Cal Orr shares his experience with FrSky radios
Cal Orr is shown with the FrSky X20RS transmitter. In the background is a Yellow Aircraft AT-6 on the right and a Yellow Aircraft Spitfire on the left. Behind Cal is a 1/2-scale, 25-foot wingspan, 70-pound Stein Adler glider. Photo by Marcia Orr.
(Author’s note: I have spent many years testing, servicing, and modifying RC radio systems. I thought I had seen it all, but the FrSky radio was different. I had often thought of it as being for quadcopters, but in the last few years, this radio has really evolved.)
W hen is it time to investigate a new radio system? For me, it was about a year and a half ago while I was flying a proven 10-foot wingspan, four EDF-powered airliner in Muncie, Indiana, and it flew away from me. I thought I had done everything right, with redundant receivers and back-up batteries. I had what turned out to be a transmitter issue. The airliner flew out of range and both receivers went into failsafe.
I looked at several radios. What caught my attention was that a couple of the systems were transmitting on both 2.4 GHz and 900 MHz simultaneously. The receiver was looking for both bands with built-in redundancy!
The FrSky radio has this built-in redundancy, and through its telemetry system, it tells you whether there is low receiver sensitivity with a Received Signal Strength Indicator (RSSI) while you can still turn the airplane around and head back home. The RSSI warning can be given to you audibly for each band of 2.4 GHz and 900 MHz.
A feature I have not seen before is a VFR warning. In the world of FrSky, VFR means valid frame rate and is given as a percentage. If, for example, VFR is 80%, eight out of 10 frames make it to the servos. A VFR warning can also be given audibly—yes, this transmitter talks. It is possible to do preflight range tests by simply putting the transmitter in range-test mode and walking away without looking at the airplane.
When you get some distance away from the model, the transmitter might start with RSSI warnings, and then VFR warnings as you continue to walk away. You can turn around and look at the airplane and, even with all of those warnings, the servos still operate. If you want more redundancy, FrSky radios are set up so that you can install up to three receivers in one model. I have done long ground range tests of up to a mile and a half and can still operate the servos. If you want more range, you can install external antennas on the transmitter and also adjust the 900 MHz output up to 1 watt.
How does all of this work in the air? I fly some 1/2-scale models with 25-foot wingspans. With larger models, we tend to fly farther away from us than we realize. I have not heard an RSSI or VFR warning while flying.
Many radios have a failsafe system. At the loss of a signal or interference, the throttle is driven low and all other channels are held at the last valid command. This failsafe works fine most of the time. I have seen failsafe problems with multiengine aircraft, where you have two or four throttle servos all mixed to the throttle channel.
The advantage of all of this mixing is that you can dial in each engine without affecting the others. However, if the radio then goes into failsafe, only the one throttle servo is driven low and the other “mixed-in” throttle servos are held at the last valid command. A workaround is to program the failsafe so that all servos are driven to a preset and you skip the hold on the flight controls. This is not a good workaround, in my opinion.
In the event of failsafe, I want all of the throttles to go low and all flight controls to be held at their last valid command. The FrSky failsafe system gives me this option. I can program any of the 24 channels independent of each other to be driven to a preset or held.
The second thing that sold me with the FrSky radio was the company’s line of telemetry modules. I really like the airspeed module. It’s a real pitot static system that gives you airspeed in real time. I programmed my transmitter so that, at a flip of a three-position switch, I can select between Off, Altitude, and Airspeed, which is verbally read to me every 3 seconds as “43 mph, 44 mph,” etc.
I have found that with a big AT-6 warbird on final, I might want to hear the airspeed every second, which means that I need to get rid of the “mph” so that I hear “43, 44, 43, 44,” etc. Yes, you can estimate the airspeed with a GPS module that actually gives the ground speed. On a calm day, the ground speed is close to the airspeed, but also keep in mind that there can be a slight delay in GPS because it must constantly recalculate the speed.
The FrSky transmitter I chose is the 24-channel X20RS with ETHOS operating system software. The X20RS transmitter includes a color touchscreen, very nice stick gimbals, and a lot of switches, levers, and knobs. The transmitter can be customized to suit your needs; I changed the stick ends and replaced two of the toggle switches.
The long toggle switch above the elevator stick is a three-position switch. I wanted two positions for on/off ignition or forward/reverse for electric flight. The long toggle switch on the top right of the transmitter, which is commonly used for electric motor cutoff, was a spring-loaded toggle. I wanted a two-position switch without the spring.
As it turns out, FrSky offers several switches that are already wired with a connector and can be easily plugged into the transmitter. Once you have changed the switch, you need to go to the software, select that switch, and then select the number of positions, whether it’s spring loaded, etc.
