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Joined 1 year ago
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Cake day: June 14th, 2023

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  • That’s an interesting point. It also implies much better efficiency at low speeds than most motors.

    Given a few generations of better semiconductor, it could end up being very interesting for (railway mostly?) traction motors.

    • Low speed high torque means you don’t need a further reduction gearbox.

    • Good performance near zero speeds mean you might not need to use braking at all aside from parking and emergencies.

    • High voltages are already widely used and available - 1500VDC nominal is an older standard for metro trains; 3kVDC is common both for older overhead and as an intermediate DC bus voltage for AC overhead. Future semiconductor generations could allow direct use of 25kV overhead (~40kVDC rectified at maximum line level) without the need for an intermediate bus, assuming the dielectric fluid was good enough.


  • Interesting.

    Needing to run in a specific fluid seems like it could pose longevity issues because a motor inherently needs a shaft to pass out of the sealed enclosure, causing ingress or egress - car AC compressors have this issue.

    If you could also make the fluid an effective refrigerant, then this could be good for refrigeration compressors. Those run entirely in a sealed system anyway.

    This seems to be a very high torque, low speed motor, operating at 360W 18Nm which means it’s 190RPM (20rad/s).

    With all the parallel plates, windage friction is going to be very high if they attempted to increase speed, which is usually the easy way to improve power density.

    2kV for a fractional HP motor is really pushing things; you would need to integrate the boost converter and inverter into the motor housing. The moment you have cables above 1kVAC or 1.5kVDC, you’re ‘high voltage’ and a raft of new rules applies.


  • Converting between Kelvin and Celsius is simple addition; converting between Rankine and Fahrenheit is simple addition. Converting between the two groups requires multiplication, and pre calculator, that’s notably harder.

    Also, all your kJ/kg/°C or BTU/lb/°F tables and factors are identical when you swap to referencing absolute zero. If you change to the other unit system, all that goes out the window.














  • If we knew what city/route/service and day, we might be able to get a better idea.

    • Sometimes operators declare a ‘fare holiday’ when everyone rides free, usually as compensation for some major fuckup previously, or for some other PR stunt. Metlink in Wellington doesn’t charge on Christmas Eve, Christmas Day, or New Year’s Eve.

    • Operators sometimes half-strike and refuse to collect fares.

    • The specific route, service, or time of day might be free.

    • It’s an express service that you can’t pay cash on (only fare cards) and it’s easier/nicer to tell you to ride for free than to tell you to get the next bus because they don’t take cash.

    • You might be part of some group (youth, students, elderly) that doesn’t have to pay.

    • Something is broken and they can’t collect fares.

    • They don’t want to deal with the big banknote you had.