Can you elaborate on this?
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the esc has to run twice as fast! very tiring 
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In general field weakening is not an efficient way to gain speed. A faster motor would be the better choice. However, if you only need more speed from time to time, it is acceptable to waste some energy by fireing additonal coils up, weakening the field.
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Variable position stators achieve the same effect as field weakening without producing back emf voltages that exceed the ratings of a typical vesc in the event of a fault that stops the pwm.
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So you can gear for torque and have the ability to go over 30mph if needed… if the battery can dump more amps and the motors can handle the heat
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Just so everyone reading is aware, there are some serious safety issues with field weakening.
If the motor is powered into a faster spin than its normal no-load speed, then any ESC failure would feel like an immediate full-brake, likely to pose significant danger to the rider. A lot more danger than a regular ESC failure at top speed, which would likely just put the board in “neutral” or “coast” mode.
Only do this at your own risk. 
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Seems like it may be safer (if the speed control can handle it) as we approach 100% duty cyle there will be no pause or cutback- the battery will dump more amps and you can keep going alittle or alot mo faster
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A much better way to test this would be to gear a rig so it has an 8mph (12.9km/h) top speed or some shit. Then push it to 16mph (25.7km/h) …
and test the fuck out of that mug at speeds you can run off
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One of the few times I wish I had a remote control car with vesc for testing this lol
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This is a great idea
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If the ESC would suddenly stop weakening the magnetic field due to a fault, would that mean that the motor would work as a generator above full speed and fry the ESC by overvolting it if the speed is high enough?
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I believe Vedder was mentioning no load or very light load speed and not human / ride load condition here. Could you please confirm Frank?
Given our tiny motors are not the best layout nor the best size to benefit from field weakening per se, and compared to vehicle size motors which will generally offer around 20-30% more to speed, I suppose you may just not be able to “overdrive” or overspeed your motor above battery voltage just with field weakening in real world conditions?
This would at least solve the issue of "if it fails everything goes boom
Unless maybe you’re bombing max throttle downhill.
Either way ability to boost the top speed is limited both by battery amps and motor saturation, so you should be safe from overspeeding (motors will give up before you risk it)
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So far all I’m seeing here is that it’s great for applications where nobody is put in danger by hardware failure… This is really cool, yeah, but it seems like it would be easier to fry a vesc this way than to fry an egg.
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Reducing the emf to help the motor to go faster on an esk8 could be sketchy af, the motor iirc speeds up to gain the back emf, speed is gained but torque is reduced, not sure how it reacts with smaller motors, would be interesting but I reckon the motor will shit itself, if anyone has contacts with motor companies like flipsky, surely they must do absolute rpm tests
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Lol 
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Sounds like the perfect candidate for the Echopper!
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Auhooo yes … Finally 
10S before
20A FW current adds about 7mph…
10S 45A though…
And a deadish 12S battery at 45A:
Afraid to push much higher… 56mph on a 10S board that topped out at 35mph before, sure. Don’t know if I will be riding this guy much anytime soon though.
Once this gets thoroughly tested and all the kinks sorted out I can see it become a thing to gear for a max of 20mph to have awesome torque but also still be able to go 35mph.
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This is why controllers supporting this feature meet Safety-Integrity-Levels for industrial and automotive
They ensure such situations never arise and that they always have full control of the motor.
Anything that doesn’t meet basic SIL or ASIL will inevitably lead to serious injuries or death.
Not sure how these people are getting such massive increases in speed; the best I got out of some maytech motors was 25% driving 60A into the negative D axis, which is hardly practical in any sense.
And this was with significant position estimation error with the sensorless observer
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So you’re telling me I shouldn’t get excited and probably shouldn’t take this thing on the road…
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