Stirling engines - Ball bearings

From what I've read, shiny wire does a better job of being a bearing on a tin can Stirling engine, but I want to see just how much extra friction a proper ball bearing race or two would add to the mix.

The friction levels are very low on these little engines.

They have to be or they just don't work.

But I want to try to make a more robust version, and perhaps even make one that is capable of doing some work.

Perhaps.

But probably not.

Any attempt to make a bigger tin can Stirling engine would also involve a lot more weight. And more weight means more wear and friction. Ball bearings will be the solution, as long as there is enough power left over to overcome the extra friction that bearings have.

That sounds a little contradictory, but bearings are really good at dealing with extra load on the rotating surfaces, but they involve a little extra friction than say... hovering in space.

So, with this in mind, I looked into small bearings.

They cost a lot.

A 12mm (internal) ball bearing race is a very standard thing that industry makes. They cost around $2 each retail, and are a weighty, very strong thing you might find in a motor bike, or in the centre of a bicycle wheel. They carry a lot of weight, and last for ever. But they have way too much friction.

The little bearings I want that are only around 1.5mm in diameter (internal) all seem to cost around $20 each. They are nothing like the robust 12mm ball bearing races I looked at.

Tiny.

Fragile. (actually not really, but compared to the 12mm version...)

Fragile.

And expensive.

But my fishing real has a dozen of the things. They cant really cost that much. It must just be that there is no real retail trade in them. I need three or four, so I thought of buying a $20 K-mart fishing reel, and pulling it to bits, and that's probably what I'll end up doing. But in the mean time, I really want to know if a bearing will be too costly in terms of friction.

I found a little computer cooling fan in my electronics junk drawer. I figured that should have at least one bearing.

These little fans don't put a lot of stress on their little bearings, but they last for ever and spin really fast, with little friction.

Last for ever, fast.

Perfect.

I started by removing all the bits that didn't look like a bearing.

How hard could it be.

Very, it turns out.

That's the little bearing inside the small brass tube.




I spent a lot of time and energy trying to get it out.

I started by trying to knock out the pin by gently placing a centre punch (made of thick wire) on the centre axle, and smacking it with a hammer as hard as I could.

That didn't work so well.

Actually that didn't work at all.

I finally got it to give some ground by taking a hacksaw to it, and cutting through all the hard plastic surrounds that held the coils to the little motor.

This left me with a much more manageable bit of kit, that even looked like it might finally surrender it's bearings.

In fact, this would be perfect if I could just get the pin out of the centre, so I could put the Stirling engine's wire crank through the centre.

Centre.

Difficult

I put one end in over the opening of a little socket so the punch could get through and hit it hard.

Nothing happened, so I turned it over and hit it again.

That's my trusty hammer at the top of the frame.

Camera shy hammer.

This time it worked.

There's a little flange on one end of the pin that was making it impossible to tap out.

An amazingly strong little flange.

I hit it hard.

A lot.



Now that the shaft was out, I needed to knock out the bearings. I tried inverting the socket so it's outside fit inside the brass sleeve, and rested against the bearing. I hit it again.

And again.

And some more.

In the end I just kept cutting.

The hacksaw was the only thing making any progress.

Who would think there would be a time where a hammer failed me.

There's no real danger of damaging the little bearings here, as the brass sleeve is soft and bearings are made of insanely tough... stuff.

The bearings came out with ease, once the brass was cut through.

It turns out that the brass sleeve is really a brass sleeve with a divider in the middle.

No amount of hammering was ever going to get the bearings out.





Oddly, after all that hammering, the bearings still roll reasonably.

Reasonably.

The reason the little fan was part of my electronics junk drawer in the first place, was because it no longer turned. I think it was the cooling fan that I replaced on my rectifier, so it was never going to work perfectly.

The bearings spun freely enough after rotating them for a while with my drill. but there was a little bump in each revolution.

This pic is of the new ball bearing raced tin can Stirling engine running on my stove-top at around 200rpm.






200rpm is around the same speed on the same heat setting as it ran before, but it no longer runs from the heat of a single candle at only 36rpm, so the bearings have increased friction a little.

