Any steam power experts out there. My robot needs you.

[Flyndaran]

I first wanted him to be powered by springs. That couldn't give him more than a half hour of output before refueling.

So on to steam power. Using a 1.31 KW output as a target, how small could I make a steam engine? Assuming really really high quality steel?

What kind of energy densities could I get from a steam accumulator?

[starslayer]

I posted in your other thread; have you considered a Stirling engine powered by some hot and near-inexhaustible source (magic, essential fuel, big ball of radiation) then it'd be able to be effectively sealed so long as it could keep radiating the heat.

Even if you don't go for a Stirling design, the actual energy density for charcoal, or even normal coal, is pretty low; at 1.3 kw consumption your poor bot is going to need to be dragging around a cart to keep refilling without some sort of non-exaustable fuel source (cornucopia item; charcoal blocks?)

In either case though I think your going to be dealing with a VERY large robot just to accommodate the engine.

Here is a 1kw Stirling generator:
http://www.cnccookbook.com/CCStirlingGenerator.htm

[Flyndaran]

The chart I found equate one pound of charcoal to 29 MJ per kilogram. I figured that to be over 3000 Calories. Does a steam engine have to run at full power all the time?

[johndallman]

Originally Posted by Flyndaran

Does a steam engine have to run at full power all the time?

No, but running them at lower power is complicated. If you just use less fuel in the same boiler, you're running at lower temperature, which means you have less efficiency and lower pressure (which probably reduces a robot's ST), and means you're using something like 75% of the fuel for 50% of the power.

The answer to this for ships is several boilers; when you don't need full power you only run some of the boilers. That lets you run part of the system at full temperature and efficiency, but means you have less steam being generated, so you can't go as fast. But multiple boilers don't sound viable for a robot anywhere near human size.

Generally, to make small high-power steam vehicles viable, you have to tweak your physics a bit. I did that for a steampunk campaign where the steam power was a central element of the setting, but doing this for a plausible TL5 looks tricky.

[Flyndaran]

I wanted to keep the hand-waving to the head of the robot only.
I guess there's going to be some below it as well.

Thanks everyone for all the help.

[whswhs]

Originally Posted by Flyndaran

The chart I found equate one pound of charcoal to 29 MJ per kilogram. I figured that to be over 3000 Calories. Does a steam engine have to run at full power all the time?

One calorie is 4.187 J. One kcal (what dieticians call a "calorie") is 4187 J. So 29 MJ is actually just a shade under 7000 kcal.

Bill Stoddard

[Flyndaran]

Originally Posted by whswhs

One calorie is 4.187 J. One kcal (what dieticians call a "calorie") is 4187 J. So 29 MJ is actually just a shade under 7000 kcal.

Bill Stoddard

I meant to say just over 3000 calories per pound as I prefer to work in american units. I didn't mean to change units without mentioning.

[Anthony]

Originally Posted by Flyndaran

The chart I found equate one pound of charcoal to 29 MJ per kilogram. I figured that to be over 3000 Calories. Does a steam engine have to run at full power all the time?

Steam engines, particularly small steam engines, aren't going to run at anything like 100% efficiency; a steam engine that resembles the TL 5 designs you'd actually want for a steampunk feel will have an efficiency under 10%, because steam pistons are particularly inefficient. A modern steam turbine is more efficient, but lacks the proper clanking and hissing noises.