4 ms·

Or you could do what they did on Apollo (forget if it was the CM or LM). They had the problem of measuring how much was in a tank, but the tank was in 0G, so a

Or you could do what they did on Apollo (forget if it was the CM or LM). They had the problem of measuring how much was in a tank, but the tank was in 0G, so a float is no good. The proposed solution was some sophisticated radiation based thing where they measured the attenuation of some radioactive source through the tank. This wound up being highly complex, and the solution was simply to have a reserve tank. When the main tank ran out, you knew you had exactly the amount in the reserve tank.

rbanffy 6y ago
Another possible solution is to measure how much fuel (or energy) got in and how much is getting out. You know the nominal capacity and you know the flow rate.
- cogman10 6y ago
  You'd have to account for charge losses (Some energy ends up just being heat while charging) but that could probably be simply guestimated on battery temp while charging and some constant factor. For example, assume a 90% charge efficiency for a battery at 20C... or whatever makes sense.
  - deleted 6y ago
    [deleted]
- Cerium 6y ago
  That technique is called Coulomb counting and is the standard way of giving a precise battery charge percentage for lithium based batteries. The battery capacity estimate is improved over time based on the previous observed amounts of energy to enter or leave the battery.
pokoleo 6y ago
They could've put a variable-sized bladder in the tank, and measured the internal pressure. Right?
brianpan 6y ago
This is the solution used on motorcycles (which don't usually have fuel gauges). There's only one tank, but in the normal position you get fuel only to a certain depth. As you're riding along, if you notice the engine running out of fuel, you reach down and flip the fuel switch and you have access to a little more fuel (and you know to head to a gas station soonish).
- manfredo 6y ago
  For motorcycles people often just use the trip odometer to estimate fuel used. Interestingly, this is similar to coulomb counting which is one of the more common methods of state of charge tracking. Technically coulomb counting would be more analogous to measuring the amount of fuel being pumped out of the tank.
- m463 6y ago
  downsides: - when you're in heavy complicated traffic and the engine starts cutting out - when you forget to flip the switch back after filling up - you more modern motorcycle with a "reserve" indicator below the speedometer (which is below your field of vision when riding and you don't notice)
- boardwaalk 6y ago
  Just for correctness: A vast majority of new motorcycles for quite a while have had fuel gauges. There are only a few brands who are obtuse about it (e.g. Aprilia).
  - the-dude 6y ago
    But I bet they still have a reserve and a 3-way fuel knob ( closed, main, reserve ).
    - barrkel 6y ago
      On fuel injected bikes, the fuel switch (on/off only) is on the fuel pump, generally bolted to the underneath of the tank, and not reachable while riding.
japanuspus 6y ago
Same trick is used on some external tanks for outboard engines: the tank has a raised separator in the bottom so that reserve fuel will be caught away from the engine intake. To access the reserve fuel you need to briefly tilt the tank. See e.g. https://imgur.com/a/9LsrjIR https://imgur.com/a/9LsrjIR

rbanffy 6y ago

Another possible solution is to measure how much fuel (or energy) got in and how much is getting out. You know the nominal capacity and you know the flow rate.

cogman10 6y ago
You'd have to account for charge losses (Some energy ends up just being heat while charging) but that could probably be simply guestimated on battery temp while charging and some constant factor. For example, assume a 90% charge efficiency for a battery at 20C... or whatever makes sense.
- deleted 6y ago
  [deleted]
Cerium 6y ago
That technique is called Coulomb counting and is the standard way of giving a precise battery charge percentage for lithium based batteries. The battery capacity estimate is improved over time based on the previous observed amounts of energy to enter or leave the battery.

pokoleo 6y ago

They could've put a variable-sized bladder in the tank, and measured the internal pressure. Right?

brianpan 6y ago

This is the solution used on motorcycles (which don't usually have fuel gauges). There's only one tank, but in the normal position you get fuel only to a certain depth. As you're riding along, if you notice the engine running out of fuel, you reach down and flip the fuel switch and you have access to a little more fuel (and you know to head to a gas station soonish).

manfredo 6y ago
For motorcycles people often just use the trip odometer to estimate fuel used. Interestingly, this is similar to coulomb counting which is one of the more common methods of state of charge tracking. Technically coulomb counting would be more analogous to measuring the amount of fuel being pumped out of the tank.
m463 6y ago
downsides: - when you're in heavy complicated traffic and the engine starts cutting out - when you forget to flip the switch back after filling up - you more modern motorcycle with a "reserve" indicator below the speedometer (which is below your field of vision when riding and you don't notice)
boardwaalk 6y ago
Just for correctness: A vast majority of new motorcycles for quite a while have had fuel gauges. There are only a few brands who are obtuse about it (e.g. Aprilia).
- the-dude 6y ago
  But I bet they still have a reserve and a 3-way fuel knob ( closed, main, reserve ).
  - barrkel 6y ago
    On fuel injected bikes, the fuel switch (on/off only) is on the fuel pump, generally bolted to the underneath of the tank, and not reachable while riding.

japanuspus 6y ago

Same trick is used on some external tanks for outboard engines: the tank has a raised separator in the bottom so that reserve fuel will be caught away from the engine intake. To access the reserve fuel you need to briefly tilt the tank. See e.g. https://imgur.com/a/9LsrjIR https://imgur.com/a/9LsrjIR