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Motor "vibration" at very low speeds - current going around stator?

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This isn't a problem - I just want to know if it's what I think it is.

My driveway is on a slight incline. Whenever I'm pulling in, if I use the "throttle" to crawl *very* slowly, I can feel a faint vibration throughout the chassis. Is this sensation the current going around the motor stator(s), or whatever they're called?
 
I think that 'vibration' is due to the coolant pump, or some other 'battery balancing' pump going on, and it happens at different times, even while stopped. My guess is you're experiencing yours on your driveway. I feel it when stopped, waiting for my wife (so car not in 'sleep' mode), or also when going slow for a little bit, like when navigating my daughter's apartment complex. The good news is it's 'normal' :).
 
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This isn't a problem - I just want to know if it's what I think it is.

My driveway is on a slight incline. Whenever I'm pulling in, if I use the "throttle" to crawl *very* slowly, I can feel a faint vibration throughout the chassis. Is this sensation the current going around the motor stator(s), or whatever they're called?

It's the effect of cogging torque, which is a phenomenon experienced by synchronous motors at low speeds. So you are feeling the rotor "snap" into alignment with the field that the stator is generating.
 
Does the front motor even work at slow speeds? I'm almost sure only the rear works (just like during regular driving), which is not synchronous. But it's still possible that's what's going on. The consensus seems to be the octovalve doing its thing.
 
I notice it when stopped or very slow speeds, doesn't happen all the time.

Its like this low rumble that goes for 1.5 seconds or so. Sometimes 2-3 in a row, and seemingly randomly. Tried to get a recording of it but happens too randomly to capture.

Hope its the same sound you guys are talking about and that there isnt a need to book a service.
 
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You're on the right track, you're feeling the variable torque basically. Unlike an ICE vehicle that has a lot of rotational momentum to smooth out natural torque spikes (among other things like torque converters which smooth it even more), we feel the torque a lot more directly.

If you had something happen to your car so that it disabled the smoothing (I can't remember how Tesla refers to it, but it's basically "microstepping" to borrow a term) you would feel the same effect at slow speeds, but much more pronounced. Basically, the torque damping is being controlled electronically.

What I don't really get is why I feel this mostly when the front motor is being used (i.e. reversing into the garage very slowly, also on a very slight incline). The front motor is an induction motor, and I'd expect to feel this due to the rear motor. It might be switching the fields on the rear motor still to "coast" it, and this might be what we're feeling. Would be interesting to see if folks with RWD cars feel this too (I think you have an AWD or Performance IIRC?).

Does the front motor even work at slow speeds? I'm almost sure only the rear works (just like during regular driving), which is not synchronous. But it's still possible that's what's going on. The consensus seems to be the octovalve doing its thing.

The front motor is used at slow speeds when in reverse, or for regen at low speeds.

I don't think there's any sort of consensus that it's the octovalve. This is the first time I've ever heard this, and most of our cars don't even have the octovalve.
 
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Would be interesting to see if folks with RWD cars feel this too (I think you have an AWD or Performance IIRC?).

Yes. We do.

In regard to front motor torque, all the graphs I've seen point towards the front motor being only energized when under heavy acceleration or when rear wheel slippage has been detected. This makes sense, as the front motor costs nothing to leave idle, but the rear motor would need to be in active torque sleep.
 
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Thanks for the info.

2019 P3D- so no octovalve - and that's the scenario that I mostly notice it in, as well: reversing slowly into my slightly inclined garage.

I imagine that the rear motor still comes into play in reverse?

In reverse, the rear motor really isn't doing anything normally (for AWD models). It's just in the "coast" or "active torque sleep" mode, if I may borrow a term from @Saabstory88.

If the front wheels slip, they'll bang it off and bang on the rear motor. My driveway has this little dip that freezes often right in line with the right side wheels. Whenever it's icy, I get to experience this. The rear rolls right over it, but as soon as the front gets to it, it slips. So both CAN bus data and physical observation confirm majority (probably sole) use of the front motor when in reverse at low speeds, in my experience.

Yes. We do.

In regard to front motor torque, all the graphs I've seen point towards the front motor being only energized when under heavy acceleration or when rear wheel slippage has been detected. This makes sense, as the front motor costs nothing to leave idle, but the rear motor would need to be in active torque sleep.

Ok cool, it's almost definitely something related to the rear motor then.

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All graphs you've seen paint an incomplete picture, but that's to be expected.

Most people don't care what the car is doing at turtle speeds. Existing graphs are basically variations of flooring it with a twist: stock, chill mode, after an update, at various SoC, etc. These are more interesting graphs even if they mean little to our everyday lives, while the everyday stuff (e.g. how the motors behave at low speeds) is mundane to most.

The front motor is also used for regen at low speeds (in Drive), but only if you've started off at a lower speed (coming down to a red light, it'll use the rear motor still). So if you're navigating a parking lot or something, the rear motor propels and the front motor handles regen. I haven't got a clue why they do this, honestly.