OK, lets build a scooter....

[Windwalker]

Regarding using an Airtank as a "Powersource" I had a cool idea to use an AirDrill or Power Grinder.. They average 3cfm @90PSI, for 22,000RPM You could probably knock the PSI down using a regulator and get better gas mileage. Also a Stepdown gear could give better torque and drop the hideously high rpm. Off a AL80 you could get about 20minutes of continous operation, Possibly. or 40 minutes from a 120. Recharges would be quick. and if something happened you could have another airsource there.

 

[ShoalDiverSA]

Aquamaniac,

I hope that DIR Tec Diver is up to the challenge! It would be great to see a Gavin replica being built - especially if you furnish plans at the end of the exercise :mean: .

I am also attempting to make a very similar scooter to the Gavin myself. At the moment, I am trying to source the motor. I have looked into a couple of options, but a trolling motor still seems to be the best idea. I am looking for a second-hand motor ideally (to keep costs down!).

What I would like to know is: do you have information on the specifications of the Gavin motor that would guide the search for an ideal motor?

I'm looking for power (kW or hp) or current - even thrust would be helpful (though this is dependent on propeller pitch). Thrust will be meaningful if I can get hold of a trolling motor and matching propeller, because these are rated in lb of thrust. From what I have gathered from my research is that the optimal speed of the motor is in the range of 1000rpm or slightly less.

Right now I am flying blind, but I have faith in the ability of *mere mortals* to manufacture a "Gavin"

Windwalker, great idea! Are you going to build a prototype? Pneumatics is not my forte!

Cheers,

Andrew

 

[Scuba_Vixen]

Air motors are only efficient at outrageous RPMs. (much like turbines and turbo chargers) They have about zip for starting torque, and often can't start under load. You'd need an incredible gear train to get one down below 1000RPM, without a Lot of loss. maybe a planetary arrangement. A regulator that will break 3000# down to several scfm at 125#, and do it while compensating for increased presure at depth isn't listed in the Mc Master Carr catalog. You'd need one way more than 3 cfm to move a scooter anyway.

Now maybe a hydrogen peroxide propulsion system might work. Those old WW2 torpedos moved along pretty well, lol

Interesting thought though, I'd stay with electric.

Darlene

 

[Aquamaniac]

ShoalDiverSA once bubbled...
Aquamaniac,

I hope that DIR Tec Diver is up to the challenge! It would be great to see a Gavin replica being built - especially if you furnish plans at the end of the exercise :mean: .

I am also attempting to make a very similar scooter to the Gavin myself. At the moment, I am trying to source the motor. I have looked into a couple of options, but a trolling motor still seems to be the best idea. I am looking for a second-hand motor ideally (to keep costs down!).

What I would like to know is: do you have information on the specifications of the Gavin motor that would guide the search for an ideal motor?

I'm looking for power (kW or hp) or current - even thrust would be helpful (though this is dependent on propeller pitch). Thrust will be meaningful if I can get hold of a trolling motor and matching propeller, because these are rated in lb of thrust. From what I have gathered from my research is that the optimal speed of the motor is in the range of 1000rpm or slightly less.

Right now I am flying blind, but I have faith in the ability of *mere mortals* to manufacture a "Gavin"

Windwalker, great idea! Are you going to build a prototype? Pneumatics is not my forte!

Cheers,

Andrew

Andrew

All Gavins use a Mako/Voyager motor. George buys old Makos, rewinds them, and puts them in his scooters. He may even be buying them direct from Oceanic now.

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

Now it must be noted that George rewinds the motors.
How is a mystery, but from what I have learned so far, I believe he is changing the number of poles, to increase the speed, without reducing torque.
New Gavs run around 200 ft/min

At this point, im not completely sure, But I think an off the shelf Mako runs 600 RPM, and the rewound version runs about 1000RPM

Being an ex motor winder, Im doing everything i can to work out the most efficient, and fastest winding data!

As soon as I work it out, Ill be sure to publish the results.

The biggest issue with trolling motors, is that you will also need to build a clutch and Variable pitch Prop. This can be cost ineffective when you can buy a used mako, with all those bits for around $700.00.

