PIC 2 Photo #2: The S-PCM receiver and 4 NES 517 servos.
Standard Features
Permission to reprint Don Edberg's article below by
Radio Control Modeler magazine or 'RCM' for short. Most of you,
like myself, have heard of RCM. RCM is a r/c magazine filled to the rim with excellent articles, hints & tips, and
other solid information.
JR/Horizon Hobby Distributors, Inc.
July 1997
By Don Edberg
I recently received a sample of JR's new XP8103 R/C system. Originally, I had planned to review only its soaring features for my monthly soaring column, but I suggested to The Boss that maybe I should look at all features of the system, since I have recently published my own computer radio book, which will be mentioned elsewhere, as well as written some instruction manuals for Brand F. The Boss said, "Okay," so here's the full-on review.
The letters "XP" mean that it's a computer radio and capable of both PCM and PPM (FM). The 8103 describes its functions: the "8" is the number of channels being transmitted; the "10" describes the number of independent models that the system can hold (ten different models' worth, you can have any combination of plane, glider, and helicopter models that total up to ten); finally, the "3" identifies that this system is a "3-in-1" system. By 3-in-1 we mean that the transmitter comes with programs and functions for the three types of model aircraft: airplanes, helicopters, and sailplanes. To choose which type of model, one enters the programming mode (by switching the transmitter on while holding down two keys) and selects that type. After selecting the model type, the system obliges by showing an illustration of that type of model on the display - cute!
The XP8103 PCM aircraft system we reviewed included a transmitter, NER-649S 9-channel S-PCM receiver, four NES-517 servos, switch harness, 600 mAh battery, charger, an aileron extension cord, frequency numbers, and manual. If you prefer, you may purchase an FM system (comes with NER-549 receiver and four NES-507 servos) or a helicopter system which comes with a 1000 mAh receiver battery and either five -517 or -531 ball bearing servos Both receivers weigh 1.5 oz. (43g).
The system's transmitter has a conventional layout (Photo #1), with a recessed on-off switch (to make difficult to turn it off accidentally), and a neck strap loop (neck strap not provided). In addition to the two dual-axis control sticks with conventional mechanical trims (each trim has a detent at its center), there are seven switches to turn various functions on and off, and three knobs. There are no sliding tab controls or side levers. It's possible to adjust both the stick length and change stick spring tension (the transmitter rear cover must be removed for the latter). Also, an optional DSC cord may be used to check servo motion without transmitting any signals. More interestingly, the DSC cord can also transfer model set-up data between two 8103 transmitters! (We weren't able to try out the transfer function.)
The 8103 transmitter case is very comfortable to hold and operate. Its antenna is a conventional "whip" type that collapses into the case and does not swivel. Perhaps the dominant feature of the 8103 is the large display in the top center.
PIC 2 Photo #2: The S-PCM receiver and 4 NES 517 servos.
One potential area of concern with this system is that it utilizes a lithium backup battery to maintain all the settings stored in memory (other brands do not require this battery). Eventually, it'll "run out of steam" and all of the memory settings will be lost. Although the system will warn you when this does occur, you will lose all the program info that you've entered. For this reason, you should write down all of these settings in the blank forms provided in the manual for this purpose (or you may transfer them to a friend's 8103, if available - this procedure will be discussed later). Editors Note: It should be mentioned here that the lithium battery lasts about five years, and that every transmitter should be checked and tuned every 3-5 years anyway, no matter what brand, so this should not be too much of an inconvenience.
Another area that the owner needs to be aware of arises because JR chooses to use reversed polarity (compared to all other manufacturers) for its transmitter chargers, so if you try to use another brand's charger, you can cause serious damage to the transmitter. One good thing is that the battery is not diode-protected, so you can use a cycler to measure its capacity without any modifications.
The 8103 system has many features that may not be familiar to readers, so we'll take a moment to review them. How you use these features is covered in the system's manual, which is fairly comprehensive and splits most of its 144 pages into three independent sections (one for each of the three model types). First, we'll look at the features that apply to all model types; then, we'll look at the type-specific menus.