The brass sleeve was replaced with a cable tie for each bearing, and it turns out that cable ties fit nicely into my adjustable screw in bearing mounts.

Having the adjustable wire crankshaft I made turned out to be worthwhile, as I would never have been able to make just this one change. The smallest change in the crank shaft, in either the displacer crank, or the power piston crank makes a lot of difference as to how well my little Stirling engine runs, so it would be very hard to tell if it didn't work because of the bearings, or because of the different crank I would have been forced to make.

So.

A success as far as this little engine up goes. The bearings are small, but should be more reliable than the a plain wire on wire bearing. And it seems the friction loss is only around a quarter of a candle.

An interesting addition to this learning thing.





120 Things in 20 years measures the amount of friction in a tin can Stirling engine in "candles". I think I just invented a new metric.

Stirling engine - Slow motion power piston video

Opps.

For some reason the video wasnt displayed on my last post.

Here is the video for those that missed it...

Stirling engines - Slow motion balloon power piston

I made a few adjustments to my little tin can Stirling engine. It now spins twice as fast, at a rate of around 210rpm. Not that that means much because the more flame you put under it the faster it goes. But it's around twice as fast as it was originally. Quite a success as far as bettering a terribly inefficient Stirling engine goes.

If you ask me.

The main adjustment I made was to replace the two sections of shaft that make contact with the supports. The original shafts and bearing surfaces were made of galvanised fencing wire.

I replaced them with a thinner grade of stainless wire. Actually it's welding wire, and is the same stuff I use whenever I mention stainless wire in the construction of my fishing lures or anything else on the blog.

Pictured here in this uncomfortably framed, but interestingly red image, is the new wire, the old wire, and a match.

The thin stainless wire makes a huge difference. It even runs without the 8g counter weight now.

The counter-weight is there to mirror the weight of the displacer, so without it, the power piston has to lift all that weight on it's own.



With the counter-weight and a minimum sized flame, it can now tick along as slowly as only 32 rpm.

Stately.

To run as slowly as 32 rpm, I found it also needed a small drop of very light lubricant (fishing reel/sewing machine oil). But it's important to note that the shaft for the displacer - the one that goes through the small hole in the can, should not be oiled. The oil burns, and leaves a sticky residue which will stop the engine.  As seen by the improvement by the slight reduction in friction, the smallest extra friction will kill these little engines. Use graphite, or just leave it with nothing.

If you did lubricate the displacer shaft, it's also possible that oil or Vaseline could get into the displacer container, and being flammable, might eventually find it's way to igniting if everything was just right.

Everything is very rarely just right, and a Stirling engine is a very safe thing to make and use because there are no pressurised containers. The making involves some sharp bits of tin can, and should probably not be built by kids, but as a finished item, it's as safe as any small candle is, so probably qualifies as relatively child friendly.

Lets say... As child friendly as a birthday cake.

Anyway, it looks like this in slow motion (sorry for the poor picture quality)...

[edit from the future - Opps, for some reason the video wasnt dropped into place.] Here it is...




Even more stately.

It's currently clunking away on my desk, running at around 60rpm on these two little flames, and has been doing so for an hour. One flame is about the size a birthday candle, and the other is around half the size of a birthday candle.

My point is it isn't using much heat compared to the last version.





I find it's sounds...

oddly soothing.



K-chunk K-chunk



120 Things in 20 years thinks that if ever I disappear, it might be because I'm off on a Stirling engined bike trip around Australia... in slow motion.

Stirling engines - Balloon Power pistons

My original balloon power piston looked like this.

It had a connecting rod glued to the centre, and the other end of that rod connected to the cam shaft. The result was that as the air was heated in the chamber with the displacer, it expanded, filled this balloon, and pushed up the connecting rod.





I think it also pulls as the air cools and contracts, but that isn't very obvious either way. In that video (see link in first sentence) you can see the balloon inflating and giving the connecting rod a little push.

I'm amazed that the air can expand and contract at such a high frequency. I'm amazed these things work at all.

My power piston design was a little rough, and to be honest I was lucky that it worked at all.

The balloon kept slipping around under it's rubber bands, making the connecting rod feel some resistance as the balloon reached it's limits of free movement. The result was some extra friction where it wasn't necessary.