Dave

 

[Aquamaniac]

Dont rule out these kind of options either........

Would need modifying, but can be a good starting point.
Clutches can be machined up, and the seals are off the shelf. All you need is the Variable Prop.

http://www.grainger.com/Grainger/motor_guide.jsp?a3=24VDC&a2=1

 

[Windwalker]

Someone here mentioned using Air for Propulsion, I thought about the regulator problem.. Couldn't a regular first stage be used? as it keeps the LP hose down around 150-200psi.... the LP hose would connect up to the Airtool. You are right about the speed problem.. Some wierd type of gear setup would be needed and I think that is the Achilles heel of trying to use an Air Turbine in this application.. The other one is keeping it dry. I don't think starting would be a problem because (if you managed to solve the gear problem) the resistance against the motor would be pretty low.

I am going to be building my own "electric" motor DPV. I purchased the "ScubaTow Torpedo" plans. I wanted to see if there was anything that I was not "getting." I am probably going to use an Metal hull and not a PVC one. This is going to screw up the ballast characteristics, so I am going to compensate with a sliding battery compartment. We shall see. I am still in the design phase.

I am also looking into a 74-80# Trolling motor for my application as well. The Motors alone can be purchased as replacements from West Marine (so I'm Told) cheaper then a Whole Trolling motor setup. Also, I was reading that Higher Voltage Motors require less battery drain and will work longer on smaller batteries.. For example a 12V .025HP motor would have a 2/3 less runtime then a 24V .025HP motor. Also I am thinking of checking out the characteristics of a 400V AC motor. (Aviation grade) Would the loss of the transformer negate the effeciency of the system. Also Higher Voltage AC motors tend to be smaller then the DC counterpart. I will have to talk to my EE dad on that one.

I'm Not a Tec Diver, so this is more just for fun then anything serious. If it Pukes out on me, I won't be a mile into a cave. With that said, I don't want it to puke out on me at 1000 feet (not saying that I am going down that far) so its going to be "Beefy"

First prototype will only be good to 250FSW due to the use of a Trolling motor (and that is where their shaft seals seem to rated at)

 

[Aquamaniac]

Windwalker once bubbled...
Also I am thinking of checking out the characteristics of a 400V AC motor. (Aviation grade) Would the loss of the transformer negate the effeciency of the system. Also Higher Voltage AC motors tend to be smaller then the DC counterpart.

True, but how would you power the AC motor?

If you were to use batteries, you would not only need to step it up, but invert it to AC.
The losses, complexity and cost would far outweight the benifits.

Dave

 

[Windwalker]

Nah.. I have a circuit design for High Voltage, It requires me to wind my on Transformer, But the Inverter / AC-DC is a very simple design and about 80%-90% efficient, and can be done solid state.

HID lights require a similar setup, except they need a starting voltage in the thousands of volts. This is no more then a Ballast modification.

I have not settled on a 400V motor. My first design is going to be a Trolling motor.

Here in Oregon there is a Surplus store called Wacky Willies, They sell all sorts of Really Neatsy Keen Motors for under $10. Most of these motors would go for more then $300 new.

I do not plan on investing lots-o-Cash on the 400V experiment.

 

[Scuba_Vixen]

Aside from a lot of technical reasons why the ac motor system isn't the better choice, 400 Volts and Water ought not to be anywhere near ech other. I'll bet they are not actually 400 volt, but 400 cycle (hertz). That was pretty common in aircraft since inductors (that means transformers and motors) for higher frequencies are much smaller and lighter than for 60 cycles. If you use a trolling motor, use an adjustable prop. Some motors have 2 or 3 speeds, but to do it, they have series dropping coils (in the motor housing at the brush end) to effect this. That just turns some batter energy to heat, instead of motion on the lower speeds.

Anyway, good luck


Darlene

 

[Windwalker]

Yes, You are right, it is 400Hz. My memory is failing me.. However, It would not be any less zap then getting hit by a HID canister light. (those things can run into the thousands of volts)

Good advice on the Trolling motor!
Thanks!