4 ms·

I think there's an agreement on the goal. I believe the poster is asking why do we need another sensor to achieve that goal? We already have a speedometer base

I think there's an agreement on the goal. I believe the poster is asking why do we need another sensor to achieve that goal? We already have a speedometer based on wheel motion. A trivial computation gives acceleration.

willis936 3y ago
What do you save by not having that sensor? Nothing. What do you lose by not having that sensor? The ability for the system to perform its requirements. I'm assuming you read the context of loss of traction being a requirement.
- WorldMaker 3y ago
  Relatedly, having a dedicated accelerometer sensor is a baseline dependency of many of other modern features like cross-comparing compass headings and GPS for map heading information (much less any of the Level 2+ "self-driving" mechanics). Most cars likely want one, anyway, even in base models. It's one of the cheapest sensors in a suite of increasingly standard sensors (in almost any form factor of device, not just cars, but phones/watches/toasters/etc).
- oceanplexian 3y ago
  > What do you save by not having that sensor? A $9000 repair bill in 6 years when your mechanic tells you “Sorry your car is immobilized and won’t start, the deceleration brake light sensor went and we need to remove the motor and 3/4 of the wiring harness to replace it”. And for anyone who thinks I’m being sarcastic, try owning a BMW or an Audi and you’ll know it’s the truth.
  - Turskarama 3y ago
    The problem there is owning an Audi or BMW, not the sensor itself.
  - willis936 3y ago
    A MEMS accelerometer is pennies. If it is critical then add redundancy and don't accept single fault tolerance. If it is optional or the signal can be estimated from other sources with acceptable error then fail gracefully. This is honestly simple stuff. Accepting less from manufacturers is a bad deal.
    - NikolaNovak 3y ago
      >>A MEMS accelerometer is pennies. That's an dishonest argument (perhaps not intentionally). NOTHING is "pennies" to a consumer when it comes to repairing a vehicle. More frequently, you pay $1,500 in labour and parts to replace something that costs "pennies" in some bulk manufacturer wholesale catalogue. Modern cars are getting more and more awesome, in terms of safety and convenience; but the sticker shock when going to dealership for repair is also becoming bigger and bigger, and it absolutely is intertwined with the significant effort to make 3rd party or even self-repair difficult to impossible. So again, IFF this is an easily replaceable part that is thought-through and cross-checked intelligently with other existing sensors, brilliant. But can you at any level understand my skepticism that any of these are true? :)
      - willis936 3y ago
        I'm not talking about the price of maintenance but the cost of manufacture. Please give generous interpretations rather than ones that fit an argumentative narrative. Assuming the topic is cost of repair rather than manufacture makes no sense when we're talking about system engineering to accomplish functional requirements.
  - mulmen 3y ago
    I have owned a troublesome 2010 BMW for 8 years now. No individual repair has been over $2,700.00. Most are closer to $1,500. I was quoted (by a dealer) $15,000.00 for engine repair once but it turned out to be a spark plug. $9,000.00 sounds like a dealer quote. Find a good independent shop.
hef19898 3y ago
Because tires can block, not all tire turn at the same speed all the time, because redundancy is a good thing... There a lot of reasons. And if the number of sensors in your car bother you, well, the early 80s, with carbs and without ABS, are last model years you can buy.
- vdqtp3 3y ago
  Many late 80s/very early 90s fuel injection vehicles have shockingly low numbers of electronic sensors also. MAP, O2, TPS, CPS is all you really need. Some of them are even analog.
- NikolaNovak 3y ago
  No need to get snarky :) Redundancy is a good thing. Do we feel manufacturers are cross-checking accelerometer with the speedometer? If not, there is no redundancy gained. On the other hand, if your speedometer is faulty, or not working, you'll know pretty fast. If your dedicated accelerometer is faulty, you might have no idea what your brake lights are doing in the back. Dunno; it just feels "we need to know acceleration, let's add an accelerometer" is a non-imaginative, add-cost, add-complexity idea. Again, if we think ABS and speedometer and the new accelerometer are being cross-checked and sanity-checked, awesome, but I'm just a bit cynical of that, compared to adding the 3rd thing to do the same thing.
  - Sohcahtoa82 3y ago
    > add-complexity idea You're on a forum where a lot of people think Kubernetes is a good idea. ;-)
    - hef19898 3y ago
      No idea what Kubernetes are, and I am serious here, since I am no software dev. On the hardware side of things, there is redundancy and complexity. Those two might look similar on the surface, they are totally different beasts so.
      - 3y ago

willis936 3y ago

What do you save by not having that sensor? Nothing. What do you lose by not having that sensor? The ability for the system to perform its requirements. I'm assuming you read the context of loss of traction being a requirement.

