Author Topic: A digital governor for model engines  (Read 3681 times)

Offline MJM460

  • Full Member
  • ****
  • Posts: 1091
  • Melbourne, Australia
Re: A digital governor for model engines
« Reply #120 on: May 22, 2020, 01:48:17 PM »
Hi Jadge, I guess that means the TS1, which was the first transistor I ever bought, is now well and truly ancient history.  And it cost a whole weeks pocket money!

Hi Kim, welcome to the growing sub-bunch of electronics enthusiasts here on the forum.  Just as well we need things like governors and ignition systems to allow us to combine our interests.  I am definitely the amateur among most of you, and it has been a great help to me on this project to find so much expertise.

Hi Gary, so long as it was food grade chloroform.  Good to hear that your mother kept an eye on your chemistry experiments.  Putting the pressure cooker on the BBQ to make steam for your boiler gets us almost back to where we started this little side track.  The aluminium pots obviously hold pressure at that level, and even with a flat bottom (unswayed) and nearly flat top, both definitely frowned upon by boiler inspectors.  I know our boiler codes are quite conservative, but copper boilers have the advantage that they tend to fail in a more predictable manner.  I am not sure about the aluminium pot, I have seen melted saucepans, but the pressure adds a new dimension to the hazard.  It would not be good to increase the pressure by adding weight to the safety valve, and definitely necessary to make sure that your method of getting steam to the engine did not disable the safety valve.  Other than that a fun idea.

Hi Awake, you didn’t miss it, but you have raised yet another issue on which there is no previous data (that I know of, anyway.) Those issues seem quite topical these days.  So perhaps you could start to build the data set.  Please let us all know how it goes.  Don’t know how you would design a double blind randomised trial for it though.

Hi Muzzer, good to hear from you.  It really has been an interesting review of the history and the progress that has brought us from those very early transistors that were first released to the market to the point where even I can build an electronic governor to control an engine, and complete the loop by joining it to a steam engine.  The integrated circuit in my little 8 pin chips probably includes the equivalent of hundreds of those early transistors. 

Well not much to report today on my governor.  My wife fell off her bike Friday, and after a few days thinking it was getting better, it took a turn for the worse.  Not a high speed crash fortunately and the ground where she landed was grassed, but she also landed on the end of the handle bar.  So I have been busy doing all the household chores, as well as organising a visit to the doctor.  Doctor says nothing obviously broken and thinks the extra aches and pains are part of healing, but ordered a scan for Tuesday to explore it further if it is not better by then.  All very time consuming, and even funny if it was not so painful.  But it has given me time to take a breath and think through where I am up to.  Also for some excellent lessons in electronics, from which I am sure that I am not the only one who has learned something new.  And time also for this great recap of the history.  I did intend to run the engine on steam, but that is still to come.

Thank you all again for looking in,

MJM460


The more I learn, the more I find that I still have to learn!

Offline steam guy willy

  • Full Member
  • ****
  • Posts: 2425
Re: A digital governor for model engines
« Reply #121 on: May 22, 2020, 02:18:02 PM »
 Hi All...interesting stuff on transistors.  NPN  PNP. matched pairs >>>> also I think I was told that they made them in the hundreds then swept them up off the floor >>>then when they tested them they put the relevant number on them ?? citation please!!  So what is the modern equivalent of an OC71 ??  also I need an EF92 for an old Sky king radio ...Using a pressure cooker for an oscillating engine would be helpful at parties for cocktails...Shaken  or Stirred. sir?.....  Now back to governors.....!!


Willy

Offline Bluechip

  • Full Member
  • ****
  • Posts: 869
  • Derbyshire
Re: A digital governor for model engines
« Reply #122 on: May 22, 2020, 02:50:53 PM »

  also I need an EF92 for an old Sky king radio ...

Willy

Good Lord .. last time I bought a valve was about 2003-4,   an EF86 for a Mullard 2-valve pre-amp a mate acquired. Quite why I don't know and I suspect neither did he.   :facepalm:  Maybe his central heating had packed up ??

Got the valve from Watford Valves and lo .. it appears they're still in business  :o

https://watfordvalves.com/product_detail.asp?id=4706

Dave

Online Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 4331
  • Switzerland
Re: A digital governor for model engines
« Reply #123 on: May 22, 2020, 07:53:21 PM »
Long long ago I made an oscillating cylinder engine from an old car brake cylinder with no more than a bench drill and luck. This was powered by my mothers pressure cooker and drove a bike dynamo. With 2kW input from the cooker it could just about light a small torch (flashlight) bulb  ::)

In response to the other part of the thread I believe that it was noted in a Monty Python sketch that you had to cook a piston engine, you couldn't eat it raw (I'll get my coat  :toilet_claw: )
Best regards

Roger

Offline Admiral_dk

  • Full Member
  • ****
  • Posts: 1720
  • Søften - Denmark
Re: A digital governor for model engines
« Reply #124 on: May 22, 2020, 09:01:21 PM »
Just to inform those interested - Valves / Tubes are still in production !!!! - unlike Germanium Transistors.

