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Wireless remote controlled plane

Discussion in 'Radio and Communications' started by p.gholap93, Mar 20, 2012.

  1. p.gholap93

    p.gholap93 Member

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    I have made an RC plane and flied it successfully using a 6 channel remote and its receiver. Now I want to make my own remote and receiver. At present I have made circuit such that as l vary pot at transmitter the pulse width variations necessary for driving servos are obtained. Now the question is what should be next circuit so that these variations can be transmitted to the receiver WIRELESSLY and also what should be receiver design for the same. Please suggest some circuits and the frequency range and crystals needed for the same.
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    R/C transmitters have to operate in strictly controlled (perhaps licenced) parts of the frequency spectrum. Your existing transmitter should have a label (or instructions) indicating its operating frequency band. Building a transmitter to operate within that band, and not produce interference outside that band (which could cause other models to crash), may be difficult if you have little experience of RF circuits.
    That said, if you google for transmitter and receiver circuits I'm sure you'll find plenty out there.
     
  3. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I have been through making my own transmitters and receivers in the early 1950's. I never want to return to that.

    More to your point, if you want something fun, different, and not likely to crash your airplane or someone else's, I would suggest focusing on making on-board electronics.

    Common examples available today are stability controls based on accelerometers and flight data recorders -- some with in-flight download capability. More advanced efforts are in navigation (GPS) and flight path control.

    How about trying to make an on-board landing helper? It would allow you to investigate controls for attitude, roll, yaw, and airspeed. All you would need to do is to control throttle and get the airplane over the runway. Given the complexity of modern radios, I suspect such inflight devices as I have mentioned are considerably simpler. There are even application notes for an autopilot by one of the accelerometer manufacturers.

    John
     
  4. dave

    Dave New Member

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  5. trash

    trash Member

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    Above points noted about reliability etc. But for educational purposes I say go for it.

    The old 27MHz radio controls used a simple 'time division multiplexing'.
    The simple way these units worked was to transmit a sync pulse and then sequentially transmit one PWM pulse for each of the servos.
    So a 27.145MHz AM signal with pulses like....

    __SSSSSSSSSS___11________222222________33333333____444_________555555_______666666_______SSSSSSSSSS______111_______ etc

    S = Sync and # is each PWM pulse switched into the channel.

    This is just the simplest method of doing it. But of course there are many others and improvements even this method.

    I too have built many different remote controls for various toys and applications. None of them I've been brave enough to apply to a real RC plane.
     
  6. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Don't forget the most common old method -- at least as used by hobbyists on 27.225 MHz -- was on/off pulse modulated CW with escapements. :D The final pulse of each control signal was held to hold position. One pulse (i.e., press the button and hold it) was right, two pulses and hold the second was left, three and hold was up, and four and hold was down. A quick blip was throttle, which was simply an exhaust obstruction. Electric? No way. The vacuum tube radios required two, sometimes three, sets of batteries.

    Agreed. That is the message I tried to give the OP.

    John
     
    Last edited: Mar 23, 2012
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Sorry, but that's a REALLY irresponsible attitude - what's 'educational' about killing a child with your poorly built (and probably illegal) radio controlled aircraft?.

    You then suggest using 27MHz, which I believe has been illegal for aircraft for a number of years, again on serious safety grounds.
     
  8. trash

    trash Member

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    I think you're taking that way out of proportion. So I will clarify my position.

    I'm saying yes to building the RC. I'm not endorsing using it in an RC plane.
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    So as the entire thread is about a radio controlled plane, why bother posting?.

    It's seriously important to use correct control systems in model aircraft!, and is why they were moved away from 27MHz.
     
  10. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I see that the OP has not come back, so maybe a little off-topic discussion of safety and regulations will explain current sensitivities.

    This marks my 60th year of flying RC models. Until very recently, all of the remarkable advances I have witnessed have been positive and have increased the safety and enjoyment of the hobby/sport. We have gone from barely controllable airplanes of 1952 to the helicopters, twin turbines, and quarter scale models of today doing precision maneuvers even full-scale aircraft can't do. Safety has also improved. In the old days, it was not that unusual for an out-of-control airplane to land on a highway, house, or yard far away. The small group I flew with used a farmer's field more than a mile from any house. Yet, we still managed to hit the occasional tree. ;) Today's models can reliably be flown in much more crowded conditions. We even have dedicated model airports with flight control procedures in place. The American AMA and its counterparts around the world have led the way, particularly in terms of safety.

    Very recently, our militaries have realized the value of unmanned aircraft. And, our governments have realized that capability could also be used by terrorists. Add to that the action of a few fools, such as the ones who did a low-level, first-person view (FPV) flight around New York city a couple of years ago, and we as the entire modeler community faced grounding.

    There are already some countries in which flying RC airplanes is virtually illegal. In the United States, rules were proposed by the FAA that would do almost the same here. Fortunately, the exemplary record of the AMA in promoting safety and education impressed enough of our politicians to get a little protection from the proposed regulations. The details of how that will play out are still uncertain. Nevertheless, it is quite painful to see something that has been such a large part of ones life wiped out by the actions of a few thoughtless individuals doing something for "education." Just because something can be done, doesn't mean it should be done.

    I cringe every time I see a post by an inquisitive person who "just" wants to make a radio to control an RC airplane. There are so many alternatives, such as I suggested in my first post, why mess with the actual RC link? I don't think Nigel's comment was an over reaction, because one thing is for sure, if some naive individual causes a model to crash into a house, it will be front page news.

    I have only mentioned the US efforts, because I am most familiar with them. I know parallel efforts by modelers in other countries are also being made. Perhaps individuals in those countries would like to chime in on this matter.

    Regards, John
     
  11. p.gholap93

    p.gholap93 Member

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    Well reading the posts I think it's near impossible to build my own radio with which I can fly my plane SAFELY. But still for LEARNING purpose I would like to know in detail about the 27MHz technique. How does one transmit sinc pulse(means how to generate it) and how does one transmit it (what kind of antenna)?
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You use a radio control encoder chip - if you could source one?.

    Or more viably, program a micro-controller to do the job.
     
  13. trash

    trash Member

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    Since this isn't an aircraft forum I thought I'd just stick with the electronics theory.

    How you synchronise your own format is up to you.
    The sync pulse is something which is obviously different from the servo pulses so that the demultiplexer can quickly lock to it from a cold start or is synchronisation is lost and it does not cause crosstalk between the channels.

    And then there are still multiple ways to run the signals. Synchronous or Asynchronous.

    Lets assume that a synchronous system is used. Each line will be 100mS long.
    We can then say that our servo channels will be 10mS long.
    All low is full left and all high is full right. 5mS on and 5mS off is center

    Each channel is separated by a 2mS guard band which will always be low

    The Sync pulse is 20mS long. Since no channel pulse is this long if any pulse is longer than 12mS the demultiplexer is reset.
    The sync pulse has guard bands of 5mS each side.

    So a signal with all the servos hard right would look like this.

    --------------------_____----------__----------__----------__----------__----------__----------_____

    <-----sync------>===< ch1 >=< ch2 >=< ch3 >=< ch4 >=< ch5 >=< ch6 >===


    Another example ch1=right ch2=left and other channels center would like like this.

    --------------------_____----------___________-----______-----______-----______-----_____

    This kind of system has issues which are resolved with more complex concepts.
    Precision timing is required for this kind of synchronous system else any jitter will cause cross talk issues.
    There is also a lot of redundancy in it and a lot of bandwidth is wasted on synchronisation or doing nothing.
    There of course there are many other more efficient ways of doing the same thing.
    This is just one example of the system some of the old 27MHz units used.

    ----
     

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