Powering Micro Sub

I am nearing completion of designing a very unique personal micro submarine.
Think of it as a submarine you wear.
It is really small, very low drag and extremely sporty in performance.
It resembles a torpedo with wings.
I need ideas on powering options to consider.
I have 36, 6 volt, 12Ahr, sealed lead acid batteries that are three years old but in great condition having served
as unused back-up or stand-by power for 36, individual, high-end earthquake sensors.
I'm looking for 2, 5Kw motors which will turn 2, 2 blade, contrarotating, 90% efficient propellers at 1000 RPM.
This will allow for ~15 knot (~17 MPH, ~28 KPH).
I'm looking for 1 hour operating time with 1 hour reserve.
I would prefer two independant systems providing redundancy for safety.
Although my space is somewhat limited, I do have about 400 pounds of capacity for both batteries and motors.
Velocity versus power is a cubic relationship in submarines.
What I am looking for is bursts of full power with the vast majority of time under low power.
In fact, the most efficient manner of operation may be only bursts of higher power and lots of gliding or drifting.
The vessel carries high inertia with a density of 63.5 pounds per cubic food (that of sea water).
Fine speed control will be necessary to avoid cavitating the propellers.
Instant reverse is on the wish list for brakes.
Simplicity is desirable and cost a consideration.
This is a personal toy and not for commercial gain.
Service pressure on the batteries will vary from +1 (ambient surface pressure)
to +2 (33 feet depth) atmospheres, (0 to +15 PSIG).
I got the batteries for free and am in no way commited to using them for this project.
The sub interior is dry (not flooded as in some designs).

Your thoughts, comments, ideas and experience appreciated.

Tom
Victoria, British Columbia, Canada (the south-west coast)

if you want to run peaks of 10kw then you will need more than those lead acid cells. i would look at high rate cells like A123 cells or zippy flightmax as its the only way you will get the peak powers you need.

Hi Submariner

Sounds like a great project. I'm curious about your quoted service pressure. If it's a dry sub doesn't that mean you'll have a pressure hull – or will it be open at the bottom like a diving bell? If you are running at two atmospheres this might have an effect on the venting ability of the sealed batteries.

Matthew, I think the lead also doubles as ballast, so weight may actually be an advantage. It shouldn't be a problem for decent lead acid batteries to deliver 10 kW bursts.

Edit: For power I would take a look at the possibility of upgrading a Seadoo type unit: http://www.seascooterexpress.com/store/sea_doo_explorer.html
A pair of them would give you redundancy and steering (but not both at the same time )

36*6*12*5c>10kW but how good are the bats? If weight is not an issue, take advantage of that (very unusual) consideration and use all that lead and MORE to reduce the load on the bats. With the burst/glide usage ts going to be hard to know what kind of run time you will get until you actually use it.

I wonder if drive systems for torpedoes can be had on the surplus market. The could make for a crazy fast mini-sub.

Probably the best match for your criteria is a pair of Mars motors (under $500ea) or a pair of Agni's at more than double the price. Personally, I would lean toward the Mars brushless, because marine environments will be harder on brushes, though this doesn't sound like a vehicle that will get high usage hours anyway.

John

I agree, lead is definitely the way to go, as this vehicle can take advantage of the weight. Also, lead acid is often actually better than LiPo in terms of high peak power delivery, where it loses out is weight and capacity, which are not a significant problem for this application.

I also think the Mars brushless is a good option, as again it's weight would be useful and not having brushes is an advantage in a high humidity working environment.

This sounds a fascinating and interesting project. I'd love to see some photos.

Jeremy

Mars and Etek both have a brushless version I believe, they are 6K motors, but would be Ideal, although they run around 3k RPM, so a reduction gear would be needed.

the SLA used for moniter and alarm circuits generaly are ment for long life, low amp loads. they have thinner plates and break down quickly under high amp loads. they are also not deep cycle batteries, so running a motor will kill them quickly
You have 2500 watts of power rated on those batteries, which would give 10k power for 15 minutes, but being SLA, the actual usable power is closer to 50% of that.
They might make good test batteries for bench testing, but I wouldn't want to trust them.
Deep cycle Marine batteries might be better, but heavy. Lipo or or high discharge LiFePO4 (like A123)would be much lighter and longer lasting.

An alternitive to the Etek and Mars would be a bank of trolling motors. they aren't as powerfull but you could use more of them. The advantage is a sealed system with the casing, gearing, water proofing, motor control, and reverse systems already worked out.

Saltwater leaking into lead/acid batteries makes a poison gas. They should be in a completely sealed off separate compartment with a moisture sensor near the bottom, and a pressure sensor which activates a warning light/buzzer (with relief valve that vents poison gas to the outside).

