Re: [PSUBS-MAILIST] linear actuators

["Alan James" <alanjames@xtra.co.nz>]

Hi Jim & Brian,

I had quite a bit of discussion with Frank over the linear actuators.

We were looking at putting them outside the hull.

In the end Frank was looking to buy Lenco trim tab actuators & just adding

a rubber bellows over the piston rod. Herve had used these on his ambient submarines.

I felt they needed to be oil compensated & tracked down a thin oil (shellsol D60) that

was less aggressive on plastic & was thin enough so that the actuators small motor

would run OK. One issue with not oil compensating them was the water pressure trying

to push the piston in, so there would be more load in one direction & less on the other.

To oil compensate you need to do something like have an external bladder to the actuator

so when the piston retracts the oil it displaces has somewhere to go.

There is an electric manipulator on the market that has oil compensated linear actuators that

are pressurized slightly above ambient.

The general consensus is that hydraulics are more reliable but actuators are cheaper & take up

less space.

Regards Alan

 

----- Original Message -----

From: JimToddPsub@aol.com

To: personal_submersibles@psubs.org

Sent: Friday, May 27, 2011 4:48 AM

Subject: Re: [PSUBS-MAILIST] linear actuators

Brian,

 

This thread on linear actuators is from September 2010.  I have some links somewhere on a supplier or two but can't look for it right now.  Maybe someone else has it more readily available.

 

Jim T.

 

In a message dated 9/13/2010 9:44:04 P.M. Central Daylight Time, alanjames@xtra.co.nz writes:

Frank,

I just ran a small 200 Watt trawling motor in the spa pool & the force

needed to rotate it while running wasn't that much.

I'm thinking that if you had a 100lb thruster the force needed to rotate

it on full power would be similar to the force needed to push a bicycle

with a 100lb person sitting on it (wouldn't it?). 

Are you sure your firgelli actuators won't do?

Also I'll try & get hold of a low viscosity mineral oil & test my motor out

in that.

Alan

----- Original Message -----

From: Alan James

To: personal_submersibles@psubs.org

Sent: Tuesday, September 14, 2010 2:02 PM

Subject: Re: [PSUBS-MAILIST] linear actuators

Hi Frank,

Some thoughts on not compensating the actuators.

I'm concerned that the bellows would rip away from their attachment as the

water pressure reduced the air inside them to 12th the size at 300ft depth,

or even worse if you did a pressure test of the sub with the actuators on it.

Also the compressed air might get past the piston seals into the actuator.

I did a quick calculation on the body strength based on a 2-3mm thickness

& epoxy fiberglass & I was getting a 1900 to 2,500 ft crush depth.

There is an O ring at the joining of the 2 halves of the body that could be a weakness.

I ran the same motor that was running rough on mineral oil, on WD40 & it went

fine. I've expressed my reservations about WD40 in actuators before, in that I had

plastic containers with WD40 in, that disintegrated over a couple of weeks.

However it might not effect anything in a Lenco actuator. If you compensated the

actuator you could maybe have full ocean depth??

I had a look at small brushless motors with the view of replacing the brushed motor

in an actuator, but they wanted NZ $239- for an RC motor, comparable sized brushed

motors were going for $30-.

Do you know what the maximum duty cycle is on the Lenco actuators?

I have two actuators with 60% & two with 10%, (6 minutes run time per hr max).

Regards Alan

 

 

 

----- Original Message -----

From: ShellyDalg@aol.com

To: personal_submersibles@psubs.org

Sent: Tuesday, September 14, 2010 4:29 AM

Subject: Re: [PSUBS-MAILIST] linear actuators

Hi Alan. I've been gone for a bit so sorry for the late reply.

Anyway, are you sure you need to compensate the actuators ?

The Lenco ones at 4-1/2 inch stroke will push 750 pounds. Enough to overcome the water pressure resistance when they extend. If the bellows is sturdy and flexible enough it should be possible to seal the whole thing up without compensating it.

The cheesey actuators I purchased from Firgelli are totally unsuited for my needs but the Lenco's sound like a real possibility if they can be completely sealed. As for the speed, the geometry of the linkage or rack-and-pinion will determine that.

Frank D.