OK, lets build a scooter....

[oxyhacker]

Anyone thinking about using a trolling motor should be aware that they tend to be high speed/low torque motors, which are the opposite of what you want for towing a diver - a diver has a lot of drag compared to your average bass boat, so a bigger, slower moving prop is desirable. So they are usually not as efficient when used on a DPV as a purpose-built high torque motor like the Mako.

Scubapro used what appeared to be a standard trolling motor powerhead made by sister company MinnKota on the Sea Shuttle DPV, which was rated for 180'. This led a lot of people into thinking a trolling motor would work just fine - not exactly so, since it turns out the Sea Shuttle motor was specially made for SP, and had a set of planetary reduction gears sandwiched into the case, a special larger, slower prop to match, and better seals.

Trolling motor seals are a concern because most of them are designed to handle only 1 atm/33'. Some will handle 60-90' for a while, and others will go much deeper, but you can't count on it. Some of the guys using these motors on homebuilt subs actually fit each motor with a scuba reg and pony bottle for active pressure compensation to try to keep them try. Others fill them with ATM fluid.

This isn't to say one shouldn't try to use a trolling motor. The seals can usually be upgraded And the inherent inefficiencies of the high speed motor and prop can be just lived with. However anyone who thinks they are going to build something equivilent to a Gavin using a trolling motor will be, odds are, disappointed.

 

[Windwalker]

The Motors I have been looking at are 1500RPM. Using a Modified "Ninja" prop (slow turning prop) in a Kort nozzle. I am not looking for something as buff as a Gavin. I don't need it. But I like building stuff, for the sake of building stuff. Then trying to improve it. The fun is in the Chase.

 

[oxyhacker]

Amen - I'd be one of the last people in the world to disagree with that!

Gavins are nice, but most of us don't need one. However, the basic Gavin design concept is hard to beat, and think there's a lot of possibilities for a low cost "fun" DPV made by combining cheaper drive with a Gavin-style housing.

For the homebuilder the nice thing about Gavin-style construction (besides that fact that it works!) is that its very much modular - since it's essentially an oversized divelight battery canister with both ends latched on, you can fit different power units just by changing or modifying the back plate, and different capacity batteries by changing the tubes. This makes it infinately upgradeable, all the way up to "real" Gavin specs should a Mako drivetrain turn up.

Windwalker once bubbled...

I am not looking for something as buff as a Gavin. I don't need it. But I like building stuff, for the sake of building stuff. Then trying to improve it. The fun is in the Chase.

 

[Windwalker]

Perhaps I should. Sounds like the modular way would keep me from having to rebuild chassis. Good Idea.

 

[ShoalDiverSA]

Aquamaniac once bubbled...


The Mako motor specs are
Speed:2.7 Mph
Thrust: 50lbs
Voltage: 24 VDC
Current: 34 Amps
Power: ~800 watts

Dave

Dave,

Been diving , so I haven't had a chance yet to say thanks.

Thanks! At least now I have something to aim for with my search.

Cheers,

Andrew

 

[ShoalDiverSA]

oxyhacker once bubbled...

Trolling motor seals are a concern because most of them are designed to handle only 1 atm/33'. Some will handle 60-90' for a while, and others will go much deeper, but you can't count on it...

...This isn't to say one shouldn't try to use a trolling motor. The seals can usually be upgraded...

I was thinking of using the trolling motor as a "rough and ready" DC motor. I would like to use a different seal though, as I have heard that some of the trolling motors even use grease as a seal!

Thinking along the lines of pool/spa motor seals (John Crane/Burgmann). These are good for about 20ATM at 1000rpm. They really have good pressure ratings at the relatively low speed of DPV motors.

Now to find that motor...

Enjoying the thread, by the way - keep it coming!

Cheers,

Andrew

 

[Aquamaniac]

Pump motor seals are perfect.
Here is what a Gavin Has.

 

[Straggler Dave]

...Any plans for a book on building scooters?

 

[oxyhacker]

We have one in the works, but it won't be for a while. It's a big subject, and a lot to build and test first.

Straggler Dave once bubbled...
...Any plans for a book on building scooters?

 

[DennisS]

oxyhacker once bubbled...
We have one in the works, but it won't be for a while. It's a big subject, and a lot to build and test first.

Sounds great, if it's as good as the reg repair book, I'll be buying a copy the first day its out