could be fixed at 100% and you would not notice the difference. This is exactly what is done in the Apex 8 computer.

The problems start when you want to use a two or four servo system, neither of which is directly catered for. Here the programmable mixers can come to the rescue, but you must be prepared to tinker a little (note to cat owners - no, not tinkle a litter...).

A four servo set-up is the easiest to deal with, so lets consider that first:
a) Use FUNCTION 65 to select 3SERVOS(90 degree). This will give one servo on fore/aft cyclic and 2 servos on lateral cyclic. Use the servo reverse and mix direction (+ or -) to get the servos operating in the correct direction.
b) Choose an auxiliary channel which is not being used for anything else - say AUX 2 (which is actually channel 7), and plug your fourth servo into it. This will be your second fore/aft servo.
c) Use a mixer (FUNCTION 51) to mix pitch (which is AUX 1, or channel 6) into AUX 2. Set the mix direction so that the servo moves the swashplate in the same direction as the other fore/aft servo when the collective stick is moved.
d) Use another mixer (FUNCTION 52) to mix fore/aft (ELEVATOR, which is channel 3) into AUX 2. Set the mix direction so that the servo moves in the opposite direction to the other fore/aft servo when the elevator stick is operated. You want to include the trim here, so set TRIM 'ON'.
e) Set a third mixer (FUNCTION 53) to mix AUX 2 back into AUX 2 in the opposite direction (-). This will disable the AUX 2 switch.

Now the only problem is to juggle with the mix ratios so that the fourth servo matches the throw of the existing elevator servo. You might assume that setting the ratio to 60% would achieve this, but it does not seem to work that way - hence my earlier remarks. As previously stated, the whole thing becomes much more difficult if you want to match it to an existing model. It is only really possible if you have some means of accurately checking each channels output from the receiver, such as a pulse counter/timer.

You will note that operation of the AUX 2 switch will cause the new servo to twitch. This is a by-product of mixing the channel with itself and is known as 'dynamic mixing'. Unless you are in the habit of continually operating this switch while flying the model around, it will not cause a problem. The whole idea here is to ensure that accidental operation, or wrong positioning, of the switch is not disastrous. If it really bothers you, the answer is to disconnect the switch instead of mixing AUX 2 back into itself. However, this is rather drastic and not really necessary.

If you want to use a two servo CCPM system (as in a Heim model), things become just a little complicated. There are (all together now!) at least three different ways of doing this and they all have their advantages and disadvantages:
1) Use a 3 servo 90 degree system, as above, and use a mixer to mix PITCH (channel 6) into ELEVATOR (channel 3) in the reverse direction to the existing mix so that collective no longer moves the elevator servo. The previously mentioned 'dynamic mixing' effect means that any rapid movement of the collective stick, will produce a temporary small change in elevator trim. This is the main disadvantage of this method.
2) Plug the elevator servo into AUX 2 and mix ELEVATOR into AUX 2. Use another mixer to disable the AUX 2 switch, as described above.
3) Make up your own 2 channel mixer by using one mixer to mix AILERON (channel 2) into PITCH (channel 6) - set TRIM 'ON' - and another mixer to mix PITCH into AILERON. The two servos will then be plugged into the aileron and pitch channels. The snag here is that the invert switch will not work correctly.

If you use 3) with a new model, there should be few problems. If you are trying to match an existing model, do it this way:
a) Set both mix ratios to 100%, in each direction, and arrange the various mix directions and servo reverse switches to obtain the desired operation.
b) Use FUNCTION 12 to set both AILERON and PITCH throws to 75% in each direction.
c) Set FUNCTION 13 to give a maximum aileron rate of 67%.
d) Use FUNCTION 68 and a pitch gauge to duplicate your existing pitch settings.
e) Make all trim corrections via FUNCTION 15.

This set-up will give a normal 100% aileron movement and maximum pitch throw, while minimising the dangers of running out of throw through overdriving the servos. Be very careful if using the stick trim levers.

One other little peculiarity of FUNCTION 65 is that it includes a facility to activate an exponential system. This does not appear to be related to the exponential available via FUNCTION 13. At the moment, it's a bit of a mystery, but I'm working on it.

The PCM-10 In PPM mode will work any existing JR FM receiver - but always use genuine JR crystals!

In PCM you will find that any mixing system will give jerky servo operation on the bench. The more complex the mixing, the more jerky it will become. It is doubtful that you will be able to tell the difference in the air, however.

This jerkiness is caused by the fact that in PCM operation the encoder has to do various sums in working out just what each combination of controls means in terms of final servo position. The actual process involved here is very complex. Remember that the stick pot is an analog device and its signal has to be converted to digital and then to PCM. After all the sums are done and the result transmitted to the receiver, the decoder then has to do a conversion from PCM to digital before sending the result to the servo. The servo then does the final process of converting the digital signal back to its own reference - the feedback pot - which is analog.

All this is done so that you can use standard digital servos. A true PCM servo would speed things up considerably - at a price. Meanwhile, it all takes time. In PPM mode the jerkiness will disappear. For this reason I prefer PPM for any model using CCPM.

Just how you program the failsafe for helicopter operation is up to you. The CAA has now clarified the position for models over 7Kg and have stated that the minimum requirement is for the throttle to close. My one experience of failsafe operation was on my Apex equipped 'Avantgarde', which had been set up to failsafe into autorotation. The model was being flown around at high speed and suddenly dropped like a stone! Fortunately, it recovered almost immediately. My recommendation is that you build your models below 7Kg and set the failsafe to 'hold'!

Finally, don't fly in the rain. The keyboard/display unit does not like it. I know of a flyer who did just this and ended up having to buy a new transmitter. Actually, I believe he had to buy a complete new outfit, but I don't believe that is really necessary. It depends who you deal with! Hopefully replacement parts are now available anyway.

Yes, it's a wonderful piece of equipment, with lots of character. Much of the 'character' is still undocumented and I wonder if even JR realise just what they have created. It can do just about anything if you are prepared to work at it, but I still feel that it is not ideal if it is your 'one-and-only' transmitter.

The complete helicopter flyer really needs a PCM-10 and an Apex CCPM. If you want to do some serious inverted flying, you probably need a PCM-9 too...

If anyone has any questions regarding the PCM-10 (or Apex), or has any new discoveries they would like to share, I would be happy to act as a 'clearing house' for these - through the magazine, of course.