100% drive unit failure rate??

[SW2Fiddler]

I am wondering how a guy who is CEO for SpaceX, a company that designs rockets for NASA can't make a working, reliable DU for a car?how can you make a f**** spaceship that is supposed to go outer space reliable enough to go there without any problems and you cand make a freaking DU for a car?how?

SpaceX is working towards reusability of their flyin' spacecraft. I assume that like me, you are accustomed to driving a car more than once without refurbishing it every time you come home...

 

[Max*]

SpaceX is working towards reusability of their flyin' spacecraft. I assume that like me, you are accustomed to driving a car more than once without refurbishing it every time you come home...

crap, I've been doing it all wrong.

 

[ecarfan]

And we're still getting catastrophic failures - like sudden propulsion loss on a highway...
Here's my DU number - AP car, delivered June 2015. Drive unit failed catastrophically and without any prior warnings, 3 days after a regular service.

It appears that total loss of propulsion is rare, as near as I can tell, and is not necessarily related to the "milling" sound. You had a sudden DU failure, but you said there was no "prior warning".

 

[mknox]

It appears that total loss of propulsion is rare, as near as I can tell, and is not necessarily related to the "milling" sound. You had a sudden DU failure, but you said there was no "prior warning".

When I had my "sudden and total loss of propulsion" is was due to the main contactors in the battery pack failing. Not sure, but I think that is a more common occurrence that the DU itself failing.

 

[vortexz]

I'm am 100% sure that they are capable of doing it. It's a time/budget/effort required issue. If the car crashed each time the DU started making noises, I bet they would have fixed it/re-engineered it by now.

Maybe it's not crashing each time but the DU is getting this problem too often, some users had their DU replaced multiple times already.It's like you'd get an ICE car and having the engine replaced like a lot of times, that would look very bad for the company.
It's not acceptable that you pay 100k for a car and it's DU is not working properly, and they can't fix it.
I really do like TESLA, but they really need to fix this !

 

[Electroman]

Like how they have drive through oil changes - a la Jeffy Lube - perhaps Tesla could pioneer drive through drive-unit replacements.

Once every 10k miles, a warning indicator comes 'Drive change needed', and then you drive to the nearest Tesla service center, and they have specific bay, you drive in. The service advisor looks up your VIN and changes the drive unit in 15 minutes and off you go. If they automate it, thats even better.

Tesla could even patent this.

 

[ohmman]

Was that necessary? If I recall correctly, Tesla wanted to buy the motor, but ended up making their own.

If you read the history of Tesla (and it's one heck of a scrappy history), you'll find that most of the time that they tried to rely on suppliers, it backfired. SpaceX has had the same setbacks with suppliers. It seems that Elon has learned to lean heavily towards doing things in-house instead of outside of the company's control. The nice thing is that the lessons learned in the development of the DU will make them a better manufacturer and better able to build future cars (at least in my view). It also shortens the customer-manufacturer feedback loop.

 

[vortexz]

Like how they have drive through oil changes - a la Jeffy Lube - perhaps Tesla could pioneer drive through drive-unit replacements.

Once every 10k miles, a warning indicator comes 'Drive change needed', and then you drive to the nearest Tesla service center, and they have specific bay, you drive in. The service advisor looks up your VIN and changes the drive unit in 15 minutes and off you go. If they automate it, thats even better.

Tesla could even patent this.

haha, good one !

 

[Sosius]

It's a serious problem, but we don't know:
- how much the process costs per swap
- how many miles per car
- any differences with new cars and units

Given that the price differential between the single motor S and the D model is $5000, I would think the drive units are not that expensive. Yes, I know that there is a size and performance difference between the P85 motor and the base 70D motors, but the $5000 price differential includes a lot more than just a motor. I would guess that the motor would actually be less than half the cost. But that's just my SWAG.

 

[Cyberax]

It appears that total loss of propulsion is rare, as near as I can tell, and is not necessarily related to the "milling" sound. You had a sudden DU failure, but you said there was no "prior warning".

I had a milling noise before, but I discounted it since "it's always been there" (from the moment I got a new car). New DU is much quieter.

 

[Electricfan]

Like how they have drive through oil changes - a la Jeffy Lube - perhaps Tesla could pioneer drive through drive-unit replacements.