The reason is that the vast majority of guitar amps use Tubes .... for the simple reason that it is much simpler to make a great sounding amp with tubes than with other technologies. The HiFi nerds are also using tubes although this is almost more religion and faith, than common sense ....
The backside is environmentally unfriendly power consumption and sensitivity to transport. There are other applications that never stopped using tubes too - but I expect this to fade out with new technology.

As to germanium transistors and diodes (I noticed somebody saying the are still in production - BUT they can't be found) are long dead is that newer tech works a lot better and has much better reliability.

Silicium is really starting to be yesterday's tech now in Power Conversion - AC/DC, DC/DC and DC/AC as Silicon Carbide (SiC) and Gallium Nitride (GaN) can cope with much higher Power, Voltage and Ampere, with much higher efficiency and reliability.

Offline steam guy willy

  • Full Member
  • ****
  • Posts: 2425
Re: A digital governor for model engines
« Reply #125 on: May 23, 2020, 02:10:12 AM »
Final word  from me about Valves/tubes. Don't forget the KT88's.................

Willy

Offline MJM460

  • Full Member
  • ****
  • Posts: 1091
  • Melbourne, Australia
Re: A digital governor for model engines
« Reply #126 on: May 23, 2020, 02:02:17 PM »
Hi Willy, I could give you a 6BM8 or two and and an ECL82.  But no EF92 unfortunately.  A long uninteresting story behind how they came to be sitting in my cupboard.  One of then has a note on it saying “used but OK”, dated in ‘87. 

I started out only aware of a few transistor ignition projects on the forum, mostly without much detail of how the designs were developed.  Not exhaustive research and I could have missed some, but I have been surprised and delighted to find so many forum members with such advanced expertise in electronics.  Perhaps there will be more governor projects now.  Especially as these little chips and the many similar ones do make the circuitry relatively easy.

I wonder who will be the first to apply one to an IC engine, with the servo not only adjusting the air and fuel flow, but also adjusting the timing accordingly.  Perhaps two servos so the timing can be separately characterised.  Or a small hit and miss which idles over a bigger range between hits.

Thank you for all the very interesting replies.  I think Roger deserves the prize for the most creative answer to the ultimate question, as to why are both pressure cookers and engines feature in this thread.

Today I achieved another two steps.  They were big ones or small, depending on your point of view.  First I revised the program to allow the servo to go further closed than before to extend the available speed range down to about 300 rpm.  In the process, I found that my equation for the relationship between the pot position and the set point speed was also limiting the range, it was not just my imposed low limit.  I had initially found the engine did not like running very slowly, so set a limit where it kept running, but it has definitely freed up quite a bit with the last few days longer runs.  I suppose not surprising, its well over a year since the last series of boiler tests, with no running since then.  Five minute runs to find the program was still not working never quite loosened it up.  I tested this on air to see that my changes had not included a new error.  But it did hunt a bit at the slow end of the range, so I need to put in that second potentiometer to allow a bit of proportional band adjustment, or perhaps a mathematical solution.

Then I fired up the boiler and ran it on steam.  It was icing in the cake to see the engine ramp itself up as the cylinder warmed and condensate cleared, until the governor came in smoothly to control the speed nicely steady.  Not too bad in the way of steam leaks, my flanges were tight, the governor valve worked just like it had on air.  No gland leaks on the glands of the governor valve or the stop valve.  The bonnet of the stop valve is only sealed by metal to metal seating.  It leaked a little, so a gasket is in order.  I will try a paper one.  The bigger leaks were from the engine piston rod and valve rod glands, so it seems like a little fiddling with repacking those is in order.  But it ran up to nearly 2000 rpm, I think that’s not bad for the simple methylated spirits burner.  Plenty of water left at the end of the run, and without detailed measurements, I think quite a lot more than on the previous running.  I will need to do a more careful test, but it appears be quite clear that restricting the speed by the governor does reduce steam consumption as you would expect.  It is tempting to make a larger fuel tank, but then, if I ran the engine faster, I could run out of water, so a gauge would be required.

