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Range finder
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Philip
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Joined: 18 Jun 2004
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Location: Queensland near Brisbane


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Range finder

I would like a range finder that will adjust a standard RC servo. How would you accomplisk this? I was thinking of using ultrasound and somehow having this information interpreted, but I really am not familiar with electronic control curcuits.
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Post Tue Oct 04, 2005 7:35 am 
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Spockie-Tech
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Location: Melbourne, Australia


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Hmm, lets see.. you wouldnt be looking to sense the range to a nearby boat and adjust gun elevation accordingly now would you ? Wink

What are the maximum and minimum ranges you will need to deal with and with what sort of precision ?

If my guess is correct, then you will be looking to sense a very "soft" low density piece of unusually shaped wood floating only marginally above a large flat potentially rippling surface at long range.. blech, potentially difficult. Sensing a nice solid 90 degree wall where the reflections are much clearer is easy.. Can you clarify the application ?

Ultrasonic waves are the normal range-sensing tech, but they might struggle a bit depending on how solid the thing you're trying to bounce the sound waves off are. Theres some good tech info on ultrasonic range finding here
http://www.robot-electronics.co.uk/htm/srf08tech.shtml
and a basic pic low power schematic here
http://hamjudo.com/sonar/
and some more info here
http://www.seattlerobotics.org/encoder/may97/sonar2.html

Another cheap option might be to canabalise one of those (relatively) cheap "ultrasonic tape measures" and see if you can read the output on the display with a pic-axe and use that to control a servo. Polaroid makes an ultrasonic ranging experimenters kit that is based on one of their early cameras that is popular with robotics experimenters

If Ultrasonics wont handle it, then it starts getting much trickier.

Laser range finders are more accurate (and expensive), but presume that the thing you're ranging will reflect your beam of light.. which might not be the case in your application. A bit of black paint could mess everything up.
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Post Tue Oct 04, 2005 7:26 pm 
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Nick
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Joined: 16 Jun 2004
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Location: Sydney, NSW


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There is a good "low tech" method that you could adapt and that is very in character for model warships. In WW2, the allies needed to fly at exactly the right hight over water when they released their dam buster bombs. Radar was out and it was all conducted at night, so optical bomb sights wouldn't work.

Some lateral thinker figured that triangulation was a great way to measure distance and fitted two spotlights front 'n back of the plane, angled down & towards each other. When the plane was at the right hight, the beams intersected on the water surface and formed a single spot.

In this example, the beam angle was fixed and the plane adjusted it's hight to aim it's bomb. In a ship's case, you would want to adjust the beam angle in sync with your gun elevation.

You could adapt that by aiming a fixed laser pointer horizontally and attaching a second laser to a servo that slaved off your gun elevation. It sounds fairly easy so far, but ther ewould be some complication with the parabolic flight path of your projectiles. That might be accomodated with a cleverly shaped cam or some electronics, but serious maths would be involved and that's where I check out.

Who said history couldn't teach us anything? Laughing
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Post Tue Oct 04, 2005 8:59 pm 
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Glen
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sonar would be the logical solution,

and thats where I check out Cool
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Post Tue Oct 04, 2005 9:38 pm 
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Spockie-Tech
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Sonar *is* sonic range-finding. Smile

Its just not often ultrasonic, since lower frequency waves are more useful in a water medium. Ultrasonic is good in air.

Sonar requires some pretty nifty signal processing though, especially in shallow water, where the distance to the bottom of the lake is probably less than the distance to the target.. you would get echo-returns from the bottom before the echo return from the boat.

All this is presuming we *are* talking about Philips "Big Guns" of course. We all might be barking totally up the wrong tree.. Smile

The big problem here is that as far as the sound waves are concerned, the boats dont look that different to the water. If they were made out of nice solid steel plates you could expect a good return, but thin balsa would be very iffy.

I think you will have to introduce some remote signal processing powered by a biological computer with visible wavelength optic sensors (eyes). Very Happy

Nicks idea of converging laser beams sounds good, but it would only work if the opponent was on the far side of your boat. if they were between your boat and you, you wouldnt be able to see the spots converge since they would be on the other side of the opponents boat.

