[PSUBS-MAILIST] Thruster Test Fail

[Alan James via Personal_Submersibles]

 My home made brushless thruster failed after 30hrs of in pool run time.The Kelly controller was flashing an error sequence indicating thehall effects sensors had failed. There are hall effect sensors on a board at the end of the motor that send information on the positionof the motor. The board is held on by a large flat nut & had comeloose so the sensors were out of position. Also the sheath of the wiresto 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 supportedwhere it is press fitted on to the propeller shaft at one end. Some out-runnermotors 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 whenthe motor stopped, so that the outer can with the magnets on it was touchingthe 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 fromabrasion, were softened & breaking up a bit. The Shell Morlina S2 BL oil I wasusing must be breaking them down. I can replace this rubber sheath with a heatresistant 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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