If a leak occurs in the operator space, it will leak less water volume if you are at a higher depth. There is a tipping point where if you reach a certain weight from in-flowing water, jettisoning your ballast will still not bring you up. This means if you encounter a pipe/valve breakage and experience leakage, you must immediately be able to jettison enough weight to bring you to the surface (where leakage will slow considerably, even if this only adds a few moments to allow you to escape.

Surface air will be moist, after diving your vessel will cool and moisture will condense. Insulation will help, and perhaps socks full of sun-dried desiccant. There's not much sun past 30-ft, you will want a point-able light.

Pressure is experienced by the square-inch, so a 3' diameter round hatch will have 2.25 square feet of area (324 square inches). Roughly 43 PSI per 100-ft, 4.3 per 10-ft, 0.43 per 0ne-foot. 8.6 PSI per 20 ft means at a depth of 20-Ft there will be a force of 2700 pounds holding the hatch shut.

If there is a leak, you will not be able to open the hatch. On a submarine escape chamber, the inside and outside pressure must be flooded and equalized before its possible to open the hatch. On the outside of the hull, you may wish to consider attaching a surplus weather balloon to be filled by an air-bottle on the inside to add bouyancy during an escape event.

Thank you all for your replies, I really appreciate it.

I am only looking for electrical advice as I believe this to be the topic

of focus on this forum.

Monster: I may have room for up to 25 more of these batteries, time will tell.

Malcolm: It is a delayed ambient system that relies on compressed air being

released into the cabin via a scuba regulator and then vented out a pressure relief valve.

What are the ramifications of 2 atmospheres pressure on battery venting.

Indeed, the weight of lead/acid is a non-issue for me. Space/power (power density)

may be more of an issue. Contrarotating props are one in front of the other,

so there is no differential thrust (steering). My steering comes from control surfaces.

vanilla ice: The batteries are in great condition. They were on stand-by, never used,

in high end earthquake sensors for three years. I've metered and load tested them all.

John: Brushes are out for me. Probably an hour a day until the novelty wears off and then

who knows... Used torpedo drive is a great idea but unavailable.

Jeremy: thank you.

Drunkskunk: Interesting. SLA's they are. Magnacharge 6-12's. If I can squeeze in 25 more

of them (making 60) would you feel any more confident? The drawback to deep-cycle marine batt's

is their size (dimensions). My maximum diameter is 20 inches with a taper on either side.

The cross-section is circular throughout the 11 foot length. It's a NACA 0015 rotated.

Of course, I need to fit in there too! That only leaves space above and below my prone position.

spinningmagnets: Understood. I'm way ahead of you.

Cheers, Tom

Have you load tested at 5c? If so how many watt hours came out? What was the voltage drop? At 10kW you're 4 to 5c which is going to going to cut capacity to 50 to 60% of rated cap like ds says. And thats assuming the bats will even take it. If they aren't designed for those kinds of loads, they could get destroyed in a few cycles.

Submariner said:

What are the ramifications of 2 atmospheres pressure on battery venting.

Click to expand...

I don't know, it was just something that crossed my mind when you mentioned two atmospheres' ambient. I believe the vents in sealed batteries are intended primarily as a safety release in the event of overcharging, but since you're unlikely to charge the batteries at depth this should not be a concern. Just to be safe though, I would contact Magnacharge (Trojan?) and ask them if there are any safety implications with using their batteries at increased pressure. With a project of this type I imagine the technical department would be interested enough to give you advice.

From the packaging point of view, the cylindrical Hawker Cyclon cells may have an advantage considering your space restrictions: http://www.enersysreservepower.com/cyc_b.asp?brandID=4

The reason I suggested the Seadoos is that everything is already packaged for this environment, and they could look cool mounted on the wingtips of an underwater jet. If your wings are also your control surfaces they could also give you even more maneuvrability. However, it sounds like your design is already well advanced and you've put a lot of thought into hydrodynamics, so ignore my schoolboy daydreams

As others have said, the Mars brushless motors would be a good choice for propulsion.

I'd love to hear more about this project, especially the hull design and pressure equalisation system, so please keep us updated.

Edited to add:
Some rough figures for battery pack
Assuming a 48V propulsion system (e.g. http://www.thunderstruck-ev.com/marskit.htm)
Pulse and glide operation with 10 kW peak would at a guesstimate call for an average power requirement of 3 kW or less.
For a dive time of one hour that means an energy requirement of 3 kWh.
For lead acid batteries you only get around half the rated capacity when using them over such a short period, so practical battery pack capacity should be 6 kWh.
6 kWh divided by 48V gives roughly 120 Ah, so this is the minimum battery capacity required.

