[PSUBS-MAILIST] Motor Issue

Mon Jul 19 09:24:14 EDT 2021

Hi Cliff,

Many thanks for the info.  Your idea of reassembling the motors with the
wooden pegs sounds like a really good idea.  Why didnt i think of that!

I will also test the alignment suggestion.  That makes good sense.  I'll do
a video so you can see how i get on.

I would like to attend a US convension at some point, I just think that
this one in October is going to be too soon, which is a shame.

regards
James

On Mon, 19 Jul 2021 at 13:27, Cliff Redus via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> James, a couple of thoughts. After diving my boat with the same MK-101
> motors, it is not uncommon to have some decolorization of the compensation
> oil. This is just small particles of the carbon brushes in suspension in
> the oil. This fluid is a dispersion and not a solution. The particles are
> in suspension in the low dielectric oil and not solubilized into the oil.
> As such, the electrical conductivity of suspension should be that of the
> virgin oil.  If the electrically conductive carbon brush dust was
> solubilized into the oil, then it could slightly affect the conductivity.
> To verify this, put some of the dark oil on a microscope slide and view
> under a microscope.  You should observe particles in suspension.
>
>  On reassembly of the MD-101, I found the best way to deal with the
> brushes is to jam a thin piece of wood between the armature and permanent
> magnets so that the commutator is axially extended by about 1 cm.  Then
> pull the springs on the brushes off to the side so they are not engaged.
> Slide the end of the housing that has the brushes into place then with a
> small screw drivers slide the springs back into place.  Then pull the wood
> wedge out and slide the armatures into its correct location.  Then, install
> the remaining end cap and insert the long retaining bolts and tighten being
> carful to centralize the fined section.
>
> As to noise and overheating issues.  I found these MD-101's are sensitive
> to radial alignment of the brushes, that is position of the housing that
> has the fin and brushes to the permanent magnet section of the thruster.
> To experience this, loosen the two long bolts enough so that if you grab
> the fin on the body of the thruster, you can rotate the brushed end
> relative to the body. Put some painters tape on both the fined side and the
> body and with a pen draw a mark across both.  When you rotate the fin,
> these marks will show the misalignment.   While the motor is running,
> rotate the fin.  When the fin is perfectly centralized the motor has
> maximum speed but when you move off center it slows down slightly and makes
> a different sound.  By rotating you can hear when the motor in set to the
> sweet spot.  It may have been that the brushed end might have been slightly
> out of alignment during the dive.
>
> Best Cliff
>
> Sorry you will not be able to attend PSubs 2021 convention.  i would have
> liked to meet you in person.
>
>
> On Monday, July 19, 2021, 06:22:56 AM CDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> Hi All
>
> Does anyone have any ideas on this?
>
> Following the dive i did last week, i had a motor issue.  The motor did
> not actually stop or fail, but during the dives it just didnt feel right.
>
> The positive wire going into the rotating penetrator would get hot after
> about 10 seconds of motor power.  I could also hear a kind of electrical
> noise from within somewhere.
>
> So, the next day i took the motor apart.  The oil (Silicone oil) was VERY
> black.
>
> I was expecting to see something had been rubbing, but i couldnt see
> anything.  It all looked fine.
>
> I put it all back together and it runs fine in air.  However, there does
> seem to be a louder motor running noise than the others.
>
> I am unsure what the issue is.  My feeling is that its carbon in the oil,
> making it conducting and hence slightly shorting out, causing the heat on
> the cable.
>
> The other motor cable did not get hot, nor did the oil go black.
>
> Again, another video here.
> https://www.youtube.com/watch?v=v_VxVfhM9t8&t=2s
>
> Would appreciate any input.  Im not sure what to do.  Buy a new motor?
> Air compensate it?
>
> Many thanks
> James
>
>
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