What I need is a bit more room for error.

With that in mind, I did some research and found what I think might be a useful design, and also came up with one myself that might work pretty well.

I found this one in use already and mine was made from a balloon neck, and a plastic bottle top.

To start with I created a plastic disk around 25mm in diameter by trimming off the sides of a plastic bottle cap. 

It was pretty easy to do with scissors, and a cut that went in a spiral gradually cutting away the side.

I also have a copper elbow that will be the power piston's basic form.

This will take the place of the ungainly plastic bottle with the hole hacked into the side as seen in the top-most picture on this post.

I cut the neck off a balloon and inserted the plastic disk. The connecting rod would be glued to the centre of this disk at the top.

The cut end of the neck is stretched over the copper elbow so that it looks like this when at it's highest. (this would be the end of the power stroke)

And like this at it's lowest.

It looks quite neat, and this is probably the design I'll use unless it proves to require too much air expansion to fill it.

My design includes the same section of balloon neck, and a cable tie to secure the top.

I tightened the cable tie with pliers  and then cut the rest of the balloon away with scissors.

It looks like this at it's lowest. Or near it's lowest.

It might be the case that this design will prove useful when used entirely at the low end. It requires much lass change in air volume to move 10mm up or down from it's pictured position.







I have no idea if it will be of any benefit to use this (green) design, but It should be easy enough to try both with my adjustable cam shaft.




120 Things in 20 years - When it comes to balloon power pistons for Stirling engines, I have standards above which, I will not go.

Stirling engines - Adjustable Stirling engine crankshaft

I've been busy making the tips of my fingers raw.

Wire seems to enjoy hurting people.

But I love the stuff.

My time learning how to make screw in eyelets for my hand made fishing lures was well spent. Every new skill I pick up seems to inform my next project. Working with wire is a really worthwhile thing to learn.

• This post appears to be in bullet point style.

One thing I don't really understand is the relationship between the size of the cams on the crankshaft and the performance of my little tin can Stirling engines. With this lack in mind, I thought I'd build a completely adjustable crank shaft.

It looks like this.

With it, it should be easy to try a stack of different configurations to see what they do.

The cams (bits that are offset from the main shaft) should offer different combinations of engine torque, and speed when they are adjusted to different heights.




I think.

Ideally I need an adjustable chamber for the displacer as well. I'll have to feed that idea through the invention engine at some stage because I have no idea on that one.

All the brass fittings come from the brass bits in strip electrical connectors.

Once the screws are undone as far as they can go, all the brass bits fall out with tap and a jiggle.

Lots of taps and jiggles actually, but they all come out in the end.





In my adjustable cam, the brass tubes that accommodate the cams have had an extra hole drilled through. Brass is very easy to drill, and a pleasure to work with. I don't think I've ever done anything with brass before.

I officially like brass.

• Bullet points

Also, many other people have used these as the adjustable bits on Stirling engines, and my only contribution to the science is to take their use to absurd levels.



120 Things in 20 years - No time to post because I'm too busy learning stuff about Stirling engines.












All the brass bits are taken from a strip of electrical connectors.

Stirling engine ver 2

I made a few changes to My little home made Stirling Engine.

Change is always required when your engine seizes after only 55 seconds.

This one ran until the plastic bits caught fire.

Much better...

The original displacer popped itself to bits when it got hot enough, so this new version has a different design that's open to air travelling through it.

The autopsy also shows why my little engine stopped so suddenly. There is only around a quarter of an inch of air above and below the displacer when it's at it's extremities, and the bottom popping off made the displacer touch the bottom of the can it was in.



I replaced the can surrounding the displacer because I had to use a can opener to get the displacer out, and reattached the power piston balloon.

In the process of building the new displacer can, I discovered a new way to drill a hole that suits my personality perfectly.

You punch a hole with a nail, then rip a circular hole with pointy nose pliers in much the same way as opening an old style tin can of fish that the eater would open with a key.





If you aren't old enough to know what I'm talking about it, count yourself lucky and get on with it. You haven't missed a thing.

I drilled a few large holes in the top and bottom of the displacer, and packed it full of stainless steel, kitchen scrubber pad.

Apparently this works, and acts as a thing called a regenerator.

