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Author Topic: Flash steam plant control.  (Read 93290 times)

gondolier88

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Re: Flash steam plant control.
« Reply #100 on: June 28, 2010, 11:21:11 AM »

Hi Ian,

I see your point about the nozzle, your consumption will be low, howevr it will still contribute, I'm sure with your skills you can probably time to the second how much shorter your runs are %)

The fan draft system was widely used on both high speed steam boats and most Navy and Merchant Navy boats. Some had dedicated 'fan engines', usually by Mumford's, even the small 50' picket boats had dedicated air tight boiler rooms and fan engines.

The prototype nearest to what your acheiving is probably the Thornycroft designed, Simpson & Strickland built 'Rose en Soliel', or 'Satanella', can't remember who built those two.

A few boats left with forced draft;

ST Canning- electric fan
SL Osborne- engine driven fan
SS Sheildhall- engine driven fan

Greg
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flashtwo

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Re: Flash steam plant control.
« Reply #101 on: June 28, 2010, 06:43:15 PM »

Hi,

Talk about 2 revs ahead and 1 rev astern.

I just been testing the monotube boiler with its new steam Induced Draught (ID) gizmo and have run into a new problem.

The plant performs superbly at high steaming conditions, but when I run with a low feed flow to enable lower RPM the boiler now starts "hunting", i.e. the boiler pressure and temperature swing increasingly up and down until the high temperature trip shuts it down.

This happens quite slowly and I never had it before the ID nozzle was fitted. I suppose as the pressure builds up, more air is drawn into the boiler improving the combustion, which causes the pressure to increase even more. Then the engine accelerates, dropping the steam pressure and reducing the combustion. The engine slows down, then the pressure builds up thus repeating the cycle.

I've tweeked the gas valve controller to counter-act the swing. It has reduced the amplitude so the high temperature trip doesn't occur, but now the gas valve servo is having to work a bit harder.

Comparing Vital Byte's boiler to the steam jet boat's, it is obvious that VB's is too restricted on the air intake around the burner. Perhaps if I open up the intake fully then the swinging will stop.

Ian.
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benjaml1

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Re: Flash steam plant control.
« Reply #102 on: June 28, 2010, 10:38:28 PM »

Are you using 3 term ( PID) control or a reactive algorithm ?
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flashtwo

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Re: Flash steam plant control.
« Reply #103 on: June 28, 2010, 11:44:48 PM »

Hi Benjamin,

I'm just using P & I (no D) coded in software.

I did set the temperature controller settings to minimum sensitivity and, even with the gas valve not changing its position and the feed flow constant, the swing would start.

This does imply that the feedback  mechanism is within the boiler design (i.e. with the ID nozzle fitted) and not in the control loops.

Giving my age away perhaps, what's the "reactive algorithm" that you mention? - sounds interesting.

Ian
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benjaml1

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Re: Flash steam plant control.
« Reply #104 on: June 29, 2010, 10:10:37 AM »

PID ( three term control) will work well as long as the required control band/range ( high & low feed) characteristics are reasonably linear.... If not, you will need two PID loops one for low range & one for high. This is called ( by Honeywell) reactive tuning. There are other programs out there which rely on "history", which memorise finite input parameters & set the control parameters for that situation after pumping them into a huge data bank. They are extremely expensive "Brainwave" being one...

My suggestion would be to search for programs that include "D" in the PID loop, failing that 2 PID loops as it would seem the control parameters are not linear across the full range....

This says it better than I can....

http://team358.org/files/programming/PIDControlTheory_rev3.pdf
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steamboatmodel

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Re: Flash steam plant control.
« Reply #105 on: June 29, 2010, 03:10:17 PM »

I studied PID loops back when I did building maintenance, never thought I would have to think about it for model boiler control. I wonder if my notes from 35 years back are still relative.
Regards,
Gerald.
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flashtwo

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Re: Flash steam plant control.
« Reply #106 on: June 29, 2010, 03:42:18 PM »

Hi,

Benjamin, you obviously have a control background - Honeywell Avionics?

I understand now, it is what I knew as adaptive control where the control terms varied according to the load of the system.

The other I knew as matrix control, where a data matrix held all the data throughout the control range and updated it under varying plant conditions.

I've never really used derivative (anticipation) control, because it amplified noise on the signal and could cause erratic control. I much preferred feed forward, which is what I use between the feed flow control loop and the temperature control loop; when the feed is increased the temperature set point is raised in anticipation of the temperature dropping and vice-versa.

I was thinking of varying the temperature control loop control terms relative to the gas valve opening value; it would be a simple linear relationship rather than an additional PID loop.

Gerald,

Yes, exactly the same principles are involved. You measure the thing you are trying to control, compare it with a desired value and then adjust an actuator which controls the thing you are measuring. It doesn't matter whether its the H&V of a building or a missile control system.

Apologies to all other Mayhemers who haven't a clue what what we are talikng about.


Ian
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gondolier88

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Re: Flash steam plant control.
« Reply #107 on: June 29, 2010, 05:53:15 PM »

Apologies to all other Mayhemers who haven't a clue what what we are talikng about.


