11 ms·

Tesla Model S Suspension Walkaround

260 points by dmmalam 13y ago

GotAnyMegadeth 13y ago
First thought was "Tesla have finally built an electric AT-ST!"
- toomuchtodo 13y ago
  Whoa. Whoa. Whoa. Mars first, then the electric AT-ST.
  - omegant 13y ago
    You really need a AT-ST for mars exploration.
  - Raphael 13y ago
    Why not both?
- cobrausn 13y ago
  I saw this post from Elon Musk yesterday after he mentioned an upcoming Tesla announcement. Almost thought the same thing. https://twitter.com/elonmusk/status/330053450261987328 https://twitter.com/elonmusk/status/330053450261987328
  - alimoeeny 13y ago
    That must be related to SpaceX not Tesla,
heironimus 13y ago
Everybody thinks this is cool, but nobody (myself included) knows enough about car suspensions to comment!
- cschmidt 13y ago
  That must be how car types feel about a lot of HN articles. It did seems to be in a bit of a foreign language to me.
- joshrotenberg 13y ago
  Heh, same. I stopped after a few paragraphs. TL;DR Tesla Model S suspension is pretty neato.
- untog 13y ago
  I think it's a symptom of "Tesla = auto upvote on HN" syndrome. If this had been "Ford Focus S Suspension Walkaround" (or "Porche 911", for that matter) I doubt we'd be seeing it on the front page.
  - enraged_camel 13y ago
    If all of your comments are this impressive, I guess I'm going to have to go with "untog = auto downvote" from now on.
    - chollida1 13y ago
      I'm not sure your comment was all that appropriate. I think untog's comment is spot on. There are lots of stories that seem to get upvoted for reasons other than their own merit. Pointing that out in this case is probably appropriate.
      - damon_c 13y ago
        He should have used a "==" though... Edit: Oh wait sorry no... I suck!
- soss 13y ago
  I work for a suspension manufacturer in the aftermarket industry for trucks, and a lot of it isn't that extraordinary. The air springs/shock absorber combination that you see there are becoming more normal across wider applications, while already coming equipped on luxury vehicles for quite some time now. The part that impresses me though is the steering knuckle (they comment on it towards the beginning), and its aluminum hollow construction. We build modified steering knuckles for trucks that provide additional lift height, but out of ductile iron in a cast mold, same as OEM specs/mfg process. So i'm kind of at a loss how they would make it hollowed out, while maintaining stability. Definitely expensive, i know billet aluminum knuckles for corvettes run about $1500/piece.
S_A_P 13y ago
When I look at this, I cannot how complicated it must be to build a world class automobile. Its all the more impressive that this is the first ground up(vs the roadster being an electric Lotus) car from a start up. Impressive indeed!
- thoughtsimple 13y ago
  More or less what I was thinking while reading the article. How do you even staff up for something like this? I guess a lot of recruiting in Detroit or something.
  - krschultz 13y ago
    "Huibert Mees is the Chassis Systems Technical Fellow responsible for the design and engineering of the Model S chassis systems. He joined Tesla from Ford Motor Company, where he was responsible for all the chassis systems and vehicle structure of the Ford GT supercar. Huibert has been working in the automotive industry for over 20 years, and was responsible for the rear suspension design of the Lincoln LS and Jaguar S-type as well as numerous advanced chassis design concepts at Ford." Both SpaceX and Tesla are largely built on skimming the superstars out of the entrenched players. There are plenty of people that are really really good at their jobs at Boeing, Lockheed, Ford, General Dynamicsm, etc. They are generally underpaid, undervalued, and given little freedom relative to their skillset. But they stick around in those companies because that's where you have to be in order to work on really cool stuff like the Ford GT 40 or a space rocket. Tesla and SpaceX offer the same cool stuff to work on, without the crappy low-value coworkers that never get fired, legacy systems holding you back, and the opportunity to do things as you believe they should be done. This is part of why the old companies will have a hard time noncompeting. Not only are SpaceX and Tesla disrupting their business, but Elon Musk is stealing from their top tier talent pool that could defend against disruption.
    - tocomment 13y ago
