Ethernet cable

Control Boards, Controllers, Tethers, Ect.
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Dave W
Posts: 5
Joined: Nov 18th, 2010, 7:22 pm

Ethernet cable

Post by Dave W »

This may be an obvious question to most of you, but I'd like to control an ROV with an ethernet cable. My question is should I be using stranded cable versus solid? My mechanical background is pointing me in the direction of the stranded. I would like to have a tether around 250 feet long. My thanks Do you think cat5e is sufficient: or should I be looking at cat6A or cat6e? My thanks, Dave W
ckleppin
Posts: 19
Joined: Nov 20th, 2010, 2:33 pm

Re: Ethernet cable

Post by ckleppin »

I would look for stranded. It will be more flexible than solid core, which is nice. Are you planning on using the ethernet for TCP/IP communication, or just using the wires for a serial connection (RS232 or RS485)? Ethernet cable is low capacitance, so if you were inclined to, it should be able to have a 250' serial connection with RS232 if the baud rate is kept low. Otherwise RS485 does not require much extra hardware either.

Ethernet communication is more complicated than serial, but if you are using a micro platform that supports it, you can get much more bandwidth from an ethernet connection. For 250', Cat5e should be more than sufficient. I doubt any of the advantages that Cat6 provide are not worth the extra cost of the cabling. The standards are pretty similar except that Cat6 operates at higher frequencies, which are generally not supported by microcontroller development boards. It might help if you notice you have noise problems, but that is about it.
Dave W
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Joined: Nov 18th, 2010, 7:22 pm

Re: Ethernet cable

Post by Dave W »

Thanks for the information it gives me a direction for my research, unfortunately it also rains on my parade. A while ago I purchased and used CCTV equipment which included three Pelco controllers. One is the 9500 series, the other two are CM9760-KDB's. After reading your response I checked the units and found that both run RS422 which in hindsight may be of no use to me. However in the 9760 models there is a relay port, and all of them have good quality joysticks possibly I can salvage those. I will do some more research as you did not mention the RS422 I will check to see if it has any redeeming qualities.

I don't know if there is something I could purchase that would plug-in to these controllers that I still may be able to use them. There is the possibility that these controllers may be obsolete or if an item is available it may not be cost-effective.

As I am still in the collecting phase and have not began to build in earnest, I think I will start with a modest ROV and learn from my mistakes. I think I would like to build a small ROV with a battery on board and controlled remotely from a joystick control box. Thanks a lot for your help any further assistance from yourself, or anyone else would be appreciated. My thanks, Dave W.
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sthone
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Re: Ethernet cable

Post by sthone »

I always use the stranded type ..... another thing I found with solid beside not being as flexible is it breaks a lot easier if it is bent back and forth a lot (which in the case of a tether is a lot) :)

-Steve
ckleppin
Posts: 19
Joined: Nov 20th, 2010, 2:33 pm

Re: Ethernet cable

Post by ckleppin »

Don't worry about the fact that I only mentioned 232 and 485, they are generally more commonly used. RS422 and RS485 are pretty similar protocols. To get into it, I would just look up the Wikipedia pages for each protocol to see the differences between them. It gets kind of technical, but I am sure that is information available that will enable you to interface with the boards pretty easily.
Dave W
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Joined: Nov 18th, 2010, 7:22 pm

Re: Ethernet cable

Post by Dave W »

Thanks for the information gentleman. I have only a couple more questions with regard to the ethernet cable. One, is there a certain life expectancy I should be looking for from a CAT 5E cable? Two, is there a benefit to using a particular color of cable shielding? (I have noticed that clear plastic deteriorates a lot faster in direct sunlight and black plastic)

I did some research comparing the RS 422 and the RS 485. Both the RS 485 and RS 422 are differential in the mode of operation. However the RS 485 can handle 32 drivers and 32 receivers on one line. The RS 422 is good for 1 driver and 10 receivers, which I think if I understand correctly I should be able to run 10 different operations on 1 ethernet cable. Both the RS 485 and the RS 422 have a max cable length of 4000 feet. Now all I have to do is to find out how to utilize the Pelco controller to send the correct commands to the ROV. Does anybody have a direction for me to go? My thanks. Dave W.
Dave W
Posts: 5
Joined: Nov 18th, 2010, 7:22 pm

Re: Ethernet cable

Post by Dave W »

So much for that idea. Upon further research, I discovered that I need a receiver to the tune of about $600. It does not make sense not knowing for sure if the controller is any good. I think I will gut a controller and use the joystick and any other useable parts. I did manage to get some parts ordered this weekend, bilge pumps, ethernet cable, relays, and some circuit boards to play with.
I have a question about radio controls. To my knowledge, when operating a model craft a control is operated passing a signal through a transmitting antenna to the model craft's receiving antenna, and from there is decoded and is directed to operate a servo. Could this be done with cable instead of radio waves from controller to the model craft? Also what is the max number of functions you could control?
Thanks Dave W.
ckleppin
Posts: 19
Joined: Nov 20th, 2010, 2:33 pm

Re: Ethernet cable

Post by ckleppin »

First, when RS422 says that it supports 1 Driver and 10 receivers, it means that 10 devices listening on the same twisted pair, waiting for one of those devices addresses to be called by the driver. RS232, 422, and 485 are all serial communication protocols, so it does not really mean 10 operations at once. The purpose of supporting 10 devices on the same line is more for if you had 10 remote sensors that were all independent of each other. The Pelco controller will really be the only device that you need to be talking to.

Second, $600 bucks for a receiver sounds like it is not really what you need for this application. I think that all you really need is a little converter that takes the RS422 serial data from the Ethernet cable and then converts it to USB.

http://www.sparkfun.com/products/9822

The above link is not exactly what you need, but effectively what happens is that when this device is plugged into your computer, it is emulated to look like a serial port which you can then use putty or a similar client to send commands over.

Third, I am not sure if it would be very easy to convert an RC controller to send the same commands via a wire instead of using RF. A possibility you can look into, although it requires a solution for the serial issues, is

http://www.pygame.org/news.html

These python Libraries are pretty easy to use, and there is a fair amount of documentation describing how to use it. If your RC controller has a USB port, it can be connected through the computer, where the inputs from the joystick are read and then transmitted via the serial connection to the micro controller, which then will turn off and on the motors. The number of functions you can control is really only limited by the micro controller.

Forth, I was wondering if you are using mechanical relays or solid state relays? Either way make sure that you have incorporate flyback diodes and possibly opto-couplers on the control lines from the micro to the relay. There are plenty of examples online of this online. Motors are inductive loads, when they are quickly switched there can be large voltage transients that can damage the motor or the micro controller.

Sorry for the long post, and I hope this helps.
Clayton
tazdevl77
Posts: 15
Joined: Dec 20th, 2010, 12:00 pm

Re: Ethernet cable

Post by tazdevl77 »

Hey guys, most of what you have posted is Greek to me... but Steve may have addressed the issue of converting an RC Controller from RF to wired system on his ROV page. Check out the link, it's about half way down the page. Tim
http://www.homebuiltrovs.com/howtocontroloptions.html
ROV-Control
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Joined: Dec 17th, 2010, 8:19 pm
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Re: Ethernet cable

Post by ROV-Control »

Maybe this link can help you ROV Shop
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