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1st Vosper MTB working torpedo completed

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1st Vosper MTB working torpedo completed

Old 05-20-2010, 03:22 AM
  #1  
Hookpilot
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Default 1st Vosper MTB working torpedo completed

Torpedo #1 is finished thanks to Tony for supplying the schematic. It has been quite a learning experience to build something this small with enough power to move the torpedo ahead of the boat after launch. I'm now figuring out how best to fire the fish from the tube. Spring power was first try, but had issues with getting a spring the right diameter. Now thinking of CO2 system to do the job. But need a mechanism to puncture the cartridge and feed gas to launch tube. Also looking at a compressed air landing gear retract system modified to do the same thing. CO2 cartridges are next to impossible to get shipped to Hawaii.

Pictures below show inner workings of the torpedo:

Mike in Honolulu
See website for more info on the Vosper MTB. I just did major rebuild of deck structures and center motor/stuffing box/prop.

http://web.me.com/hookpilot Click on "Hobbies" to see stills and video of the MTB underway.

Picture #1 showing the components. Wires leading out of the front torpedo section lead to water contacts to turn the torpedo on when it hits the water.
Picture #2 all components plus ballast lead on scale. At 430g the torpedo just breaks the surface in salt water.
Picture #3 same as #2. Showing O-ring sealing system.
Picture #4 close-up of tray with Graupner Speed 430 Race electric motor, circuit board and LiPo battery
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Old 05-20-2010, 03:45 AM
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Default RE: 1st Vosper MTB working torpedo completed

See if you can come by some Clippard Minimatic components.

You could use the MAV-2 as the main valve, and attach a one to two cubic inch
volume chamber, MAT-1 or MAT-2 to it as your gas resevoir. Firing the MAV-2 can be done with
an MPA-3p air actuator and MAV-3 poppet valve, but that may require more air
system than you want. A high torque servo might be able to actuate the MAV-2 directly...


http://www.queensown.org/technical-data-sheets-2.html

Old 05-20-2010, 04:37 AM
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Hookpilot
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Default RE: 1st Vosper MTB working torpedo completed

Umi: You are up late! It's almost midnight here in Honolulu. I'll research the parts list you provided. Thanks,

Mike
Old 05-24-2010, 08:22 PM
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electricalgod1
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Default RE: 1st Vosper MTB working torpedo completed

Good evening Mike,

First I'd like to say what a wonderful job you did on the Vosper and the torpedoes. I watched the video and it cruises very well.

I have a 4 foot Elco PT boat.
I started off with CO2 and mechanical valves but ended up going back to compressed air and 6V Clippard electric valves triggered by a MCD Switch-8 unit.
They pilot bigger Clippard valves plumbed directly below the tubes.
Both my front tubes at setup up to fire and with that 1 CO2 cartridge does not have enough volume, thats why I went back to compressed air.
Under the deck is a Robart large storage tank and I ended up installing accumulator tanks at each main valve.
I do not have a picture of the valve and accumulator arrangement but I will take one and send it to you.

Again, Nice Job!

Dino
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Old 05-24-2010, 11:52 PM
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Default RE: 1st Vosper MTB working torpedo completed

Dino:
Great setup on your Elco PT. I thought about CO2 and thought that there might not be enough volume and pressure to move the torpedo out the tube with enough force to clear the deck. I'm anxious to see your setup with the Robart tank, Clippard electric valves and accumulators. I will be firing both torpedoes at the same time as they did on the Vospers. What pressure do you pump up the large storage tank to to make this work? How heavy are your torpedoes? Mine are almost a pound apiece and 1.5" in diameter and 17 inches long. What are your launch tubes made of? I'm afraid I'll have to rebuild mine to take the pressure. Currently mine are made from Estes Model Rocket body tubes, wound paper which may just burst under a 100psi shot of compressed air. I'm looking for thin-wall brass tubing to do the job. Weight will not be much of an issue as the entire boat only weighs 17 pounds including batteries.