Based on average lead acid weights, pack weight would be 160-180 kg, plus say 20 kg for motor and controller, which is close to your specified 400 lb.

Using the 12 Ah batteries you have on hand, you would need four banks of ten batteries wired in parallel, so 40 batteries total.

Edit 2:
Re-reading, I just realised you asked about two motors. I was thinking of two props sharing a common shaft and driven in opposite directions by a single motor. Will the props be located fore and aft?

as for the batteries, lifepo4 of a123 or the bmi-cells seems to be the best suiting ones, leaving out exotics and the potentially toxic and permanently heavy ( will you actually need that weight ?) sla´s.

as for torpedo drive systems, most probably these are 3 eor more extremerly long and high-rotating outrunner motors working on one crankshaft ( the crankshaft being another similar engine wound for pure speed and driven by the torque of the outer engines at speed), most probably sporting pretty interresting batterie chmistries to put out high watts and also amps for a short peroid of time but on permanant and yearly-long standby.

to make your submarine more "military" you could put your overpressure vent eithe ron rear and play spaceship or -not really practical- on the front nose in order to form a oxigen ( which would get really hot at speed so subs most probably use other aerogas) bubble around the subby so it will glide faster as soo as you reached some mininimal speed.
admittedly this will never work out on your project, but check into the dewalt lifepo4 batteries, this part was ment to be serious

Some torpedoes still use a piston engine with a liquid oxidizer and liquid fuel. Two co-axial high-speed props counter-rotate.
Electric torpedo batteries:
http://depts.washington.edu/matseed/batteries/MSE/torpedo.html
http://www.naval-technology.com/contractors/electrical/saft/press1.html

Some fun reading about "Deep Flight Super Falcon"

http://deepflight.com/subs/index.htm

.

powering toprpedos is a quite different thing from a personal mini-sub, if i had to sketch up a preffered setup for a torpedo it would be a mixture of two or more materials, that once brought together form a exhaust gas that drived the torpedo through an array of nozzles/ valves around the body in order to reduce water friction, form a small noise footprint and have a pretty good versatility in steering the object on itself - since these motors do not have to get good mileage or good longterm durabilit anyways.

as for the mini-sub "booster" drive, a secondary propeller system on a tube that has 2 smaller propellers in sinc with a gearing ratio according the best possible float enhancement of the water moved in between both ( guessing like 1:1.75 or so) at each end of the tube could make a nice additional drive system ( make the rear engine pivoteable or but up a rudder if your two main drives allready incorporate the main rudder) could bring extra-thrust, if possible a additional front fan on the nose of the sub could work similarly with your rear propllers but this would only work on low speed and with no side-streaming if not talking about high-power solutions with a big propeller there.

as for the deep flight falcon, this in a katamaran design with the windows of reciyle-airplanes ( military?) woul dbe the coolest watercraft ever imo. 1 engine in each katamaran pontoon, and a third engine in the cabin part ( this engine being a jetski engine with big bad batteries for boosting underwater and the main engine with water jet steering over the water - underwater the batts only drive the steering jets of the middle, assisted by ruders of the engines in the pontoons).

if using a rudder araywith gyroskopic steering or self-make a simple 4+ outlet system for waterjet drives in the pontoons you could also fly not only looings but rotate and do other figures the falcon can´t do, it uses a vertical fan for elevation...


as for safety, check into the explsoives Audi uses to emergency-open stucked car doors at their upper factory-armored car upgrade series, this at a window and entry door seems recommendable.
also check into outdated ( mandatory cycles...) live vests and see if you can fix some on the outside of the capsule to remote-ignite them in a emergency situation when more upping power is needed. some of those have built-in positioning transmitters, too.
if building such a thing for moderate depths it could be a doable project for a skileld individual willed to spend 1-1ß years of his ( surely not hers 8) ) free time.

.

Quote:

"I agree, lead is definitely the way to go, as this vehicle can take advantage of the weight. Also, lead acid is often actually better than LiPo in terms of high peak power delivery, where it loses out is weight and capacity, which are not a significant problem for this application.

I also think the Mars brushless is a good option, as again it's weight would be useful and not having brushes is an advantage in a high humidity working environment.

This sounds a fascinating and interesting project. I'd love to see some photos.

