M Coupe: respect from other drivers

[dekaliber]

Originally Posted by jdoublehcubed

I think that assumption that electric motor=zero maintenance is a big part of the problem. Think of how sub-frame bushings on the Z4 are a huge bitch, because you really can't access them without taking a ton of stuff apart. Now apply that sort of poor planning to 80% of the bushings on the car. Except because the Tesla has super high torque motors, the bushings are going to get a lot more wear than bushings on most cars. That was one of the first things I noticed looking at the chassis.

Tapped aluminum is bad because its so hard to repair. Think about taking apart things on your Z4. As a general rule, bolts are used to hold things together, by passing through 2 items and then being restrained with a nut. If you mess up the nut, or the bolts get sized, etc., you just cut/torch it off and replace it. On the Tesla, chances are instead of that nut, there is a whole in the frame that has threads tapped in. When you mess up those threads, its a lot harder to fix than simply replacing a nut. You have to drill out the bad threads, then either helicoil it (retap to larger size then thread in an insert that repairs the original threads) or move to a larger bolt size. In many cases, you won't have enough space to do that without taking more items apart.

This gets worse for home mechanics, because (having less experience) they're more likely to cross thread or strip something than the dealer. And once they've done that, they may or may not have the knowledge to do a thread repair. And now some part of the car is taken apart, so how do you get it to the dealer for the repair?

These two problems are representative of the overall design sloppiness of the chassis. Design for maintainability and repair-ability is one of the absolute most important things to keep in mind when you're designing something that has to stay in service for many years and have regular maintenance done on it. If I had tapped holes in a maintenance part in one of my designs at work, I would (1) get laughed out of the design review and (2) everyone would assume I was a moron at future design reviews for missing something like that.

Those things may not be obvious to non-engineers, but they should be extremely obvious to the engineers designing the car, because they are fundamentals of design. It points to the general lack of organizational processes and institutional knowledge at Tesla; something that you could reasonable expect when a brand new company decided to make something as complex as a car.

Having a lot of friends at SpaceX, I can tell you its pretty much a hallmark of Elon Musk leadership.

Edit: donoman, thats a fair question, not at all ignorant. mostly I'm frustrated that the people who should point this kind of stuff out (tech media, car magazines, etc.) seem content to give Tesla a huge pass. Its not something that you'll notice when you first buy the car, its the kind of stuff that screws you 3 or 4 years down the road when it starts needing maintenance, so its something most owners won't think about until muh later.

Great points and very helpful explanation! My view of it is that Tesla is still very much a start-up and are (wisely) taking a very aggressive growth-oriented approach to delivering a minimally viable product to their early adopters. This is only their second vehicle and really only their first "mass" market car. How the Model S plays out for the next few years will be a good learning experience for the company and help them iterate their designs. It's much better to get something out the door and start getting feedback from customers than to build something "perfect" only to realize that you're off the mark.

The criticism about not designing for maintainability is fair but from the business perspective, likely don't impact their current target audience. The Model S is designed and priced to be bought by relatively affluent individuals who are probably not gearheads (who would more likely buy M3s, Porsches, Corvettes, etc.) I doubt there will be many Tesla owners who try to service their vehicles at home, and they can likely afford having it serviced professionally down the road.

Having worked with both Tesla and SpaceX as a supplier I can definitely attest to some aspects of their organization being run pretty poorly. At the same time, I think it's pretty incredible that such a small company has been able to pull off a product that's as good as it is even with the faults you mentioned.

[David70]

Interesting information about Tesla but without evidence of failures (and failure rates) it seems like the opinion above is they should have designed it differently and it is expected there will be problems but no proof of anything. Any proof of problems associated with the above?

[jdoublehcubed]

Originally Posted by David70

Interesting information about Tesla but without evidence of failures (and failure rates) it seems like the opinion above is they should have designed it differently and it is expected there will be problems but no proof of anything. Any proof of problems associated with the above?

Its not about failures, its about maintainability. If a bushing isn't accessible, it just isn't, it needs no further evidence.

The frustration will appear in 3 or 4 years when the maintenance comes due.

