Need some ideas please. Dethermalizer for Radio signal loss

[RAM]

Dethermalizers are used on free flight gliders to force them down if they get caught by the wind or a thermal.

I would like to do something like this on a radio controlled glider. Specifically, I would like the elevator or rudder to snap to full throw if radio signal is lost.

Do any of you have an idea how this could be done? I don't want it on a timer like the free flight gliders. I need it to engage if there is no radio input received. My first thought is to program the radio with full deflection on startup but I can't figure out how this could be done other than limiting my stick to half its range (center to end point instead of end point to end point). This should work but now I only have half the stick range available.

Any ideas?

 

[Barron.Barnett]

Look into configuring the failsafes for your radio. Set the failsafe for your controls into the full throw for whichever direction you'd like.

Just a thought.

 

[RAM]

Look into configuring the failsafes for your radio. Set the failsafe for your controls into the full throw for whichever direction you'd like.

Just a thought.

I might have to buy another radio. I have a Flysky FS-T6 and can't find much info on it.

 

[Barron.Barnett]

Shoot, it appears that the FS-T6 just cuts the PWM output if it loses connection. The only way that comes to mind to me would put strain on the servo by putting a rubber band to pull the control surface in the desired direction on signal loss.

I also saw in the same thread someone saying that it would hold last position. This would really suck because what you really need is for the servo to something specific on signal loss, not just hold in place. If everything just "holds" you have no real input into the system to know to do anything. You need at least one servo to be able to perform an action on signal loss. This way that servo can trigger everything else you need.

I'll keep thinking on a solution.

 

[Mostly Harmless]

I haven't built this (nor am I exactly sure how to), but here goes... A supplemental controller built around a PIC or Arduino microcontroller chip could be constructed that would be inserted between the elevator output on the receiver and the servo (these devices can read and output PWM signals). The device would read the pulse width from the receiver.

If the circuit reads a valid pulse width, it would send that same value to the PWM output and to the elevator servo -- essentially an unaltered pass-through of what the receiver is sending.

If (as B.B says), the PWM output from the receiver is cut when contact is lost, the device will not detect a valid pulse width... in this case, the fail-safe device will output the pulse width that sends the elevator to the desired down deflection.

In theory, this should be an appropriate fail safe to return your aircraft to the ground if the signal is lost. Since these chips can read multiple inputs and can output to multiple servos, you could even include rudder and aileron control that would put the aircraft in a gentle turn while descending.

Might need a separate power source (or could piggyback off the BEC)... but probably better to have an independent power source in case of some other failure (such as battery or BEC).

Thoughts?

 

[Barron.Barnett]

MH, That will only work in the case the PWM output stops. Which if that is the case the servo will also go limp so if you have any kind of rubber band it will pull it to an idle position.

You could spool up a micro to take the place of a rubber band and just watch the signals and then alter the outputs to your desired failsafe.

This still doesn't solve the problem if the servo goes into a hold of the last known position. If that is the case there's no change in output that the system can act on. Best bet at that point is if you got the micro controller route, put a timer in there and if there have been no input changes on any surface for some "reasonable" period of time.

Best thing to do in that case is run all your receiver outputs into the micro controller of your choice, probably Arduino, and then hook the servos up to the outputs from the micro. In normal conditions the Arduino would just pass everything through. If it detects a failsafe condition you can have it alter any of the control surfaces as you desire.

 

[Mostly Harmless]

I was assuming the PWM output from the receiver stopped completely on broken contact with the transmitter. I like the idea of a countdown timer... if no PWM changes are read from any channel for some period of time, go to the failsafe settings. If control returns, the normal pass-through condition is restored.

I think much will depend on the behavior of the system when the signal is lost.

But I like the idea of this system that could initiate a "graceful" return to ground if contact is lost. As long as we're still on paper, let's add a few accelerometers to insure that roll/pitch/yaw are consistent with a more controlled descent.

The hardware isn't that tough to assemble... as with many systems these days, it's the software that's the challenge.

 

[RAM]

Would it make any sense for me to purchase a flight controller instead of a radio that has a good failsafe? Assuming that there is a simple flight controller that would become my failsafe?

I think my problem lies in the Flysky transmitter and it's odd failsafe. If it just leaves the control surfaces in the last known position I would have to physically break the servo links on signal loss and use rubber bands or spring hinges to put it into a gentle spiral. If the radio defaulted to a neutral point on the servos I might have been able to set the plane up "wrong" i.e. sticks centered and adjust linkages so they cause a gentle spiral.