On the electronics side, I need to apply some coating to the circuit boards for long term corrosion protection.  I am also planning to put them in a sealed container.  In the open, under the engine platform is a bit too close to any steam leakage to be really suitable.  I had a simple plan when the circuit started out as one small board which contained the controller and its power supply.  But now with the power supply on a separate board, and a separate servo driver board, a bigger enclosure is required.  Also, it would be better to move the potentiometer and really all the electrical parts out to a separate enclosure.  Only the speed pickup and servo have to be near the engine.

Then on the program, I will try a second generation, revising the maths with the benefit of the learning so far.  My initial decisions are working, but some functionality could be simplified.

I guess that is the nature of a development project, the scope for just another improvement seems endless.  It might be slow progress from here as another project is calling louder each day.

MJM460
The more I learn, the more I find that I still have to learn!

Offline jadge

  • Full Member
  • ****
  • Posts: 444
  • Cambridge, UK
Re: A digital governor for model engines
« Reply #127 on: May 24, 2020, 10:17:13 AM »
As to germanium transistors and diodes (I noticed somebody saying the are still in production - BUT they can't be found) are long dead is that newer tech works a lot better and has much better reliability.

Silicium is really starting to be yesterday's tech now in Power Conversion - AC/DC, DC/DC and DC/AC as Silicon Carbide (SiC) and Gallium Nitride (GaN) can cope with much higher Power, Voltage and Ampere, with much higher efficiency and reliability.

Germanium diodes are made by American Microsemiconductor:

https://www.americanmicrosemi.com/tutorial/germanium-diodes/

I can't see silicon disappearing any time soon. I've used silicon carbide devices for a high temperature (>200°C) inverter, but the devices are expensive if you don't need the high temperature capability. Gallium nitride is good for power RF devices as it has a very high electron mobility, but it is also a high bandgap material so the forward voltage across a junction is high - can't see that being an advantage in general power devices.  :)  Ultimately engineering is all about money and silicon devices are relatively cheap.

Andrew

Offline jadge

  • Full Member
  • ****
  • Posts: 444
  • Cambridge, UK
Re: A digital governor for model engines
« Reply #128 on: May 24, 2020, 10:37:02 AM »

Just as well we need things like governors and ignition systems to allow us to combine our interests.
I had a play with ignition systems a while back for my hit 'n' miss engine. The intention was to make a system that only needed a 10:1 turns ratio in the coil. I got about 8kV on the secondary, from a 12V primary supply, before I overheated the transistor and then moved onto something else. I suspect that a 20:1 turns ratio would be better. I used an avalanche MOSFET with a fast turn off to generate a spike on the primary which should be reflected onto the secondary.

Most discrete MOSFETs have a diode from source to drain which is a consequence of the manufacturing process. In some devices the diode is characterised and can be used instead of external diodes in H-bridges for instance. In an avalanche MOSFET the breakdown voltage of the diode is specified. When a MOSFET with an inductive load turns off naturally the source voltage rises. Eventually this will over-voltage the source and blow the device. But in an avalanche MOSFET the diode breaks down first, protecting the transistor. In my system the breakdown voltage was nominally 800V. I was getting turn off times less than 100ns, which is a bit slower than I'd like. With some tweaking of the turn off driver I should be able to get below 50ns.

Andrew

Offline MJM460

  • Full Member
  • ****
  • Posts: 1091
  • Melbourne, Australia
Re: A digital governor for model engines
« Reply #129 on: May 24, 2020, 01:39:08 PM »
Hi Jadge, at my stage, I can often do a simple analysis of a circuit, at least enough to have a basic understanding of how it works.  But it is the the difference between having a feel for how it works, and the detailed considerations of the component selection, that is a whole new level.  It is most interesting to learn about the design process for your ignition system, and the differences between different though similar looking components.  I do hope that you are still developing that one and will eventually start a thread to help us all appreciate it.

I know that the voltage generated in the coil is dependent on the rate of change of current, so switching  time is obviously important.  But how did you decide on your target of 100 nS?

MJM460

The more I learn, the more I find that I still have to learn!

Offline jadge

  • Full Member
  • ****
  • Posts: 444
  • Cambridge, UK
Re: A digital governor for model engines
« Reply #130 on: May 24, 2020, 02:39:45 PM »
I know that the voltage generated in the coil is dependent on the rate of change of current, so switching  time is obviously important.  But how did you decide on your target of 100 nS?

