Jan Ridders Coffee Cup Stirling

Myfordboys circle cutter is neat for circles. Not so good for cutting down the thickness if needed. If it gets too hot a dimmer might help. All I did when I picked that was choose one of the higher power usual wall plate fitting types. From memory at the cheap end they came for something like 500w and 1kw.

I do have a tat super cheap soldering iron some where that has the bit held in with a screw from the side. It would be easy to make a suitable "bit".

John

-

I nipped down to the glory hole at the back of the workshop and dug out the cutter I made and took some pictures. Before anyone comments, I know it was electrical suicide but I did a full risk assessment and complied fully with the current PUWER regs before I used it (read: made damn certain I did not touch any live wiring!). It was made to cut some foam infill parts for use repairing Victorian ceiling coving. It is 30 inch wide and has an 8 inch throat. The wire did not come from Maplin but I think they sell it. You can see the label on my bobbin in the picture. I used a simple pin axle for the metal roller at the end, used to power the wire and also the spring tension keeps it taught when it heats up. The dimmer is a 250 watt dimmer and the whole thing works admirably. The frame was a pain to make but it seemed like the simplest solution at the time given materials to hand...

Mark

Edited By Mark C on 03/03/2016 14:16:42

Edited By Neil Wyatt on 03/03/2016 14:42:56

Wow guys, thanks very much. I repeated the leak test using water with a drop of washing-up liquid to make it wetter and some red food dye to make it easier to see. The engine's lower plate was immersed for 5 minutes.

The result may explain why the engine wouldn't run yesterday.  (Water Hammer!)

The cardboard displacer was ruined.

Stripping down the engine revealed more problems due to acetic acid corrosion. See what it did to the polish of the power cylinder bore!

It looks worse than it is, fortunately Duraglit made a huge improvement. The end of the piston was rusted again but the damage isn't serious.

I went out and bought Balsa and a Flat `At. Wearing a traditional cap in the workshop will multiply my meagre skills. Sadly I found that my traditional local ironmonger has stopped trading and I was unable to easily buy more silicone sealant.(I've gone off RTV Instant Gasket because of the fumes.) I've decided temporarily to use modelling clay as a sealant. It 's like plasticene but rather softer. I use it very successfully it to weather protect the nuts and bolts of an antenna system: it's clean, lasts outside for years and is easy to remove.

Noting advice above. I'm off to make a balsa displacer. Now I've spent money because of it I fully expect to fall over the missing polystyrene in the next 5 minute. I have the wherewithal to make a hot-wire cutter and may well end up trying it. Some of the other ideas are now in a queue because I don't want to change too many things at once.

Very many thanks for the intel that the engine works but is difficult possibly due to a design issue. I'm starting to feel that everything has to be "just so" before it will run. Watch this space!

Cheers,

Dave

Edited By SillyOldDuffer on 03/03/2016 16:50:44

Edited By SillyOldDuffer on 03/03/2016 16:53:38

Brave man Mark. Don't blame you though. Mig wire appealed to me because I had an old valve filament transformer around. Volts too high but power ok. It would have been a lot more tricky to use resistance wire and low voltages.

However using this

**LINK**

I've just ordered some of this

**LINK**

I've used them before for kanthal wire.

I've based it around 15" of wire and 5 volts. 350C and circa 4 amps. This works out at 1 1/3 watt per inch of wire which is close to figures I have seen. I used 15" to allow for some shortening if needed. The wire is about 1 ohm per foot. They sell kanthal as well. 0.7mm dia has a similar resistance value.

John

-

I've just finished the evening with a smirk on my face. The engine runs! It looks a right mess but it's going. Special thanks to Trevor, Ian SC, Howi and Gordon with apologies to anyone I forgot : there was overlapping good advice.

Problems fixed were:

1. Displacer replaced with 4mm balsa and carefully fitted to the cylinder with a gap of 1 or 2mm. Adjusted to nearly hit the lower plate on the downstroke.
2. Plasticine type modelling clay works as a sealant, at least as a temporary expedient. Wallace & Grommit taught me everything I know about making gadgets. Slight leakage was fixed by smearing extra clay into the outside gap between upper & lower plates and the acrylic tube cylinder.
3. The flywheel was more carefully re-balanced with blobs of modelling clay in lieu of blu-tac. The engine went without doing this but the improvement was obvious. More needs to be done to the flywheel.

