Underwater Camera cable control any help?

[Underwater ROV]

Hi, A few divers inc myself have made an underwater camera (ROV) with three attached motors 12v (need to be able to switch polarity to reverse ) and future plan for three other controlable motors/servos for a grab arm. I can wire these all seperately but would prefer to use as few wires as possible due to bulk etc and a cable length of about 80m with the power source above the water, 12v car battery (s). Does anybody know how we could maybe make a control circuit that would utilise a joystick or similar and code a signal to the sub. I could pay a bit (unfortunately we are not loaded - hence we are making this ourselves!) for something that would work. I am capable of building a circuit if I had a plan of some sort. Any ideas or could anyone tell me where to look.

 

[philba]

Interesting project. I would split this into 3 parts: ROV controller, comm channel and Main Controller. Also, you will want to define a control protocol though there maybe be something already made that you could just use. have you looked into low cost ROVs? there seems to be some literature on them. also there are several manufacturers. Looking at their designs could point you in a good direction.

For the comm channel, you could use RS422/RS485 and 2 wires plus a shield (though, the shield may not be necessary). These can be driven over quite large distances. There may be other approaches. I wonder if you could impose an RF signal on the power cable, thus saving wires. What do the commercial ROVs use?

The controllers really should be done with microcontrollers. The main controller would manage the joysticks and other controls, encode the information into communications packets and manage the communications. The ROV controller would receive the contrl packets, decode and apply them to the motor/servo controllers. It would probably send status information back. Motor/servo control is well understood - lots of circuits to be had.

I wonder if there is a way to cheaply use a game controller (xbox controllers have 2 joysticks and triggers and so on). The ergonomics is pretty good. Xbox uses USB so it would require more than a simple uC.

 

[The Mad Professor]

Single Coax Carries Video, Power, and Data Signals
**broken link removed**

The above link will yield a usefull circuit or two and could be developed further.

 

[Underwater ROV]

thanks

Thanks for the replies so quickly! A games controler would be great if we could make it work. We will have a laptop on board to view the camera signal so I suppose that could play a role if necessary. I will have another search around for the 'low cost ROV's' online. My electronics knowledge is sketchy to say the least, only building a few sound to light and similar simple projects in my youth from kits etc.
I have printed off that link as well for a look. Cheers
Thanks again

 

[philba]

Did you know that xbox controllers actually use USB? the connector is different, though. you can buy or make an adaptor - xbox to USB-A (PC). the XBCD driver is free - it works pretty well. google for xbcd. I've used it with a wireless XBOX controller but wired ones should work as well. You will need some sort of output (usb or serial or parallel, depending on your computer) that goes from your PC to the main controller.

That maxim link looks interesting. I wonder how much "down" bandwidth you can get - the ap notes uses a 10 hz signal which is probably too slow. what is a comfortable "control command rate" for this application? I'd guess in the low Khz at least. don't know if that will cause problems with the design in the apnote. there are schemes for using the retrace period of NTSC or PAL to transmit signals - maybe that would give more bandwidth.

 

[Underwater ROV]

Thanks for the information. Further to a link yesterday I found some websites dealing with similar machines and I am trawling through them when I get the time. Some use very basic switches and wiring which I can handle but still looking for a suitable circuit (s) to reduce the amount of cables ie reduce drag in the water. Everyones advice is appreciated. Thanks Again

 

[Nigel Goodwin]

Thanks for the information. Further to a link yesterday I found some websites dealing with similar machines and I am trawling through them when I get the time. Some use very basic switches and wiring which I can handle but still looking for a suitable circuit (s) to reduce the amount of cables ie reduce drag in the water. Everyones advice is appreciated. Thanks Again

A PIC at the top, and a PIC at the bottom, and suitable programming, would allow the data to be sent down a single cable - in a similar way to a radio controlled model, where multiple controls are sent over a single radio link.

You don't have your location entered in your details, it would be helpful to do so - you might get more offers of help from someone near you?.

For example, my 15 year old daughter is PADI qualified, so if you weren't far away I would probably be interested?.

 

[Underwater ROV]

Pic

That sounds interesting, if the signal could be sent down one cable and I guess the power down another two plus the video feed this would help alot. Could the signal be fed down one of these other wires to further reduce bulk?
Thanks again for the response. I live in the Isle of Man so not really that convenient for most people - ha. Thanks for the offer though.

 

[Nigel Goodwin]

That sounds interesting, if the signal could be sent down one cable and I guess the power down another two plus the video feed this would help alot. Could the signal be fed down one of these other wires to further reduce bulk?
Thanks again for the response. I live in the Isle of Man so not really that convenient for most people - ha. Thanks for the offer though.

It's a LOT close than it might have been!, and I have actually been to the Isle Of Man - I was horrified to find you had to be 21 years old to drink alcohol there!.

There are techniques available to send the digital data down either the power leads, or the video feed - but anything like that adds complications, and these sorts of devices really need to be as simple (and fool proof) as you can make them.

 

[Underwater ROV]

Now that looks interesting. I will have a good read when I get some time, got to do some work today - ha. Thanks very much.
21 to drink? are you sure you have the right Isle of Man? I think it's 16 or 17 for pubs or about 13 if they can talk somebody into buying it for them..ha TT races due to start practices this weekend so I might not get to the controller for a bit but I like the idea of buying a ready tested and working board! that will advance things greatly. Thanks again.. Norman

 

[Nigel Goodwin]

Now that looks interesting. I will have a good read when I get some time, got to do some work today - ha. Thanks very much.
21 to drink? are you sure you have the right Isle of Man? I think it's 16 or 17 for pubs or about 13 if they can talk somebody into buying it for them..ha TT races due to start practices this weekend so I might not get to the controller for a bit but I like the idea of buying a ready tested and working board! that will advance things greatly. Thanks again.. Norman

I was there in the early 1970's, all the pubs had signs up "RU21", so I asked why (as I drank my beer) - and was told the drinking age was 21 on the Isle - I was probably 19 at the time.

 

[Klaus]

Your comment about the power source being at the surface seems to have been overlooked by the other replies.
If your motors draw any appreciable amount of power then, at 12V, you will require fair size power wires to reduce the voltage drop at the far end. Keep in mind that the current has to travel there and back so you use 160m for your voltage drop calculations. If your power wires become too bulky for the cable you had in mind, then you have 2 potions:
1. increase the supply voltage
2. have the power source at the ROV

there's more to this project than just controlling it

Klaus

Hi, A few divers inc myself have made an underwater camera (ROV) with three attached motors 12v (need to be able to switch polarity to reverse ) and future plan for three other controlable motors/servos for a grab arm. I can wire these all seperately but would prefer to use as few wires as possible due to bulk etc and a cable length of about 80m with the power source above the water, 12v car battery (s). Does anybody know how we could maybe make a control circuit that would utilise a joystick or similar and code a signal to the sub. I could pay a bit (unfortunately we are not loaded - hence we are making this ourselves!) for something that would work. I am capable of building a circuit if I had a plan of some sort. Any ideas or could anyone tell me where to look.