Hardwire tx-rx ?? - RC Groups
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Sep 16, 2007, 05:35 PM
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Hardwire tx-rx ??

Hello i am playing around with an idea to build a rc ROV and i want to connect the reciever to the transmitter with a cable so that i can dive the sub to, lets say 100m. Anybody got any ideas
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Sep 16, 2007, 08:18 PM
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With that length of cable you might consider a balanced line system such as RS485, which uses standard RS232 protocol and some line control. It's a simple 2-wire bus system with, for example, LT485 IC's as the line interface to the microcontrollers.
Sep 17, 2007, 12:07 PM
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I have read about rs-485 and it would be perfect, but i do not know a lot about microcontrollers.. can it be used to connect a transmitter to a reciever, or do you need to program a pic and make the system from scratch? I want to keep the system simple and prefferably have all the capabilleties as integrated in a modern radiosystem.
Sep 17, 2007, 01:29 PM
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xtal's Avatar
How big of a sub/rov or how much power will you need to
pull a 100 meters of cable thru the water...the cable
has to be strong enough to handle the stress, the sub/rov must be able to handle the weight,,, this could become very interesting..............
You probably could attach a differential driver chip to an RC encoder for the control end[send ppm differentially over twisted 2 wires] to a differential reciever chip[or voltage comparator ] attached to a rc decoder chip and use ppm for control. Could also use opto isolators..
Resonable simple and should work....
And since you are hard wired you can expannd the # of channels to ??? [ dependant on noise pickup from differential cable in water, I don't have a clue]
Last edited by xtal; Sep 17, 2007 at 02:05 PM.
Sep 17, 2007, 02:11 PM
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Yepp, this can be interrestng, the rov will be aprox 100x60x40 with 6 thrusters, and will be fitted with a camera and compass, the power wil probably come from two big Lipo packs, and the main body will be made of 3M Glass bubbles mixed with epoxy resin for bouyancy. the mechanical parts is not the big problems, as i have access to the machinery to make the parts i need, my biggest challange will be the controlls.
The way i see it i wil need to have two twisted pairs down one for controls and one for camera, and the drag from the cable wil not be too much as long as it is close to neutral in water.

The first thing to adress must be the ppm, how to exstract it from the transmitter and put it in to the reciever

The ppm can probably be taken from a trainer cable, but do anyone know how to connect it to the reciever??

Ok, Did some research.. i can locate the ppm ether from the trainer outlet, or between the multiplexerchip and the rf bord, and the same for the reciever..

ordering the controller now...
Last edited by Helge; Sep 17, 2007 at 04:33 PM.
Sep 17, 2007, 06:26 PM
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xtal's Avatar
for ppm ..feed ppm to cable thru driver then you don't need a receiver,,, just a decoder and a circuit to convert the signal to a compatible input for the decoder....pic source code&hex files are available several places on net -- Bruce Abbott site and others

You may be able to kiil 2 birds with 1 stone ...by modulating a dc bias with ppm and and adding video on the rcvr end ...of course then more noise possibilities .......there may already be circuits on the net for this???

probably the most important is just how do you want to communicate
PPm, I2c, asyn Serial, so-on-so-forth. How many control channels would you need....

I think ppm would be a quick solution and easy to test..

I would probably try to use opto isolaton on trainer port if ppm is there.
Trainer port-->isolator/driver---cable---->rcvrchip-->decoder--->channels
Last edited by xtal; Sep 17, 2007 at 06:33 PM.
Sep 18, 2007, 12:57 AM
TheSteve's Avatar
If you get a receiver with the DSC port (direct servo connect) you can get a cable that will plug directly from the transmitter to the receiver. Then you'd simply need to extend that cable(within reason) and it would be good to go. I know Futaba makes such a setup.
There are probably cheaper ways if you want to modify some stuff or build a circuit but they wouldn't be as simple.

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