1/48 G7 Torpedos

[MFR1964]

If i'm correct, Dan Achur has made succesfull capacitors torpedo's, no timer needed, i run my own torps on a 1S Lipo, no timercircuit and single prop, use the counterrotation for stabilising to get a straight run, they tend to swing off when the lipo runs low.
On one charge i get about 15 runs, i did think of the capacitor way, but the configuration of my launchtubes makes it too much complicated.

Manfred.

[Monahan Steam Models]

Quick Update:

Just ran a couple more tests this morning with the largest 3 volt 3 Farad capacitor. This time the capacitor was connected directly to the motor along with the counter rotating gearbox, with the tail cone and props installed. The results were as follows:

21 seconds of total runtime in air no drag until motor completely stopped. Rate of rpm noticeably began to drop after about 4.5 seconds

8.5 seconds of total runtime with props submerged in tank of water until motor completely stopped. Rate of rpm noticeably began to drop after about 2.5 seconds

67 seconds to completely charge capacitor until current flow dropped from 500mah to zero using 3 volts

Much different results from yesterday evening’s tests that still utilized the timer module. I believe the module begins to cut out the closer the input voltage reaches 2 volts

[Monahan Steam Models]

Thank you sir!

This has been a fun design study and I hope that some of the information adds to the library of knowledge already out there.

If time permits today, I would like to run a couple more tests with the super caps. As BG has pointed out, the need for the timer module can be removed, especially if the charge capacity is well matched to the desired run time. I suspect the short running time I witnessed yesterday evening may have something to do with the timer module and not the super cap. Plan to omit the timer and LiPo in the next test and use just the super cap directly with the motor and gear box.

[Monahan Steam Models]

The various super capacitors I ordered earlier this week arrived this evening. I was anxious to see what they could do so I did some rough bench testing to start out with. All the various caps ordered are in the 8mm OD can type style. The variances are can/body length, voltage (in this case 2.7 or 3v) and Farad rating. The biggest being a 3volt, 3 Farad 8mm D x 20mm L. There were longer body super caps in this diameter available in a much higher Farad rating (6 Farad being the highest I found) but the current design constraints of the available room and ballast of the torpedo dictated the cap dimensions I chose to order and test.

Here’s what I found. I’m going to focus on the biggest super cap mentioned above. After a quick full charge on the bench top variable power supply, the 3v 3F super cap was able to run a spare motor I had on hand, (matching the currently installed in the torpedo) high performance 6mm x 15mm coreless motor for and impressive amount of time in air with no drag. Rpm’s dropped very slowly over what felt like a long time in a subtle manner. That’s not a very scientific measurement I know but I grew bored of hearing it run as it was much longer than the 5 second timer installed in the torp and I disconnected it from the super cap. Impressive to say the least.

Where the rubber meets the road. I jumped over to testing this super cap with the torpedo on the bench in air no drag as it is configured currently with the timer module, 6x15 hipo motor and counter rotating prop gearbox minus the 3.7v 60mah LiPo. At full super cap charge, the motor started out strong but faded away in power and stopped before the 5 second timer shut the power to the motor off. Ran the test a few times and same results. Need to check if the timer has a low voltage cut off before I can make any assumptions.

I followed the super cap testing up with plugging the LiPo battery back in and the torp ran strong the whole 5 seconds and for repeated back to back runs in the same charge.

ive attached a few photos of the super cap and LiPo for dimensions and weight comparisons.

The super cap is definitely a serious design consideration compared to a LiPo depending on the design. I feel if the torp design I was working on currently ran one motor, direct drive, no extra gearing or timer module, keeping everything light and clean, it is unbeatable.

[Monahan Steam Models]

Thanks BG! I was definitely happy to see the speed return to the torp again. There are still more revisions to come before I’d say the design is mature. Looking forward to playing around with the capacitors when they arrive. May not need to boost the voltage but that will depend on what the final motor choice is. Like you said earlier, weight is a huge factor and one of the main things that has driven the design choices. Performance is the next driving design factor and then ease of production like you mentioned. It’s been a fun experiment so far.

[Bob Gato]

Nick-you have "nailed" it. It goes as far and straight as you'd really want it to! I guess increasing the prop speed by a factor of 5 gave the thrust that you need- now for the really hard part-making them cheap and fast enough that if you lost them-no big deal!