PIC 3 Photo #3: The left side switches and controls.
One really nice feature of the 8103 is the "List Mode," which displays all of the functions available on the screen so there's no need to press buttons repeatedly until the desired menu appears, as on some other radios. Instead, you can just move to the one you want and enter it directly. This feature also makes it unnecessary to have a manual on hand all the time. One little idiosyncrasy of the 8103 is that to move "up" in the list of functions, you press the DN (down) key and vice versa, but you get used to it after a while.
Dual Rate (D/R) and Exponential (expo) functions are very useful ones for beginners and experts alike. Dual rates allow the pilot to switch the control authority up or down by flipping a switch, which is very handy for test flying or dealing with models whose response rates change with different flying speeds (normally dual rates are used to reduce control authority at higher speeds, where the models are usually more sensitive). The 8103 also has the option of an "automatic" rudder dual rate that changes the rudder travel limits as the throttle passes 70% of full travel.
Expo is sort of automatic dual rate, where the control response is low around the neutral position, and increases the farther you get from neutral. It's handy for models that are very sensitive around neutral, but still require lots of control movements for aerobatics.
Reversing is done in software and shown graphically on the display. The reversing function is, of course, used to make sure that the servos rotate in the proper directions when a control input is given.
"Sub Trims" are nothing more than electronic neutral adjustments. They're used after the linkages are hooked up and the controls are set to be as close to the proper neutral positions as they can be mechanically. Small amounts of sub trims are then used to make "fine adjustments" to the servo neutral positions to get them just right.
The Trim Offset function is used to make the transmitter "memorize" the existing positions of the trim levers, so that they may be moved back to their center positions. This is important when you switch among several different model memories. If you keep the trims centered, the proper positions will be maintained by the radio and you won't need to worry about changing the trim's positions for each model.
Travel Adjustments are used to specify how far the servo can move with full control motion. They're typically used to prevent any binding or pushrod interference which could jam a servo or cause increased current drain, or simply to reduce the maximum travel of the servo. Travels should be adjusted before any dual rate inputs are made.
Programmable Mixes are one of the "cool" computer radio functions. These may be used to accomplish things that are not built into the system's programming schemes. For example, you might use programmable mixes to account for some tendencies you wish to eliminate, like unwanted rolling during knife-edge flight. For that particular example, you'd mix from rudder to ailerons so that the ailerons would move slightly to stop the rolling for either direction of full rudder.
The 8103 offers six separate programmable mixing functions (three for helicopter mode) that may be used freely between any two channels, one being the master channel, and the second is the slave. Two of these mixes are unique in that they provide "multipoint" mixing functions. The multipoint function allows the user to program in "curves" that describe the mixing behavior, which is usually limited to straight lines or linear relationships. This is particularly handy for the knife-edge example given above, since the amount of roll-coupling that occurs is not linear. It may only take about 2% coupling to eliminate the rolling at half rudder, 8-10% at 3/4 rudder, while at full rudder travel it may take as much as 30%. The multipoint mixing feature allows you to explicitly input these values so that the amount of coupling is correct for all amounts of rudder travel. Even better, the mixing curves are displayed (Figure 3) while you work on them, so there's no doubt as to what you're getting. I really enjoyed working with the 8103 mixing functions. They're very well laid out and the simplest to understand that I've seen.
The Name function simply allows you to input a name or label for a particular model memory. The 8103 can accept up to eight characters for the name. This is very helpful to keep track of which model memory is being used.
PIC 4 Photo #4: Right side switches and knobs.
The Trainer function allows one to connect a transmitter to another transmitter for flight instruction. One may select whether all functions are to be controlled by either transmitter, or may select among them, so that the beginner may concentrate on one function at a time until they're ready to move on to the next one.
