1/48 G7 Torpedos

[Bob Gato]

Ha that answers the shipping problem with the caps- Lipo hybrids? I check them out thanks...

all my stuff is STILL in storage(waiting on a new condo build) but as I recall,

I think the wall thickness of the composite tube is .005" very simple to make -work out the ID that you need and find a brass or any tube that size. I then wrap parchment paper around it(parchment wont stick to anything)-so if the body tube is to be 3 inches-use a mandrel tube at least 4 " and you can wrap tape around the ends 1/2 overlapping the paper and 1/2 overlapping and sticking to the mandrel. Then take more parchment the same size as you used earlier and lay 1/2 oz cloth and resin on the paper such that it will make two turns around the body tube diameter-go easy on the resin. Then roll it like rolling a cigarette-squeeze out the trapped air , tape up the ends then I spiral wrap the whole thing with tape to set-polyester about an hour or two. There will be pin holes that can leak in the cured tube but a cotton swab and some resin will fix that-

The great part about the caps and the reed switch is that a water leak wont destroy the battery, motor or the switch.. nice typing with you, Nick-stay safe-BG

[Monahan Steam Models]

Definitely comfortable working with fiberglass. Have laid up a number of scale boat hulls over the years. Mostly been fighting it due to laziness and the added construction steps it would take to make these things. Been hoping to make it work with the aluminum tube. So far it has but I’m just hell bent on removing another half gram.

The weight savings are very promising with what you have done. The center body on this torp weighs 3.102 grams. I’d imagine the fiberglass would probably half that figure. Another consideration has been printing the center body with all the correct details but I think the minimum wall thickness would need to be kept at .032 minimum for strength which would be a no go for the width of the timer module unless I redesigned it and had it made narrower. I need a tube ID of .405”. That requirement makes the fiberglass tube a more appealing option than a printed or cast resin version.

BTW, I meant to mention a while ago, I picked up some miniature latching glass reed switches to use with the high Farad capacitors. They’re pretty slick and still compact. Would make for a pretty straight forward running gear set up. The latest capacitors are 3.8v LiPo hybrids ranging in Farad ratings from 10F to 25F. Those were the ones that needed to be shipped ground a while back due to them being stored in a charged state. I’ve since had a couple more sizes of these shipped out in the same ratings.

[Bob Gato]

If you are ok with a little fiberglass work in either polyester or epoxy-it is easy https://www.rcgroups.com/forums/show...91&postcount=6

[Monahan Steam Models]

Bob, Yes sir, early on you shared your 1/64 torpedo build and experiences. Man, I’ve lost count of how many times over the past months I’ve thought back to what you’ve said along the way and your build. Most of the time it’s when I’ve been sitting there staring at the damn torpedo saying to myself, “ great, where the heck can I shave off more weight!” Usually to make up for having to add weight from necessary design driven changes. I often go back to thinking about how you made the center body on your torpedo.

All I can say for myself is, absolute laziness coupled with pure pig headed stubbornness has effectively stopped me so far from stepping away from the much easier, ready made aluminum tube, to do something a lot more logical like you have done.

Getting the balance of factors right in the 1/48 scale torpedoes has been challenging. What you’ve accomplished in 1/64 scale is amazing!

When you changed over from aluminum tube to the custom made fiberglass tubes, did you keep them at the same .014” wall thickness? I need to go back and look at your build posts!

Nick

[He Who Shall Not Be Named]

Nick, I think that early on you might have seen posts on my trials with the 1/64 torpedoes, but being so small weight was very critical. I went so far as to strip the ground wires bare to save the weight of the insulation .Also what made the biggest difference was to change from the thin wall aluminum tubing to a two layer fiberglass body tube-it actually turned out to be positively buoyant. I am not sure how the printed body tubes do specific gravity wise...I do know that you will get it fine tuned!-Bob

You might consider casting the bodies from polyurethane resin.

And a few pointers on how to paint and mark these things.

