Coal fired Garratt K1

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Re: Coal fired Garratt K1

Post by Old Man Aaron » Wed Mar 02, 2022 3:45 am

I think I'm just barely keeping up with you. There's clearly a lot needing attention to make it run properly, and it's great to see someone putting in the hard graft to get it perfect. :salute:

This reminds me, I really ought to buy a set of reamers.. :roll:
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Mon Apr 04, 2022 10:42 pm

I have completed rebuilding the rear unit, and tested it on air. It now seems to work faultlessly both forwards and backwards.

The calculations worked out OK - after I had corrected some silly arithmetic errors. I will correct the errors in the previous posts shortly.

The back end is now reassembled to the body, and the radio control is re-connected. I hope to be able to steam test the water pump and rear unit before the weekend - and I hope to be able to add a video of that.

Then on to the front unit and the compounding valve.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sun May 29, 2022 2:14 pm

Believe it or not I have been working on this since I last posted.

That steam test didn't work out - not because of faults on the steam system, but I just couldn't get the coal to burn.
So I tried it in the multifuel burner in the house and it wouldn't burn there either. Not even in a roaring log fire.
Trying to run K1 on bits of smashed up BBQ fuel just didn't get steam to be generated fast enough - at least that is what I think was happening.

So I am in the process of making a gas fired burner for it. Not that I have given up on coal firing - but I need to get small amounts of proper coal and charcoal for this purpose. So duel fuel seems a good idea - if only so that I can separate out the issues.

So a gas tank - as big as I can get into the space previously occupied by a dummy air receiver:
IMG_2202.JPG
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All silver soldered and tested. Just needs its valve making.

In its final position:
IMG_2203.JPG
IMG_2203.JPG (1.88 MiB) Viewed 4057 times
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sun May 29, 2022 2:22 pm

I have made a ceramic gas burner to fit into the space where the coal grate and ash pan fit. Held in place by the same two pins which hold the grate and ash pan in place.

A bit speculative in that the intermediate pipe which takes the steam between the two bogies might foul it - but it's worth a try. Its just a copper tray silver soldered up, with 4 pillars sticking up into it - on which the ceramic insert will sit:
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and in position in the fire box:
IMG_2200.JPG
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I have spotted the hole in the soldering and have corrected it.

I have also completely rebuilt the front unit in the same way that I did for the rear unit. That now runs smoothly and freely on 10psi even with a valve chest leak. So a leak to solve as well.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Oct 04, 2022 3:27 pm

Since the weather has deteriorated somewhat lately I have started to try to get K1 running properly. There are so many variables and so many bits I can't get at that I have stripped the locomotive down and I am going to test and reassemble as I go. So I am starting with a bare boiler on its frames, supported on wooden blocks:
IMG_2511.JPG
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I have abandoned the gas conversion for now - I managed to buy suitable coal in very small lumps. Having taken the cab off, and dismantled the radio control I worked out quite quickly that the regulator and other valves taking steam from the manifold were not fully closed as I had set them up with the radio control:
IMG_2514.JPG
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Now the fire lit easily, and I was able to maintain 50 psi or so for an hour at which point I was concerned about water level and let the fire go out.

So to get the pump running off the loco. I had made the manual filler point part of the feed to the steam pump, thinking it was simpler that way but I don't think it worked properly like that - and with the pump removed I couldn't fill the boiler manually. The arrangement has been modified so that both pumps feed into the clack valve. The manual filler point is a bit "in my face" but I can improve it if it works:
IMG_2512.JPG
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with everything dismantled I have temporarily mounted the rear tank (which contains the electronics as well as a water tank) near by and reconnected the water level indicator:
IMG_2513.JPG
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I'd played with drain valves on the pump - but that didn't seem to help so I took them off and blanked the holes off. Lighting the fire again using charcoal soaked in meths 20psi came very quickly. At 40psi I started the blower, and opened the steam valve to the pump. That bright light from the water level indicator does mean I can't fail to see when it needs more water.
Having pushed the pump piston rod back and for a few times it started up on its own. At this stage the pump isn't connected to anything - I'm just trying to get it to run on steam.