The Timer functions provided on the 8103 are interesting. First, there's a regular timer with choice of stopwatch or countdown modes. The countdown mode is set by the owner to match the model's fuel capacity or some other desired duration, and there are ten beeps as it reaches the end time (but continues to count afterwards). The system also provides an accumulated time function separate from the timer. What is interesting is that this accumulated time is maintained independently for each model memory, so it can be used to keep track of flying hours for maintenance, etc.
The Servo function turns the display into a visual indication of where each servo is commanded to move. This "bar graph" display enables one to program in mixing functions and see how they command the servos to move, without ever having to turn on a receiver. I have used this function on other radios to set up programs while watching TV, and only have to make fine adjustments with the model turned on.
Copy, Data Transfer, and Reset functions are used to duplicate, transfer to another transmitter, and erase model memories. Copy is handy for when you'd like to experiment with some different model settings or trims but don't want to disturb your original settings. Data Transfer can be used to copy a program over to another transmitter for, say, trainer operations or so a friend can see your programming particulars. Of course, Reset is used to clear a memory out for a new group of model settings.
The Modulation selection function is used to select from FM/PPM and two types of PCM transmission: S-PCM or Z-PCM. This will, of course, depend on the receiver being used. Brand A PPM receivers will work with JR's PPM mode, but others in general will not.
These features are common to all model types. Now, we'll go on and look at the model-specific menus.
Acro Mode
The Acro Mode of the 8103 contains many special functions for fixed-wing models. Many of these are activated by the
"wing-type" menu settings, which allow you to select from Normal, for wings using one servo for both ailerons;
Flaperon, for wings with two aileron servos for two controls; and Elevon, for models without tails. Flaperon combines
the functions of flap and ailerons, while Elevon combines the functions of elevator and ailerons. In addition to these
settings, the 8103 also contains programming for the following:
Elevator to Flap Mixing is used to increase the model's pitch rate for aerobatics, and is usually used to command the
flaps to drop when up elevator is input, and vice versa. Aileron to rudder mixing is used to slave the rudder's motion
to the ailerons, so that turns are more "coordinated." The latter mixes may be commanded to be on always, to turn on
with a switch, or to turn on automatically in the landing mode. A function called "Flap knob adjustment" controls the
total response of the combined ailerons and flaps when in the flaperon mode.
The Landing System (sometimes called air brake mode in other radios) is a function which commands preset amounts of elevator, flap, and spoilers to provide a high-drag, steeper approach for more "consistent landings." The landing mode may be activated automatically by passing a specified position on the throttle stick, or manually by flipping a designated switch. Interestingly, the 8103 will not allow you to input presets for the different controls unless the activation switch is on. This will help to prevent entering numbers accidentally and having them come on by accident (since you have to activate the function to program it); this is a very good feature. By the way, the spoilers may be assigned to a knob providing proportional control, or a switch allowing on-off functioning.
The Snap Roll function is designed to provide fixed motions of the elevator, ailerons, and rudder in order to make easy and consistent snaps at the touch of the snap roll switch. You may select any combination of up or down, and right or left, to occur when the switch is flipped. There is no way to disable the snap roll switch in this system (others provide a safety where a snap roll cannot happen if, for example, the landing gear is down).
Aileron Differential function provides a way to reduce the yawing tendencies of models when aileron is applied, and only operate when there is a separate servo for each aileron. By having more up aileron travel than down travel, the tendency for the model to yaw away from the turn is reduced The Aileron to Rudder Mixing function provides another way to reduce the yawing tendency by mixing rudder to work with the motion of the ailerons, and may be set to be on always, during the landing mode, or by switch command.
Helicopter Mode
Activating the Heli Mode of the 8103 automatically turns on virtually all of the helicopter functions one could desire.
The standard array of heli flight modes is offered: normal, stunt-1 and -2, and throttle hold. Along with these flight
modes comes the standard set of curve adjustments for fine-tuning the mode's response to suit your personal tastes.
