Understanding the JR Propo X-388S Radio – Part 2

By Richard A. Eckel

©Copyright 1994 All rights reserved

In Part I of this series we covered the Model Setup Mode of the JR388 radio and explored the effects of different settings in that mode. Part II will explore the other main menu area of the radio, the Function Setup Mode. This is the mode where most of the programming takes place using either the predefined mixes or what I refer to as free mixing.

I find it useful to think of the functions in this mode in groups. The first group I call Servo Adjustments, then Predefined Mixes, Free Mixes and, for lack of a better term, Convenience Functions. For easy reference the functions are arranged under those headings in the following list. Notice that I did not have to change the sequence that they are stepped through in the radio in order to make this arrangement. (Of course you must use the UP key to step down through this list.)

Function Setup Mode

Servo Adjustments

Predefined Mixes
mix E-F
mix AL-F
mix DIFF
mix F-E
mix FL-A
mix SP:


Free Mixes
mix A
mix B
mix C
mix D
mix E
mix F

Convenience Functions

Servo Adjustments
The servo adjustments section of the Function Setup Mode allows for the adjustment of dual rate and exponential for each of the three main control functions of the airplane – aileron, rudder and elevator and settings for each servo for sub-trim and travel. Each of the dual rate controlling switches on the transmitter can have a separate setup for each of its two positions. Argueably the most common setup is for the 0 (or off) position to be a strictly linear setup and the 1 (or on) position being a reduced rate or exponential (or both). However, with the X388S you are free to program the switches with any combinations you prefer for both the 0 and 1 positions.

The reverse switches, sub-trim and travel adjustments allow you to set each of the servos in the airplane for each of these settings. These are very convienent but should be used with some caution. The plane should be set up mechanically first using the defaults for these settings (except for reversing) so that the zero point and the travels are very close to the final adjustments. Use these settings in the transmitter to do the final trims. You can overdrive servos or end up with unbalanced setups if you don’t use these setting sparingly. If your initial setup is very far off of flying trim you would do well to readjust your linkages rather than flying with extreme settings in your sub-trim and travel adjustments.

Predefined Mixes
JR has already done a lot of the programming in the radio. The predefined mixes are typical mixes that are used in sailplane flying. By assigning specific receiver channels to specific control surface servos JR was able to preprogram these mixes so that you don’t have to mix each individual servo/channel individually.

The mixes are referred to by the flying control surfaces affected rather than by channels. If you have used the appropriate receiver channels and set DUA.F, FLAPS and VTAL in the Model Setup Mode these mixes are easy. You simply decide which switch you want to activate the mix (or it can be ON all the time) and set the percentage of mixing you want to take place. Notice that the controlling switches can be set up in both positions. You don’t have to set just on or off but are free to set up the switch such that one position has perhaps a 20% mix and the other position a 60% mix. Decisions, decisions, decisions!

Also notice that you can assign several mixes to the same transmitter control switch. This means that you can activate several mixes with a single switch throw. In cases where both positions of the switch are programmable you can assign different mix setups to each position. This is where planning your setup becomes important. You need to consider how you will assign your switches so that the mixes you want are available using the minimum of switches. Keep it simple. Particularly if you actually fly eight different aircraft! It gets hard to remember which switch to flip for which mixes!

mix E-F
Mixing flaps into the elevator function can be used to sharpen your glider’s response to elevator. This function can be controlled using the FLAP switch in the up position (F-UP), the FLAP in the down position (F-DN) or the MIX switch (MXSW).

mix AL-F
Flaps mixed into the aileron function provides full length ailerons for extra roll response. You must have DUAF activated, have a separate servo for each flap and a seven channel receiver for this function to work. Like the E-F mix, this mix is controllable with the F-UP, F-DN and both MXSW switch positions.

mix DIFF
JR makes this mix available to give you an easy way to set differential on your ailerons in order to prevent adverse yaw. However, they also do not recommend using it – at least for sailplanes. They recommend the use of T.ADJ (travel adjustment) instead. This mix can effect free mixes A and B for channels 2 and 7 and it just isn’t worth the hassle it can cause if you don’t realize it. I think that it also messes up the automatic reverse differential that happens when you deploy the ailerons in a crow setup.