My coffee-cup is a vacuum type that holds heat much longer than an porcelain mug. At the moment the engine only runs on near boiling water. It goes for about 10 minutes. Don't ask how I know that it is still unpleasantly hot when spilled onto one's gentleman parts. I suffer for my art.

Before steps 2 and 3 it was obvious from the feel of the engine that it was in a better state. With heat applied It span much more freely in one direction than the other. In the forward direction a flick would result in up to 20 seconds of rotation, a significant improvement. Although the engine slowed down quickly I noticed that it was rolling gently past tdc rather more than could be explained by energy stored in the flywheel.

After fixing the minor leaks I spun the engine several times each time re-flicking it impatiently before allowing it to stop. After a fortuitous distraction I returned to find the engine still ticking over gently. It runs much more slowly than I expected - a stately 80 rpm dropping to about 45 rpm before stalling. Is this normal? I seem to remember seeing similar engines at exhibitions turning a lot faster. There will be no danger of it taking off when I add a propeller, ho, ho.

I shall have another go at it tomorrow. The flywheel isn't properly true and I think the balance can be improved. After more "running in" it needs serious cosmetic attention.

Thanks again,

Dave

Congratulations Dave, it's virtually impossible for it not to go, if you build it right, but it's the little bits that stop them going. According to JR it should do about 300 rpm on a cup of boiling water. If in future anyone has problems with one of his engines, you can E-mail him from his web site, don't forget this site as well.

Ian S C

Edited By Ian S C on 04/03/2016 09:39:52

Congratulations Dave,

well done for persisting with it. A few finishing touches and it's a very attractive little engine. It's amazinging how much interest you'll get if you demo it to people, they all think it's magic.

Trevor

Congratulations Dave,

well done for persisting with it. A few finishing touches and it's a very attractive little engine. It's amazinging how much interest you'll get if you demo it to people, they all think it's magic.

Trevor

Thanks for the congratulations: your encouragement puts the icing on my cake! I get a real buzz when something I made myself works. Much preferred to the slough of despond I fall into each time a mistake adds to my scrap bin.

Today slow progress because I have a stinking cold and getting chilled in my 6C workshop doesn't feel like a good idea.

Experimentation after small tweaks reveals that the engine still only runs slowly for just over 9 minutes from a boiling start . There may be a problem with my seals because modelling clay softens with heat. Methinks a small leak may be developing as the top plate warms up. Consequently I've ordered some silicone tubing as suggested by AJohnW. The top plate warms up more than I like so I may blacken it and replace the steel pillars with something less conductive.

I found an article on the engine by Jan Ridders in the ME archive this morning. It's in #4329, July 4 2008. Unfortunately the free plan isn't in the digital magazine - must have been a pull-out.

Many thanks for the hint that Jan can be emailed and that he has a website. (My earlier research didn't find it for some reason.)

Cheers,

Dave (atchoo)

But did you ever find the polystyrene ?

I spent over an hour searching for my diamond honing dusts last week... came across them yesterday neatly placed with files rather than abrasive papers, wire wools, and scotchbrite, honing paste or stones....

Nope pgk pgk. The elusive polystyrene must have transferred to an alternative dimension to join an Axe, Travelling Steady, Stopwatch, Camera Charger, yesterday's new bottle of Meths and my only copy of Machinery's Handbook. Not all is lost however: I know exactly where to find the Haynes manuals for all the old bangers owned by my family since 1970. I shall never need any of them again.

Edited By SillyOldDuffer on 04/03/2016 14:16:53

Don't talk to me about not being able to find things. While tidying up I have noticed that a number of things are missing. Some for so long now I've started wondering if I ever had them. Others because I have tidied them into a different place - bit like car keys usually kept in one place for a long time put them some where different and they become invisible as a result.

JR's drawing looks like he intends the displacer to have even top and bottom spacing at each end of the stroke to me. Just visually. I haven't worked it out. It might be worth doing that and adjusting either way if possible. There are arguments either way in respect to the space at the bottom.