A regenerator can often be found on a Stirling engine and acts to store heat between the hot and cold sections as the air moves between the two.



The regenerator material collects heat from the freshly heated air inside the can the displacer is in. As the heat is displaced from the hot section to the cold section, some heat is removed and stored in the material. This is a good thing, because we want the cold side of the equation to be as cooled as possible. When the cooled air returns to the hot end, it picks up the heat it dropped into the regenerator on the way through, making it heat up more rapidly.

It's not by magic that the heat knows when to sit and when to be picked up, just that the air is hotter on the way up from the heated section, and has cooled a bit at the top before coming back through the regenerator.

I put the new displacer in it's tin can, and threaded it's wire through the bottom of the top can that holds the crank shaft.










In the process of de-constructing the first version, I bent the shaft a little, and it never ran quite as smoothly again. The little Stirling engine took a lot more heat to get it going this time, but I'm not sure if it was due to the new design of the displacer, or just due to the fact that every thing was a bit warped.

Friction really kills these things, so making sure the shaft is straight is a must.

It does run, and it's going a lot faster than the first version, but I suspect that has to do with all the extra heat from using a gas burner rather than a candle, and not some gain in efficiency.

I think I now know a little more about these interesting engines, and a little more about the universe in general, and I think I'll have another go at building a better one. I'd really like to make one efficient enough to run on the waste heat from my wireless router so it could just jig around all day for free.



120 Things in 20 years is finding the universe yet more interesting as a result of building this version 2 of my first, working, home made Stirling engine.

Stirling Engines - My first Stirling engine build

In spite of my video camera running out of battery during filming, I managed to get the first (and only) moments of my first Stirling engine running.

Tis a funny kind of beast running so slowly and deliberately.

I officially like Stirling engines. Mine looked like this...

It ran for a total of about a minute before the displacer fell to bits. It was sealed airtight, and as it got hot it just popped. It turns out there isn't really any need to make it air tight.

I think.

My displacer started life as a soft drink can.

I marked out a straight line to cut it down to size.

I took a guess as to what size it should be.

I scratched a series of arcs with a bent piece of sharp wire, each at different points, to find the centre, then punctured it with a drawing pin. 

I marked out another can, but this time much shorter.

Then squashed the big one over the little one after turning the little one upside down.

This gave me a sealed can again.

I glued it with super glue.

The gluing was what killed my brand new Stirling  engine after only 60 seconds. As the heat increased, so did the pressure inside the sealed displacer, and eventually it popped open.

I poked a straight length of fencing wire through both holes, then bent and super glued one end to stop it slipping through.

My wire originally had a slight loop at the other end, but I had to cut it off to remake the thing after I glued myself to it.

Don't do that.

And if you want to be really scared, use super glue, then adjust the dials and buttons on your new camera with the same fingers.

Anyway, the main thing is stick some wire through the displacer.

Next I took a tin can and smacked a hole in it with my family's trusty meat mallet.

This meat mallet used to be my mother's (it probably still is), and was used as the household hammer for as long as I can remember.

Here we see the entire family history of hammering.

Actually that's half the family history of hammering. The other half is of course, on the other side.







So then, I took the length of wire sticking out of the displacer (soft drink can thing), and threaded it through the bottom of the tin can.











Like this.

It's a bit difficult to see, but that's the soft drink can displacer thinggy under the tin can.









Next, I took another tin can and drilled a big hole in the side.










And sanded down a small plastic bottle so that it's contour matched the tin can's.










Then cut a really big hole in the side of the small plastic bottle.

Something like a pill bottle would work.

All this, so I could glue the small plastic bottle on the side of the tin can with a big hole in the side. 

Next, I stretched a balloon over the entire little plastic bottle, and pulled the slack so that it was tight everywhere but the top.

I also glued a length of wire to the centre of the slack bit.

This, believe it or not, is something called a "power piston".

I'll explain what all this stuff does later.


Next I bent a crank shaft, and some mounting points for the wires coming from the displacer (through the bottom of the tin can), and the wire glued to the balloon (power piston)

The crankshaft has one offset bit (offset by around 8mm) to attach the displacer's wire, and another to attach the power piston wire to.

