Dear Ask-A-Nerd ... RC Models ...

[Calilasseia]

I'm interested in finding out if anyone possesses information relevant to the following:

[1] Building your own multi-channel radio control transmitter (preferably transmitting pulse-wave modulation signals to facilitate full proportional control of complex models such as helicopters);

[2] Building your own receiver to match [1] above;

[3] Possible frequency choices for the above.

If someone has both circuit diagrams, and an explanation of how the resulting circuits work, this would be ideal.

I realise I'm probably asking a lot with this topic, but any time you need bizarre insect IDs in return, I'm always about.

The reason I'm interested in PWM RC is because it's possible to obtain off the shelf servo motors here in the UK that accept PWM signals, and they don't cost a small fortune. Trouble is, though, off the shelf RC transmitters and receivers either have insufficient channels for the project I have in mind, or don't feature the type of controls I want to implement. Plus, I figured that building my own might save me a small fortune, having taken a look at the enormous price tags being charged for 2.4 GHz gear, especially by Futaba, which has just unleashed a wet-dream 18-channel control unit on the 2.5 GHz band that also supports continuous telemetry (!), but wants customers to shell out the best part of £3,000 for it. Not only is this way beyond my means, but is probably way beyond the means of anyone who isn't sitting on a big lottery win, or has the good fortune to have an oil well in the back yard.

I've just checked the OFCOM website, and the five legal frequency bands available here are:

26.960 to 27.280 MHz (old 27 MHz AM band)
34.945 to 35.305 MHz
40.66 to 41.00 MHz
433.05 to 434.79 MHz
458.5 to 459.5 MHz

Oddly, it doesn't mention 2.4 GHz as being legal for model control here in the UK, which might be a bit of a downer for people wanting that expensive Futaba kit, but there you go. These bands are all described as "licence exempt", which means I don't have to pay a licencing fee to use them, and they're specifically allocated for RC usage. The question I have here is this: which of these bands would be best suited to a custom transmitter/receiver system with, say, 12 proportional PWM channels?

Over to you, fellow Ratz.

[Azathoth]

One for Leo methinks

[Gawdzilla Sama]

Note sent to Leo at Facebook.

[Calilasseia]

Thanks guys

[hackenslash]

Ooh, I built one of those when I was about 12, a 6 channel jobby, but I haven't done much in that kind of electronics since. I might have a schematic somewhere hereabouts, but if I do, it will be based on 30 year-old technology. I'll see what I can dig up in the loft.

[leo-rcc]

Hey Cali, Zilla pointed me to this topic.

As I am not in the Netherlands atm all my relevant material on the topic is not at my disposal, but here is what I can tell you right now.

the 35MHz band is used in the EU for flying models, so unless it is a flying model you have in mind please steer clear of that frequency.

Also, 2.4GHz is legal in the UK as well as the rest of Europe, provided the maximum output does not exceed 100mA. FHSS is preferred, DSSS is currently still allowed but due to its non-hopping status to be discouraged. The UK as well as Belgium are covered in the EU guidelines for unlicensed 2.4GHz use.

Most of don't bother with building a transmitter from scratch, as we would need to have it certified with the local frequency watchdog, which in your case would be OFCOM, to ensure that commercial material does not get interference from your equipment.

The cheapest reasonable 12 channel radio set I know of is the Walkera Devo 12S, which comes with a 12 channel receiver for about 400 USD.

I hope this gets you at least started on the right track.

[leo-rcc]

Oh and with Futaba it is the sticker on the device that makes it so expensive, not the hardware inside which has been demonstrated by companies as XPS to be just as good or bad if you will as cheaper brands, though not as bad as the Turnigy stuff (which for RC purposes are still perfectly acceptable).

[Calilasseia]

Problem with off the shelf gear Leo, is that the controls I have in mind are, shall we say, exotic.

Which is one of the reasons I need to do one of two things:

[1] Cannibalise an existing transmitter and receiver kit for the electronics, and wire them into my own control setup;

[2] Build the entire thing from scratch.

