Electric Torpedo using a capacitor

[David F]

Your torpedo just made it across the Atlantic!

Thanks for making it available, Tom.

David

[salmon]

Cheers David! Let me know how it works for you and what we can do to improve.
Peace,
Tom

[salmon]

First test in making a 1/72 torpedo using a 6mm careless motor.

It looks like all would fit, tight, but fit non-the-less.


It sank. Not sank like it could float, more like a rock in a pond sank.
So, scrap the 6mm motor. I will have to go for the 3mm and see how that does. I may also cast the nose and tail in resin with buoyant filler to lighten it if needed.
I could lighten it up a little by using one capacitor, but run time would suffer. I will try with two to begin with.....We're having fun right? More to come.

[crueby]

Bummer about the wieght, but didn't you forget the warhead?!

Following along with great interest.

[jure george]

How about trying a pager motor? They are SMALL and VERY light weight. As for RPM on that single capacitor, should be pretty high. The ONLY problem would be to figure out a small jig to hold the weight that creates the vibration, usually it is pressed fit on with a small punch point to hold it to the shaft.
Don`t try to forcefully pull the weight off, did that bend the shaft and damaged the motor. You have to drill the small punch point out then the weight comes off. Then you can either turn a disc or 3D print a small round disc with the center hole the same diameter as the pager motor and you have a holder for the motor as well as some water proofing for the main torp. body cavity.

Some pager motors I have their case sizes in mm:5.47 x 4.28 x 0.05oz Other one:6.0 x 5.06 x 0.05oz

Let us know if you tried this and what happened.

Sorry about the quality of the picture, hand tremors and plain camera, I lean towards the first reason.
George

[Ralph --- SSBN 598]

I had a thought, Tom, on the weight issue.

What if you hand shape a piece of foam for the nose part and hand shape a piece of foam for the tail section and only using the fin section secured to the foam.
What that much foam counter the sinking dead weight.
Then build up paint to smooth out the foam.

[salmon]

George,
Coreless motors are pager motors. Like you said, the shaft of the motor has a weight on it that is offset causing the vibration. I need to shave a lot of weight.
Ralph, it may help, I do not have the patience to carve one tail section.
Peace,
Tom

[Ralph --- SSBN 598]

Tom, The tail section would take some time and is why I suggested just the cone section forward of the fins and use your printed fins.

Tom, could you weigh all the parts less the nose and tail?
I might be able to calculate if there would be enough foam to float the internal and tube parts.
--------------------
About the pager motor unbalance weight.
If you put the shaft end in a small vise and slowly grind at the weight .. "slowly" as to not create a lot of heat, you can split the weigh enough to pinch it and deform it so it slides of the shaft without grinding down to the shaft.
Or you can put the weight in the vice and using a small file thin the weigh down on one side until it deforms and again will slide off.

[jure george]

What I managed to do before is take a piece of hardwood, drill a length into it the diameter for the pager motor then split the wood in half,leaving a nice groove to rest the pager weight on. Then with the flat side of the weight facing upwards, I take a drill bit and drill though the dent in the weight. That relives the pinch and the weight slides off the shaft.

Might want to give it a try?

George

[Ralph --- SSBN 598]

Sorry, but I had another thought last night on the weight issue.
Scale 1/72 torpedo (Mark 48 type 19'x21"= 3.17" long and .29" diameter)

So the body is about 2.5" long.
Your torpedo has an aluminum body.
It might be you can save some weight by using a plastic soda straw for the body.
Readily available and easier than making paper tubes.

They come in different diameters.
At my local lunch spot, they have straws that could be 1/4"+ and the other place has smaller diameter straws.
I don't like the small straws!

[scott t]

Could you power on the motor and use a files to smooth the weight to round?
File the weight as it spins?

[bob the builder]

Those little motors have ZERO torque. Touch them and they'll stall. No go on turning it into a mini-lathe.

In the past, I've simply ground off the narrow side of the weight with a cutoff disc on my Dremel, going about 1/3 of the way into the shaft. The weight just pops off after that as it's pretty soft.

[David F]

Moving on to assembling some of these clever little torpedoes. (Thanks Tom!)
The photo shows the propeller and motor being lined up in my Taig lathe. I found this made it much easier to get the prop lined up and to solder the 1mm diameter brass wire on to the motor shaft. The motor is a 6mm diameter one which was amazingly cheap on eBay. Rather than use the motor mount I have wound several turns of PVC tape round it. I stick the motor in with silicone.

I have tried several tests in the home test tank and I am now waiting to see how the motor and electrics cope with the repeated "dunking."

David

[David F]

A photo and a couple of videos of Tom's clever torpedo design at the Norwich MBC model sub weekend here in the UK.
(I have used the simple design with a 6mm diameter motor and a single 1F capacitor. The end caps are stuck on with silicone rubber to provide a reasonably watertight compartment - the torpedo just floats. I remove the caps after use to let things dry out.)
A very good, simple and very cheap to construct design.
Improvements? Stop torpedo body spin so much? Straighter running?
Kids of all ages liked it!

https://youtu.be/llUKMKFTCQk

https://youtu.be/lqAYKyk4EWM

[salmon]

I see yours likes to turn. I had that with one of the test props I had until I changed the prop. Not sure I remember which one caused it, but when I put the speed boat prop in it stopped doing that. Are you using the 2 blade prop?
Body spin, I get that as well. When I designed the torpedo body I put a ~7 degree on each fin to counter the prop and try to get a slow roll. The roll is to, in theory, get a straight run.
I am open to ideas.