We are publishing this note to help different user who were finding problems with setting the throttle limits using GliderKeeper but most of this information will be useful for any FAI approved AMRT
1. A little history.
We use our RC receivers to command our motor ESC, by using one of the servo signals the receiver has for driving in principle a servo.
The “standard” servo signal is very much a pulse with a variable duration and the duration of this pulse tells the servo (or the ESC) which our position demand is.
Modern RC Transmitter/receiver use numerically encoded 2.4 GHz signals for the transmission of all the channels, very much with a proprietary format.
But there were former times that most of the transmitter used the PPM FM modulated signal (the ages of 35/40 / 72 MHz receivers and their Quartz Crystals…)
The PPM signal of these transmitters looked very much like this. This “standard” if you want to call it look very much like in this picture.
This protocol comes from the late 60´s and 70´s (of the other century) by when proportional RC servo controllers were made available to the hobby market.
In summary, the servos we use still need a signal which is a pulse with a duration between 1000 and 2000 microseconds that is repeated every 20.000 microseconds, 20 miliseconds that is 50 Hz refresh rate.
I say “standard” since there were never a firm standard and we always had differences between brands of receivers and servo manufactures and compatibility issues…
You can see in the picture a travel which corresponds to a Hitec servo but normally the 1000-2000 would correspond to + 60deg in a MKS servo
This is the type of signals a servo and an ESC will need.
In a PPM train, the different channel duration was transmitted one after the other and a final “synchrony” pulse, a longer pulse than 2300 or 2400 microseconds was transmitted at the end, so the receiver knows the next pulse is channel 1. So in 20 milliseconds you only have time enough to transmit 9 signals plus the long synchro pulse, and this is why we only had 9 channel transmitters in these times, and now you understand what PPM stands: Pulse Position Modulation, when you talk of the signal that comes will al the channels and PWM, Pulse Width Modulation when talking to the signal that goes to a single servo.
As said, normally transmitter will have an End Point adjustment for the travel of the servos this travel is expressed in % of the throw of a servo -100% would correspond to -60deg and +60deg will correspond to +100%.
In terms of our control pulse, it will correspond to 1000 and 2000 microseconds pwm pulse.
This is the type of control we use for our motor ESC´s.
Next is the FAI rule for AMRT´s our altimeters, which was written in this century but some 12 years ago (today March 2021) when most of our gears were either 35MHz or had a “brand new” 2,4GHZ brand new radio module which coded the same old architecture transmitters in the new digital transmission in 2,4GHz.
The FAI rule states that we should consider the motor is ON if the pwm signal to the ESC is greater than 1200 microseconds. Remember 1000 microseconds is the lowest signal (= 0 power) and 2000 the maximum (=MAX power).
2. Operational method.
We describe here the method to properly set your Transmitter/receiver/AMRT/ESC controller for reliable operation in an F5J competition.
The instructions below will work for sure but the otherwise it is not necessarily fulfilled… I mean you can have a setup that is not exactly what we propose but works to your satisfaction.
First of all, have available your transmitter´s, GliderKeeper and your ESC manuals for consultation.
2.1. Update GliderKeeper to the latest available Fw version in March 2022 the FAI approved version is the F_1.24 (for class 1 competitions) or S_1.24 (for class 2 competitions, i.e where Emergency Motor Restart is allowed).
Read below since if you need to update you may want to pass thru version STD__1.24.
Use GliderKeeper manual section 11. https://www.gliderkeeper.com/downloads
2.2 Set your throttle channel such as max power is +100% (2000 microseconds) and that min power is -100% (1000 microseconds pulse). Use your transmitter manual.
WARNING: When operating your plane in a novel manner and/or when at home we do recommend you remove the propeller of the model for SAFETY purposes. So in case something does not go as per your expectations and you have an unexpected motor acceleration there is no risk to persons or things.
2.3 With this motor power setting calibrate your ESC. Use your ESC Manual.
There is a variety of ESC´s ways of calibration, depending of the brand of your ESC but many times this imply to power UP The ESC at full throttle condition and move throttle signal to min and max several times, refer to ESC manual.