The engineers at FrSky will tell you that programming this transmitter is intuitive. The software might be intuitive, but it is most likely not what you are used to. This transmitter can probably do anything that you dream up; it’s not really a transmitter—it’s a computer with joysticks.
Look at the picture of the front of the transmitter. The two round wheels below the joy sticks are used for programming. The left wheel selects system (SYS), model (MDL), display (DISP), or return (RTN). The right wheel continually rotates and will allow you to walk through different steps of the program. The center button will allow you to select a feature. If you also have a touchscreen, that will aid in programming. You can immediately select a function without having to scroll through a list.
Airplane Setup
I will share my experiences setting up four different airplanes with the FrSky radio system.
My first FrSky setup was with a Piper Cub, a simple four-channel electric airplane with two aileron servos. The receiver I used was the FrSky TD R12, as pictured. I then quickly switched to the TD SR12, which is the same size and has the same looks, but it includes flight stabilization for the aileron, elevator, and/or rudder. I generally stay away from any receiver with an autopilot, gyro etc., but the point of this exercise was to see what the radio could do.
The programming took a little longer than usual since I was learning a new radio. Servo-reversing and triple rates were familiar, but I found the mix functions of the two ailerons to be a bit different from what I was used to. I added the pitot static airspeed module, along with a GPS module that I used for altitude.
The two telemetry modules were then daisy-chained together, and one connector from both modules was plugged into channel 12 of the receiver. In the transmitter, I had to program the receiver output channel 12 as my telemetry. Because my Cub is electric, I programmed the top-right long toggle switch as an engine kill to prevent accidental motor starts.
Some thought has been put into the electric motor safety switch. If, for example, the throttle stick is at half and the throttle kill switch is accidentally bumped on, the motor will not start until the throttle is pulled all the way back and advanced. The same logic is also used during flight. If, while flying, you accidentally bump the throttle kill switch, the motor will not shut down until the throttle stick is pulled all the way back.
I used flight stabilization on the rudder only. I then set up a transmitter knob that adjusts the gain from zero (off) to 200% (very sensitive). This meant that during flight, I could turn the stabilization off or infinitely adjust it to very sensitive. I made my takeoffs and landings close enough that I could see the rudder operate.
At approximately 100% to 125%, I was only using the throttle along with the aileron/elevator and not touching the rudder. The stabilization system worked very well, and I was able to find my desired gain setting in only a few minutes during the flight. I also really enjoyed having the airspeed read aloud to me every 3 seconds at the flip of a switch.
My next project was installing the FrSky radio into my Yellow Aircraft AT-6 that is powered with a Saito 450 three-cylinder radial engine. This airplane has a glow system to turn on and off, two elevators, two ailerons, three flaps, a rudder, and landing gear, along with throttle and telemetry airspeed/altitude.
This required all 12 channels and, for the purpose of redundancy, I installed two receivers and split up the controls. For example, one receiver operated the left aileron, left elevator, rudder, etc. The other receiver operated the right aileron, right elevator, flaps, etc. This “split system” gives you some control in the event of a major failure or short circuit. The two yellow battery connectors on the receivers each have their own batteries for a total of four batteries in the airplane.
Note that these receivers can be powered by a standard receiver battery plugged into an unused servo connector or, for heavy servo loads, a battery with heavier wires can be plugged into one or both yellow battery connectors. The receiver itself can operate on a wide range of batteries and voltage, but be careful that all of your servos can operate with the batteries and voltage you choose.
Also, note that the “split” radio system I described is just one method for redundancy. FrSky offers a “box” (or flight controller) that you plug all of your servos into. Up to three receivers can plug into this flight controller.
The receiver that I plugged the rudder into was an “S” receiver, and I thought I would try the same rudder stabilization that I used on the Cub. The engine on the AT-6 has a fair amount of vibration; therefore, the receivers were mounted in loose foam. This mounting drove the stabilization nuts. The receiver needs to be solidly secured to the fuselage. I guess I am old school, but I don’t like to introduce vibration to a receiver.
I did not use flight stabilization on the AT-6, but I had the thought that I could use a third receiver that only operated the rudder and the rudder stabilization. I really enjoy flying this airplane with the FrSky transmitter! If any airplane needs a readout of airspeed on the final approach, it’s an AT-6.
I have a Yellow Aircraft Spitfire powered by an O.S. 300 twin glow engine. I thought I had spent a lot of time setting up the AT-6, but here I went again.
The model memory of the FrSky transmitter has a “clone” feature that allows you to copy a model memory, and then you have a backup. I found the clone feature to be useful when setting up an airplane. If I really messed up a mix (or some other function), I would just switch to one of the clones and rebind the receivers to the new model memory—it was easier than trying to fix what I had broken.
