The Ecorun 2.0 Stirling Engine Kit is from Exergia – Ideas for Light & Energy by Thomas Shmidt. Available through www.newenergyshop.com
This is a blow by blow documentary of the building of a Ecrorun 2.0 Stirling Engine Kit. The article is both the way I built the engine and has the potential to be helpful to anyone building the engine who might need some more information than that given in the good instructions.
Elapsed Time 0:00 – Initial impressions & Unpacking
The engine arrived in this neat little box about 100mm square. The packaging protected the kit as it travelled from Germany to Australia via various public postal services. On the outside was all the appropriate customs paperwork and for a change it was marked as what it was. Overseas companies that put “gift” on things really piss me off – customs are not stupid. I don’t want to be on the receiving end of a fine for incorrectly declared contents. I'm pleased Thomas marked the package and included proper documentation. I buy a lot of little kits from overseas for myself and I've had enough contact with customs to know they really do log everything that arrives for a person.
Inside the box was the kit, an instruction manual, a brochure and of course foam peanuts.
The kit comes packed into its own displacer cylinder with the instruction manual in a clear plastic bag.
There are approximately 150 individual parts.
I opened all the little bags and sorted out the components. I checked them against the parts list in the back of the manual to ensure everything was present before I started. While most of the components were fairly obvious, I had to flip through the diagrams in some cases to work out what was what. Flipping around was something that became a little annoying during the build. I would prefer that each assembly’s instructions were with the diagram of that assembly – this simple change would save a lot of time. There was an error in the parts list and diagram, on page 9 the part labelled E.1 is the power cylinder F.1. This was the only error I found and is much better than my usual experience with a low price kit. The kit is made up of clean stamped cardboard parts, plastic (laser or water cut) parts and metal parts. All of the screws and nuts are common metric sizes easy to replace if you lose one during the build.
The instructions seem clear with a factually correct preamble about Stirling engine history. There is a section on the design and some construction hints and the list of necessary tools. I used some tools not on this list, but only because I had them at hand. I could have done it with the list given.
Elapsed Time 0:10 Candle Rack Assembly
This is a big sub assembly. It takes quite some time to make and is probably the most complex of the whole engine. If you find the going hard at this point, don’t give up – it speeds up from here and gets much easier.
Building this assembly reinforced my thought that the assembly instructions and parts diagram should be on the same page. I ended up pulling apart the book so I could see both at once instead of flipping around the pages.
The first piece of advice is excellent (and you’ll see why later) in that you should read the entire instructions for the sub assembly before touching any of it.
I tried to build the rings of the rack following the instructions but could not get the holes to line up. A glance at the colour picture on the front page of the instructions showed me what was wrong. In the can the cardboard strips that make up the ring came bent with the coloured pink side inwards. It is supposed to face outwards. It would have been better if they’d been packed in the can that way. I re-bent them and bolted them together without further issue once I realised the problem. I had to be careful and gentle rebending them. Because I had to re-bend them they were not as round as they should be. This problem solved itself as the build progressed.
The next part of this sub assembly called for building and fixing the legs. I felt the disc would be better next because it would pull the rings into the right shape once it was affixed. The disc was very straight forward to make.
The next part of the assembly fixes the disc into the rings as the tea candle seat. I think it would have been better to depart from the instructions and fix the angle brackets to the long screws then bolt to the disc instead of the other way around. This would be less fiddly.
The final part of this assembly is building and fixing the three legs for the stand. I put them together then when ready to fix them to the ring I found I should have read the instructions properly and had to take them apart again then put them back together the right way – they’re fixed to the rings as they’re made not after they’re made.
The legs and the disc together pulled the ring into a circular shape and gave this floppy assembly rigidity. The final step is to tighten everything up – this would be easier if the legs didn’t block access to the screw heads! I perservered with doing up the nuts. It is probably just as well you cannot get to the heads because it stops you over-tightening and wrecking the rings.
The candle stand assembly is complete.
Elapsed Time 0:50 Top Cover Assembly
This time I read the whole assembly instruction before I started work on the assembly. I started by cleaning up the power cylinder. The instructions call for sand paper and a craft knife. You could use this, but I used small jewellers’ files, find wet and dry paper and a final polish using stiff cardboard. It was fairly clean and the inside edge had already been cleaned up. I was very careful to ensure the base of the cylinder was completely flat to ensure it sealed well with the top cover later. The cylinder is made of aluminium which polishes well with stiff cardboard. I wiped the cylinder very carefully after this practice and test fit the graphite power piston. It is really important that the cylinder and power piston don’t get any metal dust as they might bind and jam.