Thanks for the pictures and information. I need to research the Clippard electric valves and accumulators to see how to plumb the system.

Mike in Honolulu
Old 05-27-2010, 08:14 PM
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Default RE: 1st Vosper MTB working torpedo completed

Good evening Mike,

Glad to be of service.

I believe the last time I tested with dummy torpedoes, it took 80psi to clear the deck.

The tubes are spun from aluminum tubing (Metal Supermarkets 1" ID, 1.25" OD tubing) from measurements taken off of the Dumas kit wooden tubes. 1" was the ID that I needed, so that meant I only needed to cut the OD. Then I cut off the ends and trimmed them up holding the tube in a collet. The ends are aluminum round stock drilled and fitted with the Dumas kit pieces. They are super glued to the tubes.

All I have is dummy torpedoes made up. I have been trying to come up with counter rotating props like the ones on www.pt-boat.com. I may just end up with a single prop.

If Clippard valves are not common in Hawaii, you can also use Numatics brand. They have a small 12 or 24vdc valves. I choose the 6V because at the time I was running 8.4V packs, 6V is not common so I had to wait a while. Both Clippard and Numatics stock 12 and 24 vdc. I have included a reference that I got from a site for the CO2 cannon for a R/C tank.

I will get pictures of my valves and accumulators on the weekend(been working late this week)

Dino

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Old 05-27-2010, 09:01 PM
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Default RE: 1st Vosper MTB working torpedo completed

Do these torpedos shoot out in front of the boat? If so, I would think the compressed air power you need is to ensure the torpedos are still moving fast enough the boat doesn't run them over once they hit the water....until their own propellors get a bite..... vs merely a deck clearance issue. I see a big slow-down once they hit the water for a second or two.

Ever think of using hair-spray and an ignitor? Google Potato-Cannon for ideas. Rule of thumb for them is to have the barrel volume 1.5 times the combustion chamber volume.

Some Potato Cannons do use compressed air and shoot a potato up to 500 yards or so on 100 psi. There's a fair bit of info on quick release valves for these on the net as well.

Or...an Estes model rocket engine in the torpedo......now that would be cool, although perhaps not that realistic.

Anyway, very cool MTB and nice job on the torpedos.
Old 05-28-2010, 01:28 AM
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Default RE: 1st Vosper MTB working torpedo completed

Dino:
Great workup on your system. I think because of the greater mass and physical size of my torpedoes the CFM flow will need to be much higher to achieve a pulse of high pressure air behind the torpedo. Based on that, all the tubing and valves must have a larger inside diameter, say 3/8" or even 1/2". The engineer I've spoken with at Clippard suggested 1/2" diameter valve ports and SCFM (standard cubic foot-per-minute flow rates of around 19. And that's for each torpedo. I don't plan on installing enough compressed air storage for more than one shot. This will do two things: 1. keep the size and weight down of the cylinder, and 2: eliminate trying to quickly shut the valve to save air for the next shot. I'll pump up the tanks after each run. I'm also looking at using a manually operated 2-way valve and simply attach a throw arm between a Futaba servo and the valve toggle switch. That way I don't run into installing another battery just to fire the pneumatic electric valve. Next post I'll send a few pictures of how the torpedo must fly as it leaves the tube.

Mike
Old 05-28-2010, 03:23 AM
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Default RE: 1st Vosper MTB working torpedo completed


ORIGINAL: Argess

Do these torpedos shoot out in front of the boat? If so, I would think the compressed air power you need is to ensure the torpedos are still moving fast enough the boat doesn't run them over once they hit the water....until their own propellors get a bite..... vs merely a deck clearance issue. I see a big slow-down once they hit the water for a second or two.

Ever think of using hair-spray and an ignitor? Google Potato-Cannon for ideas. Rule of thumb for them is to have the barrel volume 1.5 times the combustion chamber volume.

Some Potato Cannons do use compressed air and shoot a potato up to 500 yards or so on 100 psi. There's a fair bit of info on quick release valves for these on the net as well.

Or...an Estes model rocket engine in the torpedo......now that would be cool, although perhaps not that realistic.

