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Re: [PSUBS-MAILIST] Electric Actuators on "Git Kraken"



Hi Frank,
Here's a thought that may have potential.
You could use a variable resister similar to this one
http://w3.id.tue.nl/fileadmin/id/objects/E-Atelier/Phidgets/Hardware/Images/1112.jpg
& fit it in your secondary expansion boot or in a small housing below the boot. Have a
mechanical link from the top of the boot to the slider. Again use the voltmeter for position indication.
The boot would be moving in & out corresponding to the piston movement. You would possibly need a
bellows that wasn't tapered; like they have on motorbike shocks.
Alan
 
 
 
----- Original Message -----
Sent: Tuesday, February 02, 2010 6:38 AM
Subject: Re: [PSUBS-MAILIST] Electric Actuators on "Git Kraken"

Hi Alan.Good photos. The use of a bicycle innertube is a good idea as it will expand and is easily replaced.
Might be a little thin though. The power steering boots I'm using are pretty strong at about 3/16 inch thick.
I had originally planned on using a plastic tube bladder that could collapse as the oil was drained away, like has been proposed for the Minnkota motors for compensation but the actuators move more oil in/out than the motors would, so I went with a larger bladder. 
As for depth, well, it's true that the pressure is equalized. That's the whole purpose of "oil compensation". But it just seems that a more "robust" system like high pressure hydraulics would be more likely to withstand the rigors of deep diving.
I really went with the electric actuator method because I liked the idea of using electrical thru-hulls ( only takes one) over a supply/return hydraulic system where two thru-hulls are needed. OK provided I can get it sealed up.
That, and the fact that an electric pump and all the related plumbing and pressurized oil reservoir of a HP hydraulic system makes the system more complicated ( high maintenance) and expensive to build and maintain/replace.
For "position sensing" I wonder if it's possible to add a magnet to the stroke some where and then put a series of sealed magnetic switches next to it to sense position. One problem I foresee would be the number of wires needed to get the signal from several positions. The wires would be quite small but a multi prong thru-hull can get pretty complicated.
Seems like it would be better to just shell out the money for the MinnKota actuators and use the "off-the-shelf" rocker switch with the led graph. The Lenco actuators can be had on Ebay and they too have an LED thing to show position. Again, the wiring is a six wire cable making the thru-hull more complicated.
I've been leaning toward adding another pair of windows to the sub on the sides so the dive planes would be visible. My current window design needs some additional work to reach my intended depth so when I fix that problem I will be adding the other two windows also. Always better to have good visibility. For now though, I'm still trying to get her ready for the July convention so any big changes will have to wait for next year.
I made a quick sketch of the CV joint bladder. It fits in the little space between the hull and ballast tank and if it works will be easily maintained. Once all these components are fabricated I'll pressure test them in a bench-top chamber to see what problems pop up.
Frank D.