Once every 10k miles, a warning indicator comes 'Drive change needed', and then you drive to the nearest Tesla service center, and they have specific bay, you drive in. The service advisor looks up your VIN and changes the drive unit in 15 minutes and off you go. If they automate it, thats even better.

Tesla could even patent this.

If it gets worse, they could do it at the car wash, so every weekend you get your wash/wax and a new DU.

 

[Tslynk67]

Given that the price differential between the single motor S and the D model is $5000, I would think the drive units are not that expensive. Yes, I know that there is a size and performance difference between the P85 motor and the base 70D motors, but the $5000 price differential includes a lot more than just a motor. I would guess that the motor would actually be less than half the cost. But that's just my SWAG.

Isn't the biggest difference between the S85 and P85 the inverter?

 

[kort677]

Isn't the biggest difference between the S85 and P85 the inverter?

no, AFAIK there is no difference in the rear unit, there is just an added inverter for the front axle

 

[wdolson]

Vortexz,
You underestimate the difficulty of what it being done at Tesla. When these guys/gals mention high power density, they are not kidding. The Tesla drive unit is unlike anything ever developed for a car and it is no surprise that it will take some de-weeding.

Much was made of opening up Tesla's patents but that is not where the value resides. The real value is in the scars and associated solutions that come from working through these exact types of problems. We are just lucky enough on this forum to have people who have some insight to similar issues thus allowing us all to paint a mental image of what it going on.

It's called institutional knowledge. It's all that stuff that isn't written down in a manual anywhere that people pick up from osmosis on the job. Many times it can't be captured in a book, it comes out of the culture of the business.

There is a great edition of This American Life about NUMMI, which was the previous owner of Tesla's factory. It was a joint partnership between Toyota and GM. The US government was pressuring Japanese car makers to build cars here and GM desperately needed to learn Japan's secrets so they could build cars better. GM had an idled plant in Fremont, CA that was known as the worst in the GM system. They produced terrible cars and had terrible union problems. That became the NUMMI plant.

Toyota hired back most of the laid off GM workers and many went to Japan for training in other Toyota plants. The GM people thought they were nuts to hire the malcontents that shut down the factory the first time. Toyota was very open in showing GM managers everything because they knew GM was going to have a lot of problem copying them. The secret sauce was the institutional knowledge that is only learned by doing things and not by looking around.

Once the plant was up and running, GM cycled a lot of managers through the plant to learn the secrets. They started picking up on the new way of doing things but initially they were incapable of transferring that knowledge to other GM plants because it was a mindset, not a procedure. Eventually GM did begin to change as those low level managers began to replace older managers set in their ways and they started changing the mindset. When GM went bankrupt, their quality and way of doing things had improved dramatically, but the changes came too late.

Tesla is building up a huge amount of institutional knowledge of how to design and build high performance electric cars nobody else has. Apple is trying to poach that knowledge hiring away people and they might figure it out eventually, but I think they will repeat a number of Tesla's early mistakes because they have zero institutional knowledge about building cars.

 

[flathillll]

And we're still getting catastrophic failures - like sudden propulsion loss on a highway, even with new cars.

- - - Updated - - -


Here's my DU number - AP car, delivered June 2015. Drive unit failed catastrophically and without any prior warnings, 3 days after a regular service.

Parts Replaced or Added
Part Quantity

ASY,DRIVE,UNIT,COMPLETE,3.0-150,REAR 1 (1037000-00-F)

- - - Updated - - -


I don't think so. The sound is a symptom of an impending drive unit failure. Just like a knocking rod in a regular ICE car. You might get a fair amount of mileage from a failing unit, but eventually it will fail catastrophically.

It also looks like Tesla has poor diagnostics for this problem - the car can't sense that something is out of order until it's too late.

- - - Updated - - -


That's not right. Tesla uses an asynchronous motor, its shaft does not need to be 'grounded' and it won't help anyway.


You mean non-conductive, not simply non-magnetic? It's unlikely to help.

Edit:

I read the linked PDF. It's quite interesting - turns out that the problem is not caused by magnetic fields, but rather by the way the motor power output is controlled.

Modern motors use PWM (Pulse-Width Modulation) to control the current - essentially switching voltage completely on and off several hundred thousand times a second. The ratio between 'off' and 'on' periods regulates the power output.