Ian

Thanks!!! :o

Give me springs and diaphragms any day!

Just joking, I for one, and I'm very sure I'm not alone here, respect your take on what is a most versatile and dynamic part of model engineering/mosel boating, and you never know what else these control systems may one day manage...

Greg
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benjaml1

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Re: Flash steam plant control.
« Reply #108 on: June 29, 2010, 06:15:11 PM »

Thanks!!! :o

Give me springs and diaphragms any day! Greg

Interestingly enough PID control systems were made/functioned using springs/bellows/restrictor & levers in the good ole pneumatic days...Well before micro processors & are still in use all around the world...  :-))
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gondolier88

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Re: Flash steam plant control.
« Reply #109 on: June 29, 2010, 08:35:09 PM »

Ahh, i'm stuck in the good ole days, I don't feel so bad now :-))

Greg
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benjaml1

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Re: Flash steam plant control.
« Reply #110 on: June 29, 2010, 11:02:46 PM »

I have been offered a position with the nuclear energy peeps, not based on my neuvo technical intellect but my archaic knowledge of so say redundant pneumatic control systems...  :-))

Tried retirement & found that boring, 61 years old & going back to work...EH! I love a challenge    :-)

May be able to buy more steam goodies now...  ok2

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gondolier88

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Re: Flash steam plant control.
« Reply #111 on: June 29, 2010, 11:36:22 PM »

I see, so our 21st century powerstations recognise that steam should be mechanical not electric, but us model boaters think better, Mayhem to a 'T'! {-)

Greg
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benjaml1

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Re: Flash steam plant control.
« Reply #112 on: June 30, 2010, 08:53:47 AM »

I see, so our 21st century powerstations recognise that steam should be mechanical not electric, but us model boaters think better, Mayhem to a 'T'! {-)

Greg


 {-)  :-))
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flashtwo

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Re: Flash steam plant control.
« Reply #113 on: June 30, 2010, 09:30:20 AM »

Hi,

Wasn't it annoying when you found that tiny hole drilled in the flapper caused by the fine rust particles in the compressed air - it always used creep up unexpectantly.

Honestly, the old pneumatic systems were superb in a hostile environment of heat, humidity and dust and IF the compressed air was maintained to good quality they would last for years unattended, but the slightest bit of damp air and the compressed airlines would rust internally and you would be on the downhill path.

I started my career in a small power station that had no electronics at all, not even thermionic valves - it was purely hydraulic and pneumatic and, if you talked about using electronics, the old guard thought you were from another planet!

Saying that, despite all the computing power, the last link in the chain is still the hydraulic/pneumatic actuator though increasingly being replaced by electric actuators.

Can you imagine one of the old Taylor controllers on a model boat! No.

All the best

Ian.
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flashtwo

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Re: Flash steam plant control.
« Reply #114 on: July 08, 2010, 08:26:02 AM »

Hi,

Just to let you know that "Vital Byte" will be displayed and demonstrated at the Guildford Model Engineering Society steam rally this weekend, 10th & 11th July, 2010.

This V.B. will have its new control system and other modifications in operation.

See http://www.gmes.org.uk/find.htm for details of the Society's location.

Hope to see a few Mayhemers there as usual.

Ian.
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flashtwo

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Re: Flash steam plant control.
« Reply #115 on: July 11, 2010, 08:20:44 PM »

Hi flashsteamers,

New failure mode!!!!@~###

Yesterday and today at the Guildford Steam Rally, Vital Byte was put through its paces, but only for about 10-15 minutes.

Yesterday V.B. experienced a heavy clunking sound after about 10 minutes of near silent running. The sound seem to come from the prop shaft rather than the engine, but finally the power train seized and the boat was hauled out of the water.

I removed the cylinder covers and, although one piston needed tightening slightly, there was no apparent engine problem. I then found the prop shaft shear pin had fallen out after over a years service. I replaced then pin but found that the shaft seized at certain positions, but, if I lent on the stern, it would free up. I concluded that the very hot sun ( it was 31degC!) had caused the hull to warp during it's open air display.

Today I ensured that the shaft would turn whilst it was on diasplay and everything was ok. Then after several hours it was time for a pool demo and again after about 10 minutes of perfect running the shaft seized again!

What a puzzle.

Suspecting the pool water temperature, I put my max/min thermometer (its amazing what useful junk one carries) in the pool and recorded 27degC! The only thing I could think of was that I have some reiinforcing aluminium strip under the stern that was expanding and causing the hull to "hog", thus causing mis-alignment of the engine to prop shaft coupling. Normally, I run V.B. in the local lake where the temperature is quite low thus avoiding this problem.

Solution: open up the gap on the dog-tooth coupling to increase its tolerance.

There was another chap there with a tug powered by a D10 engine and his loc-tighted prop became loose on the prop shaft - whether this was to do with water temperature, I don't know.

Ian.
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flashtwo

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Re: Flash steam plant control.
« Reply #116 on: July 15, 2010, 12:42:08 PM »

Hi,

Here is a photo showing the fully tested and working AE-35 controller now being used on Vital Byte. With it is last years somewhat larger prototype and a 4inch piece of 7/8th brass for scale.