Each curve has five programmable points, and independent settings are available for both the throttle curve and pitch
curve for each of the three flight modes. The curves are clearly shown on the 8103's display and are very easy to
program.
The Hovering Throttle and Hovering Pitch knobs may be used to fine-adjust the positions of the three middle points of their respective curves, and a special "exponential" function smoothes the throttle curve shape between the defined points (not to be confused with exponential control response function) A Pitch Trim knob may be used to adjust the rotor rpm directly from the transmitter case.
The 8103 is set up so that throttle trim is only active in normal flight and is disabled in other flight modes. You can
select whether channel 7, which may be used to control gyro sensitivity, is slaved to the rudder D/R switch or not. In
addition to the model type - independent functions listed before the Acro Mode, you get the following heli functions:
Stunt Trim is used to provide fixed offsets in order to trim the helicopter for forward flight without having to touch
the trim tabs. There are separate settings for aileron, elevator, and rudder. An inverted switch electronically
reverses rudder and elevator for inverted flight, for those who prefer to do it that way.
Throttle Hold locks the engine to a fixed throttle position and is usually used for practicing autorotations. It decouples the throttle from the collective stick so that the pilot can leave the engine near idle and practice, then deactivate and abort the landing, if necessary.
Revolution/Acceleration Mixing mixes throttle to tail rotor to counteract torque effects from the main rotation. Two separate revo mix settings are provided, one for normal flight and one for stunt-1 and -2. Acceleration Mixing provides a way of compensating for abrupt throttle motions, and a rudder offset setting is provided for correcting yaw during throttle hold.
Gyro Sensitivity may either be selected manually by the rudder D/R switch or automatically by the selected flight mode. Fairly detailed set-up instructions are given for its use.
Sailplane Mode
The Sailplane Mode of the 8103 contains the sailplane functions one needs to control a competition model with four wing
servos, and a conventional or V-tail. Interestingly, the type of tail is selected in the "Wing Type" menu. The Function
List menu for sailplanes includes:
Elevator to Flap Mixing is used to increase the model's pitch rate for tight thermal turns, similar to its function in
the Acro Mode. It may be selectively turned on and off or always on. Flap to Elevator Mixing is used to eliminate
pitching tendencies when the flaps are raised or lowered, and may be set independently for each direction of flap motion.
Aileron to Flap Mix is used to make the flaps move with the ailerons so that the model's roll rate will increase due to a larger amount of aileron control surface available. This mixing may be turned on always, or may be switched on and off by flipping one of several switches.
Flap-Aileron Mix couples the motion of the ailerons to that of the flaps so that full-span camber changes may be made. Like other mixing functions, it may be on all the time or switched off and on with one of two switches. Differential and Ail-Rud Mix both function the same as in the Acro Mode, helping to reduce yawing to the outside during turns.
Butterfly (Crow) Mixing is a function that allows the spoiler stick (throttle stick) to move the ailerons and flaps to provide a slower, steeper descent for predictable landings. There is also compensation to the elevator so that you can eliminate the pitching that commonly occurs with butterfly commands. You may define a reference or start position anywhere in the spoiler stick's travel.
To get used to these functions quickly, the manual provides two pages of terse but detailed set-up instructions. It tells how to program in the instructions necessary to get the model to have either launch or reflex (penetrate or speed mode) positions. This will help the novice get into the air more quickly.
All in all, the JR XP8103 is a very powerful, yet relatively inexpensive, radio control system. Its large display with clear illustration of many of the available functions and mixes makes it very easy to program and use. If you are in the market for a new 3-in-1 radio system, you should strongly consider the 8103. Table 1 shows how it compares to two similar radios on the market: Airtronics' Stylus and Futaba's 8U.
The Guide to Computer Radio Control Systems book referred to earlier is available in the U.S. for $19.00
postpaid 1st class from Dynamic Modelling, 4922-J Rochelle Ave., Irvine, CA 92604-2941, (949) 552-1812 or
Don's toll free number at 1-888-770-1812. Or via email:
Don Edberg