Finally, DIY DPV sneak peak...

[V. G. McGillicuddy]

Hi Guys!
I am almost finished building my first DPV. So far I have only tested it on the surface, but it seems to work well.
I don't have much experience, but I did discover that attaching a common tire valve to the main body enables me to pressurize the DPV, which makes finding leaks easy.
On a website called psubs.org, they say that Minn Kota rates their motors to a depth of 33 feet, and people have taken them to 100 feet with a failure rate of about 4 to 5 percent.
Also, on the Psubs website, they say that filling the motor housing with transformer oil is an effective way to waterproof it. I believe someone mentioned something along those lines earlier in this thread. Does anyone know the best way to do this? If so, where can I get transformer oil?

Just my 2 cents' worth.

Regards,
V. G. McG.

 

[mddolson]

Just a quick note: some transformer oils are commonly PCB's poly-chloro-biphenols. They are nasty carsinogenics. (Cancer causing agents) I would avoid them at all costs.

Mike D

 

[Cold_Under_Here]

Ohh wicked!!!

 

[Jorbar1551]

Can someone give me instructions on how to build a dpv? Also, how much did building your own dpv cost?

Jordan

 

[Jorbar1551]

Willy, im looking to make my own dpv, could you give me some advice so i can maybe not make some stupid mistakes?

Jordan

 

[DiverBuoy]

Now here, we are talking:

 

[Larry Horne]

Starting DPV Project Next Week

All,

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I am starting a PDV project this weekend. I plan on using a Minn Kota 55lb thrust trolling unit lower unit for the motor with a 3 blade prop (new $125 motor, $35 prop). I am going to hand form a composite body. I have a few questions to throw out to you all. If the motor gets wet, its $15 in parts to overhaul.........easy. I'm going new verses used because of contacts in the business and new will provide performace IAW specs.

1) Over all design. I have two options. Linear body like a Apollo or Torpedo. Or something like that shown in the images attached. This is basically a trolling motor lower unit shoved up into a battery compartment. I perfer the torpedo design. Has anyone any info on the Shakespeare Submobile? What is its depth rating? The Tiger Ray uses a trolling motor configuration and rates it to 125 ft. Any thoughts as to what depth a stock Minn Kota will test to? I read one thread here where one of you re machined the seal locations for additional seals? Since I plan composite material either design is doable. Thoughts?

2) What is the pressure in pounds per square inch to be expected at 150ft? Can anyone help me with the formula to calculate?

3) Can Minn Kota motors run dry or does the lower unit transfer heat via the housing for general cooling? My tech personl locally indicated they can run dry but wet is the preferable obviously. Thoughts here is that I can add a second degree of water sealing by extending the output shaft and running it through a water tight seal outboard of the trolling unit lower unit. Basically placing the motor inside a water tight compartment on the stern of the unit.

4) Batteries. I can locate a 12V 55Ah sealed lead battery. The trolling unit pulls 45A on high speed. Battery weight is 39#. Is there another option? This may provide 30 - 45 minutes of good run time before the voltage drops too much where repeated cycles will damage the battery. Are there better options such as runnig smalleer twin batteries? Thoughts?

5) Motor modifications. If I take the motor unit direct from the factory what improvements can I do to increase the possibility of getting greater that 100' out of it. They are simple units, double sping shaft seals, casing o-ring, and o-rings on the two studs holding the assembly together. My thoughts are to cover the heads of the bolts with a polyurethane sealant and maybe try improving the body gasket. not certain much more is doable unless I take the approach like one of the posters here and replace the shaft seals with better units. Thoughts?

Well this is enough to chew on now.

Any and all technical advice is appreciated.

Larry
VA

 

[mddolson]

DPV (diver propulsion vehicle)
1) Normal trolling motors are not rated for pressure. (ie 3-5 ft) So they relyon simple sliding seals on the bearings and grease fille to prevent water ingress. I machined my bearing seats to take an add-on ureathane shaft seal. It worked for me.

2)Pressure at 150 ft (sea water) form basic scuba class there is 1 tm every 33 ft so P= 14.7/33 = 0.445 psi/ft x 150 = 67 psi.

3)Cann't comment on MinKota motors.

4) Thing to remember is that lead acid batteries drop in voltage as they are used. So you will not get full current/power at the end of a dive/charge. I considered using 3 x 6 volt batteries , but running from 2 at start and switching in the fresh battery as voltage dropped in the two prime batteris.

5) re Washer seals: ther are stainless steel washers with a moulded o-ring on the inner diameter . Check McMaster Carr.

regards

Mike D

 

[jgarysmith]

Just go out a buy a new Apollo.


Just kidding, I know Larry

Good luck on it so you can build me one when you are done with yours.

Why don't you start a new thread with your questions. You might get more responses with it.

 

[Larry Horne]

Mike D,

Thanks for the reply.

Here is one to ponder over (no laughing or assuming I'm too naive).

I have continued to do some off line investigation of submersibles used in various DoD research projects (my work affiliates) and found claims that a certain company well known in the States for design and test small remote submersibles has used the Minn Kota 40# thrust to depths of 300ft (134 psi effectively) with only minor modifications, none directly related to the sealing of the unit. I have this information from 2 sources including the vendor who sells the units to this company. Its the same vendor I am purchasing the 55# thrust lower unit from.

Their modifications include relocating the exit point for the electrical leads for the brushes/armature. They move them to the rear of the unit verses having them come out of the top. This allows them to place the unit in the stern of the vehicle with out the problems encountered by Williydiver with the power leads.

I have disassembled the Minn Kota and their design for shaft seals includes two (2) dynamic seals in line or in parallel. By this I mean a seal that has a small spring around the inner diameter opening which maintains a certain constant pressure on the shaft back to back with another identical seal.

Isn't this similar to the modification that you performed to your unit? Does it sound to you as though the manufacture may have improved the design?

I in no way assume depth containment to 300ft but may make a test rig for the shaft seals where by I pressure test them to 70 psi. I can do this with a hose clamp, rubber boot, and bicycle pump. Pressurize the boot and see if it holds constant pressure.

Thanks for the input on the other items.

Lar