The next stage is to prove it runs mounted on the loco and actually pumps water.



So there is some video showing it running on steam. The first part was the first of it running - very quickly - and lots of steam leaking. After closing the valve I just tightened the bolts holding the end caps and the lid on the valve chamber - which got rid of 90 percent of the steam leaks. The second part of the video shows the result running much more slowly , and with little steam escaping (there is still some so some new gaskets might be in order eventually):

https://www.dropbox.com/s/a2jostpwid45m ... 1.mp4?dl=0

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Oct 04, 2022 3:44 pm

I have sorted out a few leaks - whistle valve and manual filler - and I have remounted the pump onto the chassis, and connected it to the clack valve as well as a temporary water supply. As things are set up I can connect compressed air to a fitting mounted instead of the safety valve. I have proved that the pump is actually pumping water by removing the manual filler and letting the pump run on air while pumping water out of the filler hole.

So lighting the fire again this time with some coal as well as charcoal, I had it running for another hour - and again let the fire go out. Another bit of video with it pumping water into the boiler:

https://www.dropbox.com/s/9n0hn9nye9cqv ... 2.MOV?dl=0

So I'm now setting up the rear bogie to get that to run.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sun Oct 23, 2022 3:04 pm

I am still working on this - I haven't just given up!

So running the rear unit on steam.

Each time I light the fire in this I get more used to the technique of getting the fire to light and stay in. Im also managing to control the water level in the boiler - manually most of the time. But more of that later.

In the following videos you can hear the exhaust of the weir pump - in fact you cant miss it!

A short section of video with the rear unit running in ahead gear on about 50psi, and the throttle half open:

https://www.dropbox.com/s/eje9dgmsugylf ... 9.MOV?dl=0

There is still some steam coming from somewhere but it is running, and continues to run with the throttle only slightly open, once it has warmed up. Those are 15mm diameter pistons by the way.

I transferred the steam supply to the front bogie, and repeated the exercise:

https://www.dropbox.com/s/xhz649f6li5xk ... 0.MOV?dl=0

You can see that it is running quite erratically - which is exactly what the rear unit did at this stage. That is in reverse - and this next bit of video shows it in ahead:

https://www.dropbox.com/s/p09vzud82lriu ... 1.MOV?dl=0

This time you can see definite hesitation and a plume of steam in time with the hesitation. So that is piston stem seals in need of repacking (They are already tight). But it is running and consistently down to 18psi. (These are 20mm diameter pistons so it should run on low pressure).

So I will correct the stem seals and try the front unit again tomorrow.

Back to running the boiler. I have been using the fan to provide the draft, rather than the blower. It is just easier to be able to concentrate on the fault finding rather than running the boiler. So for example I can use the water bottle to pump water into the boiler even though it makes the pressure drop. I can keep the fire glowing red with the fan.

The water pump is running nicely, and I have had it going constantly as I have been testing - it only stops when the boiler pressure drops below 20psi. It is pumping water - I can see the level in the dish feeding it dropping. However it isn't keeping up with the water being converted to steam, so every often I have to stop playing and pump water by hand (and then wait for the pressure to rise). So that is a pretty fundamental piece of information.

A redesign required there I think. I wonder how much bigger I can make the pump piston? I have LBSC's drawing for his weir pump, so Im going to look at the relationships between steam piston diameter and water pump piston diameter.

Still I am making progress.

Trevor

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Re: Coal fired Garratt K1

Post by ge_rik » Sun Oct 23, 2022 4:40 pm

I can't profess to fully understanding - I could hear the sound on the video but not sure I detected any movement. It did sound as if your fix worked, though.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sun Oct 23, 2022 7:54 pm

ge_rik wrote: Sun Oct 23, 2022 4:40 pm I can't profess to fully understanding - I could hear the sound on the video but not sure I detected any movement. It did sound as if your fix worked, though.

