Dual Motors Provide Redundency

[Cottonwood]

Old aviation saying (OT, sorry): When you lose an engine in a twin-engine aircraft, the remaining engine has just enough power to get you to the scene of the accident.

:biggrin:

From personal and direct experience, losing an engine in my twin-ICE led to a smooth, calm, controlled descent to a good airport, and an uneventful landing...the biggest problem that I had, was to explain to the Customs and Border Patrol people why I did not land at a port of entry airport, given the uneventful landing. They finally caught on that continuing on with one engine was not a good thing.

An extra engine is a very good thing!

 

[ecarfan]

An extra engine is a very good thing!

It certainly is in an airplane!

But at this point we have no idea what happens in a Model S "D" if one motor or inverter fails. I would hope and assume that the car will continue to drive normally on just one motor, with reduced power and acceleration of course, since the two drivetrains are not physically connected.

 

[stevezzzz]

As a pilot how years ago had a catastrophic engine failure in flight, having the second was not "enough to get you to the scene of the accident". It saved my life and I was able to land normally at closest airport many miles away.

Important point that has some adjacency to this discussion. Have to be able to feather the prop in order for such a smooth outcome. Without that, drag can be a big issue. So too having one motor fail in a Tesla.. If it stays connected, grinding about, going home on one is unlikely.

Statistically true, but mostly related to the high accident rate which is due to pilot error, which is largely due to insufficient/inadequate training and preparation. I've had an engine fail in a twin, and although I could have made a safe off-airport landing, the second engine allowed me to make a nice, safe on-airport landing at my destination airport about 100 miles further on. (Mountainous terrain meant that no other airport was closer than my destination.)

From personal and direct experience, losing an engine in my twin-ICE led to a smooth, calm, controlled descent to a good airport, and an uneventful landing...the biggest problem that I had, was to explain to the Customs and Border Patrol people why I did not land at a port of entry airport, given the uneventful landing. They finally caught on that continuing on with one engine was not a good thing.

An extra engine is a very good thing!

Yeah, you're all absolutely right: the old saying I quoted is a little glib, but it does contain a kernel of truth. As a glider pilot, engine failures don't hold much terror for me when I'm flying an airplane, but I still think long and hard about flying a single-engine plane over mountainous terrain or at night, where an engine failure can leave you with precious few options. A second engine in those scenarios is much more likely to result in a good outcome.

 

[aronth5]

Saw a video today where Elon Musk does a test drive of a D with a Bloomberg reporter that I hadn't seen. This test drive is basically the same thing everyone else got other than being done personally by Elon.

But there is one bit of info I hadn't seen anywhere else. Around 20 seconds into the video Elon says:



I have no doubt that's true with a P85D given that the vehicle has the same motor as the RWD vehicles for the rear motor. But I wonder how true that is in the 60D and 85D with a smaller rear motor. I guess there could be a limp mode where you can drive but not very fast on just one of the motors in the other models.

Any thoughts?

It certainly is in an airplane!

But at this point we have no idea what happens in a Model S "D" if one motor or inverter fails. I would hope and assume that the car will continue to drive normally on just one motor, with reduced power and acceleration of course, since the two drivetrains are not physically connected.

Well actually yes we do have an idea what happens. Elon is quoted as saying the 2nd motor provides redundancy and while we don't know the exact details I think it is fair to say that in most scenarios the car will continue driving.

 

[breser]

Well actually yes we do have an idea what happens. Elon is quoted as saying the 2nd motor provides redundancy and while we don't know the exact details I think it is fair to say that in most scenarios the car will continue driving.

Elon has been proven wrong on a lot of off hand comments he's made over the years. Part of the reason I started this thread was because I was wondering if anyone had any idea how much truth was in Elon's statement or if Elon wasn't just making optimistic statements. Given the comments made here there may be some failures where one motor fails in a way that doesn't disengage with the axles and makes it difficult to drive with the other motor. I haven't seen any other mention of this redundancy. So I'm inclined to believe this is Elon saying something he probably shouldn't have.

 

[Saghost]

Elon has been proven wrong on a lot of off hand comments he's made over the years. Part of the reason I started this thread was because I was wondering if anyone had any idea how much truth was in Elon's statement or if Elon wasn't just making optimistic statements. Given the comments made here there may be some failures where one motor fails in a way that doesn't disengage with the axles and makes it difficult to drive with the other motor. I haven't seen any other mention of this redundancy. So I'm inclined to believe this is Elon saying something he probably shouldn't have.

I don't think there's much question that failure of one motor/inverter won't affect the other one. Thus, there's redundancy. A catastrophic failure in the gearbox will leave the car undriveable - but so would a catastrophic steering rack failure, or ball joint failure, or any of several other wheel/suspension bits. It doesn't mean the second motor won't work - just that driving the car on it is impractical.

So the redundancy is real and demonstrable. Whether it is relevant depends on the likelihood of the various types of failures.
Walter

 

[aronth5]

Elon has been proven wrong on a lot of off hand comments he's made over the years. Part of the reason I started this thread was because I was wondering if anyone had any idea how much truth was in Elon's statement or if Elon wasn't just making optimistic statements. Given the comments made here there may be some failures where one motor fails in a way that doesn't disengage with the axles and makes it difficult to drive with the other motor. I haven't seen any other mention of this redundancy. So I'm inclined to believe this is Elon saying something he probably shouldn't have.

Yes, Elon has been proven wrong especially when it comes to dates and other business related statements. But when it comes to how the car actually works his track record is pretty darn good.

 

[ecarfan]

Well actually yes we do have an idea what happens. Elon is quoted as saying the 2nd motor provides redundancy and while we don't know the exact details I think it is fair to say that in most scenarios the car will continue driving.

Thanks, apparently I missed that statement from him.

And I agree when it comes to engineering issues Elon I take him at his word. As far as him being overly optimistic on timeframes for achieving stated goals, sure it often takes longer than he would like (and he has publicly admitted as much) but there is nothing wrong with setting ambitious goals and timelines! That's what good leaders do.

 

[jerry33]

And I agree when it comes to engineering issues Elon I take him at his word. As far as him being overly optimistic on timeframes for achieving stated goals, sure it often takes longer than he would like (and he has publicly admitted as much) but there is nothing wrong with setting ambitious goals and timelines! That's what good leaders do.

As long as they don't put so much pressure on the employees to meet the stated dates that unfinished buggy products get rolled out.