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Unread 23-11-2003, 19:41
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kmcclary kmcclary is offline
Founder 830/1015;Mentor 66/470/1502
FRC #0470 (Alpha Omega Robotics)
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Quote:
Originally posted by Justin Stiltner I posted this in another thread but its good info...

http://www.rchelibase.com/radio/index.html

[...] from this paper i found out that nearly all 3-7 channel non computer radios use the same encoder chip... so that means that your 4 channel ground radio can actually transmit 7 channels of data, all you have to do is free the extra input pins on the encoder (they are grounded) and attach your pot and voltage reference and you now have an 7 channel radio!!
Be careful... If you're planning on jacking in our standard PC Joystick, watch your pot values. PC Joysticks run from 90K-100K (Flightsticks are about 93K), whereas many R/C pots are closer to 5K. That may be able to be compensated for via a capacitor change in the R/C.

It depends on how they're doing the encoding. Many radios are using a small CPU for multichannel encoding, cause they're CHEAP. But you're right. You should always peek under the hood to see if they give you more channels than are brought out to the case controls.

Quote:
Originally posted by Justin Stiltner I posted this in another thread but its good info...
http://www.rchelibase.com/radio/index.htmlbtw ive looked in my radios and it seems that to retune one you would only need to replace the crystal, maby a few coils and adjust a few trimmers if i can get my hands on an frequency counter i may try it myself
Maybe, maybe not. You can't change a 27MHz rig to a 75MHz one. You may be able to shift from 72MHz to 75MHz though. However, be warned that FCC rules state that to legally modify a transmitter in the US you have to either be a Ham (be a licensed Amateur Radio Operator), or hold a First Class FCC License.

There are exceptions under Part 15 of the FCC rules for building VERY low power transmitters, but I was told at the hobby store this week that people who modify R/C transmitters are definitely regulated, even if you're only attempting to switch channels on one to another allocated frequency. That was news to me, and I haven't had time to verify it yet. (It may be an attempt to encourage business...) You USED to be able to at least switch your own crystals within a single band, but now my local shop is claiming that's true only if the radio is designed for user plug-in crystals, and to insure compliance the FCC is now taking a harder stand WRT people who take the soldering iron to transmitter circuitry.

Now home brew encoders are fair game. You can always build your own 8-channel encoder, and pipe it into the already established transmitter brick! If it's worth it to you to save a few bucks, you may be able to take a standard 2-channel car r/c transmitter and some 555 timers, and build your own 8-channel transmitter. You'll still need the receiver though, so I'm not sure it's worth the time. Great learning experience though. Back in college I built my own 8-channel R/C encoder and decoder with an Ace R/C kit. VERY simple circuits.

Hmmm... I wonder... Anyone have a source for cheap prebuilt R/C transmitter and receiver "upgrade bricks" (transmitter/receiver only modules that fit into some modular radio line) to which we can tie our own encoders and decoders? THAT may be a cheap way to go!

- Keith
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