      How specifically did he recruit them? Did he just show up at the factory one day? (I'm really interested in the detailed logistical steps of how one starts a brand new car company)
DEinspanjer 13y ago
Pretty pictures, but I just like how I can push the buttons on my screen and make the car go up and down. ;) Actually, when I first read this doc a couple of weeks back, it showed me the reason for something I had noticed. If I have my foot on the brake while changing the suspension level, I've noticed that when I let off the brakes, the wheels shift a bit. Turns out that for the front tires, it doesn't lift and lower straight up and down. There is a bit of horizontal motion as well.
alimoeeny 13y ago
So HN Tesla owners, how happy are you with the car itself, not considering the ideas behind electric cars and what not, just with the car and driving experience and charging, worrying about running out of juice ...?
- tlb 13y ago
  It's fantastic. Best thing I've ever driven, regardless of environmental impact. It's silent and odorless, responds instantly and precisely, and it seats 5 adults + 2 kids comfortably. A niche benefit: I live in the mountains and it handles going down much better than gas cars, where you have to downshift and use engine braking to avoid burning the brakes. It uses 12 miles of range going up, and gains 4 back going down so the average is close to a flat road of the same distance.
  - TallGuyShort 13y ago
    I'm curious about how it handles downhills. I would've thought that without engine braking you would have to rely exclusively on the brakes and would thus burn them up even more. Does the Tesla have another mechanism? Or just insanely efficient brakes?
    - furyg3 13y ago
      It has regenerative breaking, which is effectively 'engine breaking'. Engine breaking on an electric car puts electricity back into the batteries. The brakes you see in the photos are for breaking, hard (full stop, quick stop, racing).
      - Dylan16807 13y ago
        braking.
  - laacz 13y ago
    5 adults + 2 kids comfortably? In a car with max 5 seatbelts?
deadfall 13y ago
Has anyone wrecked one of them yet? I bet trying to get it fixed would be ridiculous.
- pyre 13y ago
  How much would Google self-driving car equipment reduce the time between charges? I imagine that such a system would mean fewer accidents.
NDizzle 13y ago
I'll never look at my Galant VR4's suspension the same again. I knew it was old and bad, but this really drives that point home.
cake 13y ago
Pretty amazing yet totally normal not to see any exhaust system that I'm used to see on every car ;-)
becauseracecar 13y ago
Car suspension tuning is a very subtle and difficult black art. It's all about what's happening dynamically in response to transient inputs (go around a corner, hit a bump, etc.). I believe Lotus does a lot of engineering consulting helping other manufacturers dial in suspensions. I wouldn't be surprised if Tesla had them consult. Even some of the big car companies have trouble dialing in suspension on their own (I'm looking at you underdamped Japanese cars). European brands tend to be really good at this, and can take the same raw materials that everyone else is working with and create superior setups. Porsche somehow manages to start with the 911 where they stick the engine way out behind the rear axle (high polar moment of inertia, poor front/rear weight distribution) and make it handle beautifully. VW cars also tend to have great suspension tuning. Being able to keep the weight low to the ground in the Tesla contributes to a low center of gravity and I imagine must really help enormously. Also the body under-tray is beautiful, like something you'd expect to see on a purpose built race car, probably helps a lot with the aerodynamics. I imagine more and more cars will get similar under-trays to improve aerodynamics and fuel efficiency. It's interesting there is strong anti-dive geometry built into the car, probably to avoid problems with throttle lift oversteer caused by inexperienced drivers. I wonder if the current Model S handling leaves anything to be desired when driven to it's absolute limits and how the car would handle with some of the anti-dive geometry removed. Removing this geometry is a common mod on some cars.
- ams6110 13y ago
  The first Tesla (Roadster) was built on a Lotus Elise chassis.
- josephlord 13y ago
