Will it lost the data on the so long wire Nigel? The distance is about 500m, and I don't believe that the signal can come your control board.

As you give 5V or 25V at the joystick, the signal will lost in a distance of 10m to 15m. As we will see that the voltage at COM port is about 25 to -25V and we cannot connect 2 PC as they are as far as 15m from each other.

So, if use you RS232, you can send it as far as 10 - 15m, and at each end of 15m, you put an ampli to strengthen the signal.....

Yeah, transmition in a distance of 500m, but don't use anything else to amplify is quite new to meeh. And as you want the realtime control and a good signal to control the servo, you should try my solution. Because your problem is not how to connect to the servo with a limit number of wires but the transmision.

And if you don't mind, pls tell meeh your solution, because it's interesting.

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The width of the pulses sets the position of the servo's, you simply vary the width, and the servo moves accordingly.

I've no idea what you would need to do for 500m of wire, you would need to experiment to see what happens - as a minimum I would expect to have to feed a fair amount of power into the cable to try and overcome capacitance and losses. It might not be possible at all, and a more complicated scheme could be needed.

But regardless, the circuit above is how the servo's should be connected, and shows the signals they require.

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Hi falleafd,

I wasn't suggesting it was a complete solution, merely a starting point for experimention - the first thing you would need to find out is how far it would work over, obviously one factor that would affect this is the source impedance of the pulse generators. You could add amplifiers to increase their capacity, and you could also add buffers at the receiving end.

As for RS232, the distance available is inversely proportional to the speed (to some extent) - I see no problem working a great deal further than 10-15m at the kind of speeds require for working a pair of servo's (1200 baud would be more than fast enough). For that matter, how about 20mA current loop?, isn't that more reliable over longer distances.

My very first suggestion was to use a standard radio control transmitter and receiver, although now we know the range is 500m, it's probably a bit too far (apart from any interference problems). I also suggested using the encoder/decoder chips from the radio control system to send the signals down a pair of wires.

How about using a standard radio control transmitter and receiver, but removing the aerials and connecting them via 500m of coax cable?.

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hi.
i also really intrested in your project , since i also decided to built small robo some what simillar to your project.
so i request you to send me all information regarding with this project.
i hope you will help me.
thanking you.

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Hi friends,
i am the student of Engineering & i am in Final year & belongs to branch Electronics & Telecomm.I am going to prepare a project related to topics like Robotics, PC based projects.

 

It's true that we may transmit upto more than 15m with serial communication from PIC, but it's risk to signal. It's oki if we can use upto 20m or 30m..

But in this case, I suggest to use serial with amplified circuit at each end of 15 or 20 or 30m. With a small circuit but it's about 10 - 30 circuit betwen the wires. Well, terrible... I myself cannot imagine what I suggested, but if you have to build wire connection, I think it's a good way.

Yes, as Nigel said, RF is better.

I have no more ideas. It's very difficult to transmit so far as 500m with signal from PIC or other MCs.

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mail@falleaf.net
English forums at PIC Vietnam - Vietnamese Electronics forums
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Distributor of Microchip in Vietnam

 

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

 

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.

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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

 

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.

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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.

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English forums at PIC Vietnam - Vietnamese Electronics forums
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Distributor of Microchip in Vietnam

 

You could use a radio like the ones use to control RC airplanes Check Towerhobbies Radio
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:
http://www.seattlerobotics.org/guide/servos.html
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