WorldMaker 3y ago
Relatedly, having a dedicated accelerometer sensor is a baseline dependency of many of other modern features like cross-comparing compass headings and GPS for map heading information (much less any of the Level 2+ "self-driving" mechanics). Most cars likely want one, anyway, even in base models. It's one of the cheapest sensors in a suite of increasingly standard sensors (in almost any form factor of device, not just cars, but phones/watches/toasters/etc).
oceanplexian 3y ago
> What do you save by not having that sensor? A $9000 repair bill in 6 years when your mechanic tells you “Sorry your car is immobilized and won’t start, the deceleration brake light sensor went and we need to remove the motor and 3/4 of the wiring harness to replace it”. And for anyone who thinks I’m being sarcastic, try owning a BMW or an Audi and you’ll know it’s the truth.
- Turskarama 3y ago
  The problem there is owning an Audi or BMW, not the sensor itself.
- willis936 3y ago
  A MEMS accelerometer is pennies. If it is critical then add redundancy and don't accept single fault tolerance. If it is optional or the signal can be estimated from other sources with acceptable error then fail gracefully. This is honestly simple stuff. Accepting less from manufacturers is a bad deal.
  - NikolaNovak 3y ago
    >>A MEMS accelerometer is pennies. That's an dishonest argument (perhaps not intentionally). NOTHING is "pennies" to a consumer when it comes to repairing a vehicle. More frequently, you pay $1,500 in labour and parts to replace something that costs "pennies" in some bulk manufacturer wholesale catalogue. Modern cars are getting more and more awesome, in terms of safety and convenience; but the sticker shock when going to dealership for repair is also becoming bigger and bigger, and it absolutely is intertwined with the significant effort to make 3rd party or even self-repair difficult to impossible. So again, IFF this is an easily replaceable part that is thought-through and cross-checked intelligently with other existing sensors, brilliant. But can you at any level understand my skepticism that any of these are true? :)
    - willis936 3y ago
      I'm not talking about the price of maintenance but the cost of manufacture. Please give generous interpretations rather than ones that fit an argumentative narrative. Assuming the topic is cost of repair rather than manufacture makes no sense when we're talking about system engineering to accomplish functional requirements.
- mulmen 3y ago
  I have owned a troublesome 2010 BMW for 8 years now. No individual repair has been over $2,700.00. Most are closer to $1,500. I was quoted (by a dealer) $15,000.00 for engine repair once but it turned out to be a spark plug. $9,000.00 sounds like a dealer quote. Find a good independent shop.

hef19898 3y ago

Because tires can block, not all tire turn at the same speed all the time, because redundancy is a good thing... There a lot of reasons. And if the number of sensors in your car bother you, well, the early 80s, with carbs and without ABS, are last model years you can buy.

vdqtp3 3y ago
Many late 80s/very early 90s fuel injection vehicles have shockingly low numbers of electronic sensors also. MAP, O2, TPS, CPS is all you really need. Some of them are even analog.
NikolaNovak 3y ago
No need to get snarky :) Redundancy is a good thing. Do we feel manufacturers are cross-checking accelerometer with the speedometer? If not, there is no redundancy gained. On the other hand, if your speedometer is faulty, or not working, you'll know pretty fast. If your dedicated accelerometer is faulty, you might have no idea what your brake lights are doing in the back. Dunno; it just feels "we need to know acceleration, let's add an accelerometer" is a non-imaginative, add-cost, add-complexity idea. Again, if we think ABS and speedometer and the new accelerometer are being cross-checked and sanity-checked, awesome, but I'm just a bit cynical of that, compared to adding the 3rd thing to do the same thing.
- Sohcahtoa82 3y ago
  > add-complexity idea You're on a forum where a lot of people think Kubernetes is a good idea. ;-)
  - hef19898 3y ago
    No idea what Kubernetes are, and I am serious here, since I am no software dev. On the hardware side of things, there is redundancy and complexity. Those two might look similar on the surface, they are totally different beasts so.
    - 3y ago