John

-

Tidying up is fatal. As far as I'm concerned it renders things invisible. And it's so annoying when stuff I lost by tidying turns up out to be in plain sight - a month or two later! Scanning with a torch CSI style whilst constantly repeating the name of the missing item helps but I'm pretty hopeless. Forgetful bloke with machine tools might make a good sitcom.

Great minds think alike. I fiddled with the displacer just as you suggest this afternoon. It didn't make much difference but that may be because a bigger problem is masking the effect.

Nonetheless I was pleased with today's improvements. Although the engine still won't go faster than 80 rpm I increased the run time per boil from 6 minutes to 26 minutes with more careful sealing, balancing of the flywheel and "running in". The next big thing is the flywheel. It wobbles because the axle hole is oval at one end. Not sure how that happened but I admit to being the only suspect. It's a workshop job to fix and I'm not up to it until recovered from an exceptionally severe case of man-flu.

Dave

It's all down to our brain filling things we often see automatically Dave. Not an age problem so if keys are always kept on a side table and moved to the mantle piece there's a good chance we wont see them if we look quickly. Feeling irritable seems to make it worse.

LOL When it's the car keys I usually ask the wife to look. She doesn't drive so sees them immediately.

On these low temperature ones I want to try and come up with my own design. JR outlines some rules on these and others do to in more or less the same way. So I have scrounged every design I can lay my hands on and done a few simple sums to see if the "rules" make sense - not really just very very loosely. So loosely it's a bit of a nonsense. So I'm intending to make the stroke of the power cylinder adjustable but wanted to use a Ross yoke as it would be nicer to watch - if it works.

John

-

.

+1 for that, John

**LINK**

MichaelG.

The "sums" and design aspects of these engines has started to intrigue me too. I've been wondering if there is any practical way of measuring what goes on inside a small low temperature cylinder. James Watt's indicator provided information that helped enormously with heat engine theory and practice. Something similar for a small Stirling engine looks to be well out of my league though.

The Ross Yoke is a new one on me and led me to find another interesting website. Fascinating! It needs 8 bearings though - yet more friction for a model to overcome.

Regards,

Dave (still snivelling)

I was thinking in terms of one like this

**LINK**

This link is pretty good for explaining what should happen but it can't be that perfect in practice

**LINK**

There are some ideas of relative sizes from a design perspective on JR site. A bloke called Schmidt was the first to analyse them - complicated but I wouldn't assume they the sums work - they wont. Easier. There is a link to a simulator off the stirlingengine.org site probably based on Schmidt. If say all sizes are left the same but the diameter of the power piston or it's stroke is increased as would be expected from the theory more power is generated. JR explains the problem with that when they are working at low temperatures. The higher the compression ratio the more power that can be produced. The compression ratio is simply the ratio of the volume change with the power piston at each end of it's stroke. All of the low temperature ones I have seen come out very close to 1 It seems bigger models that take more heat can be as high as 1.1 to 1.2 - according to a book I bought years ago.

There are a couple of video's on the Phillips engine on youtube. They seem to be the only people who have really improved them. A long time ago as well. The other sort that people like NASA use which are more recent are called pistonless. There are loads of video's on making those on youtube out of tin cans. Just search for Stirling engines.

Last edit. Millions have been spent on them measuring everything imaginable - doesn't seem to have helped. There are some thesis about as well. Looks like some one has tried to use finite element analysis even accounting for uneven air mixing and friction just from the air moving about.

John

-

Edited By Ajohnw on 04/03/2016 23:40:31

Edited By Ajohnw on 04/03/2016 23:44:40

Edited By Ajohnw on 04/03/2016 23:45:14

John,

That Kontax Ross-Yoke is delightful ... thanks for the Vimeo link.

The assembly instructions for the Kontax kit are exemplary !!

MichaelG.

Edited By Michael Gilligan on 05/03/2016 08:29:02

I have a book on the history of heat engines, and it's got some indicator diagrams in it.

Quite a variety of shapes.

Neil

Study all the info . you can find, calculate relative volumes of power piston and displacer, write it all down, study some more and try to make sense of it. That way madness lies. There are two things to remember- the engine is driven by expansion of the working medium.- The temps. are absolute ie add measured temp to 274 9 deg. centigrade. And apologies to all who already know this.