DIY 3D-printed electric waterjet duty cycle saturation at 89% causes Fault 18 cutout FOC observer issue?

Build, Repair & Mod
1

Been developing a DIY electric waterjet propulsion unit for surfboard/foilboard use. 85mm impeller, rewound outrunner on 14S, Flipsky 75350 ESC on VESC firmware.

Latest test session hit 49.8 kg thrust before cutout. The limiting factor isn’t current (capped at 250A — tested up to 450A limit with same result) or temperature — it’s duty cycle saturation at ~89%. ESC throws Fault 18 (ABS_OVER_CURRENT) right at that point, but I suspect FOC observer instability at high ERPM rather than a true overcurrent event.

Enabling Slow ABS Current Limit pushed the cutout threshold from ~9,100 to ~9,500 RPM, which supports the observer instability theory over actual current spike.

Questions:

  • Anyone experienced duty cycle as the hard ceiling rather than current/temp?
  • Is there a reliable way to stabilize FOC observer at high ERPM/high duty?

VESC log CSV and test footage attached below.
(https://youtube.com/shorts/zx7pIpfH4nU)

2

Check FW 6.06 or later for the overmodulation settings
That will get you more RPM at low input voltages / low kV motors

Could also be saturation or other effects in the motor that limit the system…

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3

Thanks! I’m on FW 7.0 — I can see the Overmodulation Factor in Advanced tab, currently set to 1.000. Will try increasing it to 1.1~1.2 and report back with results.

4

If I remeber right OM higher than 1.15 gives no more gain, so 1.15 should be fine.
You can also try saturation compensation.

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5

Thanks! It reaches 9,600 RPM, and since there’s only a 400 RPM gap to 10,000, I’ll try 1.1~1.15 and report back with results!

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