Hi Brian,Just a normal linear actuator that has an electric motor turning a screw (threaded rod) wich has a nut on it that slides in a groove & is attached to a piston. As the screw turns the nut winds up & down the threaded rod & pushes the piston out the end. The oil is to make it pressure resistant, but you can't just fill it with oil as when the piston moves in & out there is a change in the internal volume. To counter that I was intending to attach plastic hosing to the actuator body & feed the oil through it to a reservoir bag. This will keep the internal oil at ambient pressure & take up the changes in internal oil volume.Alan
From: "ojaivalleybeefarm @dslextreme.com" <ojaivalleybeefarm@dslextreme.com> Sent: Fri, 27 May, 2011 12:52:59 PM
Subject: Re: [PSUBS-MAILIST] linear actuators
Hi Alan,Are you describing a electric hydraulic actuator or just electric with a screw? It sounds like a electric hydraulic since you stated that it had a piston and needed a reservoir.. I like the idea of a electric hydraulic because you could get a lot more force out of it and you only have to get a wire to it. But I could probably live with a screw set up also.BrianOn Thu, May 26, 2011 at 1:05 PM, Alan James <alanjames@xtra.co.nz> wrote:
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 addinga 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) thatwas less aggressive on plastic & was thin enough so that the actuators small motorwould run OK. One issue with not oil compensating them was the water pressure tryingto 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 actuatorso 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 thatare pressurized slightly above ambient.The general consensus is that hydraulics are more reliable but actuators are cheaper & take upless space.Regards Alan----- Original Message -----Sent: Friday, May 27, 2011 4:48 AMSubject: Re: [PSUBS-MAILIST] linear actuatorsBrian,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 forceneeded to rotate it while running wasn't that much.I'm thinking that if you had a 100lb thruster the force needed to rotateit on full power would be similar to the force needed to push a bicyclewith 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 outin that.Alan----- Original Message -----From: Alan JamesSent: Tuesday, September 14, 2010 2:02 PMSubject: Re: [PSUBS-MAILIST] linear actuatorsHi Frank,Some thoughts on not compensating the actuators.I'm concerned that the bellows would rip away from their attachment as thewater 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 wentfine. I've expressed my reservations about WD40 in actuators before, in that I hadplastic containers with WD40 in, that disintegrated over a couple of weeks.However it might not effect anything in a Lenco actuator. If you compensated theactuator you could maybe have full ocean depth??I had a look at small brushless motors with the view of replacing the brushed motorin an actuator, but they wanted NZ $239- for an RC motor, comparable sized brushedmotors 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.comSent: Tuesday, September 14, 2010 4:29 AMSubject: Re: [PSUBS-MAILIST] linear actuatorsHi 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.