Access Receiver Setup

[stickshift53]

I keep looking and looking but have failed to find an explanation of the "receiver options". When you go into setup it shows the 7ms PWM and the 25mw Tele. I just need to know about them and what is the benefit of turning telemetry off?

 

[Konrad]

That is a large set of questions. Where are you finding these options? But yes FrSky does a horrible job of explaining their tech (not just their tech but the tech being used).

7ms is the data rate of S-bus. Most analog servos can only handle a 20ms data rate. (This data rate/refresh rate is what triggers the analog servo amp to fire (drive) the output transistors. Going too fast, like 7ms, will in all likelihood burn out the power transistors in an analog servo. Analog servos aren't designed to handle this high speed duty cycle. Digital servo amps have their own internal frequency that triggers the output. (This is the high pitched buzz one sometimes hears with digital servos)).

7ms is great for digital devices such as gyros, flight controller and servos as it allows for the updating of data (input changes) at about 3 times the rate of analog systems. This means faster response times.

Turning off telemetry is great for extending range. (less noise near the receiving antennas.) It also allows for more band width for the important control data. Also if using multiple RX one can shut down the telemetry on one RX so as to not step on the other's telemetry output. It also lower the RX power drain

 

[HENNY]

Konrad just to clarify a couple of your comments.
The tech stickshift53 is asking about is mostly Opentx tech, not FRsky.

Sbus speed has nothing to do with the speed sent to the PWM servos pins of the receiver. SBUS speed is the data rate between the TX and RX, the receiver processes this Sbus data before sending it to the PWM output. You can see when you are setting up the number of channels the SBUS speed changes dependent on the number off channels you select. 8, or more. Changing this does not effect the PWM output. If you doubt me take a look with your scope at a PWM output.

On a telemetry receiver turning off the telemetry at the TX does not increase the range. This is because when using telemetry data packets are push pulled between the TX and RX. So when the receiver is receiving telemetry data the return telemetry is momentarily turned off at the RX and TX in a push pull arrangement. The exception was the long range receiver that had no telemetry but this receiver used a completely different transmission protocol.

 

[Konrad]

Thank you.

OpenTX doesn't do the RX. The RX is a FrSky product. You can see this FS & HS speeds in the FrSky RX manuals.

I think we are confusing the PWM width 1ms to 2ms with most servos using 1.5ms as the center position. And that of the pulse train refresh rate which for most analog RX is 50 hertz (20ms). Unless the S-Bus serial speed is slowed down by the RX decoder the servo will see the positioning data at a rate of 7ms (the S-Bus speed) rather than the classic analog 20ms refresh rate. The servo PWM pulse will still be about 2ms. This is why it is highly recommended NOT to use analog servos when using channel expanders as these do not slow down this S-bus rate. This 7ms will in all likelihood burn up analog servos as this refresh rate is used as the clock to drive (fire) the output transistors in analog servos.

The TX/RX Telemetry on/off ramping does add noise that often does cut down on the range.

 

[stickshift53]

I bring up the model settings for the aircraft that I am flying, scroll down to the receiver, long click it, then select options. This is where I find the options to set up these options on the receiver. So does anyone know what the 25mw Tele means?

 

[Konrad]

Miliwatt is a power rating. Lowest possible is the best.

So Henny is correct these are OpenTX options you are concerned with?

 

[HENNY]

The 25mwatt is more to do with the EU standard. Normal Telemetry power for FCC is rated at 100mwatt.

 

[Landru]

In a small 1m DLG I built earlier this year, the servos (analogs in this case) were necessarily close to the receiver antennas. A cramped fuselage didn't provide any other easy option. Reducing the telemetry power to 25mW eliminated the constant slight jitter in servos. Since the small model won't ever be flown to any significant distance, I wasn't concerned about the reduction in telemetry range.

In another model which uses 25mW telemetry power, I have heard the dreaded "telemetry lost" alarm. That model uses a Ghost system, and Ghost provides only one option for telemetry power (25mW). If I had been flying on 100mW for both telemetry and control signal, I would have been more concerned. Under those conditions, I think a telemetry lost alert is a good indicator that you're flying on the edge of safe range -- or past it, at least momentarily.

 

[Wayne]

Don't mess with the options.. The stock setup is the best.

Don't know why you would want to drop the telemetry wattage.. I guess if you only flew indoors or something it would be good to reduce the battery drain in the aircraft.

I honestly do not know a real world advantage to the HS mode for the servos, it just adds risk for analog servos.

 

[stickshift53]

Thanks for the replies. That's why I asked as I had no idea what they were for.

 

[Wayne]

There are a lot of features in these radios. If you don't know for sure what they do, it is best to avoid them.

We have found some interesting settings on radios when they come in for service. It happens.. The documentation is not great, so we are kind of left to playing with things sometimes to see what they do. Heck, I made a programming bug in one of my models many years ago.. I have been fixing it forever.. Finally just tossed out that model memory and started fresh, so much happier.

 

[stickshift53]

Now all I need to do is figure out this A2 voltage thing. I have several of the Archer SR-10Pro receivers and just got a 4 channel this week. A2 always showed 0 volts but when I hit discover sensors on the 4 channel, it shows 13.1 volts on the A2 voltage. I had read some in the past but never worried about it. What does the A2 mean and why did it pop up on the 4 channel?

 

[HENNY]

A2 means Analog 2 input. Originally this was used with the analog air speed sensor. However it can be used to measure any analog voltage but the range has to stay within the 0 to 3.2 volt range. This is because the receivers internal logic is 3.2 volt logic. The fact that it reads 13.1 volts means it has floated high as there is no pull down resister in circuit. So if you want to use it for measuring you Lipo battery pack voltage this has to be pre-conditioned to stay within the maximum range of 3.2 volts. So a simple voltage divider will do the job. I have attached my crude circuit diagram. This is a divide by 12 circuit using 1/4 watt resistor and a bit of soldering and this circuit can be used up to 10S . Once installed you need to calibrate and editing the A2 line in the telemetry page. Using the ratio perimeter so it equals the measured voltage at the flight pack. Once this is complete you will be able to use the A2 voltage to warn you of low or critical pack voltage or a range of other voice alerts.

The Archer R8 already has these resistors mounted inside the receiver so you can connect the flight pack voltage without pre-conditioning, but you need to check other receivers as connecting flight pack to other receiver will permanently damage it.

Go to it?

 

[stickshift53]

No thanks, i'm good without adding anymore to it. I can do without the A2. On all of my other planes I have voltage sensors and get all of my readings. I was just curious why all of a sudden it worked on the 4 channel. Thanks for explaining.

 

[HENNY]

The A2 function has been there on many of the X series and all the Archer receivers.