Jump to content

Recommended Posts

I love the elegance of the Pan-Cam. My question concerns going the other direction. Underwater!

I have been tinkering with making a pan-tilt camera mount/housing for a middle school so they would have an underwater camera for science fair projects.

In case you don't know, you can't transmit RF underwater. With that serious handicap, my question is: Has anyone built something that I can use to transmit the signals to servos over a wire? I'm open to suggestions on what to use for the control sticks too. I would assume a potentiometer with the wiper on a lever. Maybe a video game controller?!

All signals would be transmitted down a single umbillical. This would include the control for the drive motors, ballast tank controls, video, and the pan/tilt signals.

The other question I have, concerns software. Does anyone have ideas about software that I could use to send the signals from a laptop and view the video on in the same application? That would be the optimum software, if I have to have a small window in front of the live video feed, to control the servos, I guess I could cope.

Share this post


Link to post
Share on other sites

You can transmit RF under water, it's a fast growing and very specialised aera. Don't ask me the technical details though because I don't know. Just have a look at the latest copy of Unmanned Vehicles and you will see them.

Terry

Share this post


Link to post
Share on other sites

Not very specialised, but my experiences with a R/C submarine a few years ago suggested that you _can_ use 40MHz (the legal R/C boat frequency in the UK) to penetrate fresh water to a few feet, but this is crucially dependent upon what else is in the water! Swimming pools tend to contain a lot of ionised material to keep it fresh (e.g. Chlorine), and seawater is just as bad - the moment the aerial goes below the water, you lose contact, but fresh water (lakes, pools) are better i.e. you can control it when the trailing aerial is under the surface.

I still remember a photograph of an enthusiast and his sub underwater, wearing an aqualung and using a fully waterproofed (but otherwise conventional) 72MHz (US) transmitter!

I note a fair amount of interest in underwater cameras out there e.g.

Submarine camera

Share this post


Link to post
Share on other sites

Sorry, to clarify - get a 40MHz Transmitter & receiver from any boat/car model shop, and you will get good control even in sea water, as long as you make sure the end of the receiver aerial doesn't go below the water surface ie. make an extended (insulated wire, put some glue over the end to stop water ingress) aerial wire, terminating in a little bit sticking up above a little float!

No experience with transmitting video, but I suspect that, again, an extended transmitter aerial up to your float, with (say) a 1/4 wavelength sticking up (3.125cm), could work fine.

Share this post


Link to post
Share on other sites

I appreciate the replies, not exactly what I was hoping for.

We have to have an umbillical (cable) to control the motors on the ROV anyway. We will probably be at least 20 feet deep in salt water. I was hoping there was an easy way to fool the servos so that we can use direct wired switches or something. The cost to purchase the transmitter and receiver just for camera control is prohibitive for a donated/volunteer project.

Does anyone have detailed technical specifications on the signals that drive the servos? I am an electronics tech and can probably come up with an inexpensive circuit that may work. I just need to know the critical parameters that I need to simulate.

What do you view your video on? Do you feed it into a computer? Or do you use a TV out in the field? If a computer, what kind of software do you use?

Thanks!

Steve

Share this post


Link to post
Share on other sites

It sounds like you want to control your servos over a serial cable.

I googled up these guys, seems fairly reasonable.

http://www.imagesco.com/catalog/servobds/s...servoboard.html

There are probably other solutions.

Why not just feed the video signal up a wire to a capture board

on the computer?

The only other wrinkle might be sending the signals 20 feet without

some sort of line driver, amp or buffer.

Perhaps you can e-mail the people who make the servo board for

advice.

-Dave

Share this post


Link to post
Share on other sites

Yep, if it was me I would use one of those CCTV cables that has a video, audio and power wire all in one cable. Send the video up the video wire and a PPM R/C signal down the audio wire to control the servo's.

Terry

Share this post


Link to post
Share on other sites

That's the stuff I was hoping to find. The original intent was always to bring the video feed through the umbillical. We actually have a 100ft length of professional ROV umbillical. (neutrally bouyant, actually pretty high tech) The pros use thousands of feet of unbroken cable. If it gets cut near the end, (the last couple hundred feet) they will cut it and throw it away. We got them to send us a "scrap" This cable is video ready, and the plan is to use as few wires as necessary to drive the ballast tanks, the drive motors, and the camera pan/tilt.

I like the direct parallel port drive setup. That or something like this http://www.rentron.com/PICX5.htm (found it today)

We may have to write some custom software to allow for the ease of control that I would like to have. I would like to either click on the video window and it pans/tilts to center on that spot, or sliders on the bottom and side so that, when you slide them, the servo moves the camera to point that direction. Even better might be a capability to click and drag on the video feed to be able to track a fish or other subject across the screen.

I think I have found enough information to get me started.

Thanks guys!

Steve

Share this post


Link to post
Share on other sites

Hi Steve!

Thinking about it, there are some pitfalls to using a capture card.

Some cards run slowly and have trouble presenting a picture in real time.

This may be doubly true if you are using the computer to control the

servos.

It may be best and certainly simpler to feed the camera into a video

monitor. To save money you could use a TV, the larger screen would be

more impressive and more people could view it at the same time.

-Dave

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×