Anyway, very cool MTB and nice job on the torpedos.
Argess:

The torpedoes must leave the boat with enough velocity to clear the deck and land far enough ahead of the speeding MTB to give the torpedoes time to accelerate. The torpedo has a water contact switch located in the tailpiece. It's two small brass rods flush with the surface of the torpedo. As soon as the torpedo hits the water, the motor starts and stops when it beaches itself, drains the LiPo below 6V, or I pick it up out of the water. I'll be experimenting with different propellers and probably in time build a torpedo with contra-rotating propellers like the real thing.

I've looked at springs, CO2 cartridges, rubber bands, and compressed air to fire these things. Springs would be ideal if I could find the right diameter and compression. The company that gave me 4 free springs to play with wanted to charge $400 US to custom fabricate a pair of springs. I still have 3 left that have not been stretched. If I could find a way to stretch them and not increase their diameter, I'd be set. The amount they grow in diameter is very small, but just enough to make for a tight fit in the launch tube and therefore unusable. Compressed air is the leading technology at this point.

Mike
Old 05-28-2010, 06:20 AM
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Default RE: 1st Vosper MTB working torpedo completed

Water-activated switch?.......I'm impressed?

The problem with calculating the air pressure is because of too many unknown factors. For example, the torpedo won't get the full effect due to air leaking past it...between it and the tube, unless you add wadding. Another factor is the effeciency of the dump valve.

Another issue are the caluclations themsleves. Say you used a compressed air cylinder the same volume as the torpedo cylinder and charged it to 80 psi. When the valve is first opened, 80 psi would start pushing the torpedo out and the force is easy to calculate, however the pressure would continue to drop and just as the torpedo was about to leave the tube, the pressure would be down to half, or 40 psi, so the force is now half as well. Need a little calculus for that, and although a head-scratcher, it's probably not that bad to figure out. I think I'd tend to fit as large a compressed air cylinder as I could in the model, and then experiment with different air pressures until I acheived the desired goal, although having some calculations done helps with a starting point.

For a compressed air tank, you can probably find a commercial one, or possibly convert a propane tank or fire extinguisher for the purpose. For pressures of 100 psi or less, you could make one out of pressure rated PVC, although I prefer ABS. Even though ABS is not pressure rated, it should merely split open where the PVC can generate shrapnel.

If you like springs, you may find you can decrease the diameter by firmly twisting them during the stretching process....i.e. with one end held stationary, rotate the other end as you stretch it to keep the diameter where you want it.

I have no doubt you will achieve success shortly and I'm looking forward to a video (hint, hint).
Old 05-28-2010, 04:32 PM
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Default RE: 1st Vosper MTB working torpedo completed

Dino: Question- Why did you place accumulators in the system? Is your system set up to fire once and then come back in to recharge the storage tank? I'm thinking of two 45 cu-in 100psi compressed air tanks, one for each tube. Each storage tank delivers air through 1/4" or 3/8" tubing to a Tee fitting. One leg us used to hook to a compressor or pump to charge the tank. The other leg runs to a servo valve that can dump the tank air quickly through 1/4" or 3/8" tubing to the back of the torpedo tube. The pneumatic solenoid valve must be able to deliver the air at a rate of at least 20 SCFM. I'm still looking for a fast opening 2-way valve that will accept 1/4 or 3/8" plumbing. This seems to be the simplest way to do compressed air, 2 bottles, 2 valves. I'm hoping that I have enough reserve built into such a system that I can play with the pressure to get the performance I need and not run out of air.

Thanks,

Mike
Old 05-28-2010, 08:14 PM
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Default RE: 1st Vosper MTB working torpedo completed

Mike,

I built in the accumulators to give extra volume when I tried to use CO2. I ended up leaving them in.
The mechanical way is the way I started, but I decided to get fancy.
I am able to load the system at home to 150 psi through a SMC pressure booster and on the road with CO2 through a ROCK CO2 regulator.
All of my stuff was trial and error.
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