  "Porsche somehow manages to start with the 911 where they stick the engine way out behind the rear axle (high polar moment of inertia, poor front/rear weight distribution) and make it handle beautifully." Actually there are some benefits to the arrangement. The high polar moment of inertia actually should make any spin slower to start and easier to catch than a mid engine arrangement. Under hard braking the weight shifts forwards so the weight distribution changes to more balanced than with other arrangements. Under power the weight is over the rear wheels for power out of the corner. A 911 behaves differently to other cars but I'm not sure the arrangement is actually worse in most dynamic scenarios. Understeer into the corners is the main dynamic weakness when pushed really hard and can be compensated for by trail braking into the corners. I guess you can get into trouble if you go into a corner too fast, panic brake and lose the rear end but if you are used to the set up you can make use of it. [I've only driven a 1980's 911 so maybe I'm over extrapolating to all rear engined cars and I've never tried a mid engined car. This book is really good at explaining how do get the most out of different weight distributions and has some fun stories (I've got the first edition but it probably isn't much different): http://www.amazon.co.uk/Porsche-High-performance-Driving-Handbook-Elford/dp/0760327548 http://www.amazon.co.uk/Porsche-High-performance-Driving-Han...]
stephengillie 13y ago
Those batteries sure take up a lot of space. I wonder what their physical volume is -- compared to a 15 gallon gasoline tank. The slide-out brake pads are a neat idea, but I'm wondering why, as the caliper still has to be removed during a brake change to pull off the rotor. Those aluminum pieces can't be cheap. Neither can the 4-piston brake calipers. Nor the armored underbelly. It's definitely performance-oriented.
- grecy 13y ago
  > The slide-out brake pads are a neat idea Every car I've ever worked on with calipers has slide out pads just like that... > as the caliper still has to be removed during a brake change to pull off the rotor Although pad changes are much more frequent than rotor changes, so it makes sense.
  - stephengillie 13y ago
    I've worked on many domestic and foreign cars, and I've never seen slide-out calipers. Most have a window so you can check pad and rotor thickness, but none have a slide-out section. Even if you don't replace the rotor, you still have to remove have it turned (grinding the contact surfaces flat again), so the new pads make good contact, instead of being pressed against the ridges and valleys left in the rotor from the worn-out pad. It just seems like a bit of over-engineering.
    - sbierwagen 13y ago
      This isn't quite my field, but I've been told you only need to have a rotor turned if it's warped or scored; otherwise you can just change out the pads, then apply the brakes heavily to conform them to the rotor surface.
      - grecy 13y ago
        That's exactly what I have always done.
dmmalam 13y ago
For comparison the McLaren MP4-12C [1] has probably the most trick setup you'd see this side of a early 90s Williams F1 car [2][3]. Notice on the 12C how the rebound/compression dampers from each corner are cross connected instead of a roll bar, and the z spring at the back to resist high downforce. Considering the Williams F1 active system was developed for the 1992 season, I'm kinda disappointed that no fully active system has ever hit a production car. The best we've seen is active damping on several cars. Bose had a pretty cool prototype [4], but never hit prod. The neat thing about electromagnetic damper/springs is that they can regen for a EV. If your unfamiliar with car mechanics, then this is a good serious of short video tutorials [5]. [1] http://www.edmunds.com/car-reviews/track-tests/2012-mclaren-mp4-12c-suspension-walkaround.html http://www.edmunds.com/car-reviews/track-tests/2012-mclaren-... [2] http://vimeo.com/22195303 http://vimeo.com/22195303 [3] http://scarbsf1.com/williams_active/WilliamsF1_ACTIVE_SUSPENSION_SYSTEMS.htm http://scarbsf1.com/williams_active/WilliamsF1_ACTIVE_SUSPEN... [4] http://www.bose.com/controller?url=/automotive/bose_suspension/index.jsp http://www.bose.com/controller?url=/automotive/bose_suspensi... [5] http://www.youtube.com/playlist?list=PLE067A7397E1AF108 http://www.youtube.com/playlist?list=PLE067A7397E1AF108
- incision 13y ago
