Newbie, and dive propulsion vehicles

[buluayam]

Hello everyone,

Firstly, hi! I'm a newcomer to these forums, and wanted to start off my thread by saying hello

Secondly, I wanted to apologise in advance for a couple of things - one, if I'm posting in the wrong section of the forums then sorry! Second, I'm not actually a diver, so I'm not too sure if I qualify to be part of these discussions - I do have a strong interest in diving however

I am a technologist, and am involved in developing novel forms of propulsion devices. The reason why I am posting on this forum is because, I currently have a design for a propulsion unit that I think holds many advantages over existing designs (such as power to weight ratio, size, noise, etc) - and am interested in adapting this unit to becoming a diver propulsion unit.

However, before I go into serious development for this application, there's obviously a need for a real commercial application and demand before I can attract funding etc. It's with this in mind that I thought I could perhaps get some views from experienced divers on a forum like this!

** If this sort of a thread is not encouraged then I apologise again, and please feel free to remove my thread if it is inappropriate **

Could I ask a few questions?

1) What sort of applications would a DPV be useful for - both recreational/technical/commercial?

2) Is the DPV an application where there is demand for? As far as I understand, it is a very niche application and the market size for such an application is small - even for commercial uses. However, I wondered whether this is because an application like a DPV isn't extremely useful, or is it because of the limitations of current designs (that I plan to address)?

3) Are there any DPV users here? Could you tell me more about what you think of existing DPVs, ie the pros and cons - and what features/characteristics would really 'get your blood boiling'?

I think I'll leave the questions to these three for the moment, thank you everyone in advance for your patience and replies!

 

[SEDATE]

Welcome on Board buluayam

 

[Jon]

I've owned one for about 10 years and I've alos used many different types over the years. My gripes with DPV's are as follows:

First, the Run Time stinks- way too short! I know that some companies are now playing around with NIMH batter packs to double the runtime, but even that is too short. It also brings me to my second issue- cost.

Second, expense. Scooters are not cheap and the cheap ones aren't worth a crap. The really good ones can cost as much as a used car. The NIMH batter packs can add on at least another $1,200 to the purchase price over the traditional lead-acid batteries. They may double the runtime but at too steep a price for most.

Last, they are heavy. If you want to get any kind of a runtime you need extra batteries and then they get really heavy! We actually have a crane on the back of one dive boat to pull my father-in-law's Gavin out of the water.

Still, I would put up with the bulk if there could be a big leap in runtime- i want hours not minutes in this department.

Hope that helps,

Jon

 

[buluayam]

Thanks for that! Those are exactly the issues that my design is able to address, giving me more of a confirmation of the choice of application.

Do you know if the DPV is a popular piece of kit amongst divers?

I will check back here regularly to see how other forum members respond to this thread, and will definitely keep everyone updated about my progress with this too

And, hopefully sometime in the near future become part of the diving community myself too!

 

[Jon]

It depends upon the diver. Most newbies won't use one, but all of my techdiving buddies have at least one- some of them have as many as 3.

For tech diving they make life much easier since we have on 5-6 tanks and all kinds of other crap that makes swimming a bit more of a challenge- drysuits, cansiter lights, reels, liftbags, back-up lights, cameras, ect....

Jon

 

[buluayam]

Another question; there are two possible configurations that I could adapt the propulsion unit into a DPV:

The first, is following the typical hand-held configuration where the diver has to hang on to the unit and ride on top/side/behind the vehicle;

The second, is to adapt the unit so that it is able to mount itself unobtrusively on the diver, say for example on the rebreather pack. I think this is possible as what I intend to design will be considerably smaller than existing designs, and I could easily allow for control of the unit (speed etc) at a position accessible to the diver whilst having the unit hands-free.

Would this be desirable? From feedback I have had, I guess it would depend on application; a lot of people I have spoken to have expressed a greater preference towards having a hands-free unit (provided it is compact, light, and accessible enough), however I wondered whether the increase in bulk of the overall diver would be a detriment in certain situations?

What do you think about this? Thanks

 

[Jon]

Speaking for me, I would never buy a tank mounted unit.

I, now, use my scooter mostly for freediving so have no tank to mount it on. My father-in-law has his video camera/ ligth system mounted onto his scooter and uses it as a camera dolly.

We also use our scooter to blow holes out in the sand when diving certain types of shipwrecks- there's no way you could do this with a tank mounted unit.

Many of the tech divers I know will carry two scooters with them when in a cave- one dragging behind them clipped off between their legs in case the first one dies while in a cave.

I vote for the hand held model- divers can always hook up a harness system to it to drage themselves throught he water with little effort.

Here are a few shots for you to look at. The first one is how I attach myself to my scooter when freediving. I have a clip on my scooter that attaches to the "scooter ring" on my belt. If I were scuba diving it would attach to the scooter ring on my harness- see the picture of my dive buddy in full gear to see how that goes. I also wear a simple belt with a crotch strap on it to make the pull of the scooter easier on my arms. On the back of the belt I carry a small spare air in case my scooter floods at depth.

NOTE: I do not use a sapre air for scuba diving since it offers no 'real' back up- just for freediving with a scooter!