Rik
I suppose I was trying to express the idea that the boiler was creating enough steam for the pump to run at the same time as it was supplying 15mm diameter cylinders running fast. It had to be running in the videos even if you couldn't see it because you could hear its distinctive exhaust sound. You can see and hear it in this clip:

https://www.dropbox.com/s/6qi02j42s23xd ... 4.MOV?dl=0


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Re: Coal fired Garratt K1

Post by ge_rik » Mon Oct 24, 2022 9:05 am

Trevor Thompson wrote: Sun Oct 23, 2022 7:54 pm
ge_rik wrote: Sun Oct 23, 2022 4:40 pm I can't profess to fully understanding - I could hear the sound on the video but not sure I detected any movement. It did sound as if your fix worked, though.

Rik
I suppose I was trying to express the idea that the boiler was creating enough steam for the pump to run at the same time as it was supplying 15mm diameter cylinders running fast. It had to be running in the videos even if you couldn't see it because you could hear its distinctive exhaust sound. You can see and hear it in this clip:

https://www.dropbox.com/s/6qi02j42s23xd ... 4.MOV?dl=0


Trevor
:thumbright:

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Oct 28, 2022 12:55 pm

I have the water pump in bits to make some adjustments so that I can maximise the amount of water it pumps per stroke - it clearly isn't going to keep the boiler topped up as it is. So while I wait for some stainless to make a modified pump ram from I have been re-assembling the rear of the locomotive.

That is the rear bogie back in place, with a shorter section of pipe connecting it permanently. I have been surprised by how difficult it was to get the pipe off the connectors - so I have just shortened the pipe. No attempt at hose clips seem necessary. A much simpler arrangement than the original where I had attempted to copy the full size ball joints.

The tank is refitted, and the cab. I have reassembled the radio control. Of course I have a clearer idea of where the various steam valves need to be when the steam is fully off, and fully on. The blower, whistle, and water pump valves all work as required on the servos. In other words the throws are correct:
IMG_2553.JPG
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Philip recently mentioned using the inertia control on a deltang transmitter to control a servo - I have the servo for the pump connected to the inertia control. A servo can be controlled by the button on top of the transmitter (next to the inertia control) and that control can be transferred to the inertia control by a bit of reprogramming. A warning - its easy to mess the transmitter programming up if you get it wrong. I did.

Now to the bit which explains why I am writing all of this.

The throttle (regulator) does not rotate as much as I want it to. I have used emax 9051 servos on all of these controls. In the next photo you can see the regulator fully closed. The servo is the centre one of the three behind the metal box:
IMG_2554.JPG
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I have included the transmitter in the photo showing the throttle position. The throttle is the large brass lever.

Now the same with the controllers throttle fully open:
IMG_2558.JPG
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I estimate that the servo output is rotating through 60 degrees. Because the throttle is linked directly to the servo arm, the throttle has also rotated through 60 degrees. The connection allows them both to rotate in unison. So a servo which rotated through 360 degrees would move the throttle through 360 degrees. I would really like that rotation to be about 180 degrees! How can I achieve that? Will some other form of servo do that and perhaps fit into the same space - or at least fit without excessive modification?

I have adjusted the throws on this servo to their maximum that the receiver will allow using the shorting plugs and the receiver instructions. Interestingly when I use the same servo on a servo tester the servo moves through about 95 degrees. Also an emaxES08MD moves through over 100 degrees on the tester.

I would prefer to modify the servo side of this control rather than the throttle valve itself. If only because getting that valve off means taking the cab off, the radio control to bits, and disassembling all the other valves to the right of the throttle to get it off.( I could have designed that better!).

So is there a servo out there that I could use to replace the throttle servo with?

Trevor
Last edited by Trevor Thompson on Fri Oct 28, 2022 5:59 pm, edited 1 time in total.

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Re: Coal fired Garratt K1

Post by philipy » Fri Oct 28, 2022 1:16 pm

Trevor Thompson wrote: Fri Oct 28, 2022 12:55 pm
The throttle (regulator) does not rotate as much as I want it to. I have used max 9051 servos on all of these controls. In the next photo you can see the regulator fully closed. The servo is the centre one of the three behind the metal box:
....... I would really like that rotation to be about 180 degrees! How can I achieve that? Will some other form of servo do that and perhaps fit into the same space - or at least fit without excessive modification?