  Also, for an overview of all sorts of automotive engineering for the curious, I highly recommend the Bosch Automotive Handbook [1]. 1: http://www.amazon.com/Bosch-Automotive-Handbook-Robert-GmbH/dp/0837616867 http://www.amazon.com/Bosch-Automotive-Handbook-Robert-GmbH/...
- ricardobeat 13y ago
  Ah, I remember seeing the Bose videos and wondering when it would hit the market. I'm also waiting for those airless spoked tires! Mercedes and BMW have their own active suspension systems that are standard in the high-end models, not sure if they look as magic as Bose's.
  - dmmalam 13y ago
    Pretty much all systems marketed as 'active' aren't really 'fully active'. Remember from mechanics/Differential Eqns, a suspension system is basically a damped harmonic oscillator. The two main constants are the springing and damping. The majority of cars just have electronically variable dampers. ie the same oem parts from bilstein/dephi/bosch with some silly marketing acronym on like Porsche PASM, MagneRide etc. Some have variable strength roll bars, but roll bars are really just a 'hack' anyway. Very few have used a variable springing system (Merc ABC). An air suspension can change springing and ride height, but's it's slow. In addition to low latency damping/springing adjustments/ride height, a fully active system in able to apply force into the suspension so the attitude of each corner is under complete software control, milli by milli. You can have a perfectly smooth ride, but no roll. All current non-active designs are a compromise between sporty and confort (high vs low springing/damping constants, and movements in attitude due to accelerating/braking/downforce/cornering/road surface. The main problem with fully active is that it uses quite a bit of power and is very complex. Here's some more info http://www.autozine.org/technical_school/suspension/tech_suspension3.htm http://www.autozine.org/technical_school/suspension/tech_sus...
tocomment 13y ago
Why is the regenerative braking limited to .25g? Even if they can't charge the battery faster than that, couldn't they dissipate the extra power some other way?
- kbuck 13y ago
  They effectively do dissipate the extra energy already - as heat, from the physical brakes. If they can't charge the battery faster than .25g of breaking would provide, there's no reason to put increased stress on the engine (it's much more expensive than a physical braking system).
- dmmalam 13y ago
  Some electric trains actually do this, they dump the energy as heat in a bank of resistors. The motor on a tesla is on the rear axel, but most braking power is dissipated from the front axel due to the weight transfer. The question is if you also had a front axel motor (like the Model X), how much regen could you do. I remember reading somewhere that induction motors don't regen that well at low RPMs, hence you need to supplement with friction brakes. Anyone with a better understanding care to comment; would it be possible to build a car with no friction brakes, just 100% regen? I suppose you could always apply a counter torque to the motor.
  - jstanley 13y ago
    "would it be possible to build a car with no friction brakes, just 100% regen?" No. The force provided by regenerative braking is proportional to your speed. Without friction, it would be impossible to reach 0 speed.
    - dmmalam 13y ago
      So the regen force would still exist (?), just it would be really small, and so taking a long time to fully stop. Would it be possible to apply a reverse torque to the electric motor to decelerate faster. For example, I'm thinking about a hypothetical race car that could have no traditional hydraulic braking system to save weight, a large amount unsprung.
Moto7451 13y ago
They have a Model S sans bodywork (just the lower frame, drivetrain, and suspension) at the Tesla Store here at the 3rd Street Promenade in Santa Monica. If you get a chance to stop in a Tesla Store, it's definitely worth it to see the intricacies of the suspension.
nwhitehead 13y ago
Reading about suspensions reminds me of the inerter (J-damper) [1] used in F1 racing. It was discovered by analogy with electrical circuits; it was the missing mechanical part corresponding to a capacitor. [1] http://en.wikipedia.org/wiki/Inerter_(mechanical_networks) http://en.wikipedia.org/wiki/Inerter_(mechanical_networks)
jleader 13y ago
"21x8.5 inches +40mm" on the wheels. Gotta love the auto industry's ambivalent relationship with the metric system! Too bad they didn't try a little harder, they probably could have expressed one of the dimensions in micro-furlongs.

