Frequency Hopping experiments on the NRF24 & full tx/rx

[jmp_blackfoot]

Brrrrr !

There will be doughnuts and coffee.

[jmp_blackfoot]

Finished two receivers with NanoRF boards (Micro USB version) and end connectors for a tight installation.
First I removed the USB connector and the reset button.

Then I prepared the connector.

Finally, I wired the negative and positive busses and fitted the lot in the holes left when removing the USB connector.

The decoupling 100µF+100nF capacitors fit where the reset button used to be. The big 5V LEDs are all I had, still the receivers weigh less than 5.5 gram each.

[Phil_G]

Very neat. Dont forget to post photos of your 'Freeze Fly' Jean-Marie

[jmp_blackfoot]

The Freeze Fly was not as frozen as the forecast promised. The temperature was all of +3°C and the wind only about 12 mph. A dozen flyers showed up, most of them with foam ready-to-fly toys. I flew my faithful ruder-only Windmill (https://outerzone.co.uk/plan_details.asp?ID=13903) with the just finished NRF system in a metal box Futaba 2 channel transmitter. All went well (as expected) and during the following chat session around the donuts and coffee, I got one member quite interested in Mode-zero and the NRF system. Thanks again to you, Phil, for this great start to my 2025 flying season.

[Phil_G]

The more the merrier Jean-Marie. It would be particularly nice to see more oldies taking up single-channel again. Even 1+1
Looks to be a great facility you have there, if we had a similar set-up at our club the yobs would immediately destroy it. Our reinforced steel cabin has been broken into 4 times, 2 ride-on mowers stolen (or is it 3?), we cant even keep a solar panel hidden on the roof for more than a few days. The UK is in a sorry state and it seems to be getting worse
I'd not seen the 'Windmill' before and reading up on Outerzone it looked quite scary - 5lb, 0.45cu in engine, rudder only ....but then I saw yours was 2/3 scale, much more manageable! Looks very 'Ken Willardy' I think. Its a great shame we dont have the competitions we used to, comps used to push development quickly - look at Fossie's 'Phase' gliders
Cheers & thanks for the report!
Phil

[Shaun]

Remember the s/c Lightening I did Phil? .That was originally designed for a 5cc / 0.29 cu in glo motor and a sequential esc.

[jmp_blackfoot]

Now, for something completely different:
I do not know if the following will be of any use or even interest to anyone, although it may give some ideas to convert say a Staveley or Flight Link system using the original servos, but I am really having fun doing it.
In 1987(!) I built a few servos with an analog amplifier of my own design, see attached pdf, which I'll have to fly one day just to prove they work.
Having the opportunity now to play with the NRF FHSS system, I realised the receiver could drive these servos directly.
The modified receiver sketch for a three analog servo system is attached. Changes are identified on lines 44-45 and 261-262. The idea is to shorten the frame time down to 4 ms and the output pulses so they vary between 100 and 1100 µs, with 600 µs being neutral. The former requires a modified Servo.h library file, see attached ("ServoA3ch.pdf" should be renamed "Servo.h" before use), while the second is done on lines 261-262 of the the receiver sketch. Channel 4 is output as a fixed 600 µs pulse and channels 1, 2 and 3 are the control output pulses. The analog signal is extracted by subtracting the fixed channel 4 pulse from each control output. This is accomplished by connecting the channel 4 output to the center tap (0V) line of the servo battery and the channel 1 to 3 outputs to the analog input of their relative servo so that the fixed 600 µs channel 4 appears as a negative pulse, while the control channel pulse is a positive pulse, the averaged voltage being the resulting input signal to the servo as shown on the attached oscilloscope pictures. The receiver requires its own battery, see attached photo (the external 180k/100nF RC has now been moved back inside the servo). The above generates a +/- 0.4V control voltage to the servo with the 3.3V Pro Mini version of the receiver, which suits my servos and seemed to have been more or less the standard in the 1960's, see attached Accutrol ad. With a NanoRF version and 5V, the control voltage would increase to +/- 0.6V or the frame time could be increased to 6 ms..
Four channels with a 6ms frame time or even two channels with a 3 ms frame time will also work.
The transmitter sketch needs not be altered.

[jmp_blackfoot]

I discovered on Amazon some "Pogo" test pins with a diameter of only 0.68 mm:
"Yosoo Spring Pressure Test Probe Pogo Pin P50-B1 Dia 0.68mm Length 16mm 75g Pack of 100 Gold"
These will fit into a 2.54 mm pitch connector like the six-pin one used to program the arduino Nano-RF.
The RF-Nano PCB has six pads for in circuit programming in the same pattern as the programmer connector pinout, so I made a "nail-bed" with six Pogo pins, a piece of test PCB and four 1.6 mm screws and nuts..
Programming the RF-Nano is a breeze now..;

[Pchristy]

That is a very neat way of providing an output for an analogue servo! I love it!

It reminds me a bit of the infamous Sinclair class D audio amplifier!

Well done!

--
Pete

[jmp_blackfoot]

Thank you!
I currently fly my "Windmill" rudder-only model with a "hybrid" NRF24 receiver which can drive either a modern digital servo or an analog servo and an ESC.
It is in fact a regular receiver, only with a reduced frame time of 5 ms and channel two being a reversed version of the normal channel one (1->2 ms). Channel three is your normal throttle channel (1->2 ms). In the Aduino sketch, I just limited the channel number to three to allow for the 5 ms frame and rewrote the servo outputs like this:
ch1.write(data.aileron); ch2.write(3000 - data.aileron); ch3.write(data.throttle); // ch4.write(data.rudder); // Servo outputs // Modified 250129
and in servo.h:
#define MIN_PULSE_WIDTH 544 // the shortest pulse sent to a servo
#define MAX_PULSE_WIDTH 2400 // the longest pulse sent to a servo
#define DEFAULT_PULSE_WIDTH 1500 // default pulse width when servo is attached
#define REFRESH_INTERVAL 5000 // minimum time to refresh servos in microseconds
When connected to drive the analog servo (channel two out to the servo battery center point, channel one out to the servo input, receiver powered from the ESC BEC)) the resulting signal is +/- 1V with an RF-Nano (5V) or +/- 0.66V with a Pro-Mini (3.3V). Pictures show the shapes of the output signal to the analog servo (timings were for an earlier experiment).
The analog output amplitude can be reduced by adjusting the frame length.