The problem is that electrically insulated rotor acts as a plate of an electric capacitor (with stator as the second plate). And if you have a capacitor connected to an AC circuit then there'll be a current flowing through a capacitor. With 'old' asynchronous motors that used 3-phase grid electricity at 60Hz to drive them the induced current was completely negligible, but with modern high-frequency PWM-controlled motors it becomes appreciable.

There are two ways to solve it: either insulate the rotor and stator completely, so that no breakdown can not occur, or provide a low-resistance path between rotor and stator. The aim of both approaches is to make sure that the breakdown doesn't happen in a tiny contact spot where the bearing balls contact the outer ring (through a thin film of grease).

I love how you were absolutely sure grounding would not help until you read a paper on it. you need to examine yourself and stop pretending to be an expert

 

[Cyberax]

Actually, I was quite right. Magnetic fields are not to blame if the linked PDF is right. And there can't be difference in magnetic vs. nonmagnetic materials - it will matter only if magnetic hysteresis is significant (think of an inductive cooker), but that just doesn't happen in asynchronous motors. Eddy currents _can_ happen, but they don't care about magnetic properties.

I understand the physics in asynchronous motors and I actually worked with them, but they were of older variety that used good old resistor circuits to control power output instead of fancy new IGBTs.

 

[scottm]

+1 Flathilll, my thoughts too.

But no point correcting the Internet.

It would be so cool to be working at Tesla on this issue right now, ground breaking stuff... get it?! Bad joke.

 

[kennybobby]

I ran my original issue through an visual audio spectrum analyzer and posted it on YouTube. You can "see" the sound happening (and hear it) too. Let me find it ...

So that is what the microphone recording would show on an oscilloscope. The next step would be to look at the power spectral density to identify the frequency and energy content, Drive Unit and AM Radio Implications - Page 2

 

[flathillll]

I knew the Roadster had ceramic bearings but now we have two sources that confirm the Model S has ceramic bearings on the motor shaft. Jack Rickard thinks all they have done is move the problem into the gearbox bearings by not grounding the shaft, and yes stray flux can also damge bearings but here the accelerated failure mode is pitting caused by arcing as alluded to in the pdf

I wonder if the liquid cooling thru the shaft is making this even harder to fix. You think you fix it but the problem just moves. They may end up using ceramic bearings in the gearbox, but that may not be refit without machining to fit larger OD bearings. The simple solution is to ground the shaft but that is the last resort. The goal is a million mile drivetrain with no service. Everyone know an AC motor is "brushless" and they want to keep it that way from a perception point of view.


In any case Jack Rickard and a couple other folks have complete working model s drive units om their workbench as we speake

 

[Pollux]

Hi, @wdolson,

You have written with such clarity that even a non-EE can follow along.

That said, from earlier discussion in this thread and a video that got posted, I am under the impression that the bearings are ceramic rather than metallic.

How should I reconcile that statement with what you have written? I would have thought that current flow, eddies, and so forth would not be an issue in a ceramic bearing.

Thanks,
Alan

Actually Tesla is on version 17 of the driver units. They just use letters instead of numbers.

If you want to see more problems, continue insisting on a redesign. The bigger the changes, the more room there is for new problems. Re-starting from scratch has the advantage of lessons learned, but there are all sorts of bugs that can creep in that weren't in the original design. They are approaching a true fix for the drive unit problem now, starting over from scratch would create more problems than it solved unless the root of the problem was a core design flaw, which is rare and does not sound like it is the case here.

It sounds to me like they have had some trouble isolating the cause of the problem, but they have zeroed in on micro-pitting of the bearings fairly recently. The last couple of revisions are probably different attempts to mitigate the problem. This is a difficult problem to diagnose, it only happens with wear to the motors, so any change they make will take a while to be sure if it worked or not, though they are probably out thrashing some mules to test the changes. Additionally, if it is due to eddy currents flowing through the bearings, eddy currents are notoriously difficult to measure. If you know specific spots where they are flowing, you can put measuring instruments in those spots, but to see how they got to those spots can be difficult to measure.

Electrical current is like water flowing through metal. It prefers a good channel, like a copper wire, but it will flow over flat land too. Water you can see where it is and where it isn't, and it's fairly easy to measure it where it isn't obvious to the eye, but current can't be seen and can only be detected with instruments. One way is to measure the electric field generated by the current flowing through metal. This is not difficult in something like a wire where you know the channel for the current. In something like a metal chassis, especially one with complex curves like the drive unit, it's very tough to isolate how much current is where.