I also used the clone feature on the Spitfire; it’s not that different from the AT-6. I started with a clone of the AT-6 and renamed it Spitfire. The Spitfire only has two flap servos and required some servo reversing and rate adjustments, but I was finished.
The last airplane I would like to share with you is a 1/2-scale glider, the Stein Adler, which was originally set up for aerotow. The glider has a 25-foot wingspan, is 12 feet from nose to tail, and weighs 70 pounds. I also added an electric power pod using a BadAss (Innov8tive Designs) motor that delivers approximately 30 pounds of thrust with a 12-cell LiPo battery. My power pod and battery setup make the flying weight close to 76 pounds. The overall weight of the power pod system is more than 6 pounds, but the glider has a lot of nose weight, some of which could be removed when installing the LiPo batteries.
The controls on the glider are basic: elevator, ailerons, rudder, speed brakes, tow release, and throttle when the power pod is installed. There are no flaps or spoilers on the wing.
I used two FrSky 10-channel receivers without flight stabilization. Each receiver is powered with two battery packs for a total of four packs in the glider. This receiver and battery arrangement satisfied a requirement for a model of more than 55 pounds. The split redundant system is much like my other two warbirds.
The speed brakes on the Stein Adler are slots that extend out of the top and bottom of each inboard wing (see the picture at the top of the next page). I operate the speed brakes from a proportional lever on the transmitter’s right edge. These brakes really slow down the glider, and when the brakes are retracted, the glider does not speed up. The speed brakes are so effective that I was having an unwanted yaw as the brakes were deployed and retracted. By operating each wing half’s speed brake on different channels, I can fine-tune each brake to match the other.
Through another mix, the right speed brake deploys slightly with right rudder, and the left speed brake deploys slightly with left rudder. My rudder speed-brake yaw mix is tied into the rudder triple-rate switch. I now have yaw control from each receiver since one has rudder and the other has speed brakes.
As stated above, the Stein Adler does not have flaps or spoilers, just 5-foot-long ailerons, so I added flaperons and spoilerons with a mix in the transmitter. On the left edge of the transmitter is another proportional slider with a detent when the slider is in mid-position. As I pull the slider back, both ailerons drop down as flaps. When I push this slider forward, both ailerons move upward for spoilers. In all cases, the aileron stick also operates both ailerons as ailerons.
I have flown the Stein Adler at events where we were allowed to fly above the typical altitude restrictions with prior authorization, and altitude and airspeed are always good to know. When it is time to land, I try to hold the glider off of the ground with the flaps, and then, when that center wheel hits, I go to full spoiler to stick it to the ground.
The transmitter features I have talked about so far are for individual model memories or airplanes. There is also a “global” feature that, once programmed, applies to all models. I use a countdown timer that is activated with the throttle stick. While the times might be different from model to model, my basic layout on the main screen, audio countdown, and reset button on the back are all the same from model to model.
This transmitter talks to you. I want all of the audio features to be the same from model to model. The volume is on a slider on the front of the transmitter at the lower center. The airspeed and altitude are spoken at the flip of a three-position switch in the upper left corner.
Every time I activate a switch, the transmitter can tell me what I just selected, such as, “rudder mid-rate.” I can also have an audio indication if I hit a switch that I am not using, which states, “Inoperable.”
There is also a “checklist” feature. When the transmitter is first turned on, it will not transmit until your switches are in your desired startup position; for example, low throttle and down landing gear. You can put all switches and rates in a startup position if you like.
There is an online feature called the ETHOS Suite, where you can send FrSky a model memory if you want help with a mix, etc. If you have just purchased a new ARF or even a BNF airplane, go to the ETHOS Suite and it’s probably there. Download that model to your transmitter and you are ready to fly. If you later want more throws or mixes, you can do that as well.
I mentioned BNF airplanes. FrSky offers a 2.4 GHz transmitter module (2.4 GHz only—not 900 MHz) that plugs into the back of this transmitter. You can enable this module from a model memory while your other models might be using FrSky receivers. This 2.4 GHz transmitter module will operate with many receivers on the market, including Spektrum’s DSM2 and DSMX receivers.
Do you have a friend who wants to learn to fly? How about a wireless buddy-box system where you can program the channels that you want them to have? Give the student elevator and aileron and you keep all other functions, including the trims.
As I stated before, if you can think it up, this transmitter can probably do it. I wish you luck with yours.
SOURCES
- FrSky North America
(714) 987-3100
frskyna.com - Innov8tive Designs
(442) 515-0745
innov8tivedesigns.com