Correct, Faraday's law of induction states that:

v = -L(di/dt)

In words the voltage equals minus the inductance times the rate of change of current. I wanted a fall time of a few tens of nanoseconds. Simple 74 series logic switches in a few nanoseconds but switching a MOSFET is a bit trickier. While the gate input resistance of a MOSFET is high it is also capacitive. The important parameter on datasheets is total gate charge. This is number of coulombs that need to be supplied to the gate to turn the device on, and which have to be removed to turn the device off. Coulombs are current times time. For the MOSFET I used the total gate charge is 52nC, worst case. If I want to switch in 10ns then I need to remove 5.2A for 10ns. That is quite demanding. And the switching times are close to what my oscilloscope can measure. If we aim for 50ns then the current requirement drops to 1.04A which is easier to achieve.

Andrew

Offline Admiral_dk

  • Full Member
  • ****
  • Posts: 1720
  • Søften - Denmark
Re: A digital governor for model engines
« Reply #131 on: May 24, 2020, 10:10:35 PM »
Quote
Germanium diodes are made by American Microsemiconductor:

https://www.americanmicrosemi.com/tutorial/germanium-diodes/

OK - thank you Andrew on setting me straight on this one - but also strange as a big part of the music industry sobs over that they can't get any Germanium Diodes .... + Googling do not bring them up -> people pays a small fortune for NOS Russian Ge Diodes as they apparently are the last available in the World ....

Quote
I can't see silicon disappearing any time soon. I've used silicon carbide devices for a high temperature (>200°C) inverter, but the devices are expensive if you don't need the high temperature capability. Gallium nitride is good for power RF devices as it has a very high electron mobility, but it is also a high bandgap material so the forward voltage across a junction is high - can't see that being an advantage in general power devices.  :)  Ultimately engineering is all about money and silicon devices are relatively cheap.

I have started to see both kinds in consumer products - but I will agree that silicon will not disappear anytime soon in IC's and many other components - I just added the comment as an indicator about time and progress always moves forward.

Sorry about straying outside this thread MJM.

Offline MJM460

  • Full Member
  • ****
  • Posts: 1091
  • Melbourne, Australia
Re: A digital governor for model engines
« Reply #132 on: May 25, 2020, 01:31:16 PM »
Hi Jadge, that is some current to manage.  Not what I would usually expect in the base/gate circuit of an electronic application, and I can imagine the difficulty of handling it. 

Just looking at the equation for Faradays law again, I noticed the analogy with the mechanical system in Newton’s law, where to change that state of uniform motion, you need an external force.  Mathematically this becomes Force equal time rate of change of momentum.  As momentum equals mass times velocity, and for practical purposes mass does not change.  The direction of the force is opposite the direction of the velocity, so

   F = - m (dv/dt) 

A very similar equation, complete with the - sign.  So we have a component of an analogue computer.  It reminds me we had an introduction to those over 50 years ago when digital computing thought 16 k was a huge memory, but mostly forgotten now.

I have used both the induction and the momentum applications before, just never noticed the similarity.

Hi Admiral, no need to apologise.  The historical points coming out are quite interesting, and just reinforce the understanding of the wide range of interests we all share.  Quite a few hiding their lights under bushels.  Perhaps we need a chatterbox thread about electronics, or another, but more advanced governor project by one of our experts.

My posts will be a bit further apart now as the governor seems to be complete and working.  I will do some of the little tidy up jobs I have mentioned, as fill in jobs over the coming winter evenings.  But they won’t be very exciting to describe.  If something fundamental changes, I will certainly describe it, otherwise just a final report when they are done. 

Now that the best weather of our year is over, we will be allowed overnight trips from next week, so have some catching up to do.

MJM460


The more I learn, the more I find that I still have to learn!

Offline steam guy willy

  • Full Member
  • ****
  • Posts: 2425
Re: A digital governor for model engines
« Reply #133 on: May 26, 2020, 01:44:16 PM »
I do not agree with your interpretation of Copyright Jason, each case must be considered in context.

In the future if any one has any concerns about a post could they please use the "Report to Moderators"  feature, rather than taking it upon themselves to police our forum. Thank you.

Jo


Hi Jo, nothing do with copywrite and just wondered if you recognise the castings for this ancient table engine that someone gave me a photo of ...it was in a derelict house that someone visited just before it was being demolished ...no further details however ....Thanks

willy

Online Jasonb

  • Full Member
  • *****
  • Posts: 7182
  • Surrey, UK
Re: A digital governor for model engines
« Reply #134 on: May 26, 2020, 02:41:10 PM »
looks a bit like a Tayport, how do the sizes compare?

http://www.brunell.com/product.asp?cookiecheck=yes&P_ID=126&numLanguageID=1