Jeremy"

Thanks Jeremy, I'd like to pursue your line of thinking.
I have access to two, brushless, axial flux PMSM motor prototypes that a friend has been developing,
full-time, for a couple of years now. His biggest struggle seems to be the controller.
Can you tell me more about the $22 ones you found in China?
He's recommending 36 volts for my application.
I'm thinking of a total of 48 of the SLA 6-12's I mentioned previously.
So, 6 in series, then 4 of those in parallel (24) for each motor. Times two, totals 48 batteries.
The motors are unique in that they are hollow in the middle allowing me to run a solid shaft from one
through a hollow shaft from the other, counter-rotating, directly to the props!
They would turn ~1000 RPM under the kind of load I'm going to have at speed, so no gearing!
I'd like to run a double (or dual, I don't know the terminology) potentiometer from a common knob
for dual speed control without loosing the safety of double system redundancy.
The motors are a little less power than I'd hoped at 4 kw. ~92% efficient should yield 13 - 14 knots
instead of the 15 knots I was aiming for.
A "momentary on" switch would give me full reverse for brakes (hopefully never needed).
If you personal message me your email address, I'll send you some drawings of my project.
I'm unable to post them for some reason.
Thanks for your interest.

Tom

Submariner,

I thought you wanted no brushes on the motors, so I don't think potentiometers are going to be sufficient control.

I take it that you'll be flying through the water in an always buoyant craft, so wouldn't you rather have the increased maneuverability of counter rotating props on 2 separate shafts? Also, with counter rotating props on a single shaft, the high prop efficiency you're talking about doesn't feel right. Please direct me to something I can sink my teeth into supporting that, because if true wouldn't we see a lot of watercraft with that type of rig?

Lastly, how at those speeds do you "fly" around a cable or line already secured under water? I'd hate to see you in a death trap with no means of escape when you get tangled in something already so common.

John

Malcolm,

I only just saw your second edit.
The props are one in front of the other, far aft with a small protective cowling.
You are correct, a great deal of thought, design, calculating, modeling, consulting, evolving, compromising,
prioritising, hair pulling, considering, reconsidering, arguing, debating, conceding, evaluating, pondering,
cataloguing, and repeating have already been done.
That is why I am only looking for electrical help on this forum as I understand it to be a good source.

Thanks for your interest, calculations and comments. I will let you know how things develop.

Tom

"Small protective cowling" over the props...At that low speed a Kort nozzle will give you a gain in efficiency along with the protection you want.

Yes, there's lots of electrical expertise around here and they're very generous with their assistance. They'll need more info about your motors, and probably the best section to post the specific questions is in the Technical forum, which isn't restricted just to ebikes. There's more activity with all the guru's there.

Personally, I'd like details about your motors including price, because I will be looking for motors very soon to power an electric catamaran.

John

Not to disencourage you or something, but please also take your time to have an underwater emergency exit strategy if something fails.

Just reflext what you would think of others if reading stuff like ( unaltered complete string excerped from your post above):

"I have access to two, brushless, axial flux PMSM motor prototypes that a friend has been developing,
full-time, for a couple of years now. His biggest struggle seems to be the controller.
Can you tell me more about the $22 ones you found in China?
He's recommending 36 volts for my application.
I'm thinking of a total of 48 of the SLA 6-12's"

Statements like these not only smell but allready taste like as if "fail" was to occure, and you don´t want to have this several feet below the sea´s surface with no plan b not reliant of strategy a.

As for emergency batterie power with no need to get maintenance charge and outstanding power density check into reusable Silver-zinc (Ag-Zn) batteries from like saft, this is military stuff but on public avail ( allthough costly).

Here is some inspiration for Jeremy and Drunkskunk who I am still hoping to hear back from.

I've corresponded quite a bit with Cliff Redus the designer/builder of the R300.

He's still in sea trials and semi-retired with way to much time and money on his hands.

He must have $200 to $500 K into this sub, WOW.

http://www.psubs.org/projects/1237684922/r300submersible/

Cheers, Tom

.

amazing videos, what a great vehicle.

as for the price of such builts,i believe it an be had cheaper. the father of a loose friend family of my parents built a 17 x 3.5 x 5 meter steel boat in his friggin garden. it took him over 10 years but lesser than 40k dollars total cost ( including engine and everything interiour and installation) at actual costs as he was doing most of it on himself. another 15 k dollars had to be paid to finally get it transported into the water and anoter lump sum for the homologationing of the ship but: if doing most stuff on your own or have a social environment with machining capabilies on cheap avail it can be done at a price competitive with nicer kit cars, even moe in the times of the virtual bays as for parts sourcing.

I don't think I would really trust a $22 chinese controller for a project like this. I would suggest at least a Kelly controller or perhaps a Curtis or Sevcon industrial strength controller.