mix F-E
Mixing a bit of elevator into the flap function can correct the pitch change associated with flap deployment on landing or launching. It can be controlled with both Flap up and down (FU+D) setting of the FLAP switch, with the MXSW or with the flap down (F-DN) setting of the FLAP switch. If you can’t decide on a combination with one of these settings remember that you can always set up an additional mix with the free mixes using another switch. Decisions, decisions, decisions!

mix FL-A
Don’t ask me why the previous mixes abbreviated flaps as F but now its abbreviated FL. It’s one of those mysteries that man was not meant to understand! But aside from that, this is a nice mix for getting full trailing edge camber or reflex. It is probably most often used to set up the FLAP switch for launch camber and speed reflex by using the FLAP switch FU+D positions. But it can also be controlled by the Mix switch (MXSW) or the down position of the FLAP switch (F-DN) or, like the other mixes it can be ON all the time. You pay your money and make your choices.

mix SP
Now here’s a mix that earns its keep. It mixes three functions in one menu item – elevator, ailerons (as flaps) and flaps. It mixes these three to the spoiler stick on the transmitter and allows you to choose the stick’s neutral position by setting its offset (OFFSET). This mix can be changed or activated with the CROW switch (both BTF0 and BTF1 positions are programmable).

One interesting detail with this mix is that if you set the OFFSET to the lower stick position the ratch trim for the spoiler stick will still trim the flaps when the spoiler stick is below halfway but not if it is above halfway. If you set the OFFSET in the high spoiler stick position the ratchet trim is disabled. Go figure. But sometimes with some planes it is handy to trim in a little camber when you are working a thermal.

Ok, so here’s a function that doesn’t fit my general category – nothing’s perfect. I guess they just had to put it somewhere and this seemed as good a place as any. This function allows you to disable the pots on the transmitter that are used for trim functions.

If you look back at the pot control table from Part I you can see how the pot functions change with the Model Setup Mode selections. The POT.5 function will only cycle through and enable or disable the trim pots that are activated because of the Model Setup Mode selections. Don’t be disconcerted when this menu sequence changes from one model to another.

Free Mixing
In addition to the above preprogrammed mixes, JR has put six additional programmable mixes into the X388S, mixes A thru F. I call them free mixes since you are free to mix any channels you want. All of these mixes are not created equal however. They differ in the switches that can be used to control them, whether or not you can preset an offset and whether they include other mixes. In some situations using mix E or F may be more appropriate than using mix A or B.

Table 2.1 gives a quick view of each of the mixes and its capabilities. Two of the settings are none intuitive. The offset here refers to the amount of master channel offset before the mix is applied. A setting of zero means that the mix is applied immediately when the master moves. A setting of 50% would mean that the master would have to move half of its defined throw before the mix would start.


mix A X X X X     X  
mix B X X     X X X  
mix C X X     X X X  
mix D X X X X        
mix E X X X X     X X
mix F X X     X X X X

INCLUDE is another tricky concept. (At least I thought it was.) It’s just waiting to get you in trouble if you use the E or F mixes. Essentially INCLUDE means that the mix will be applied to a slave mix if the master channel has also been defined as a slave. For example, suppose you want to have a little elevator applied with rudder and your rudder is already mixed to your ailerons. If you use mix A and mix elevator to rudder you will only get elevator when you control the rudder with the left stick. If you use mix E you will get elevator mix both when you use the left stick and when you use the aileron stick (since the rudder is slaved to the ailerons). The problems come when you use mix D or E without realizing that it will effect an existing slave mix in addition to the master you specified. Work out your control scheme carefully before you use mix E or F.

Mix D is also a special case. Mix D comes preprogrammed to mix rudder(4) to ailerons(2). JR put this in because so many pilots use this mix. You can change the mix to any two channels you want but the D mix does not have settable offset so if you want to set an offset you need to choose another free mix to use.

As you can see the JR X-388s has a wealth of mixing available. It is extremely unlikely that any one aircraft will use up all the mixing capabilities of the radio. With an understanding of the differences in the free mixes it is likely that you can find one that will perform the mixing that you want in any situation.

In Part III its time to put our understanding of the radio to work. I will propose a setup procedure to use with a new (or existing) model and let you in on a couple of mixing tips to get you started with the free mixes.

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