The top cover was completed without any particular dramas. The small screws and nuts were a bit frustrating. I eventually nicked my wife’s eyebrow tweezers to hold them! When I dropped them I used a slightly magnetised knife blade to get them back from awkward spots.
Elapsed Time 1:20 Crankshaft Support Assembly
The first task was to build the crank supports. These are put together following the instructions by stacking the components .
A short time later we end up with the supports put together and mounted properly perpendicular to the top cover. I checked this with a small machinist square and made some adjustments. You could also use a ruler or triangle shape. This assembly went together very quickly. From here on in the build process speeds up considerably. Perhaps the earlier assemblies should have been further broken down to keep the steps reasonably even in time and effort.
Elapsed Time 1:35 Propeller Assembly
I differed from the instructions slightly at this point by assembling the blades and bolting them together loosely at their outer end. The instructions called for building them on the crank but this way seemed easier. It was easier to keep them together and bolt them to the crank now that they were assembled. To avoid breaking through the cardboard I tightened the screws using a jeweller’s screw driver and held the nuts in my finger nails. I'd advise checking these screws before every run. I considered using some Loctite but wasn't sure what it might do to the cardboard. I think in hindsight I will reset just the outer screws with Loctite because I wouldn't want one in the eye flung off at 500rpm!
Once I completed the assembly I temporarily mounted it and tested it for balance and spin. It moved freely and would continue to spin for quite some seconds. The instructions don’t tell you what to do with the blade with an extra hole in it. In case it isn’t obvious the third hole goes over the crank pin.
Elapsed Time 1:40 Fit and Adjust Crank Assembly
Natural light started to fail me at this point so I took a quick break and got a drink, some munchies and put on the room lights.
Coming back I started the crank and disc assembly. The instructions call for hammering the extra pin in the kit through the centre hole of the crank disk to enlarge it. I loaded the pin into a small pin vice drill and used it to drill its way into the hole. I think this gave a better result. I think that if you are not able to do this, I’d consider heating the pin in hot water before trying to push it in.
The next thing I did was to clean up and debur the disc. It was fairly clean but needed a little TLC. I dropped a bead during the assembly of the crank and it simply vanished! Fortunately there are some spares in the kit. If you lost them all some glass beads from your local arts and craft store would do.
This shot shows the finished crank and disc assembly affixed to the propeller. A gentle tap on the propeller set it spinning freely so assembly is going well so far.
You can see in these shots the progress on the cranks with fitting the tubes and pins. You can also see how small the little beads that are used for bearings are - no wonder I lost one!
The next step is to put the connecting rods together. The design uses metal pins and flexible tubes to make this simple. This is one of the reasons that the work does not have to be perfect for the engine to run.
Once the conrods were done, I connected up the power piston and test fit it to the crank. It was bottoming out at BDC (bottom dead centre) so I had to adjust it by pulling the steel pin upwards on the conrod to shorten the stroke. This is a really simple adjustment and very good design idea.
In this shot you can see the power piston at TDC (top dead centre) showing that it nearly but doesn’t quite pop out of the cylinder.
Elapsed Time 1:55 Displacer piston and conrod assembly.
Argh! The first thing the instruction in this section say made me change the setup in the previous assembly. I had to remove and rotate the power piston conrod so the pin would face the support structure. An improvement to the instruction would be to move the advice about the pins facing the support structure into the previous section.
Building the displacer and conrod connection was exactly the same as the power piston. The displacer piston was topping out at TDC so had to be adjusted to that it would not touch the top cover.You can be generous here because there is no chance of it bottoming out in the can. The pins simply are not long enough to allow it. I adjust both by hauling the connecting pins upwards in the tubes using pliers without disassembly. The displacer is the foam pad in the photo.
Elapsed Time 2:00
All finished and time to light up.
I lit the candle and waited for the engine to heat up for a couple of minutes then gave the prop a spin. It seemed to bounce then started to pathetically run backwards (anti clockwise). I adjusted the crank timing a little past 90 degrees and tried again and off it went. I tinkered with it for a bit and achieved just on 500rpm as measured with my little electronic tachometer.
I decided to see how strong it was and stuck my finger in the fan. While it did stop I won’t do that again – this is a fairly powerful engine for such a small one. The can gets quite warm - while I don't think it is an issue I would not leave the engine unattended or leave it with children unsupervised.
As I mentioned in the product review, I really enjoyed this build and at the end of it have a magnificent little running engine for a very low financial outlay. I highly recommend this kit for beginners and seasoned model engineers alike. It is a fantastic way to make a foray into the Stirling engine and offers a path to bring the jaded short attention span youth (was I any different as a kid - I think not :) into the hobby.