Captain Nemo12

I believe that someone earlier in this forum asked about building small torpedoes using pen tubes, well I had a little free time last night and I thought about trying this out:

I took out the ink tube inside the pen and the end cap too, leaving space inside the pen tube for propulsion. To propel the torp, I've thought about using small motors in those mini subs (I'm sure that others have thought about this method as well) but to fit the battery and connection wires inside such a small space is just too much work, propel and compressed air could work with a valve but I've settled for something new: Rubberband power!!!


Just like in indoor free-flight airplanes, I simply installed a similar shaft and propeller system along with a rubberband inside the tube, unlike motors and batteries, you don't have to waterproof these because there's no electronics inside. Simply wind up the prop and watch the torp go!! I've included some pics I took during "construction". The blue object in the last photos is a small motor used to wind up the shaft mechanically, I'm a lazy person I guess...

Well, there's still problems to tackle and I'm happy to say that it works, unlike propel torps, which might set off on their own if there is pressure changes inside the torp, you can use this method in smaller subs without worrying about explosions. Right rubberband sizes and lengths might improve the performance!

magnumball

Please give us more instructions for this pen torp. I have been looking for the torp holy grail

Captain Nemo12

It's quite simple really, what I simply did was that I took out the ink tube and replaced it with a plastic/wooden rod that serves as the shaft. I cut the shaft into two halves, and I replaced the longer half by a rubber bands, simply thread the shaft with the rubber band through the pen along with the endcap (silver end of pen in the picture) attach the other end of the rubber band with glue once threaded through the pen, add a prop to the other end of the shaft, wind it up and watch it go!

The one I made is pretty small so the travelling distance is pretty short, I figured if you can find one of those marker pen tubes with a thick diameter, you can fit a more powerful rubber band which can release more power before returning to its original elasticity. I barely costs a cent and everything you need is right at home!

Captain Nemo12

sorry, typo, It barely costs a cent to make

RC Sumo

Cap!!!
I remember discussing this with you in either your Kilo post or in the Wally mart sub forum. Anyway, I had thought of using Sharpie pen cases because of their shape, size and construction. But you did it!!! Now....
what about using a Sharpie case...and then use some kind of shaft, perhaps metal like a piece of a coat hanger, and bend one end like a hook. Think of those great balsa wood planes you get @ the grocery store. The rubberband ones. They have a simple metal hook to mount the rubberband and the other end has the mounted prop. You could eve use props off old toys or models...... the blunt end of the PenTorp would need to have some kind of end cap to put the rubberband through..... just thinking aloud here. But You got this started Cap!! AWESOME!...... now about a launching mechanism........

RC Sumo

well here's the expensive part...$2.50 : http://www2.towerhobbies.com/cgi-bin...?&I=LXBH79&P=0 micro boat prop.

Captain Nemo12

Hi,

You basically got the idea there! Sharpie pens could work, along with any other type of pen or marker who has a tube diameter of 1 cm or more. As for the shaft, it does not matter what kind (brass, metal, plastic...) as long as it can be threaded through the end of the pen. I included a diagram of the "X-rayed" torp. In the picture, the blue thing at the top is actually a piece of wood with the rubber band across, glued at the top of the pen tube to keep the band in place, as you can see, the other end of the band is attached to the top of the shaft. As for the prop, I simply cut out a prop shape out of clear PVC sheet, pierced the middle with a nail, bent the blades at an angle, and mounted it at the end of the shaft!

For the launching mechanism, all you have to do is come up with some kind of stick attached to a servo disk to keep the prop from spinning, to fire, make the servo disk spin, unblocking the prop blades and releasing the elasticity. The torpedo should travel forward!!

RC Sumo

well here's the expensive part...$2.50 : http://www2.towerhobbies.com/cgi-bin...?&I=LXBH79&P=0 micro boat prop.

RC Sumo

whoops...i hate double posts....anyway...have you launched one in the testing facility yet? perhaps a sink or bathtub?

