[PSUBS-MAILIST] Magnetic Couplers

Mon Oct 9 20:35:16 EDT 2017

 Alan you are a wealth of information. When I built my magnetic coupled drive, I used regular roller bearings and housed them in oil with a compensator.  Glad I did now, mind you I have been looking at going with a water lubricated bearing but that idea is not getting traction.  I plan on putting that drive back into Gamma.  It works better than two side thrusters.Hank
    On Monday, October 9, 2017, 5:50:45 PM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Passing on more info from Technadynes FAQ.
We have discussed magnetic couplers before, which have an external
water lubricated bearing. It says below that they last 2000hrs at best, & this is
severely reduced in messy water.
Good to see some of these things quantified!

The thrusters have an MTBF of 20,000 hours. However, it is very important to remember that the propeller bearings are lubricated by the sea water. If the sea water is clean, the bearings will last for 2,000 hours. If the sea water is sandy (when operating on the bottom) the bearing life is severely reduced. It is easy to check for propeller bearing wear, just by rocking the propeller back and forth. And replacing the bearings takes only several minutes and the bearings are really inexpensive.

Alan

Sent from my iPad

> On 9/10/2017, at 6:01 PM, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Just passing on some information from technadyne's thruster Q&A
> that I thought was interesting. The question was whether you could put
> the thruster from full forward to full reverse instantaneously. 
> 
> No!! It is necessary that your system has a time based ramp from zero speed to full speed and from full speed to zero speed in both forward and reverse. If you are controlling the thrusters with hand operated joystick, the time required to move the joystick from one position to another is probably enough for the thrusters. However, if you are driving the thrusters with computer, it is essential that you program a linear ramp into the thruster control algorithm. The reason that this time based ramp is necessary is because the thrusters generate back EMF and the back EMF is much greater when the speed changes very rapidly. For example, if the time ramp from full power forward to full power reverse is 20ms, the back EMF current spikes will be 10-20 times greater than the steady state current (we have actually measured this). If this ramp is increased to 50ms, then the back EMF current spikes will be about 4-8 times the steady state current. And increase the ramp to over 100ms!
 , !
> and the current spikes will be about 2 times the steady state current. Make the ramp as long as you can and contact the factory if you have any questions.
> Alan
> 
> 
> Sent from my iPad
> 
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20171010/661bd294/attachment.html>