The two offset, (bent out) bits, are at 90 degrees to each other.

So from the left...

straight, then down, then straight, then back up to the original.

That makes the first cranky bit.

Then continuing straight, then back, then straight, then forward back to the original plane.

That makes the next cranky bit.

If you look at the crankshaft end on, if one crank was at 12 o'clock, the other would be at 3 o'clock (or 9)

I found this almost impossible to get on camera (or to explain), but it looks like this.

It's probably best seen on the video.

The crankshaft is lightly held in place with two inverted U shaped bits of wire taped to the sides. (just visible near the top, left rim of the device)

I stuck a cardboard disk about the size of a CD onto the end of the shaft to act as a flywheel, and then added nuts and bolts with blu-tac until the thing was balanced.

To get them in the right spot, I put the disk in a random place, and if it rolled back to a different position, I'd stick on a weight so it wouldn't.

I should have been able to do this with just one weight of the correct size, but for some reason it was beyond me.

So...

• The displacer is the soft drink can thing inside the bottom can. 
• The bottom can is sealed ([buy - EDIT  - note from the future-  Who makes errors like this?] by the top tin can) except for the small hole in it's top that has the displacers wire poking through.
• The displacer travels up and down inside the bottom tin can with a total travel of around 1cm.
• The displacer gets very close to the top and bottom of it's tin can container, but never actually touches.
• The displacers wire is connected to the crankshaft (between pink beads)
• The power piston (pink balloon) is floopy, and connects to the crankshaft 90 degrees offset from the displacer's crank.
• The top tin can is there to hold up all the other kit, and as the top seal for the chamber holding the displacer (soft drink can thing)
• When the air inside the bottom tin can heats up it expands, forcing the power piston up. This turns the crank and gives the device its power.
• As the device rotates, and the displacer moves down, forcing the air up and away from the heat, so it cools and contracts. 
• When it contracts, the power piston is sucked down.

That's pretty much it. Repeat as desired, or until something breaks. 

Some light oil can be added to any surfaces that have friction. (where the displacer wire moves up and down into the bottom tin is a high friction area)

==============>>> IMPORTANT!!! Note from the future - It turns out you probably shouldn't add oil to the point where the wire slides through the can. There's a chance of explosion as the oil is heated to a gas. <<<================

120 things in 20 years - I made a Stirling engine!

Stirling engine - Success!

I just made an engine!

I even think I got it on video.

It ran for about a minute at around 78 rpm before making a popping sound and seizing up.

Which would have been perfect if it was connected to an old record player...

playing a very short song...

that I only wanted to hear once.

The camera battery went flat during filming, but but the video should be on there. I'll find out tomorrow. If not, I'll just fix it.

Yay me!

More later...



120 Things in 20 years is very pleased with itself       :{)

Stirling Engines - My second attempt

I think I may have actually built something.

Or nearly built something.

It looks like this and almost works.

Most of that junk in the picture isn't part of it. The bits that are part of it are the bits that look like a Stirling engine.

Sometimes Stirling engines look like tin cans, and wire, and pink balloons. They also look like cardboard disks with blu-tac stuck weights all over the place to act as a flywheel.



I planned on posting a video of it working today, but it doesn't.

What it does do is spin around freely for a few seconds when you spin the flywheel. It also has a displacer and power piston that are configured in such a way as to do what they are meant to.

I think.

When I put it on the stove top, it nearly feels a bit like it's trying to work, then smoke starts pouring out of the seals, so I take it off the heat before it catches fire.

Who knew tape might burn.

Yes. That's right. I thought I'd make my engine using gaffer tape for the seals.

It doesn't work so well.

Tomorrow, I'll buy some glue. I seem to remember hearing of someone who used two part epoxy on a real engine crankcase, so it should cope with the heat.

Maybe.

My next choice will be solder. Solder melts when you get it hot, so I'm guessing that wont work so well either.

But the glue might.

If it works, I'll put up a big build post. If it doesn't I'll try something different.




120 Things in 20 years - Using a random evolutionary approach to building a Stirling engine. Chuck some bits in a bag, shake, then cull anything that doesn't work like a Stirling engine. I'll get there eventually.