I'm not particularly worried about having to run a custom piece of kit by OFCOM, after all, if I can build a piece of kit that works and complies with the law, that'll be a nice feather in my cap.

The system I have in mind involves four rotor hubs, with pitch axis and roll axis control on all four hubs, for maximum control flexibility. Which also means that I'll need some way of putting the throttle controls on the joysticks to allow me proper HOTAS control of the finished project. I was thinking of building joystick handles with mouse wheel type controls in them, so that I could provide fine throttle control at the same time as providing directional control, which will need two joysticks for the idea I have in mind.

With respect to the matter of providing power transmission to the rotor hub from internally mounted motors (in order to keep the polar moment of inertia down to a minimum), I've worked out a cradle system with bevel gears that allows the transmission to be delivered to each rotor hub regardless of how much it tilts. I piddled around with some Lego to establish the basic concept and the Lego version works, even without proper bevel gears, so once I have a robust assembly with proper bevel gears, it should work. Likewise, I've worked out the mechanical details for the control system for each pair of rotor hubs, so that I can have the forward and rear hubs pitch and tilt independently, whilst the bevel gear cradle provides power transmission without me needing flexible drive shafts, and also facilitates setting up the rotor hubs with coaxial rotors via another bevel gear cradle assembly in each hub.

Additionally, I've worked out a nice scheme for the undercarriage, again by building a Lego proof of concept demonstrator, and it works. I can have wheel bogies with 2 axles on the ends of the undercarriage, and the mechanical setup I've devised allows the undercarriage to retract whilst keeping the wheel bogies in the same horizontal orientation they adopt on the ground, using a moving parallelogram arrangement. Now all I need to do is devise some nice undercarriage doors to go with them.

At this point Leo, you've probably worked out the sort of thing I'm thinking of building.

[leo-rcc]

Honestly I am not sure what you are building but I'd love to see a buildplan.

As for the transmitter, re-wiring an existing tx is quite easy specially the cheaper ones as it is still analogue on the sticks and switches. Just a matter of hooking up the right pots or resistors on the right channel. Just keep the tx in airplane mode so there is no swashplate mixing etc.

Verstuurd van mijn GT-P1000 met Tapatalk

[Pensioner]

Honestly I am not sure what you are building but I'd love to see a buildplan.

As for the transmitter, re-wiring an existing tx is quite easy specially the cheaper ones as it is still analogue on the sticks and switches. Just a matter of hooking up the right pots or resistors on the right channel. Just keep the tx in airplane mode so there is no swashplate mixing etc.

Verstuurd van mijn GT-P1000 met Tapatalk

I also would like to know what Cali is building as well. My first thoughts would be for him to buy a couple of secondhand 6 channel 35 meg Transmitters and receiversas they are cheap as chips these days. I have a couple of sets of JR on different frequency and I will see if there is any interference when the receivers are close together.

I’m teaching my son to fly radio controlled model aircraft, the model I’m using is a 10 foot span powered glider which I designed 20 years ago to carry a 35mm camera.
The first photo is the aircraft, the second one is a photo taken with the film camera.





A few weeks ago I bought a Olympus 14 meg compact digital Camera for £50, set up the camera in the glider and went for a test flight on Saturday last. The quality is amazing compared to the film camera.

[Pensioner]

http://www.ebay.co.uk/itm/Futaba-T6X-FM ... 4d035941f3

[leo-rcc]

[quote="Pensioner"of]
I’m teaching my son to fly radio controlled model aircraft, the model I’m using is a 10 foot span powered glider which I designed 20 years ago to carry a 35mm camera.
...

A few weeks ago I bought a Olympus 14 meg compact digital Camera for £50, set up the camera in the glider and went for a test flight on Saturday last. The quality is amazing compared to the film camera.
[/quote]

Excellent pics Pen. I'm looking into getting a quadcopter for covering RC races at the club. I also have a powered glider with a cam built in for video footage higher up.

The main "problem" with 2.4GHz is modelmatch, so it is tricky to 2 receivers on the same model memory setting. With 35MHz or 40MHz that is less of an issue unless you have an expensive MPX system or something. But then you are more prone to outside interference.