I wish I had thought of all this before I bought my first radio

 

[joshuabardwell]

FlySky's lack of configurable failsafe is one of its main deficits. Perhaps the FS-T6 can be modded to take a JR module, in which case I'd strongly recommend the FrSky DJT module. Alternatively, you can probably do the DHT module.

EDIT: Bingo.

 

[RAM]

FlySky's lack of configurable failsafe is one of its main deficits. Perhaps the FS-T6 can be modded to take a JR module, in which case I'd strongly recommend the FrSky DJT module. Alternatively, you can probably do the DHT module.

EDIT: Bingo.

Nice find, thanks.

 

[Mostly Harmless]

What!??!?! Buy something ready made? Where's the fun in that???

Certainly, the approach I was developing would probably be challenging ... and likely ending up more expensive than an off-the-shelf system. But still fun to think about -- I may try to develop this idea just for grins.

Being somewhat new to today's R/C (I used to fly nitro 30 years ago), I'm still learning about the radio systems.

What is the JR Module? Is it a transmitter module that takes the place of the FS-T6's built-in RF transmitter? And uses a different protocol that allows the use of a different receiver? I really need to delve into this aspect of the hobby....

 

[joshuabardwell]

What is the JR Module? Is it a transmitter module that takes the place of the FS-T6's built-in RF transmitter?

Yes. So a "JR module bay" is a standard size bay that is in the back of a transmitter, and it has a standardized pinout that provides power, ground, data, and whatever other pins are necessary to communicate to the radio. The radio has the circuitry and hardware for interpreting the inputs (gimbals, switches, etc...) and mapping that to an output signal. The output signal is fed to the radio module which takes care of the RF-related wizardry. In the case of a telemetry system, the module receives as well as transmits.

Take the Turnigy 9xr Pro for example:



That hole in the back is the JR module bay.



And here's a FrSky DJT JR module, which would go into that hole, and allow the radio to talk to FrSky receivers. On the other hand, this...



...s an EzUHF JR module, which lets the radio talk to 433 MHz receivers.

And for the old-timers among us, this...



... is a 72 MHz FM module (with multi-channel capability--no swapping out your crystal to change channels, swanky!)

So the JR module bay provides a standardized way of changing which protocol and frequency your radio transmits on.

The FrSky DHT module is basically the exact same thing, except that it fits inside the radio, for cases where the radio doesn't have a JR module. You disconnect the radio's original circuitry and connect the DHT module in its place.

 

[RAM]

After watching the vid you posted I found this one from RC Model Reviews. He explains the why, how and what for a little better but not for my radio

I still have one question. My radio is a 6 Channel. The kit is an 8 channel. How can that work?

 

[RAM]

My search skills are faltering. Look what I found http://flitetest.com/articles/diy-2-4ghz-radio-upgrade/

 

[Mostly Harmless]

Very impressive... Today's R/C electronics constitutes a brave new world for me. I'd wager that some of the off-the-shelf receiver / flight control systems already do much of what I'm thinking about trying with an Arduino.

Thanks for the info!

 

[RAM]

$56.50 for the kit and receiver off ebay. Should have it in a few days. Many thanks for the help and ideas.

 

[joshuabardwell]

'd wager that some of the off-the-shelf receiver / flight control systems already do much of what I'm thinking about trying with an Arduino.

Indubitably. Look at the APM ground station for example.

 

[mesolost]

easy, setup your servo so that when it's centered the elevator is actually deflected down - then in your transmitter set your sub-trim to accommodate this ^_^ your fail safe is now set.

 

[RAM]

easy, setup your servo so that when it's centered the elevator is actually deflected down - then in your transmitter set your sub-trim to accommodate this ^_^ your fail safe is now set.

That was one of the ideas but the default failsafe on my radio leaves all settings at their last input.

 

[rcspaceflight]

The programmable radio route doesn't make any sense to me. If you lose signal, how can the transmitter tell the plane what to do?

Anyways. What comes to mind is the "black box" I made. If I lost signal (or battery) a 120db alarm would go off. What if you built the same thing but instead of powering an alarm it would power a system that forces the elevator to jam in one direction.

For the system to force it into a dive, what if you hook up a second servo to the control rod for the elevator. This second servo being hooked up to the middle of the control rod. No matter how the main servo is working the second one would kink the control rod to force the elevator to be fully jammed up. (Or down depending on how it's hooked up.) You would need a thinner wire for the control rod and a strong servo that can bend it to force the control rod taught. If that makes any sense. It's like if you're fly fishing. You can either reel in the line or pull on the line to bring the fly closer.

The article I wrote about my "black box" is long winded. Here is the wiring diagram for it: