small servo project, I really need HELP

okay guys
well we reach almost a dead end : ) . anyway i will try to test a very long ire and see how the signal will act. only for curiousuity reasons..... but please if some one has any idea again that will be great.
however can we get back to NIgel first suggestion to use RF ...
can you just explain more for me the encoder/decoder chip from radio control system. and how can i satrt such a thing , and is there any kind of cheap RF recivers you know ????? and i guess that using RF for more than 500 m is not a big problem , right ????
thanx guys

fakahany1 said:

okay guys
well we reach almost a dead end : ) . anyway i will try to test a very long ire and see how the signal will act. only for curiousuity reasons..... but please if some one has any idea again that will be great.
however can we get back to NIgel first suggestion to use RF ...
can you just explain more for me the encoder/decoder chip from radio control system. and how can i satrt such a thing , and is there any kind of cheap RF recivers you know ????? and i guess that using RF for more than 500 m is not a big problem , right ????
thanx guys

Click to expand...

You can buy various radio control transmitter/receiver kits, which usually come with at least two servo's as well - they are amazingly cheap these days. The systems are available with various channels, for your application you only need two channels, but four and six are common as well - two channel ones are usually intended for radio controlled cars, giving steering and speed (including reverse).

So the transmitter includes the joysticks, an encoder IC, and an RF transmitter. The recive includes a radio receiver, and a decoder IC, which provides signals compatible with the standard servo's.

I would suggest buying such a system and getting everything working as you need, then worry about extending the range - it's hard to say how far they will work, generally with model planes they work further than you can see the direction of the plane.

hello Nigel
well , am searching for a suitabel RC system , a cheap one , but usually if you are talking about RC cars systems , that uses 2 channel radios they are most of teh times with limited range to about 350 yards or something, however i do beleive that there is mosre and i need time to look for it .....
however, if am stuck with this 2 channel thing with limited range, how is it possible to increase the range, taking in mind that in my part of country there are no restriction on RC toys and systems....
Thanx alot Nigel for you suppourt

fakahany1 said:

hello Nigel
well , am searching for a suitabel RC system , a cheap one , but usually if you are talking about RC cars systems , that uses 2 channel radios they are most of teh times with limited range to about 350 yards or something, however i do beleive that there is mosre and i need time to look for it .....
however, if am stuck with this 2 channel thing with limited range, how is it possible to increase the range, taking in mind that in my part of country there are no restriction on RC toys and systems....

Click to expand...

An easy way, for a fixed installation, would be to increase the aerial efficiency - the small whip on the transmitter, and short wire on the receiver are grossly inefficient. Replacing them both with suitable size dipoles, correctly aligned with each other, should increase the range a great deal.

Well, I saw that Microchip also have some RF transceiver from several of KHz to 13.5 MHz. You may try it. I think it's good.

Come to www.microchip.com and goto products/ RF devices.

Or you may buy some Chinese remote control toys which has upto 6 channel with servo control and they use 27MHz to 40MHz.

I think it's good enough. But for 500m, perhaps you can buy a cellphone toys, and it works goods. The price is only about 10 - 30 USD.

You could use a radio like the ones use to control RC airplanes Check **broken link removed**
This radio has a range of 500 yards.... as you know 1 yard is about 0.9 meters, so that is a little bit closer than you wanted to. But you can always use a mix of RF and long (but shorter :lol: wires).

A servo functions easily. A 1ms pulse will move the servo to the right all the way. And a 2ms pulse will move the servo all the way to the left. A 1.5ms pulse will position the servo in the middle. Anything else can be derived from there, keeping in mind that some servos will not rotate a complete 180 degrees while others will go over 180 degres. The receiver will receive and spit out a 1-2ms pulse.

The signal ideally should be a 5V signal, as battery depletes or as distance increase that signal voltage decreases. I am going to guess that the servo will accept CMOS voltage levels so I would check the voltage you are getting (will need and oscilloscope) and if it is lower than 3.5V then you will need a amplifier (which is as easy as the signal going thru an inverter twice).

My second idea is to use RS485 instead of RS232. RS232 is based on voltage reference to the power ground, where noise can be easly entered, speed is lower, the max distance you will get is about 30-40 meters. While RS485 use a diferential voltage to comunicate and let you have a long cable about 1200 meter (4000 ft). Then you will need a microcontoller that sends the data in RS232 format and a RS485 converter to be able to send the data. You can also add more than one "receiver" to the circuit, and adrress them. The problem here is the development of the board... not difficult at all!, but you need some research and development.

So there two options, one almost readily available, the other one a one shot development easily reprodudeable and cheaper.

Ivancho

Here's a link for a page which might be helpful to you:

It's a short tutorial on how the servos operate.

For a PIC you can in theory run about 8-10 servos, if you update them every 20msec. To do it over I2C would be easy, if distance wasn't a problem.

Seeing as how you want to run 500m though, using a wire just becomes a problem in it's self. Either wireless with good antennas, or fiber optic would be your choices. I don't know what kind of protocol you would use for a single strand of fiber, but If you use 2 strands, or use a longer wavelength IR(960nm) and a visible light sensitive transcever(use a blue LED, that way there is no interference with the IR one) on the same strand, you might be able to use I2C or RS232 to communcate.

Probably far from perfect, but just my idea.

If you wan't to get fancy if you could put a yagi antenna on a motorized mount that tracks the robot.

do you have any experiance in ic programming
specialy Mcontroller

do you have any experiance in ic programming
specialy Mcontroller