Captain Nemo12

Yes, in fact I think I have to make another one form a thicker tube, I have also attached a second prop at the end of the shaft to increase speed! I think I have time to squeeze in a few tests or two, rubber ducky bearing 018!! Open tube #1!! Load and FIRE!!!!!!

-pkh-

My Feedback: (2)

This one's cheaper...

http://www2.towerhobbies.com/cgi-bin...?&I=LXE470&P=0

-pkh-

My Feedback: (2)

...Seems like if you put some stabilizer fins on the tube, it would help keep the rubber band torque from spinning the pen tube instead of just the prop... might get a little more distance out of it...

Captain Nemo12

I made the thicker version of the torp this afternoon, I increased the rubber band length by adding another piece, the torpedo body has been lengthened as well. Anyways, the torpedo works successfully in the water, I added a series of fins on the side of the tube to stabilize the run, the end of fins are bent at an angle to contribute to the speed (Thanks for reminding, pkh! ). It's very cold out there, the water is FREEZING COLD, my hands are still getting the chills[&:][&:], oh well, building torpedoes is not without its casualties... Here are pictures of the Pentorp V2!!

Captain Nemo12

Well, it seems that the stabilizer fins didn't do their trick..... I'm now thinking about fitting small weights along the bottom of the tube to count the torque. Meanwhile here's a picture of the V2 along with my 1/52th scale U-52 U-boat!! Which is the boat I plan to test this torp on! It's almost complete, I'm scratchbuilding the 2nd half soon.

magnumball

can you post any video of the launch of this torpedo?

Captain Nemo12

As soon as I get my u-boat complete, first I'm planning to run the boat with no torpedo instlled, just to trim it, etc. If I hand launch it, it's pretty hard to hold a camera and film while launching the torp at the same time, when the sub will be complete I will install the torpedo and do my best to catch a shot!

theflyingscotsman

wow how do u launch it.i made a few and we are construting a pvc launcher with a gate and the gate is raised with a r c electro magnet.





Flippin Sweet!
~~~Nepoleon Dynamite~~~

Captain Nemo12

If you want to launch this torpedo, all you have to do is come up with some sort of mechanism to block the props from spinning, to launch, unblock the prop and the torpedo should travel forward! I'm always interested in new approaches to this subject, feel free to post your ideas!

RC Sumo

what about folding prop (like a R/C glider) and then you can push it through a tube via a servo?

Captain Nemo12

how will you go about keeping the prop from spinning and releasing energy?

RC Sumo

hadn't thought that part out too much I guess. How about making one of the sides of the launch tube flat inside. just large enough to keep the prop from spinning, but not so tight the servo can't push it out. I submit exhibit A, my poorly draw sketch:

Captain Nemo12

That clarifies the idea a bit it'll be kinda cool though. If you can make a midget torpedo launching sub in a big scale, like the German Seehund Midget sub in WWII, it has two torpedoes on the side, if you can make the tubes out of PVC, attach a powerful rubberband with a longer length, that'd be a hell of a firing!

Check out the picture of the Seehund

dieFluggeister

Hey guys, just a thought. To counteract the torque problem you just need a prop on each end connected to the same rubber band. Counter-rotating props. Fins needed for tracking of course.

Benthehen

but wouldnt it still be going the same way? i think that would make it worse. it has to have a perty complicated gearbox to make it have contra-rotating props.

benthehen

dieFluggeister

Actually, when viewed from either end one propellor would turn clockwise and the other, counterclockwise. With one left turning prop and one right turning prop you would be set.

If the torpedo were travelling on the surface where part of the props were out of the water then I think you are right that it would track poorly. I was assuming they were running submerged.

How about this... The problem is the pen tube has the same amount of torque on it but in the opposite direction as the prop, thus the pen tube wants to spin in the opposite direction wasting engergy. Instead of trying to figure some kind of complicated gearbox weights, etc., just simply affix a contra prop to the body of the pen tube direcly ahead of the prop on the shaft. The prop shaft turns one way, the pen body turns the other way, and each are driving a prop in the opposing directions. Stabilizing fins not used.