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Re: [PSUBS-MAILIST] linear actuators



Hi Phil,
I've attached a cheaper actuator that's opened up that I had on file.
The idea is to clamp a rubber bellows from the body to about
an inch from the end of the piston, or over the top of any coupling
that the piston attaches to. The actuator & the bellows are filled
with oil & there is an additional external flexible reservoir to take up excess oil
when the piston is retracted.
There is a flow through  from the bellows to the actuator body & reservoir.
I'm intending to attach the actuator to a rack turning a pinion so I get a full
180 degree rotation of the motors. 
Hope that's clear.
Regards Alan
 
----- Original Message -----
Sent: Monday, September 13, 2010 10:34 AM
Subject: Re: [PSUBS-MAILIST] linear actuators

Alan
Are you using the actuators in a 'suck & blow' mode or are they directly couple to the pivot arm - a la hydraulic or pneumatic pistons?
----- Original Message -----
From: Alan James
Sent: Sunday, September 12, 2010 2:10 PM
Subject: Re: [PSUBS-MAILIST] linear actuators

Thanks Phil,
I just broke some plastic in the motor trying to put more tension on the springs.
I've got 6 actuators lying about, & they all need to go at full speed to get a reasonable
piston extension speed.
I've been persisting with the idea of compensating linear actuators as has Frank, but are
now wondering about the merits of it. I'm thinking my options are to buy something like
a Lenco trim tab actuator & change the gearing to speed it up & replace the motor with
a brushless one. Or make one up from scratch.
Do you have any thoughts on hydraulics V electric pistons? I'm mainly using them for
rotating my motors, wich will be counter balanced, so not too much force is required.
Also have thoughts of using them on a light weight manipulator.
Regards Alan
 
----- Original Message -----
Sent: Monday, September 13, 2010 8:25 AM
Subject: Re: [PSUBS-MAILIST] linear actuators

Hi, Alan
Ditto Vance's response re viscosity - but if the motor run 'jerkily' when oil comped it's usually a sign of the brushes 'floating' - that is, the oil is thrown away from the rotor surface by centrifugal force and 'lifts' the brushes -which causes the brushes to lose contact momentarily - it's a function of motor speed,viscosity and spring tension. If the motor runs at a lower rpm the spring tension is sufficient to maintain contact - so,when at high speed - the brushes float, the motor is 'off', the rpm slows, the brushes regain contact and the rpm goes up, the brushes float and so on. Hence the herky-jerky.
    Would seem that the simple remedy is to increase spring tension on the brushes - but if the motor is a variable speed ( in the case of a lineal actuator - they come both ways, fixed speed and variable) then at lower rpm, the brushes will contact the rotor at greater force and will wear down quickly, contaminating the comp oil and making it conductive - which is, of course, no bueno. You can tell a contaminated motor pretty easily, after the fact , since your nice clear baby-bum oil is now black or dark grey!
Jes' so you know!
 
----- Original Message -----
From: Alan James
Sent: Sunday, September 12, 2010 11:55 AM
Subject: Re: [PSUBS-MAILIST] linear actuators

Thanks Vance,
the motors are only a couple of inches long & lack any screws to take
them apart.
One of the thoughts behind testing them was that perhaps these small
motors don't run as well in oil as larger motors.
I'll try it with the WD40.
Alan
----- Original Message -----
Sent: Monday, September 13, 2010 12:36 AM
Subject: Re: [PSUBS-MAILIST] linear actuators

It may be the viscosity, rather than the brushes. Brushed motors have run well in oil for decades. Is there any way to add a little tension to the brush spring?
Vance



-----Original Message-----
From: Alan James <alanjames@xtra.co.nz>
To: personal_submersibles@psubs.org
Sent: Sun, Sep 12, 2010 6:10 am
Subject: [PSUBS-MAILIST] linear actuators

Hi all,
I just filled a linear actuator motor up with baby oil (mineral oil)
to see how it went. It was running rough. It would run consistently
but jerky, it ran slightly better in reverse.
It occurred to me that most electric linear actuator motors were probably
brushed DC & wouldn't run that well with oil compensation.
I used the mineral oil instead of the WD40 (wich is more commonly used
in larger motors), because in experiments I found  WD40 dissolved some
plastics in time, & there were plastic components in my actuators that it might effect.
Not sure where to go with this one. Hydraulics?
Alan
 

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