.......So is there a servo out there that I could use to replace the throttle servo with?

Simple answer is Yes!
I came across several when I was looking for a Continuous one.
Do a google search for: " 180 degree rotation servo. "
This is one that came up but there are others.
https://www.mouser.co.uk/ProductDetail/ ... aUEALw_wcB
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Oct 28, 2022 8:05 pm

Thanks - I have never noticed these before. The 180 degree servo's tend to be bigger ones, but a few are little bigger than the ones I have been using. Further thinking required before cutting anything!

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Oct 28, 2022 8:51 pm

I have been searching the internet.

I have found particular EMAX servo which has the same dimensions as the ones in the loco. The specification says that it can rotate a maximum of 160 degrees. It is a digital servo, and I think that means it uses pulse width modulation (PWM?). It can rotate up to 160 degrees with an input signal varying from 600 to 2400 micro Seconds (the greek symbol MU which I cant find on my keyboard).

I also found references to Hitec and EMax making servo programmers which could be used to alter the rotation angle of some of their respective servos. Of course no one has these in stock and the information on websites is sparse.

So I think I am going to have to buy one to see if it works as a direct replacement.


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Re: Coal fired Garratt K1

Post by SimonWood » Mon Oct 31, 2022 9:07 am

I can't help with the servos, so I will watch and learn.

But I can at least help with µ which is ⌥M :D

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Nov 01, 2022 7:13 pm

SimonWood wrote: Mon Oct 31, 2022 9:07 am I can't help with the servos, so I will watch and learn.

But I can at least help with µ which is ⌥M :D
Well that was easy - I worked out that the first symbols are the "option" button - and after that it is straight forward!

An update on the servo question. I have asked Andy Rutter at Micron. He is going to investigate whether the RC102 can be reprogrammed to give the bandwidth ( I suppose that is the best term to describe the range of frequencies that it can provide to a servo ). If it can't he has offered to programme one of his new receivers to do it. That means buying a new receiver - but I am making a number of locos so it isn't an issue really.

So I suppose the answer to my original question is that the receiver can't control a 180 degree servo as it stands, on the basis that they all seem to use a wider range of frequencies than a normal servo.

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Re: Coal fired Garratt K1

Post by philipy » Tue Nov 01, 2022 8:17 pm

I'm somewhat surprised that your Rx102 can't do what you want, but if Andy doesn't immediately have an answer I guess it must be an issue.
As I said, my AustroDaimler uses an Rx 41d-22 to raise and lower the roof, and other than programming which output pad to use, it didn't need any other adjustments to be able to run a 360degree rotation servo. My Tx control is by a Tx22 and that simply needed the inertia knob reprogramming to output PWM on Ch4 and that is just a question of holding the switch for the correct length of time ( I think the Tx24 has a similar system).

It is possible to hack a normal servo to be 360/Continuous, ( or presumably whatever angle you want) but it involves opening it up and some micro surgery and I didn't feel up to it myself, particularly with the micro servo I wanted to use. As I understand it, there is a pin on a potentiomer which stops its rotation at the normal angle and that gets filed off and then the pot gets replace by a couple of fixed resistors.There are numerous Youtube videos on how to do it though.

BTW, the 'bandwidth' you referred to is actually the Mark-Space ratio of the Pulse Width Modulation. The Tx generates and transmits a square wave and at the mid-point, the mark (high) and space (low) are equal in both length and amplitude and the servo is centred. If you turn the knob one way the spaces get shorter and, obviously the marks get longer. If you turn the knob the other way, the spaces get longer and the marks get shorter. The electronics in the servo recognise this and adjust the rotation direction and speed, accordingly.
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Re: Coal fired Garratt K1

Post by -steves- » Wed Nov 02, 2022 10:13 am

I have modified small servos to get 180 degree out of them, with varying success. It's very simple you just add a small resistor on each side of the motor connector, they can be quite a tight fit.

HOWEVER

Some servos do not respond well to this and start to stall at each end as it hits a physical stop inside the servo, of course eventually it will burn out the electronics.

