[Dylan16807]

> I think you were emulating the ABS module right? In that case, the spinning out of control is actually probably your fault. If you had not emulated this, the system would realise there is an ABS fault (from the messages not being present) and not use the ABS reported speed. It might even fall back to motor speed automatically.

If the ABS unit getting stuck causes that kind of acceleration then I'm going to point most of the fault at the control logic.

[formerly_proven]

ABS faults can do way more dangerous things than indirectly command 5 Nm of torque in a no-load situation.

[Zak]

I have experienced a spurious ABS activation while braking from highway speed on an offramp. It was terrifying, and would have led to a crash had there been any traffic when I rolled through the stop sign at the bottom with the ABS still chattering.

That vehicle got its ABS fuse pulled.

[aetherspawn]

Not really.. it will only be applying 5Nm or so which is such a small amount of torque that you could likely stop the wheel with your hand (equivalent to holding up 500g object with 1m ruler)

He is spoofing an ABS message from a working vehicle that says “no faults present” on a vehicle that is clearly full of faults.

[aetherspawn]

ABS are usually ASIL D rated (ISO 26262) which means they have an on board watchdog, redundant processor with voting system, etc. so this failure mode (locked up and still sending) is considered impossible by design.

[Szpadel]

sure, but I would think some special case when we expect car to have 0 speed to not request any torque from its motor. IMO three is no case where car should request any torque when been in neutral

[aetherspawn]

If I had to take a guess why… it probably thinks that you’re sitting on a hill and doesn’t want you to roll back.

[Dylan16807]

> Not really.. it will only be applying 5Nm or so which is such a small amount of torque that you could likely stop the wheel with your hand (equivalent to holding up 500g object with 1m ruler)

It's good that it's small but I'm still not thrilled about this control loop.

> He is spoofing an ABS message from a working vehicle that says “no faults present” on a vehicle that is clearly full of faults.

My point is that the same messages would happen if you had a fully working vehicle and then the ABS unit locked up in a way that didn't interrupt sending.

[numpad0]

It's not acceleration, it's torque application. There is a slight difference in nuances between those.

[Dylan16807]

The problem is that it's doing both when it's only supposed to do one.

[numpad0]

No, constant torque against nothing is infinite RPM. Imagine a space capsule with a stuck roll thruster.

[Dylan16807]

Please explain how that is a "no". You just described a situation where it would be doing both when it's not supposed to. In the analogy, the thruster is supposed to turn off once it starts spinning, but it doesn't.

The entire reason this mechanism exists is that resistance can be significantly nonzero and needs to be adjusted for. It's just doing the adjustment in a flawed way.

[numpad0]

Sorry if it sounded dismissive, but, I mean, modern motor control formulae[1][2] don't have a term for RPM. Motor controller derives new output state from just torque and instantaneous state of the motor, RPM is somewhat externally controlled unless that version of formula is in use. Hence the capsule analogy: F=ma for constant F means a > 0 and (rotational)velocity monotonically increases.

It doesn't make instinctive sense to me too that motor people haven't been thinking RPM-first for some time, but apparently they're not.

1: https://en.wikipedia.org/wiki/Vector_control_(motor)

2: https://en.wikipedia.org/wiki/Direct_torque_control

[Dylan16807]

> Motor controller derives new output state from just torque and instantaneous state of the motor

And the way it makes the motor state advance causes acceleration. It doesn't matter what variable goes into the formula, especially since you can convert freely. I'm pointing at the output and what I find scary about it. What comes first doesn't matter, I'd have the same issue even if I'm looking at the control formula from a jerk-first perspective.

And I don't really see the value of the "against nothing" analogy because the reason it's increasing torque is because it thinks there's resistance.