[Monahan Steam Models]

I was thinking of using a reed possibly too! Nice! I was hoping the parts would show up today but it looks like they didn’t go out last night and were shipped this morning instead.

In the meantime I got impatient and pulled the smaller motor and 5:1 gearbox out and put the more powerful motor used in previous tests back in. It’s connected direct drive to the counter rotating gear box. Night and day difference in performance. Think I might’ve had a small amount of prop slippage on the outer shaft. Need to secure them to the shafts better.

Here’s a couple videos from this evening. It’s still set to run for 5 seconds.

https://youtu.be/Y5ZVUpzDYmo

https://youtu.be/DZtCqIuVByw

[Bob Gato]

I am using a 3.3F 2.7V supercap but in a direct drive setting (no gear reduction)-and it goes like hell. I see what you mean about finding the 6v caps-the diameter increases with the higher voltage in order to get the capacitance (F) up -when you get the 2.7Vs that you ordered, I am curious as to how the series circuit works out-I think that you can charge them in series...you might have to trial and error the charge voltage though.

And if all else fails-you should be able to use double throw magnetic reed switches to run in series and charge in parallel-no booster necessary

[Monahan Steam Models]

BG,

I was thinking about other design options last night regarding the use of super caps. The drawback I see to running caps in series is the potential need to charge each cap separately at 2.7volts then switch them to a series configuration. There are probably some simple ways to do this. One simple option for example could be using a jumper to switch between individual charging input then series output.

So far I’ve been not having luck finding a 5-6 bolt high farad super cap in ideal dimensions. I’m sure they are out there.

Another idea would be to run a single 2.5-3volt super cap with a high farad rating and then use a voltage step up booster. Check these out: https://www.pololu.com/product/2115

I have some of these step up boosters already but in a 12v step up for the torpedo launcher micro pneumatic solenoid valves

[Bob Gato]

HaHa-I hate when that happens...Since I don't need 6v caps I am not sure-the farads are a little high and it needs to be tested on your motor to see how fast they dump their charge-I think they would be good and they're cheap enough-but I like the series Idea...it allows for weight distribution.

[Monahan Steam Models]

BG, we must’ve been posting at the same time because I did not see the link in your updated post. Thank you for posting that, I will ask my buddy what he thinks. I like the voltage rating on that one better

[Monahan Steam Models]

Awesome thank you again for the info! I’m interested to see how they work with this project. After this morning’s crash course from my EE buddy I searched a couple places that I’ve purchased electronic components from. Both Digikey and Newark electronics had a selection of super caps. 8mm is a great size, so I wound up ordering some 8mm by 13mm long 1F and 1.5F caps from both suppliers. In the 8mm diameter range both suppliers offered various caps in voltages ranging from 2.5, 2.7 and 3.0 volts. I chose the 2.7v caps so they could be wired in series to get 5.4 volts at 1F or 1.5F. I think the 1.5F caps will arrive tomorrow

[Bob Gato]

As I'm sure that you will find out-they aren't just ordinary capacitors-they are classed as super or ultra capacitors-they take and hold a charge like a battery.You'll probably be looking at 8mm in diameter, 6.3volts. the higher the farads(uf) the slower it will discharge you will have to try them to see how they drive the motor-they are quite cheap on ebay-sold by the batch.
Nick, ask your friend-this might be a good starting point https://www.mouser.com/ProductDetail...hoC0fEQAvD_BwE

[Monahan Steam Models]

Just got off the phone with a life long close friend who has his master’s degree in electrical engineering and still currently works as a senior EE. Long story short, I got a very thorough instant education on all things capacitors as well as some other EE tips. Got homework to do now!

[Monahan Steam Models]

Wow, that’s impressive! Please educate me on what to look for when searching for suitable capacitors. My experience with using them is almost zero hahaha! I’d like to keep the voltage at 6v incase I still want to use the timer. It seems the easiest thing to try at the moment as per your helpful suggestions is to up the voltage from the 3.7 LiPo battery to a 6 volt capacitor instead by simply swapping the battery out for a capacitor. This would be a super quick modification that could be made to the current design as it is configured at the moment. Thanks!