My newest incan

I got it for Christmas. It outputs ~1 candlepower @ 2500rpm. :devil:



Okay, fine, it's not a lamp, it's a stirling engine, but it does emit light, and this seems like the kind of crowd that could appreciate it anyway.

Very nice

I wouldn't mind being given one as a gift, but I can already see how far back in her head my wife's eyes would roll if I suggested it.

What would be appropriate for CPF would be to use it to turn a dynamo to run a LED.

It might need a boost driver though

They make miniature dynamo-powered streetlight accessories, among other things. The black blob on the crankshaft is a drive pulley for just that purpose.

Dunno how my wife would react, since she doesn't exist yet, but my mom was nice enough to humor me. Her father back in the Olde Country used to have all kinds of mechanical and electrical certifications, so she has a bit of fondness for stuff like this too.

Neat! How does it work exactly? And what are you going to use it for?

Heh. Pretty much all I'm using it for is something to make my desk vibrate and dispose of my stash of 99% isopropyl alcohol from the bathroom. Sure is fun when it gets cranked up, though. I just like to watch it and zone out. (I don't watch much TV.)

The way a stirling engine works is: the hot cylinder gets heated by external combustion, the air inside the hot cylinder expands and drives the piston at the top, and then a second piston moves forward into the hot cylinder to force all the air out so it can't keep absorbing heat. The air then dissipates its heat into the heatsink at the top, cools off a bit, contracts, and the top piston moved down again. Meanwhile, the second piston moves backward so the air can go back into the hot cylinder to heat up again, and the process repeats. Wikipedia has a good article about it. Their power-to-size ratios aren't as high as internal-combustion engines, but external-combustion engines can run on any heat source, and the stirling engine is safer than a steam engine because there's no boiler to explode.

Interesting! Looks like a high-quality item.

BTW, the pic is too large - please could you resize it to comply with Rule 3.

fyrstormer said:

I got it for Christmas. It outputs ~1 candlepower @ 2500rpm. :devil:

Click to expand...

What's the formula for converting candlepower in to horsepower?

:nana:

Nice toy! I've always wanted one---seriously!


Karl

Nice Sterling fyrstormer, looks like fun. I recently drew up some plans to build a mini Sterling or similar steam engine. My supervisor would rather me play with miniatures than the 300HP's at work :naughty:

DM51 said:

Interesting! Looks like a high-quality item.

BTW, the pic is too large - please could you resize it to comply with Rule 3.

Click to expand...

Image resized. Odd, I thought I told Photobucket to auto-size everything to 800x600, but it looks like they only check to make sure the horizontal size is correct, and because this was a portrait image, it was already narrower than the maximum width I specified.

It is definitely high quality, but like all good German engines, it requires special lube. The engine is tuned to make barely more torque than it needs to overcome its own friction, since it is only a model, and regular oil will produce too much drag on the top cylinder. Since I got the pre-built version, they neglected to include the special dry ceramic lube the top cylinder requires, so I had to hunt that down online. Graphite powder from my trusty drafting-pencil sharpener seems to suffice well enough in the meantime. Fortunately, sewing machine oil works fine on all the pivoting parts, and on the sliding rod the bottom piston is attached to.

DUQ said:

Nice Sterling fyrstormer, looks like fun. I recently drew up some plans to build a mini Sterling or similar steam engine. My supervisor would rather me play with miniatures than the 300HP's at work :naughty:

Click to expand...

A stirling engine is not a steam engine, just a hot-air engine. You probably knew that, but I wanted to re-state for the benefit of anyone who might be confused.

I've thought many times about getting a mini steam engine, and I may yet get one, but heating even a small tank of water to 250 degrees or so requires more energy than can be provided by the alcohol burner that came with my stirling engine. That means I'd have to use a more energy-dense fuel than alcohol (such as Esbit tablets), and most of those smell funny (Esbit tablets smell like dead fish) or produce toxic exhaust. In addition, I'd have to fiddle with it more, monitoring the water level and the steam pressure and all that, which may be fun for some people but it doesn't interest me much. I just want to see the thing run like gangbusters.

What I like about the stirling engine is I can fill the lamp with alcohol, light it, let the hot cylinder warm up for 30 seconds or so, and give it a spin. After that, the engine idles for a minute or two until the metal parts stop stealing all the input energy, and then it fires up to full speed. Once it's running, I can just sit and watch it, or ignore it, and not have to worry about something unspeakable happening if I happen to get distracted -- the worst that can happen is the lamp runs out of alcohol and the wick burns down.

I've spent rather a lot of time observing this little engine in operation since Christmas, and I think I've discovered something that could use a bit of improvement.

Neither the top piston nor the sliding rod attached to the bottom piston are sealed, but the engine is made with such tight tolerances that when I remove or reinstall the top piston it takes several seconds for air to sneak past the sides of the piston and equalize the air pressure. This is obviously a good thing for efficiency since it means a minimum of power will be wasted by hot air leaking between the top piston and the cylinder walls, but I think it causes the engine to run slower than it could during warmup.

The reason is: in the few hundredths of a second that the air is in the cold side of the engine (the area where the top piston is), there is no way it can dissipate ALL its heat and return to room temperature, so it will remain at higher-than-ambient pressure and fight against the top piston when the air is getting pushed back into the hot side of the engine. Once the engine has reached operating temperature and the air inside is no longer experiencing a net gain in temperature with each engine cycle, the effect of recompressing the still-hot air will be minimal since it will just behave like a normal spring -- however, during warmup, the air will be a little hotter with each engine cycle and the air that can no longer fit inside the engine will have to leak past the top piston to escape.

Having to recompress air that is at too high a pressure (due to its density and the heat it has absorbed) until the excess pressure can leak past the top piston wastes energy. I think the engine design could be improved by drilling a small breather hole at the very top of the piston's travel, so after the air has done its work of driving the piston, any excess pressure can escape easily instead of having to be forced out. I'll have to get a spare engine block to test this on, though, because I'm definitely not going to mess up the one I got for Christmas in case it doesn't work.

I've been playing with my new toy every day since Christmas. Figured out a few things.

First of all, the plastic bushings in the rocker arm were a pain in the neck, because there was no way to tighten the pivot screws properly without deforming the bushings and making the pivots bind up. Fortunately, there were identical brass bushings available for a different model, and they work splendidly. As a side benefit, I can oil them, though I have to be careful about applying too much oil -- the reciprocating motion will shake loose any excess, and the top piston REALLY doesn't like being contaminated with oil.

Nano Oil works way better than 3-in-1. I expected it would, but the amount of difference is remarkable. The engine speeds up immediately instead of needing to heat up to thin-out the oil first.

The top piston is a strange creature. It has a large surface area that can scuff against the brass cylinder, so minimizing friction is of paramount importance, but at the same time any liquid lubrication will cause massive drag and prevent the engine from speeding up beyond idle. The German company that makes the engine actually recommends a dry ceramic paste, smeared on so thin as to be transparent but slightly hazy in appearance. Boy, that stuff works great, whatever it is. I wouldn't use it on anything I can use liquid lubrication on, but it's completely stopped the appearance of wear on the cylinder walls, and it doesn't drag at all, so the engine runs like gangbusters.

If anyone wants to play with the ceramic paste, to see if it's useful in other applications, I got it here: http://www.ministeam.com/acatalog/Boehm_Parts.html It comes in a little plastic syringe and it's EXTREMELY difficult to squeeze out, but only a tiny bit is necessary so it's not a huge problem.