Category Archives: Toys

Böhm Stirling Engine HB13

I got the finest Christmas gift imaginable: a Böhm Stirling Engine HB13. I will write a few things about it here.

Compared to a Steam Engine
I also own a Wilesco D10. Don’t know if you want to get a Stirling Engine or a Steam Engine?

The Steam Engine is more robust and less sensitive to friction. It is more powerful and can be used to power different toys and accessories.

The Stirling Engine is more clean, more silent, and requires less preparation and cleaning up. The Stirling engine feels more safe as there is much lower pressure involved, and no boiling water.

Building it
I got the build-it-yourself Bausatz. That was a good thing. The website indicates it takes about 2h to assemble. Well, if you are that fast you are really good, but it does not take so much longer. You need a set of torx drivers, and you need to not lose any parts (some parts are very small). If you dont see well, or your hand is not very stable, dont build it yourself.

The tricky part with building it was the little liquids, fluids and grease. My package came with SuperGlue for the Ball bearings – very well – I know how to use it and the package said super glue. Then there was some oil – you can add it later, dont worry while building. Finally there was something called “White ceramic grease” – I suggest you wait with that one too! First build and test drive – then add oil and grease if needed.

The good thing with building it yourself is that if you later feel like cleaning/lubricating/fixing it, you already know all the parts and taking it apart a little will not scare you.

Fuel and fire
The instructions tell you to use 96% ethanol – great if you can purchase it legally. I cant. However, there is denaturated alcohol available for sale – in Sweden it is called Rödsprit – and it works very well.

Now, I had some problems getting my Engine running in the beginning. I suspected friction, too much ceramic grease and too little ceramic grease. In fact, there was a slight draught/wind where I ran the machine and the flame did not heat the heating cylinder perfectly. So my first advice; protect the machine/fire with little boxes/walls to ensure the flame is completely still and effective.

You may need to heat the machine for up to a minute before it can pick up speed. Give it some time before you proceed with checking the friction.

Friction
The Stirling engine does not have much extra power and a little friction can make it fail. If you disconnect the Working Piston / Arbeitskolben you can manually carefully slowly move it up and down. This should be quite hard due to air pressure. If you remove it completely you can let the machine spin freely. It should be quite noiseless and spin easily. If you spin the wheels it should do 3-4 revolutions before coming to a halt (with the Working Piston in place you barely get one revolution). I applied a little oil to the Displace axle / Verdrängerachse as well as to the Crank Shaft (where the connecing rods connect to it).

The amount of Ceramic Grease required on the Working Piston is minimal. I first added enough when building it. I then added far to much when trying to make the machine run better. I finally removed almost all grease I could both from cylinder and piston to make it work again.

Improving it
I find it weird that there is absolutely no insulation between Heating Cylinder and Cooling Cylinder. After all, it is difference in temperature between these two cylinders that make the machine work. I tried to add a thin layer of something between the two cylinders – so far not with very good result. A thin piece of hobby plywood did not maintain pressure/vacuum, and the machine did not run at all. A thin piece of cardboard appeared to work – the machine quickly accelerated, but when reaching top speed it quickly slowed down, to accelerate again. It kept “oscillating” in this way until i shut it down. Perhaps the design has a natural top speed – after all, air is shuffled back and forth, and has to change temperature, and this might require some milliseconds per revolution. I now run the machine with a paper insulation about 0.2mm thick. It works very fine, dont know if it really improves anything though.

I also tried to cool down the cooling cylinder by spraying it with little water. This helps surpisingly little, and is not required. With proper fireing the heating cylinder remains much warmer than the cooling cylinder anyway.

Performance
My machine, when fueled by spirit (denaturated ethanol) runs faster and faster with time. First minutes about 500 rpm. Later above 1000 rpm, and sometimes I have been able to get it up to 2000rpm, after like 20-30 minutes of continous operation.

If I power it with a tea candle (remember, not allowed since it soothens the model) it runs between 400-500 rpm for a while (perhaps up to 10 minutes). After that it comes to a halt.

My conclusion is that the machine essentially runs better at high temperature, but that the tea candle does not produce enough heat to keep the temperature difference up at high temperatures.

Measuring RPM
How do I measure RPM of my Stirling Engine? A device that listens to audio and measures RPM is called “Acoustic Tachometer”. I tried to find one for my iOS device and for my Symbian device with no success (however, there is supposed to be an app for Android simply called RPM).

