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Re: [PSUBS-MAILIST] RimTec Magnetic Clutches

Thanks Paul.
 
I found both of those links very helpful and informative. I knew what the term pulse meant, I also knew what modulation is, but I  did not know what pulse width modulation meant in relation to
 
controlling a motor's speed. That second link explained and made it clear to me. Thanks very much. I have been laboring under a misconception. I was thinking somehow a switch ITSELF would
 
control. the speed. I see now that I need something more than just a simple switch. Now the problem is what exactly do I need to modulate the width of the electrical pulse and can I find that small enough
 
to somehow waterproof or encase it and how do I waterproof the control that varies the pulse modulation? How do I get away from having to "O" ring a shaft on a knob??
 
Thanks very much for your helpful info Paul.
 
Bill.
 
 
----- Original Message -----
Sent: Monday, October 24, 2005 1:12 PM
Subject: Re: [PSUBS-MAILIST] RimTec Magnetic Clutches

Bill,

I'd say a couple of reasons for using relays are to minimize the size of your control switches and shorten the length of your high current electrical lines.  A bonus reason would be to keep that high current away from the operator!  Here's a Minnkota FAQ page that helps you estimate wire size or gauge for their motors. 
http://www.minnkotamotors.com/support/faq.asp

They work through a short example of 20ft of wire and a 37amp draw and recommend a 6awg wire which is about a sixth of an inch in diameter.  So as your amperage and wire sizes increase I think you start to look more and more at controlling it remotely with a relay.

But like you say, you have a different situation where you don't want just an on-off control for your motors.  A relay, as I understand it, is just an on-off remote switch.  It sounds like you want a pulse width modulation motor controller to get good smooth control and more efficiency out of your battery/motor combo.  Minnkota calls it their Maximizer and here's another link that discusses a custom built PWM control for a robot:
http://www.robotwars.ecs.soton.ac.uk/file/pwm_motor_control.html

But after all these notes, I have no comments on immersing the whole thing in a wet sub.  :-)


Paul






On 10/24/05, Akins <lakins1@tampabay.rr.com> wrote:
Hi Byron.
 
I have a completely wet, dual cockpits, wetsub Byron, it isn't ambient. I already have my minnkota mounted to the hull using
 
a motor mount I made from an old stop sign I cut and bent. If you would like to see my sub's set up you have to belong to yahoo because the
 
pictures are at my yahoo group site at this link.... http://groups.yahoo.com/group/The_Warbird_Recovery_Team/  once you get there and sign in to yahoo,
 
just click on the "photos" section on the left of the page in the yellow column and the album is the first one called "my two person wetsub".
 
Thanks for the info on the hydraulic thrusters but I've already got my minnkota motor mounted. I just need to decide whether to oil or air equalize it.
 
Right now I am on the hunt for magnetic variable speed reed switches to activate the relay to the motor. One thing I am wondering
 
about is WHY do I even need a relay solenoid? Why couldn't I just wire it direct from the battery to the switch and then to the motor? Does it have
 
something to do with too high a voltage or amps going thru the switch and that is not good or something like that? I'm not real good at the
 
electrical stuff. Also I am wondering how a magnetic switch could possibly be variable if it just clicked in a solenoid relay?
 
As you suggested I have talked to some of the ROV guys. I am a member of the yahoo group called "Robotrov"  at this link......
 
http://groups.yahoo.com/group/robotrov/?yguid=204005530      which is a group for robotics and ROV's. Unfortunately even though one of them
 
responded to my post at the group, his link and info did not lead me to switches I need. His link sent me to a site with electronic circuit boards
 
that would be used inside a sealed unit in a ROV for instance. I need something small and compact that I can use either in the cockpit or attached
 
to the joystick in my wetsub. I thought about using a mercury switch and rigging it so that I could just turn it to make contact. If the attitude of my
 
sub was always horizontal that wouldn't be a problem but if things got a bit murky underwater and the sub was not horizontal and I got disoriented the mercury
 
switch might make contact when I did not want it to. So I decided to not use it and to continue to try and locate the magnetic reed switches.
 
Ideally I would like to find a magnetic reed switch that was already waterproof and sealed, but if I can't find one waterproofed, I could rig it up in
 
a real small piece of pvc pipe I guess.
 
Bill.
 
 
 
 
----- Original Message -----
Sent: Monday, October 24, 2005 5:57 AM
Subject: Re: [PSUBS-MAILIST] RimTec Magnetic Clutches
Have you thought of talking to some of the thruster guys?  All of  the ROV's out there ( except el-cheapo cheapo toys) have some external thrusters.   They are almost always electric.  I worked for Deep  Sea Systems, Inc. as a consultant for about six months, and have been friends with Chris  Nicholson (owner/pres) for twenty years.    If you can catch Chris's imagination, he can be a world of help.  He builds and sells electric thrusters.
 
Innovatum is another group.
 
Slightly different subject, but I gotta ask:
 
Have you considered hydraulic thruster motors?  You keep the pump inside the sub and use through-hull fittings to run hydraulic motors outside.    Putting a piece of  pipe fitting through a sub wall for hydraulic hoses is lots easier than either electric feed-throughs or a shaftdrive with a stuffing gland.
 
Or bite the bullet, use the stuffing gland or o-rings on the spinning motor shaft, design for drips and put a small bilge pump under it venting overboard.  Need a good check valve and a stout pump for ambient, but its doable.