[edit from the future - For anyone concerned that time may not be linear any more, this post was actually written two days ago, but for some reason didn't get posted. As a result the post after this one was actually two days after this one.]

Stirling engines - My first Stirling engine

Sometimes I struggle a bit with certain aspects of construction, but in this case I wasn't even certain of what I was attempting to construct.

Most of the problems trend around a certain frantic waste of pace and failure to pay attention to detail.

This time was no different.

A Stirling engines basic list of components include a cylinder, a displacer, and a crankshaft.

They also include a hot bit, and a cold bit.

It's the difference between the hot bit and the cold bit that makes a Stirling engine an engine.

There's also another really important bit, called the power piston. The power piston is connected to the same crank shaft, but on another crank. This crank is offset from the displacer's crank by 90 degrees.

I'm not really sure how it does what it does, but this is my first attempt at making a Stirling engine.

The power piston is the bit that's missing, because I didn't get that far.


Some of the other missing bits include the rest of the components that make up a Stirling engine.



120 Things in 20 years - On a scale of one to ten, where one is a total fail, and ten is a total success, I wouldn't bother rating my first attempt at making a Stirling engine.

Stirling engines - A complete history of Engines

Some time ago, somebody invented the steam engine. The steam engine works by heating water in an airtight container to make steam. The steam is massively expanded water, and the result is lots of pressure.  Once you have lots of pressure you bleed a bit of that pressure intermittently into a piston, and the piston gets pushed. Connect that to a crank, and you have rotational motion, and an industrial revolution. You also have lots of factory workers being blown up in hideous, explosive  accidents, with all the screaming, and loss of productivity that goes with being killed.

Later someone invented the internal combustion engine, and the turbine engine. These run on fossil fuel. They had a pretty good run until somebody discovered it was making us sick and killing everyone.

The turbine engine is a big thing you tend to stick to the ground in a power plant and make electricity. That way the factories could all have much safer working conditions where hardly anyone ever got blown up, but it also kills the earth a bit. Just a little every day. And sometimes some of them explode anyway. That's not so good, because some use uranium to make the heat, and that never ends well.

Anyway...

The internal combustion engine tends to be used in portable things like cars, because they pack such a lot of punch for such a small weight in fuel. They also kill the world, just a little bit each day, and sometimes explode, and sometimes just mash into each other, and mash into other things that tend to be near roads. They do a lot of mashing.

The main advantage with the turbine, and internal combustion engines, is that they spread out the damage. Just one or two people from any given factory at any given time get killed by them rather than taking out half the factory's workforce all in one go like a steam engine disaster might. The mayhem and disaster is spread out so that each factory takes just a small share of the disruption to productivity. Except perhaps with the uranium stuff. I think that's why Australia is shipping all our uranium to distant countries. To move it as far away as possible.

Anyway...

A Stirling engine on the other hand is a slightly more peaceful beast that doesn't really do a lot, but what it does, it does pretty thoughtfully. Historically it fits between the steam engine and the stuff we use today (2013, just in case someone reads this in 40 years). The Stirling engine is an engine that uses the difference in heat between two of it's bits of kit, to make stuff spin around without all the explosions.

There.

That's the design description out of the way.

It's very safe, because it doesn't have a pressurised container. It needs a source of heat, but that can be solar, or waste heat from something else. Rotting compost, your wireless router, whatever. They are not a very powerful engine, which is why the internal combustion engine took over, and they are not very responsive to sudden changes in desired power output. That's also why the internal combustion engine took over. And they are not very powerful... Internal combustion engine blah blah blah.

So...

The most beneficial thing as far as I'm concerned is that they wont blow up and kill me.

They're not very useful. But that's not going to stop me making one.

The kind of thing that will stop me making one, is more likely to be that I have no idea how.

I've never made an engine before, and have also never met anyone who has, but it turns out they are a pretty simple kind of beast, and with a bit of luck, wire, string, and the total combined wealth of human knowledge stored on the Internet, I might be able to make one.

People are very clever, and there are some really helpful ones out there that are willing to help me.

I'll be trying to make a very small Stirling engine that runs on the power of a small candle, that will do no work, but will hopefully work.



120 Things in 20 years - Stirling engine - It might go round and round.