ALSO

Be VERY careful ordering 180 degree servos, they can be a standard servo which will require the mod to be done to get that 180 degree from a standard controller.

I used my servos in a centre cab loco to have the driver rotate 180 degrees to face the correct direction of the loco. It worked, but MAJOR size chokes were needed to eliminate chatter in the servo movement, obviously down to feedback from the motor which already had capacitors on. Not something you would need to worry about on a live steamer.
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Nov 04, 2022 10:21 pm

Thanks for all of the comments on servos and how they work. There is always something new to learn!

I have a response from Andy. The receiver cant be reprogrammed to provide the extreme mark space ratios that the servo I identified requires to rotate through 160 degrees. The digital 180 degree servos I have found all seem to use the extended mark space ratios that I quoted.

He has offered to reprogramme one of the new receivers that he makes to do this. I am not quite sure how to proceed. I am going to think about it. I realise that everyone else manages with normal servos - so maybe I need to look at my regulator!

I have finished modifying the water pump to increase the amount of water it pumps. I have recently bought a copy of LBSC's drawing for the weir pump. Perhaps I should have done that a long time ago - it would have saved me reinventing the wheel.

Anyway the pump ram is now 5mm diameter (rather than 4mm), and the pump is moving through its full range of movement ( in other words the piston travels from one end of the cylinder to almost the other end - near enough as far as it can go - before the lever reverses the motion).

I have done some tidying up - remaking the tube which connects the steam "engine" to the pump body.

I have also changed the lever which moves the first valve as the piston reaches each end of its travel, and adjusted it.
IMG_2561.JPG
IMG_2561.JPG (2.06 MiB) Viewed 3135 times
It has been tested on air, and it works smoothly and freely , as well as pumping much more water. So its back to testing the pump and the front unit on steam.

I have a plan to create my own version of the steam operated "simpling valve" which allows the loco to start off as a simple expansion loco, and then convert to compound when it's moving. More of that in due course.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Nov 04, 2022 10:43 pm

This simpling valve. Another experiment!

In compound mode the steam from the high pressure cylinders goes through the low pressure cylinders and then to exhaust, In simple mode the steam from the high pressure cylinders goes straight to the exhaust, and a new steam supply feeds the low pressure cylinders directly from the boiler.

The mechanism which does this is a cross between the steam pump and a normal slide valve. The locomotive has a separate steam supply which is used to operate a this mechanism to set it in simple expansion mode. The mechanism consists of a piston in a cylinder ( fairly standard 8mm diameter piston) operating a valve rod. The valve rod is connected to a slide valve - fairly standard 8mm diameter. Normally the side valve covers the connection to the exhaust, and exposes a connection to the input to the low pressure cylinders (on the front bogie). When the piston moves the valve it exposes the connection to exhaust and covers the connection to the low pressure cylinders. The steam which moves the piston also goes via a pressure relief valve to the input to the low pressure cylinders. The pressure valve (set to say 20 psi) makes sure that the piston stays pushed over - and stops the steam back feeding when in normal compound operation ( that might move the piston into simple mode!)



The only new idea (as far as I know) is to use a spring under the valve so that the valve rod holds the valve down onto the valve face. I have used that twice - once in a reverser for my "Idris" and in the steam pump I have just finished modifying. It seems like a good way to ensure that a valve which is on its side stays pressed against the valve face when there is no steam to hold it there. In this case it is intended to hold the valve down against the steam in the hole that it covers. The strength of the spring will have to be carefully chosen to be sufficient to hold the valve down but not so much that the piston can't move it. I have done this before - on Idris, although that was moved by a servo rather than a piston.
Screenshot 2022-11-04 at 22.23.35.png
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In the drawing using the "x ray view" the piston is on the left and the valve on the right. The pressure relief valve is in the block at the back on the left, and all the interconnections for steam are in the block under the valve. As it stands - and it is a first draft - it will all fit between the wheels and give room to make the steam and exhaust connections with ptfe tube. I can probably make it bigger and that will be sorted out before I cut metal.

Trevor

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