I doubt the ammo they use would follow any significantly curved ballistic path at the short ranges involved, or they probably wouldnt have enough penetration power.

I take it stepping up the laser power and burning holes in them would be seen as unsporting ? Wink
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Post Tue Oct 04, 2005 10:22 pm 
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Glen
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hehe that would be a great new battleship kind of thing.. youve got the old style crusiers and battleships and the new style future technologies. sorta like that philadelphia project (or whatever the movie with the dissappearing ship is Razz )

the K.I.S.S route would be a metal storm type thing and just shower a massive spray of BBs all over the place. which would no doubt be entertaining.

maybe passive sonar, listen for the loudest noise point the guns toward them and start spraying BBs up and down at a particular range of angles. youd pretty well be assured of a hit that way. wonder if the big guns boats would be louder than your average back ground noise in a lake... Rolling Eyes
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Post Tue Oct 04, 2005 10:50 pm 
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DumHed
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This is what you need: http://cs-people.bu.edu/aaron/turret/turret.htm

Check out the test video Smile
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Post Tue Oct 04, 2005 11:15 pm 
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Big AL
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Joined: 16 Oct 2004
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hmmmmm can any one think of autonamus bots using that Smile
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Post Tue Oct 04, 2005 11:56 pm 
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Archer



Joined: 08 Aug 2005
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Location: Canberra


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i want a turret like that to stop ppl killing my pc when im not around ( think i would be able to buy one Twisted Evil

Post Wed Oct 05, 2005 1:53 am 
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original_carnage
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Why have second rate weapon systems?????

Not only is this Aussie designed and made, these are reguarded as the worlds most deadly firearms....

http://www.metalstorm.com/

have a look at the "area denial" tripod system.....
anyone not seen the movie "Aliens"...??

PS don't forget your "black box" dog tags near this baby, you don't want to be identified as hostile....
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Post Wed Oct 05, 2005 10:52 am 
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Philip
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Joined: 18 Jun 2004
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Location: Queensland near Brisbane


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You got me in one. Target hit and sunk.

Big Gun ships must be shot at or near the waterline to be effective. Water must run into the many holes to flood the hull. Ball bearings will skip on the water's surface so the cannons cannot be aimed too low or the ball bearings will bounce up and strike above the waterline.

There are many factors to consider and eliminating the need to elevate the guns would make life easier. You might be looking at a 100 mm long barrel from 30 m. You would all be familiar with the pressures the operator feels when involved in combat.

The range would be 500 mm and up to about 3 or 4 m.

I will read the links provided. I may not understand them, however.

Thank you all for your help.
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Post Wed Oct 05, 2005 3:54 pm 
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Philip
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The picture at the bottom of the page shows the path of the bearings. You can see that a shot accurate to about 600 mm should suffice. http://www.ausbg.org/bbg/index.htm
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Post Wed Oct 05, 2005 4:36 pm 
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dyrodium
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It wouldn't work for sensing range and such, but if you wanted to keep the turrets aimed at the optimum level for low level penetration. would you be able to use a gyroscope? It works for the moped keeping it stable... lol just a thought. Very Happy
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Post Thu Oct 06, 2005 2:59 pm 
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Philip
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A gyro would keep the cannons level on rough water, Dyrodium. However, the reason I want to use a range finder is that the angle to the waterline varies as the distance to the target varies.

From the above links; I believe that I would be able to use a SRF04 and couple it to a PICAXE. (This is only from one nights reading so I may be wrong) The PICAXE could be programmed to control the cannon elevation servos according to the output of the ultrasonic range sensor up to three meters.

The ultrasonic tape measure, as posted by Brett, might be better as it might not be affected by reflections from waves on the water.

PICAXEs appear very flexible. (I repeat that this is from a newbie point of view)
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Post Thu Oct 06, 2005 5:55 pm 
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DumHed
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what if you had a sort of gimbal system to keep the cannon pointed at the right level for a medium range shot, with a servo operated correction (just moving the balance point of a pendulum, etc) so that you can do a rough range adjustment from the controller.

Most of the time you'd basically be selecting between neutral, close, or far and with time you'd get better at accurately selecting the range.

The gimbal setup would keep the cannon level as the boat moved too.
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Post Thu Oct 06, 2005 7:23 pm 
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