260 points by dmmalam 13y ago

GotAnyMegadeth 13y ago

First thought was "Tesla have finally built an electric AT-ST!"

toomuchtodo 13y ago
Whoa. Whoa. Whoa. Mars first, then the electric AT-ST.
- omegant 13y ago
  You really need a AT-ST for mars exploration.
- Raphael 13y ago
  Why not both?
cobrausn 13y ago
I saw this post from Elon Musk yesterday after he mentioned an upcoming Tesla announcement. Almost thought the same thing. https://twitter.com/elonmusk/status/330053450261987328 https://twitter.com/elonmusk/status/330053450261987328
- alimoeeny 13y ago
  That must be related to SpaceX not Tesla,

heironimus 13y ago

Everybody thinks this is cool, but nobody (myself included) knows enough about car suspensions to comment!

cschmidt 13y ago
That must be how car types feel about a lot of HN articles. It did seems to be in a bit of a foreign language to me.
joshrotenberg 13y ago
Heh, same. I stopped after a few paragraphs. TL;DR Tesla Model S suspension is pretty neato.
untog 13y ago
I think it's a symptom of "Tesla = auto upvote on HN" syndrome. If this had been "Ford Focus S Suspension Walkaround" (or "Porche 911", for that matter) I doubt we'd be seeing it on the front page.
- enraged_camel 13y ago
  If all of your comments are this impressive, I guess I'm going to have to go with "untog = auto downvote" from now on.
  - chollida1 13y ago
    I'm not sure your comment was all that appropriate. I think untog's comment is spot on. There are lots of stories that seem to get upvoted for reasons other than their own merit. Pointing that out in this case is probably appropriate.
    - damon_c 13y ago
      He should have used a "==" though... Edit: Oh wait sorry no... I suck!
soss 13y ago
I work for a suspension manufacturer in the aftermarket industry for trucks, and a lot of it isn't that extraordinary. The air springs/shock absorber combination that you see there are becoming more normal across wider applications, while already coming equipped on luxury vehicles for quite some time now. The part that impresses me though is the steering knuckle (they comment on it towards the beginning), and its aluminum hollow construction. We build modified steering knuckles for trucks that provide additional lift height, but out of ductile iron in a cast mold, same as OEM specs/mfg process. So i'm kind of at a loss how they would make it hollowed out, while maintaining stability. Definitely expensive, i know billet aluminum knuckles for corvettes run about $1500/piece.

S_A_P 13y ago

When I look at this, I cannot how complicated it must be to build a world class automobile. Its all the more impressive that this is the first ground up(vs the roadster being an electric Lotus) car from a start up. Impressive indeed!

thoughtsimple 13y ago
More or less what I was thinking while reading the article. How do you even staff up for something like this? I guess a lot of recruiting in Detroit or something.
- krschultz 13y ago
  "Huibert Mees is the Chassis Systems Technical Fellow responsible for the design and engineering of the Model S chassis systems. He joined Tesla from Ford Motor Company, where he was responsible for all the chassis systems and vehicle structure of the Ford GT supercar. Huibert has been working in the automotive industry for over 20 years, and was responsible for the rear suspension design of the Lincoln LS and Jaguar S-type as well as numerous advanced chassis design concepts at Ford." Both SpaceX and Tesla are largely built on skimming the superstars out of the entrenched players. There are plenty of people that are really really good at their jobs at Boeing, Lockheed, Ford, General Dynamicsm, etc. They are generally underpaid, undervalued, and given little freedom relative to their skillset. But they stick around in those companies because that's where you have to be in order to work on really cool stuff like the Ford GT 40 or a space rocket. Tesla and SpaceX offer the same cool stuff to work on, without the crappy low-value coworkers that never get fired, legacy systems holding you back, and the opportunity to do things as you believe they should be done. This is part of why the old companies will have a hard time noncompeting. Not only are SpaceX and Tesla disrupting their business, but Elon Musk is stealing from their top tier talent pool that could defend against disruption.
  - tocomment 13y ago
    How specifically did he recruit them? Did he just show up at the factory one day? (I'm really interested in the detailed logistical steps of how one starts a brand new car company)

