RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

Some direction please?

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Old 07-31-2006, 02:37 PM
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asinla
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Default Some direction please?

Hi. i know this has probably been covered 100000 times but i could not find much myself. I am a noobie to radios and was wondering if someone could point me in the direction of some online resources that explain things like....

1. Crystals....do they need to match the tx and rx etc
2. Seperates...and how a tx can be used with various aircraft
3. General wiring of seperates esp things like Batt Eliminators and how to get power to an rx.
4. General theory of RC transmitters and how they work.

Thanks so much. I have an RD6000 and just want to get the theory in my head about how this stuff all fits together before I run off and buy crystals and bit's and pieces.

Any help is much appreciated.

asinla
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Old 07-31-2006, 02:48 PM
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cobra26
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Default RE: Some direction please?

asinla,

I don't know if these sites have everything you're looking for, but you might want to check them out for some basics:

http://www.masportaviator.com/

http://www.easyrc.com/
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Old 07-31-2006, 04:57 PM
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asinla
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Default RE: Some direction please?

Thanks for those. I think I am getting somewhere. Still not sure about some things regarding crystals. Any other informative sites??

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Old 07-31-2006, 05:09 PM
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Default RE: Some direction please?

Yes the crystal need to match in both frequency and conversion, either single or dual. To keep it simple get the crystal that matches the manufacturer. Leave the Tx crystal alone. Your not allowed to mess with it unless you have the tools and equipment to realign the TX or you have a TX with a changable modual. The Rx. If you get an airtronics Rx get an airtronics RX crystal, if you get a hitec Rx get a hitec crystal. It'll say on the spec weather it's single or dual conversion. With that TX just get dual conversion equipment.

Basically your Tx is dumb system, meaning is doesn't know or care what it operates. It sends a signal and the rx decodes it and adjust the signal to the servo, the servo reads it and it moves, this is repeated many times a second so it appears to be a fluid operation. You put the servo in the right place in the plane to actuate a control surface.

Depending on the TX you can mix channels together like elevons and v-tail. With elevon the ailerons and elevator are mixed so two control surfaces move together and opposite, this is for wings and delta type aircraft. v-tail is for planes with a v-tail. the elevator and rudder are mixed and move just like the elevons. this is common on many gliders and pylon racers. Most of the planes are going to have one servo per channel operating one surface. Many planes have 2 servos for the ailerons in which you buy a y-harness to hook 2 servos to one channel and they work together with one servo in each wing half controlling an aileron. Most trainers use one servo for both ailerons.


Most electrics with have a BEC. This allows you to plug the main battery to the ESC and the control wire is plugged into the RX, usually channel 3 and that supplies power to the RX and servos. The BEC is basically a voltage regulator on the ESC that regulates the power down to 5.5-6 volts for the Rx. On the high power electrics 80+ AMPs there usually is no BEC because of the inability to regulate the voltage low enough for the rx so you have to use a separate battery or get a voltage regulator. The wiring on the RX is fairly simple. The + and - are on a power block meaning everything is connected together so you can plug a battery into any channel and it will power the whole unit, the BATT position is there just for the inept. The third wire is a control wire and controls you device, servos ESC actuators and whatnot.

AS far as how it works. FM The servo reads a 1-2 millisecond digital pulse. It's centered at 1.5 milliseconds in which your servo will center at. This pulse width is varied with the stick position or switch position between 1 and 2 milliseconds, there is one of these pulses for each channel. Not sure how it's separated within the transmission signal. With PCM the TX sends a digital (pulse code modulation) just like a digital audio signal and the rx decodes this and converts it to the 1-2 milliseconds pulse.

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Old 07-31-2006, 05:26 PM
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Default RE: Some direction please?

And thank you redfox435cat.

That is just what I was needing. Two more questions though if you wouldn't mind? I have a heli with an E-Flite 4 in 1 rx. A Multirotor heli. I was told, or rather I read online that in order to control this heli with my RD6000, all I had to do was get a Futaba single conversion short crystal for the rx. After reading what you have said in your post I am not sure this will work. Any ideas on how to do it then? Also, some rx's are not made by Futaba, JR, Airtronics or Hitec. i.e. Century or many others. Do any crystals work in these?

Thanks so much for taking the time with your lengthy and very informative reply. Once again, the people on these forums do the hobby a great service.

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Old 07-31-2006, 09:27 PM
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Default RE: Some direction please?

I don't know. I remember using a dual conversion short crystal for mine but I used my Futaba controller so I'm not sure, that was a few years ago, aand it did have intereance. with this kind of model it’s not going be more than 50 feet away. Either way a futaba crystal won't work with airtronic since the shift is differant. With any brand of RX get the crystal that matches the manufacturer brand. for a cirrus RX get a cirrus crystal, FMA get an FMA crystal. I'm saying you can get a hitec RX and when you do get a hitec crystal. 9 times out of ten when you order from a place online like tower they give you the reference to the right crystal. like this. The rx is set up for jr/air and in the description it gives a link to the right crystal. I'm not trying to push tower but even when I buy from the LHS I do my research and find part numbers here

[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCXM9&P=0]reciever[/link]
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXHHR8&P=0]gws[/link]
[link=http://www.horizonhobby.com/Products/Default.aspx?ProdID=FMA508FM72J]FMA[/link]with horizon click on the acssesories link.


I guess forgot one spec if you are looking to deviate from the manufacturer. You need to make sure the RX is set up with the right shift. negative and positive shift. When the TX transmits it actually sends two frequencies, it's part of how the signal is imbedded in itself. One is set on the designated channel and the other is about 5Khz off. In positive shift it's 5khz above and negative it's 5khx below. JR/AIR is pos and HItec/futaba is neg, most off brand stuff has shift selectable or 2 different types of a model of RX for this. Hitec stuff is selectable. This is why I say keep it simple and just stick to the manufacturer.
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Old 08-01-2006, 02:04 PM
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asinla
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Default RE: Some direction please?

Thanks so much Redfox! This will really help me. I know that the RD6000 can do positive or negative shift, so I guess I'll just have to get the short xtal and see what happens. At least I know now how xtals and such talk to each other.... I was planning to change both xtals..I though that you need a different set of xtals for each plane or heli you fly. What I can deduce from your post is that the tx xtal remains the same at all times!! so I guess you just buy some more xtals of the same channel/freq to match the tx? I'll figure it out!

Thanks again for the help. I hope others find this info useful.

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Old 08-03-2006, 09:08 PM
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Default RE: Some direction please?

My Blade CX works with my Futaba so it is negative shift. Rather than guess SC or DC, look here, a whole subforum on Eflite Helis. http://www.rcuniverse.com/forum/forumid_447/tt.htm RCGroups.com is also a good source for electrics especially. Good luck!
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