I ended up programming my own Acoustic Tachometer. It runs in Linux and listens to /dev/dsp, and tells the RPM. It works, but not perfectly. The output has to be interpreted. I may improve it and/or share it some day. Feel free to comment if you are interested – I am happy to share my source code. But I guess the number of people who have a Stirling Engine AND compiles their own linux-binaries is quite small. I’d like to write an iOS version though, but my algorithm has to be better first.

Photographing a model backdrop

I decided my model train layout (Märklin Z) needed proper background image (a backdrop). If you google for it, you find many nice backdrops for sale. Those are probably fantastic, but I did not find one that works for me.

I will start with the result.

Backdrop

This is a panorama that is 180×15 cm, and most standard backdrops I found were not so extreme panoramas as I wanted. Also, when making it myself I could get the landscape I wanted.

Photographing
This is what you need:

  1. A location with unobstructed view over the horizon
  2. Good weather conditions, preferably the sun in your back
  3. A tripod

And of course, you need a camera. I made use of the following features of my Nikon P7000 when photographing my panorama.

  1. RAW mode (to ensure white balance etc are identical for all pictures)
  2. Delayed shutter or remote shutter (to keep camera absolutely still)
  3. Manual mode (you want the same shutter speed and aperture for each picture
  4. Grid 3×3 (to help with proper overlap
  5. Horizontal indicator (to help getting the horizon straight
  6. 200 mm equivalent zoom (to be able to take several pictures at a limited horizon stretch)

I only rotated the camera using the tripod between each picture, keeping the horizon exactly in the middle of the pictures, and I let the pictures overlap 1/3.

Essentially, the math goes like this. I wanted at least about 150-200 dpi for my final print of 180 cm. This requires a picture that is about 15000 pixels wide. Ideally I would use a camera with 15000×10000 pixel sensor (that is 150MPixels) and just crop the picture. I have no such camera, but my Nikon P7000 is about 3600 pixels wide. With an overlap of 1/3, it means each picture contributes with only 2400 pixels, so I need a series of about 6 pictures to get a 15000 pixels wide result. Now this is where telezoom comes into play. At 200mm, each picture is about 10 degrees. The more telezoom you can get, the shorter horizon you can work with.

Dont overexpose! You want the sky blue – not white. If you have UV filters and stuff – great. But I suggest you underexpose a bit.

Panorama stiching
I used Ubuntu and tools that come with it to create my panorama.

First I imported all my series into Shotwell. That means, I let Shotwell do the RAW developing, which turned out ok (all pictures had the same white balance, etc) – perhaps I was just lucky. I picked my best series, and exported all pictures from that series at highest quality.

Second, I used Hugin Panorama Creator to create the actual panorama. I choose Lens Type = Panoramic (Cylindrical). This is a lie (and at 200mm it is a small lie), but it created the completely straight horizon I wanted.

Finally, I did some cropping and color adjustments in Gimp.

Printing
How to print something that is 180×15 cm? My first idea was to print several standard 15×10 cm photos and just display them next to each other. Problem is, you never know if the crop your pictures a little bit, and in this case it would destroy the result completely.

I ended up (in Gimp), cutting my 15000 pixel panorama into 3 pieces (each 60x15cm), and pasting the 3 pieces to a 5600×4000 image. I left white margins around each piece.

I then sent my single big picture to print on standard photo paper in 70x50cm. I cut out the 3 pieces with a razor and mounted them next to each other.

Conclusions
I did not have so high expectations. My plan was to learn from my first attempt and do everything over again a few times. But my first result was really above expectations – and very much good enough for my purpose.

You do not need higher DPI than I had (15000 pixels for 180 cm). You can probably do with less.

I am very happy with my sky (~RGB=135,166,186) and the sea colors (~RGB=32,63,97).

Printing on normal photo paper was good – the result is nice. The edges between them are not perfect though.

Pulling your Märklin Z 86501

Isn’t it annoying? You just set up your new Märklin Z-layout, but the tracks are a little bit dirty, rusty or whatever, and the the trains stop all the time.

You bring out your item 86501 Gleisreinigungswagen, but it is too heavy to pull up your long 3% slopes. And it is not so practical to just go downhill.

This is what I did:

How to pull your 86501

Several advantages:

  • Double pulling power
  • If one engine loses electrical contact, the other one takes over
  • Looks good!

Hope you found this helpful!