DEinspanjer 13y ago

Pretty pictures, but I just like how I can push the buttons on my screen and make the car go up and down. ;) Actually, when I first read this doc a couple of weeks back, it showed me the reason for something I had noticed. If I have my foot on the brake while changing the suspension level, I've noticed that when I let off the brakes, the wheels shift a bit. Turns out that for the front tires, it doesn't lift and lower straight up and down. There is a bit of horizontal motion as well.

alimoeeny 13y ago

So HN Tesla owners, how happy are you with the car itself, not considering the ideas behind electric cars and what not, just with the car and driving experience and charging, worrying about running out of juice ...?

tlb 13y ago
It's fantastic. Best thing I've ever driven, regardless of environmental impact. It's silent and odorless, responds instantly and precisely, and it seats 5 adults + 2 kids comfortably. A niche benefit: I live in the mountains and it handles going down much better than gas cars, where you have to downshift and use engine braking to avoid burning the brakes. It uses 12 miles of range going up, and gains 4 back going down so the average is close to a flat road of the same distance.
- TallGuyShort 13y ago
  I'm curious about how it handles downhills. I would've thought that without engine braking you would have to rely exclusively on the brakes and would thus burn them up even more. Does the Tesla have another mechanism? Or just insanely efficient brakes?
  - furyg3 13y ago
    It has regenerative breaking, which is effectively 'engine breaking'. Engine breaking on an electric car puts electricity back into the batteries. The brakes you see in the photos are for breaking, hard (full stop, quick stop, racing).
    - Dylan16807 13y ago
      braking.
- laacz 13y ago
  5 adults + 2 kids comfortably? In a car with max 5 seatbelts?

deadfall 13y ago

Has anyone wrecked one of them yet? I bet trying to get it fixed would be ridiculous.

pyre 13y ago
How much would Google self-driving car equipment reduce the time between charges? I imagine that such a system would mean fewer accidents.

NDizzle 13y ago

I'll never look at my Galant VR4's suspension the same again. I knew it was old and bad, but this really drives that point home.

cake 13y ago

Pretty amazing yet totally normal not to see any exhaust system that I'm used to see on every car ;-)

becauseracecar 13y ago

Car suspension tuning is a very subtle and difficult black art. It's all about what's happening dynamically in response to transient inputs (go around a corner, hit a bump, etc.). I believe Lotus does a lot of engineering consulting helping other manufacturers dial in suspensions. I wouldn't be surprised if Tesla had them consult. Even some of the big car companies have trouble dialing in suspension on their own (I'm looking at you underdamped Japanese cars). European brands tend to be really good at this, and can take the same raw materials that everyone else is working with and create superior setups. Porsche somehow manages to start with the 911 where they stick the engine way out behind the rear axle (high polar moment of inertia, poor front/rear weight distribution) and make it handle beautifully. VW cars also tend to have great suspension tuning. Being able to keep the weight low to the ground in the Tesla contributes to a low center of gravity and I imagine must really help enormously. Also the body under-tray is beautiful, like something you'd expect to see on a purpose built race car, probably helps a lot with the aerodynamics. I imagine more and more cars will get similar under-trays to improve aerodynamics and fuel efficiency. It's interesting there is strong anti-dive geometry built into the car, probably to avoid problems with throttle lift oversteer caused by inexperienced drivers. I wonder if the current Model S handling leaves anything to be desired when driven to it's absolute limits and how the car would handle with some of the anti-dive geometry removed. Removing this geometry is a common mod on some cars.