The AE-35 has basically the same functionality as the prototype, but uses smaller PICs for the pumps and engine RPM processing. The display processing and control functions are each in their dedicated 16F877s PICs and the PICs talk to each other via a serial link that enables a lot more data sharing.

The AE-35 still has the capability of being re-programmed and has had it's software code tidied up and simplified in parts. Having a dedicated display PIC gives a more reliable response to the push buttons located on the operator's control console.

Ian.
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benjaml1

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Re: Flash steam plant control.
« Reply #117 on: July 16, 2010, 11:52:48 AM »

Impressive....  :-))
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flashtwo

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Re: Flash steam plant control.
« Reply #118 on: July 17, 2010, 09:15:31 AM »

Thanks Benjamin...

No sooner was the AE-35 unit in V.B. then it was out for another software mod.

With the old system I could have the desired steam temperature set by the steam pressure, via an equation, to give the steam saturation temperature appropriate to the prevailing pressure. It did, however, suffer from instability if the steam demand suddenly changed causing the pressure to change and consequently the desired steam temperature.

The latest mod links the desired steam temperature with the desired feed flow (set by the radio transmitter). As the desired feed flow increases, it is anticipated by the controller that the steam and pressure will increase with an appropriate increase in saturation temperature. If the heat input isn't increased accordingly, then wet steam conditions would be experienced.

The new mod addresses this problem by adding a proportion of the feed demand value as an offset on the manually set desired steam temperature. Since the feed demand is a constant, though manually adjustable, the system is stable in its operation.

Next project a computer controlled flash steam calliope? Then I could really start playing some tunes on it!

Ian.
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benjaml1

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Re: Flash steam plant control.
« Reply #119 on: July 17, 2010, 11:12:36 AM »

It amazes me the level of technology that has found it's way into steam model building. I'm still in the stone age.... :embarrassed:
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steamboatmodel

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Re: Flash steam plant control.
« Reply #120 on: July 17, 2010, 06:10:19 PM »

It looks impressive. I haven't used a 16F877 PIC yet, I am still working out the basics (in assembly and C ) with a PIC 2 starter Kit with the 16F690 pic. I also have a 16F627, 16F628 to play with once I get them down I will then advance to a 16F886 28pin pic and then the 16F887 44pin pic. So far I have done the "Hello World" bit and got the leds to flash without letting any magic smoke out, my next step is to do servo positioning and reading RC signals.
Regards,
Gerald.
PS It was much easier learning things forty years ago when I was in my twenties. Then I would write notes and remember things without having to look at the notes, now I not only have to write the notes, I have to remember where I put the notes and the right glasses to read them.
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flashtwo

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Re: Flash steam plant control.
« Reply #121 on: July 19, 2010, 08:07:39 PM »

Hi,

Vital Byte produced her best performance yet at the Blackheath Club meeting on Sunday.

The meeting was really for the straight runners, but Steamboat Phil encouraged me to get V.B. out on the water before the competition started.

Before launching, V.B. had the honour of being inspected by Alan Rayman one of the authors of "Experimental Flash Steam" - I hope he approves of the modern technology!

Several of the members were proud owners of Alan's boilers and engines, some being 30 years old or more.

All the changes made to V.B. over the last six months came to fruition - a good quick start and then she was off with her new prop, new computer and new boiler coil.  I gradually pushed her up through the power range, by remotely increasing the feed, to a very good speed and fine hull waves. She did many full power change-overs from ahead to astern and back with the engine accelerating to 730RPM during the change (maximum recording is working ok now);  not bad for a 72lb displacement hull shaped like a box. The average RPM for the run was 480.

A couple of mid-pond shut-downs were made and she auto-restarted on both occasions. Three point turns - no problem.

A second successful run was made in the afternoon, though with one minor problem of the feed inlet plastic pipe coming adrift and causing her to ship water; I had inadvertently dislodged the pipe when installing the lead ballast. Despite the minor hic-cup, Steamboat Phil and his son took a video for one of Phil's talks on flash steam.

One remaining problem - I've now got to build a proper boat!

Ian
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SteamboatPhil

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Re: Flash steam plant control.
« Reply #122 on: July 19, 2010, 11:37:10 PM »

A good day was had by all at Blackheath on Sunday, with Vital Byte steaming around most of the day.

Here is Vital Byte in action  :-))
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flashtwo

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Re: Flash steam plant control.
« Reply #123 on: July 20, 2010, 09:53:09 AM »

Thanks very much Phill for the photo - its always a bit difficult to operate the transmitter and take photos at the same time.

Its very interesting to see the hull wave, it seems to be one complete wavelength, which may indicate that the boat is travelling at hull speed.

I've got very limited knowledge in that area, so I would be very appreciative of any comments regarding hull speed waveform from Mayhemers with that experience.

Ian.
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SteamboatPhil

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Re: Flash steam plant control.
« Reply #124 on: July 20, 2010, 11:40:23 AM »

Here you Ian a slightly better bow shot  :-))
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