It is now the moment you may want to update your GliderKeeper to the STD version and in Keeper Conf menu set the “training mode”. This will make possible you operate and calibrate your ESC with GliderKeeper in line, since in this mode any throttle control from GliderKeeper is inhibited and you can play exactly as in a competition, you can in this mode see the display and notice when Emergency is detected.
2.4 Arrange your Throttle stick, slider or switch to your preferences.
You want somehow to have a stable Motor OFF position a Max Power position and being able to modulate the power in the area of Motor ON (> 1200 microseconds) to craw with the motor ON during the first 30 seconds of your flight…
3. The Dark Side of Emergency Motor
The new rules for emergency motor do allow for exerting power after this initial single shot of power during launch. And AMRT has to return control to pilot. This is accepted to be good for safety and very much for economy since it allows pilot to recover a hull from a compromised situation.
But it has a dark side:
The pilot may fall off the “cliff” of 1200 microseconds. I call it when unintentionally the pilot overpasses the 1200 microsecond’s threshold.
Imagine you were climbing in to a nice place in second 4 of your climb and you want to explore at low power, you retract your power to as low as possible, say 1202 microseconds. After 5 more seconds you change your mind and want to go somewhere else. You push the throttle again and make at the end the 10 minutes. But SURPRISE the AMRT has declared you used emergency: the signal noise stole your 1000 points!
This can happen, since the receiver and AMRt will have some noise in detecting this 1202 microseconds, which were above the 1200 isn´t it?
Let´s analyse this flight (courtesy of Anna Schütz)
We can see in the dwell moment that GliderKeeper was catching a signal which has noise: max in this period was 1301 and min was 1284 not a constant value. This noise will be present with more or less amplitude and the worst for this noise is that it will change with things we cannot control like the actual cable layout, you install the wires slightly differently every time you close the plane, temperature, radio interferences…
So you are very warmly suggested you do not set your dwell power any near 1200 microsecond. Our recommendation is you can set it 1220 microseconds or above. So you never pass thru this boundary and miserably loose one flight.
This circumstance did not happen in previous FAI regulation where, you may have lost the throttle control but the flight will give you some good points.
You can achieve this by setting a dual rate for your throttle, when motor ON you may vary your throttle between 1220 and 2100 for example and with motor OFF you have a constant 1000 microseconds.
Me, I have a 3 position switch with 1000 1300 2000 microseconds respectively. But do not follow totally since it is not likely I will ever win F5J championship…
4. Proposal for setting your plane.
We recommend a setting that has a “throttle Arm” switch and a slider to modulate your power. We leave the location of them to your preferences and flight mode.
If you are smarter than the machine, you can play with the green arrow a little upper or lower to accommodate your ESC and your climb strategy. What is clear is that if you fall below the 1200 microseconds cliff, you are likely to lose your flight, or at least your climb manoeuvre.
This is the same graph but in transmitter % values.
5. Conclusions
In summary by setting appropriately min and max setting of your Throttle your will be able to enjoy full power from your motor.
GliderKeeper Fw 1.24 will accept a max signal of 2300 and a minimum signal of 850. If those values (noise inclusive) are exceeded for more than 50 samples (0,1 secs), GliderKeeper will lock the signal for safety to the lowest value recorded.
I recommend not to go any near these edges since while having the biggest resolution maybe useful when doing stabilisation of a drone or helicopter it will not bring much more controllability to your plane as propeller torque is by far more affected by ambient conditions than this resolution improvement.
Also do not sit near 1200 microseconds since the noise can be greater than expected Gliderkeeper has got a hysteresis of 5 samples and 5 microseconds which are smaller than noise in most of occasions.
If you want to have as low power as possible is this dwell then what you have to do is “increase” the value of 0 power to say, 1100 microseconds, recalibrate your ESC again. You do not need to make the top power too high since at low power it has a minimal effect.