[PSUBS-MAILIST] Pneumatic Manipulator

Sat Mar 17 16:04:08 EDT 2018

Hank,
I am not thinking of the Lenco actuator as they are reasonably expensive,
especially if you are going to change motors & modify them.
I was thinking of buying a brushless motor with planetary gear head &
oil compensating that & having an open frame that the threaded rod &
piston are fixed in. When I say "open frame" you would need to stop any
large bits of muck getting jammed in the mechanism.
There are motor controllers that you can get position feed back from to
limit the stroke in both directions. You can also set a limit on the amps
so you can't burn the motor out under load.
Alan

Sent from my iPad

> On 18/03/2018, at 8:42 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Alan, the motor housing is not sealed from the shaft housing.
> Hank
> 
> On Saturday, March 17, 2018, 11:55:19 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> Alan, the picture is deceiving, at the base of the gear set there is a bushing to support the rotating shaft and I had to drill a air passage in that area.  The ss rod is hollow and the oil can not get in and out of that void easily.
> Hank
> 
> On Saturday, March 17, 2018, 8:53:53 AM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> Hank,
> thanks for the advice on the pneumatics.
> Several years ago I was looking for replacement gears for the lenco to
> speed up the travel on one of the longer stroked models. 
> Looking at the diagram below, oil could move down the spiral of the 
> threaded rod, into the ram. As the ram moved in and out oil could follow
> it down this path. However on the diagram there looks to be a circular disc
> with an O ring seal at the head of the threaded rod, this would need to
> be drilled through. 
> If you could attach a hose fitting where the wires come
> out you could run oil & wires out through a hose. Put a T on the hose for
> the wires to come out & continue the other branch to a compensator.
>    I had liked your idea of a pneumatic cylinder with motor & planetary
> gear box in it, but as you found, it could be a lot of mucking about when
> there is an off the shelf item.
> I have drawings for an oil compensator & there is not much to them.
> Replacing the motor with brushless could be a hasle & it seems quite an
> expence buying a Lenco actuator & butchering it.
> I will have another Google & think about things.
> Alan
> 
> 
> 
> <image1.JPG>
> Sent from my iPad
> 
>> On 18/03/2018, at 1:05 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> 
>> Alan,
>> I did some experimenting with air cylinders and started testing joints with mechanical resistance to reduce or stop the bounce.  I made up disks that went between the arm joints that could be tensioned to act like brake disks.  Kinda like a motorcycle clutch.  This does work to an extent but counterproductive from an energy conservation point of view.
>> With your knowledge of brushless motors and controlling them, it would seem your direction should be to modify a Lenco actuator by removing the motor and replacing it with a brushless motor to oil fill it.   There is one small challenge thought, and that is to relieve the oil trapped behind the threaded rod.  The threaded rod spins inside a fixed nut with very tight tolerance.  the tight tolerance may not let the oil flow when a void is created by the rod extending.  I started to drill holes in the ss rod to create an oil passage way but stopped for fear of creating a bigger problem thus holding up the project.  
>> If you want to collaborate on making an oil filled actuator by converting a Lenco actuator, I would be in.
>> If your concern with these actuators is the short stroke, don't be.  The arm can be designed with stroke multipliers, that is already in my plan for the next generation arm.
>> Hank
>> 
>> 
>> On Saturday, March 17, 2018, 3:54:24 AM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> 
>> 
>> Thanks Steve,
>> I thought there might be a solenoid valve that gave a good variable control over
>> the flow.
>> I did experiment quite a bit with linear actuators, but thought pneumatics might
>> be a lot simpler. The commercial deep sea linear actuators are oil filled & use 
>> brushless motors. As I found out, the small brushed motors don't run so well in
>> oil. They have external oil reservoirs to compensate for the piston movement &
>> an overpressure. Can always re-look at them.
>> Cheers Alan
>> 
>> 
>> 
>> Sent from my iPad
>> 
>>> On 17/03/2018, at 3:58 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>> 
>>> Hi Alan,
>>> I've done a little with pneumatic cylinders and I think it will be very difficult to achieve any kind of accurate positioning. Pneumatic is fine if you only need a cylinder to be fully extended or retracted (as is used for industrial automation) but anything mid way is likely to need a complicated feedback/control system.
>>> 
>>> Even considering as a perfect system, if you have varying force/load, to avoid movement you must have an equally varying pressure in the cylinder. Increasing pressure in the cylinder doesn't help because you then need to increase pressure in the opposite side and then the tendency to resist a disturbing force is not much different anyway. (And if using a single rod cylinder, the pressures in each end need to be different to achieve the same force due to area of the piston) Throw in real world considerations of static friction and dynamic friction and it's harder again to reach and hold a desired position.
>>> 
>>> I'm a bit surprised you haven't already ordered a cheap pneumatic cylinder for some concept testing :).  That should give you a feel pretty quickly if it's doable or not.
>>> 
>>> Cheers,
>>> Steve Fordyce
>>> 
>>> On 17 Mar 2018 7:27 am, "Alan via Personal_Submersibles" <personal_submersibles at psubs.org> wrote:
>>> Have thought a lot about pneumatic manipulators.
>>> Hank has commented several times that they are too "spongy".
>>> If you had pressure relief valves or similar in the system set at something
>>> like 30 psi, so there was always a minimum of 30 psi either side of the piston;
>>> would this make it a lot less "spongey".
>>> You would now need to put an extra 30psi in to get the same force.
>>> It would mean more air, but it is not likely you would be using the manipulator
>>> every dive, & it would be a small quantity compared with blowing a ballast tank.
>>> Has this been done before?
>>> Cheers Alan
>>> 
>>> 
>>> 
>>> Sent from my iPad
>>> 
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