[PSUBS-MAILIST] Thruster Test Fail

[Alec Smyth via Personal_Submersibles]

Congrats Alan, that sounds like a very effective test with actionable
conclusions. My suggestion would be to change only one thing at a time in
the next iteration. For instance, if you changed the Morlina to silicone
AND the sheathing material at the same time, you wouldn't really know
whether the issue was the oil or the plastic. Thirty hours strikes me as
pretty good endurance for a first run!

Best,

Alec

On Fri, Dec 16, 2016 at 4:29 AM, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> My home made brushless thruster failed after 30hrs of in pool run time.
> The Kelly controller was flashing an error sequence indicating the
> hall effects sensors had failed. There are hall effect sensors on a
> board at the end of the motor that send information on the position
> of the motor. The board is held on by a large flat nut & had come
> loose so the sensors were out of position. Also the sheath of the wires
> to the sensor board had melted.
> Possibly the fact that oil was being thrown out of the thruster housing
> & up the wiring tube by centrifugal force, caused the motor to over heat &
> melt the sheathing.
>    The outer can of the motor that rotates (out-runner motor) is only
> supported
> where it is press fitted on to the propeller shaft at one end. Some
> out-runner
> motors have a large bearing that supports the cup like other end of the
> can.
> Due to the fact I didn't have a very snug press fit, the can was pulling
> off center when
> the motor stopped, so that the outer can with the magnets on it was
> touching
> the stator. This caused it to start roughly. It would center when running.
>    The sheathing on the wires running out of the motor, to protect them
> from
> abrasion, were softened & breaking up a bit. The Shell Morlina S2 BL oil I
> was
> using must be breaking them down. I can replace this rubber sheath with a
> heat
> resistant sheathing (as my other motors have) but can't be sure that this
> oil won't
> break down the coating on the motor windings. Maybe I'll change to 10 cst
> silicone.
>   On the positive, the general design of the thruster worked well, the
> motor performed
> with comparable or better thrust per Watt than most commercial thrusters .
> The outside of the
> can never heated up. One day it ran continuously for 13hrs. It started
> well initially, & could
> run at slow speeds.
>    Am thankful that I could identify a number of issues with just the one
> test & will
> have a good think about this over Christmas.
> Alan
>
>
>
>
>
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