[David70]

Originally Posted by jdoublehcubed

Tapped aluminum is bad because its so hard to repair. Think about taking apart things on your Z4. As a general rule, bolts are used to hold things together, by passing through 2 items and then being restrained with a nut. If you mess up the nut, or the bolts get sized, etc., you just cut/torch it off and replace it. On the Tesla, chances are instead of that nut, there is a whole in the frame that has threads tapped in. When you mess up those threads, its a lot harder to fix than simply replacing a nut. You have to drill out the bad threads, then either helicoil it (retap to larger size then thread in an insert that repairs the original threads) or move to a larger bolt size. In many cases, you won't have enough space to do that without taking more items apart.

This gets worse for home mechanics, because (having less experience) they're more likely to cross thread or strip something than the dealer. And once they've done that, they may or may not have the knowledge to do a thread repair. And now some part of the car is taken apart, so how do you get it to the dealer for the repair?

Pictures of the subframe on the last Audi A3 (what I have) and GTI also with threaded aluminum connections. When installing bolts you need to make sure you don't cross thread them and you need to torque them correctly. I have never heard of an issue with this and have removed and replaced bolts in the subframe without a problem.

[IMG]Subframe by dmorrowzzz, on Flickr[/IMG]

[IMG]Subframe1 by dmorrowzzz, on Flickr[/IMG]

[sipman]

I see your point about tapped aluminum, but to play devils advocate... Isn't the point to prove to the public just how far you can go in an all electric car today? Not about tomorrow or how long you can own the car for. By eliminating the nuts, they are pulling out as much weight as they can without entering into cost prohibitive exotic materials.
I know we can't applying Moore's Law to electric vehicles here, but once the energy storage problem takes it's next leap forwards, aren't these cars going to become obsolete for the customer base they are targeting?

What does interest me in what you've observed is did you see if the quick-swap battery bolts are also tapped aluminum? One extra question. I'm not an engineer, but do electric motors require bushings? My understanding is they serve to isolate the vibration of an engine from the body, but a motor is usually balanced and spins at much faster rates. Are they comparable between gas and electric?

[jdoublehcubed]

Sipman, I think you're right, that may be what they were going for, but I still disagree with them that it was the right choice. Eliminating all the nuts on the car is probably only 2 to 3 pounds; hardly worth the high cost of repairs down the road. And if it was really about weight savings, they could have used a t-nut style drop in insert; same amount of frame material is removed, but the threaded portion is replaceable.

I did not see the bottom of the chassis, it was sitting on the floor, rather than on a display lift. I really hope they were at least smart enough not to put those bolts into tapped aluminum. That could suddenly turn your 60 second battery swap into a 3 hour repair.

For the bushings, two ways of thinking on the electric/gas question. Yes, electric motors generally vibrate less, so its reasonable to assume they need less/smaller bushings. However, think about all of the bushings on a Z4. Only 4 (ish?) of them are connected to the engine/transmission, the rest of them are part of the suspension. The need to isolate the body/frame from the suspension isn't going to change much going from a gas to an electric engine, so the majority of the bushings are going to be unaffected by that.

Second way of thinking, yes, they vibrate less, but they also have much less rotating inertia, and so will be spun up to speed and down to idle a lot more often. So, less constant, low level vibration, but a lot more high torque shocks to the mounts and drive train as the motor goes from idle to high speed very quickly.

I thought that the electric motors on the tesla were mounted with bushings, but I'm not 100% sure. They're sort of trapped in a cage at the rear of the car formed by the chassis and the subframe, the bushings I saw in that area could be either motor mounts or subframe bushings.

For the energy storage problem, you're right, if battery technology suddenly takes a 10X leap forward, all of the electric cars on the road, maybe even all cars on the road, will suddenly be obsolete. However, since lithium ion batteries were introduced commercially in the 90s, there hasn't been more than a 50% increase in the energy density (watt-hours per pound) of commercially viable batteries (and I think I'm way overestimating that at 50%, its probably more like 20%). Energy storage density is a hugely difficult problem, one that gets a ton of R&D money and still isn't progressing very fast, so I don't think we can expect any major progress on that area any time soon.