ams6110 13y ago
The first Tesla (Roadster) was built on a Lotus Elise chassis.
josephlord 13y ago
"Porsche somehow manages to start with the 911 where they stick the engine way out behind the rear axle (high polar moment of inertia, poor front/rear weight distribution) and make it handle beautifully." Actually there are some benefits to the arrangement. The high polar moment of inertia actually should make any spin slower to start and easier to catch than a mid engine arrangement. Under hard braking the weight shifts forwards so the weight distribution changes to more balanced than with other arrangements. Under power the weight is over the rear wheels for power out of the corner. A 911 behaves differently to other cars but I'm not sure the arrangement is actually worse in most dynamic scenarios. Understeer into the corners is the main dynamic weakness when pushed really hard and can be compensated for by trail braking into the corners. I guess you can get into trouble if you go into a corner too fast, panic brake and lose the rear end but if you are used to the set up you can make use of it. [I've only driven a 1980's 911 so maybe I'm over extrapolating to all rear engined cars and I've never tried a mid engined car. This book is really good at explaining how do get the most out of different weight distributions and has some fun stories (I've got the first edition but it probably isn't much different): http://www.amazon.co.uk/Porsche-High-performance-Driving-Handbook-Elford/dp/0760327548 http://www.amazon.co.uk/Porsche-High-performance-Driving-Han...]

stephengillie 13y ago

Those batteries sure take up a lot of space. I wonder what their physical volume is -- compared to a 15 gallon gasoline tank. The slide-out brake pads are a neat idea, but I'm wondering why, as the caliper still has to be removed during a brake change to pull off the rotor. Those aluminum pieces can't be cheap. Neither can the 4-piston brake calipers. Nor the armored underbelly. It's definitely performance-oriented.

grecy 13y ago
> The slide-out brake pads are a neat idea Every car I've ever worked on with calipers has slide out pads just like that... > as the caliper still has to be removed during a brake change to pull off the rotor Although pad changes are much more frequent than rotor changes, so it makes sense.
- stephengillie 13y ago
  I've worked on many domestic and foreign cars, and I've never seen slide-out calipers. Most have a window so you can check pad and rotor thickness, but none have a slide-out section. Even if you don't replace the rotor, you still have to remove have it turned (grinding the contact surfaces flat again), so the new pads make good contact, instead of being pressed against the ridges and valleys left in the rotor from the worn-out pad. It just seems like a bit of over-engineering.
  - sbierwagen 13y ago
    This isn't quite my field, but I've been told you only need to have a rotor turned if it's warped or scored; otherwise you can just change out the pads, then apply the brakes heavily to conform them to the rotor surface.
    - grecy 13y ago
      That's exactly what I have always done.

dmmalam 13y ago

For comparison the McLaren MP4-12C [1] has probably the most trick setup you'd see this side of a early 90s Williams F1 car [2][3]. Notice on the 12C how the rebound/compression dampers from each corner are cross connected instead of a roll bar, and the z spring at the back to resist high downforce. Considering the Williams F1 active system was developed for the 1992 season, I'm kinda disappointed that no fully active system has ever hit a production car. The best we've seen is active damping on several cars. Bose had a pretty cool prototype [4], but never hit prod. The neat thing about electromagnetic damper/springs is that they can regen for a EV. If your unfamiliar with car mechanics, then this is a good serious of short video tutorials [5]. [1] http://www.edmunds.com/car-reviews/track-tests/2012-mclaren-mp4-12c-suspension-walkaround.html http://www.edmunds.com/car-reviews/track-tests/2012-mclaren-... [2] http://vimeo.com/22195303 http://vimeo.com/22195303 [3] http://scarbsf1.com/williams_active/WilliamsF1_ACTIVE_SUSPENSION_SYSTEMS.htm http://scarbsf1.com/williams_active/WilliamsF1_ACTIVE_SUSPEN... [4] http://www.bose.com/controller?url=/automotive/bose_suspension/index.jsp http://www.bose.com/controller?url=/automotive/bose_suspensi... [5] http://www.youtube.com/playlist?list=PLE067A7397E1AF108 http://www.youtube.com/playlist?list=PLE067A7397E1AF108

