Remember that you still have 4000 lbs of mass to stop so even with regen when you need to stop you will need pretty substantial brakes.
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Sure but with the Roadster, max regen is say 40 kW. If it weights 2700 lbs and is going 60 mph, that's about 440 kJ of energy to shed. So 60 to 0 mph on regen alone would take about 11 seconds.
(Anyone know the tested stopping time or distance of the Roadster?) If instead you stand on the brakes and it goes from 60 to 0 in 2 seconds, then regen's got 80 kJ and the remaining 360 kJ went to the brakes. That's about 82% for the friction brakes. Though at some point it was stated that regen cuts out during ABS and TC events, so maybe it's even more than that. Anyhow, clearly the more aggressive the stop, the more energy goes into the friction brakes.
Ok so 60 to 0 mph in 118 ft is about 2.7 seconds (assuming constant acceleration).
That gives 107 kilojoules to regen assuming constant max at 40 kW, leaving about 76% for the friction brakes. Though I suspect the regen behavior is more complicated than that.
That gives 107 kilojoules to regen assuming constant max at 40 kW, leaving about 76% for the friction brakes. Though I suspect the regen behavior is more complicated than that.
JRP3
Hyperactive Member
So even in a rare panic stop regen is taking at least 20% of the braking load, and in normal driving much more than that. I guess things get complicated when regen is shut off with a full pack, then it's all brakes. However since both panic stops and no regen are rare I think the brakes could be downsized some and switched to aluminum since they don't need the durability to stand up to full braking force repeatedly.
Has anyone watched the kW gauge in a 2.5 during a "panic stop" (hopefully under controlled conditions!) and checked to see if full regen persists throughout?
In the Leaf, I see regen ease off as I push the brake pedal hard. Maybe it has something to do with the way ABS works, and they need to transition back to friction brakes only for the hardest stops?
The Roadster may be entirely different from the Leaf, but the Leaf behavior suggests that there may be reason to not always have full regen even when braking hard.
Note, the Leaf is FWD, and the Roadster RWD, so it is little bit of an "apples to oranges" comparison.
In the Leaf, I see regen ease off as I push the brake pedal hard. Maybe it has something to do with the way ABS works, and they need to transition back to friction brakes only for the hardest stops?
The Roadster may be entirely different from the Leaf, but the Leaf behavior suggests that there may be reason to not always have full regen even when braking hard.
Note, the Leaf is FWD, and the Roadster RWD, so it is little bit of an "apples to oranges" comparison.
TXjak
Owner/Investor/Advocate
firmware
Please elaborate on the security implications, I'd like to understand them. If you have any references, links would be appreciated.
Please elaborate on the security implications, I'd like to understand them. If you have any references, links would be appreciated.
Protocols can be cracked. Anything subject to over the air updates is vulnerable. A malicious hacker could try to screw up your car by uploading an new OS or at the very least execute a denial of service attack causing whatever havoc with the system. That said, I believe OnStar has the ability to do things like remotely start cars and such, or so movies have lead me to believe
, so I'm guessing this has been a solved problem. The question is, is there a government standard for it? I know for medical devices there are standards you have to meet to prove your device can't be tampered with by frequency bursts screwing with the electronics.
bonnie
I play a nice person on twitter.
Yes, both electromagnetic emissions and immunity standards for medical devices - and for anything that can access/interact with (or be accessed by) a remote database/other software, a detailed risk assessment and testing showing that the software can withstand attacks, that the interaction cannot harm the device, etc. I often wish electronic voting machines, cars, etc were subject to the same standards. It's mostly risk-driven ... for instance, if a power supply fails on a piece of lab equipment testing for a non-critical value, that power supply is not as heavily tested. But the same power supply on a ventilator for home use will not only be heavily tested, a design response to make it fail safe will be required ... because if that power supply fails, someone will likely die. Puts the testing where it has the biggest impact on outcome.
gg_got_a_tesla
Model S: VIN 65513, Model 3: VIN 1913
All remote communication with cars (OnStar as well) happens over your good ol' cellular networks under the covers. So, OTA communication/upgrades will be as secure as your cell phone call / data connection.
SByer
'08 #383
That said, I believe OnStar has the ability to do things like remotely start cars and such, or so movies have lead me to believe
I just think it hasn't really been concentrated on. I have no idea what firewall the OnStar OTA connection is behind - because the cell network is certainly vulnerable, and the car's internal networks aren't secure either (http://www.autosec.org/faq.html). If they didn't design the integration into the car's systems from the viewpoint of 'it will be hacked', well...
I'm not saying it couldn't be done, at least to a reasonable security level. See the verified boot section of the Chromium OS Security Overview. But you really have to plan for it very early in the process.
That's not necessarily true. There's been a tremendous amount of work about how to do secure communication over insecure channels. This is, for instance, how software vendors are able to securely send updates over the (very insecure) internet. Essentially, they digitally sign the updates and then have the receiving end reject anything that's not properly signed. Then, as long as the signing algorithm isn't broken and the private key isn't compromised, tampering with data as it's in transmission will just result in a failed update, not a malicious patch being applied.
There are other techniques that would allow, for instance, transmitting logs in such a way that they couldn't be read by someone in the middle, even if he can alter the traffic. This is how SSL/https works.
I have no idea whether Tesla did this properly, however. I hope they're more computer savvy than the traditional manufacturers, but that's just a hope.
OnStar's a joke. My friend Stefan Savage, a professor at UCSD, broke it a while ago and showed how he could do roughly anything to any car he wanted. [Edit: Stefan in fact never made such a claim; see my later post.]
http://www.autosec.org/pubs/cars-oakland2010.pdf
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TXjak
Owner/Investor/Advocate
firmware updates
Well, if the dealer is located hundreds of miles beyond your car's range, you might have a different opinion.
Well, if the dealer is located hundreds of miles beyond your car's range, you might have a different opinion.
That's the case with any recall/fix issue on a car. If Tesla doesn't have repair option in all major cities, then I won't be getting one. Anyone living in the boonies has issues with car repair in general and this one more thing isn't a big deal. You certainly don't want your car updated all the time OTA. History with other regularly updated devices shows that's a bad plan (various PS3, iphone, etc, broken by updates).
TXjak
Owner/Investor/Advocate
Aside from the distance problem (perhaps you haven't heard of the "Tesla Ranger" mobile service team), they could easily make the firmware update procedure only happen if a security procedure (key, password, etc.) were followed in the car at a standstill.
Tesla Rangers: Coming to your neighborhood: Tesla Mobile Service Rangers make house calls | Blog | Tesla Motors
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Stefan wrote to me and asked me to say that he never claimed to "break" OnStar. I was presenting my own interpretation. You should read his papers to see exactly what he did and didn't do.
racevpr
Member
I've had my 2011 Roadster over two years now, and I noticed my ability to turn on the security is disable as soon as the "Maintenance Required" message is displayed every year.
Last year the car was still under warranty, and I had Tesla do the annual which restored the security arm feature. This year it is out of warranty and I plan on doing my own annual,
and a wondering how to restore the security arm feature.
Last year the car was still under warranty, and I had Tesla do the annual which restored the security arm feature. This year it is out of warranty and I plan on doing my own annual,
and a wondering how to restore the security arm feature.