Jon

 

[Old Man Dave]

I've often wondered if an aqualung tank could be used as a power source. If you had a tank with 100 cu ft of air compressed to 232 bar driving an air motor with a prop how long a duration would that give. Sure you'd have a sream of bubbles but you could exhaust them behind you. You wouldn't need to waterproof anything and no electrics, all mechanical/pneumatic. Would be lighter than batterries and you could keep spare tanks on board if they just slotted in/on.
Some clever person out there work out the power/duration! If I'm a genius and I haven't got a patent, just make sure I get a free one (or two) when they're in production.
Dave

 

[Jon]

Dave,

Someone came out with that in the late 80's/ early 90's. You could even hook it up to double tanks if you wanted for a longer duration.

The main problem with the system was that it was only good for very shallow diving- the deeper you went the greater the amount of gas that was used to drive the motor.

Jon

 

[Old Man Dave]

Couple of things occur to me about that Jon.
Can see why that might be. Assuming the motor uses some kind of axial piston set up then the external pressure on the open end (connecting rod/crank/rotor) would increase with depth. Therefore the air pressure needed to drive it would increased with depth. So assume it wouild equate to breathing through a reg. I get 80 minutes at 30ft but only 25 minutes at 100ft, 2 bar versus 4 bar.
However tanks are much bigger nowadays compared to 20 years ago, in terms of volume of air contained due to much higher pressures.
Maybe for freediving or scuba down to say 60 ft someone should look at this again. Can see that deep techy diving would be out.
It all comes down to maths and experimentation really. Exactly how long would a tank last as a power source at say 60ft. How would that compare to batteries? Still see some advantage in the non electrics and plentiful supply of spare tanks.
Suppose if it were that good an idea someone would be doing it.
Oh well no fortune to be made again :waterwork
Dave

 

[buluayam]

Thanks for the replies. It is interesting to see the views of people who have actually used the vehicles!

The oxygen tank idea sounds interesting, however I am not too sure if it is practical (especially as described at lower depths) - I guess it would depend on what sort of thrust you are looking for, and what type of air pressure needs to be expelled to produce this rotation. A lot would depend on the propeller you would be using as well, as depending on the pitch you would require different amounts of torque to rotate the prop at a required speed and thrust production.

I am looking to couple Li-polymers to the unit, which offers very exciting possibilities in terms of power to size ratio - I know many manufacturers are not keen to try them for commercial purposes since Li-poly are relatively new and unproven, but hey, that's what us technologists are for eh?

 

[Old Man Dave]

What's a Li-polymer and how do you use one?
Dave

 

[buluayam]

Hi,

Sorry, the topic was on power sources (like batts and gas tanks) so I thought you might know

Li-polymer are Lithium polymer batteries - almost the same as Lithium ion batteries, but in a quasi-solid form.

There are many grades of these batteries that can be had, but I am in contact with a manufacturer at the moment who is able to supply these sorts of batteries to me that have 5 times the power-to-size ratio compared to that of conventional lead acids - basically, I have the use of smaller sized (and lighter!) batteries to produce the same power requirements as conventional DPV batts, or conversely produce much longer running times.

The quasi-solid form is advantageous for my design as it allows the batteries to be shaped to a shape that I can design around - no more big blocks of car batteries that take up so much shape, the batteries can be molded into a particular shape that I can then pack into available cavities in the vehicle design.

 

[Jon]

I looked it up after you posted it and it sounds interesting- but the websites I found that that it is very expensive at the moment and you would need to find a specific size to mass-produce to make it worth while.

I currently use lead acid batteries in my scooter, but I see where they now offer a new version of the scooter, which looks the same as far as I can tell, that has NIMH batteries in it and delivers about twice the burn time. The only downside is that it costs an extra $1,200 just for that battery! They also say that you can't use the newer NIMH battery inthe older scooter- any idea why not? I would think it would just plug into the same spot if you have the correct wiring harness on it.

Another good site to post would be over on "The Deco Stop". It's a tech diving list that has a lot of scooter driving scuba divers on it who may give you more detailed feedback- this list is about 95% freedivers, some of us who happen to scuba dive as well.

Jon

 

[buluayam]

The Li-Polymer batteries are indeed very expensive. Fortunately I am in contact with a manufacturer who is able to do them relatively cheaply for me, which is one of the reasons why I am considering coupling them to the diver unit - and of course, the performance of the batteries are another reason.

I am personally not too familiar with battery technology, except for a superficial understanding of them. I deal more with the motor/propulsion side of things! Off the top of my head, I can think of two possible reasons why the battery does not fit with your old scooter (if it doesn't! It might just do):

1) It could be possible that the ratings of the batteries do not match the old scooter configuration - this would result in either a poor performance, or in an extreme case (very unlikely for this application) over-current production in the machine and burning out the machine.

2) I am not sure if this is the case for the NiMh, but for some types of batteries (like the Li-ion) you require an additional controller in order to control the discharge rates etc - the battery characteristics vary from material to material and it's not always just a simple plug-and-play matter!

In truth I don't really know, although those are some of the things that come to mind immediately - I may be completely wrong! If you are truly interested, then I don't mind looking into NiMh batts to find out for you.

Thanks for the Deco Stop link, I'll look it up and post something there

Edit: Oh, another question that just popped into my mind, what is the ideal speed for a DPV? I know this changes depending on the diver, but why I'm asking: As far as I understand, there are limitations to how fast a diver should be moving through the water, especially for technical diving due to the rebreathers/mask? Could someone enlighten me about this?