incision 13y ago
Also, for an overview of all sorts of automotive engineering for the curious, I highly recommend the Bosch Automotive Handbook [1]. 1: http://www.amazon.com/Bosch-Automotive-Handbook-Robert-GmbH/dp/0837616867 http://www.amazon.com/Bosch-Automotive-Handbook-Robert-GmbH/...
ricardobeat 13y ago
Ah, I remember seeing the Bose videos and wondering when it would hit the market. I'm also waiting for those airless spoked tires! Mercedes and BMW have their own active suspension systems that are standard in the high-end models, not sure if they look as magic as Bose's.
- dmmalam 13y ago
  Pretty much all systems marketed as 'active' aren't really 'fully active'. Remember from mechanics/Differential Eqns, a suspension system is basically a damped harmonic oscillator. The two main constants are the springing and damping. The majority of cars just have electronically variable dampers. ie the same oem parts from bilstein/dephi/bosch with some silly marketing acronym on like Porsche PASM, MagneRide etc. Some have variable strength roll bars, but roll bars are really just a 'hack' anyway. Very few have used a variable springing system (Merc ABC). An air suspension can change springing and ride height, but's it's slow. In addition to low latency damping/springing adjustments/ride height, a fully active system in able to apply force into the suspension so the attitude of each corner is under complete software control, milli by milli. You can have a perfectly smooth ride, but no roll. All current non-active designs are a compromise between sporty and confort (high vs low springing/damping constants, and movements in attitude due to accelerating/braking/downforce/cornering/road surface. The main problem with fully active is that it uses quite a bit of power and is very complex. Here's some more info http://www.autozine.org/technical_school/suspension/tech_suspension3.htm http://www.autozine.org/technical_school/suspension/tech_sus...

tocomment 13y ago

Why is the regenerative braking limited to .25g? Even if they can't charge the battery faster than that, couldn't they dissipate the extra power some other way?

kbuck 13y ago
They effectively do dissipate the extra energy already - as heat, from the physical brakes. If they can't charge the battery faster than .25g of breaking would provide, there's no reason to put increased stress on the engine (it's much more expensive than a physical braking system).
dmmalam 13y ago
Some electric trains actually do this, they dump the energy as heat in a bank of resistors. The motor on a tesla is on the rear axel, but most braking power is dissipated from the front axel due to the weight transfer. The question is if you also had a front axel motor (like the Model X), how much regen could you do. I remember reading somewhere that induction motors don't regen that well at low RPMs, hence you need to supplement with friction brakes. Anyone with a better understanding care to comment; would it be possible to build a car with no friction brakes, just 100% regen? I suppose you could always apply a counter torque to the motor.
- jstanley 13y ago
  "would it be possible to build a car with no friction brakes, just 100% regen?" No. The force provided by regenerative braking is proportional to your speed. Without friction, it would be impossible to reach 0 speed.
  - dmmalam 13y ago
    So the regen force would still exist (?), just it would be really small, and so taking a long time to fully stop. Would it be possible to apply a reverse torque to the electric motor to decelerate faster. For example, I'm thinking about a hypothetical race car that could have no traditional hydraulic braking system to save weight, a large amount unsprung.

Moto7451 13y ago

They have a Model S sans bodywork (just the lower frame, drivetrain, and suspension) at the Tesla Store here at the 3rd Street Promenade in Santa Monica. If you get a chance to stop in a Tesla Store, it's definitely worth it to see the intricacies of the suspension.

nwhitehead 13y ago

Reading about suspensions reminds me of the inerter (J-damper) [1] used in F1 racing. It was discovered by analogy with electrical circuits; it was the missing mechanical part corresponding to a capacitor. [1] http://en.wikipedia.org/wiki/Inerter_(mechanical_networks) http://en.wikipedia.org/wiki/Inerter_(mechanical_networks)

jleader 13y ago

"21x8.5 inches +40mm" on the wheels. Gotta love the auto industry's ambivalent relationship with the metric system! Too bad they didn't try a little harder, they probably could have expressed one of the dimensions in micro-furlongs.