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I don’t know the details… but my dad was a rural mail carrier for awhile, and the roughness of the driving they do is difficult to understand. Rural carriers o

I don’t know the details… but my dad was a rural mail carrier for awhile, and the roughness of the driving they do is difficult to understand. Rural carriers operate their own vehicles. The wear and tear was nuts… for example we would change brake pads every 2-3 weeks. I think USPS wants to operate vehicles for many years. I’d guess they may have determined that the regen braking or batteries for hybrid couldn’t sustain the harsh conditions within the operating cost envelope.

blagie 2y ago
FWIW: Regen breaking has a lot less wear than normal breaking. Normal breaking needs to convert the energy into heat through friction, which wears things down. Storing that energy means nothing has to be worn down. For an application like this one, it's possible to use capacitors instead of batteries for a near-infinite lifespan too. A supercapacitor won't store enough charge for driving any sane distance, but for one stop and acceleration (regen breaking), it's perfectly adequate.
- ygra 2y ago
  Buses sometimes have flywheels for that purpose, too. Although that also has weight and space, so may not be worthwhile for a vehicle where both are needed for its primary purpose.
  - blagie 2y ago
    Interesting. Where I live, the stops are too long for a flywheel to make any sense. The postal worker will usually deliver to a mailbox serving several houses, and will often have packages. Perhaps in the suburbs, where there are individual mailboxes for each house, it could work well. Still, if we take 8000 lbs, times (10mph)^2, and divide by 2, we get about 35kJ. First supercap which came up in a Google search does 1kJ for <$10. So it's like $350, and will have far less maintenance and better efficiency than a flywheel. If we do 20mph -- although goodness knows mail trucks here don't go nearly that fast for start-and-stop between mailboxes -- it's $1400. Even 40mpg would be around $5k. So it's very cheap (and, electronically, very easy), at least for this use case. For highway speeds, it'd be a different story.
windowsrookie 2y ago
2-3 weeks to change brake pads seems incredibly excessive and to be honest I don't believe it. I delivered Pizzas for more than 5 years, and my brake pads would still last 20,000+ miles.

blagie 2y ago

FWIW: Regen breaking has a lot less wear than normal breaking. Normal breaking needs to convert the energy into heat through friction, which wears things down. Storing that energy means nothing has to be worn down. For an application like this one, it's possible to use capacitors instead of batteries for a near-infinite lifespan too. A supercapacitor won't store enough charge for driving any sane distance, but for one stop and acceleration (regen breaking), it's perfectly adequate.

ygra 2y ago
Buses sometimes have flywheels for that purpose, too. Although that also has weight and space, so may not be worthwhile for a vehicle where both are needed for its primary purpose.
- blagie 2y ago
  Interesting. Where I live, the stops are too long for a flywheel to make any sense. The postal worker will usually deliver to a mailbox serving several houses, and will often have packages. Perhaps in the suburbs, where there are individual mailboxes for each house, it could work well. Still, if we take 8000 lbs, times (10mph)^2, and divide by 2, we get about 35kJ. First supercap which came up in a Google search does 1kJ for <$10. So it's like $350, and will have far less maintenance and better efficiency than a flywheel. If we do 20mph -- although goodness knows mail trucks here don't go nearly that fast for start-and-stop between mailboxes -- it's $1400. Even 40mpg would be around $5k. So it's very cheap (and, electronically, very easy), at least for this use case. For highway speeds, it'd be a different story.

windowsrookie 2y ago

2-3 weeks to change brake pads seems incredibly excessive and to be honest I don't believe it. I delivered Pizzas for more than 5 years, and my brake pads would still last 20,000+ miles.