[Bob Gato]

Nick, I think that early on you might have seen posts on my trials with the 1/64 torpedoes, but being so small weight was very critical. I went so far as to strip the ground wires bare to save the weight of the insulation .Also what made the biggest difference was to change from the thin wall aluminum tubing to a two layer fiberglass body tube-it actually turned out to be positively buoyant. I am not sure how the printed body tubes do specific gravity wise...I do know that you will get it fine tuned!-Bob

[Monahan Steam Models]

Thanks Bob! The battery has been stepped up to a 90mAh LiPo that is the exact same size as the 60mAh battery I was using before but is .050 of a gram lighter in weight. I had ordered these 2 months ago and they finally arrived last week. So far the new battery has appeared to solve the over current shutdown issues. I was able to track the shutdowns to the battery and not the timer module. The motor is the heavier 6mm x 15mm unit. This combo works well. The video I posted was still using the 60mAh pack and the torpedo was shutting down 4 seconds into the 5 second runtime.

Paint schemes is definitely on the list of things to do. The overall design is about 95% there. It is working out that last 5% that is taking a lot of minor adjustments to the internal bits. The fight now is for weight and ballast. Trying to shave off 100ths of grams. The torpedo is exactly to scale down to the props. This version weighs 11.635 grams. The center of gravity, currently is .060” aft of where I would like it to be. Even so the torp floats at the end of the run and performs well in the water. If this current design turns out to be the best balance of factors achievable, then it simply is what it is.

I’d like to try to get the weight down to 11.1 grams with the center of gravity roughly about .010” aft of the center. Most of the weight that needs to be shaved off is in the tail assembly. In order to shave that much weight, I need to once again switch back to the 6mm x 12mm motor, remove the full length aluminum stuffing box and go back to just using a machined short length Delrin bushing where the prop shafts exit the tail cone. There’s a few other minor tweaks that will need to be done but this should get the torpedo to the target weight and CG. The make it or break it part of this next test will be wether or not the 6mm X 12mm motor will play nice or not with the rest of the components. In previous tests it did not due to being slightly less powerful than the 6x15 motor, but I have since been able to remove a small amount of friction that was still in the transmission assembly.

Nick

[Bob Gato]

I'd say that you have nailed it!...what more is there to do? -paint schemes? Nice work, sir!

[Monahan Steam Models]

A bit more testing and I think we are there

[Monahan Steam Models]

Video link from last week. They’re running straight now. About to start testing the latest version this week.

https://youtu.be/BUV2kb3e_DA

[Monahan Steam Models]

Thanks Trout !

[trout]

Watched your video. Nice straight run! Well done.

[Monahan Steam Models]

Ha! I wish I felt I had it well handled but Thank you! Great idea on bypassing the timer. Will definitely try that and report back. Thanks!

[Bob Gato]

Well I see that you have a good handle on it, Nick! -I guess the brownout possibility would be easy to check-just bypass the timer? the other scenarios might be a little tougher-We'll stay tuned...

[Monahan Steam Models]

Hey Good Morning Bob,

The LiPo does have a built in low voltage protection circuit which I am purely guessing also protects against excessive current draw from what I’ve read on the interwebz.

These batteries are sourced from sellers on flea bay. Would love to have the actual data sheets for them but I believe these cells are only rated at 1C like most standard LiPo’s not intended for performance applications.

I am not clear if the timer module also has a protection circuit but if I recall correctly, I believe they are rated for 2A. The motor draws 0.7A with no load (props spinning in air) and 1.49A with the props fully submerged. So far, I’m only seeing premature shutdowns if something gets snagged in the props or towards the end of a run. Even then it has not been reliably consistent.

Testing the battery after a run, the volt meter shows typically 3.7-3.8 volts. At full charge you can get multiple runs before the voltage noticeably drops.

The shutdowns due to the battery protection circuit is pure speculation at this point. There may be a brown out situation that is occurring that could be turning off the timer. No idea but will need to do some trouble shooting to pin point the issue. Wish these timer modules had a couple more run time settings than the 3 and 5 second options. Other than that I am very happy with them.

Would like to listen to what others have to say about their experiences with small LiPo’s and these timer modules.



P.S. I have a new video of this current design running in the pond. Need to upload it to YouTube so I can post a link here. It is posted on the Model rc-submarines Face Book page currently.