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[KNO3]

I should add that this problem (not starting after reversing the gear while the steam is off) appears in some engines but not all. It really depends on the type of reversing gear and how much the valves can lift from the port faces in the steam chest.

Here you can see my Cheddar Gemini engine which reliably restarts after shutting down air and moving reversing the gear: https://www.youtube.com/watch?v=BQ3ZeM2keZs


And here my Graham TVR1A on steam, being reversed while running (perhaps not the best way to reverse because it strains the gear more): https://www.youtube.com/watch?v=Gv05K6qeTkk

[KNO3]

There is also the question if reversing while the engine runs is advisable, that is, if it won't damage any engine components. This is not easy to answer because it depends a lot on how the engine is built and how sturdy certain parts are. When you reverse the engine while running, you force the mechanism to move against steam pressure and against its own inertia of the moving parts.

It is probably fine to assume that in model engines (at low pressure) the risk of damaging the reversing gear this way isn't great. But this depends also on the type of engine. Some reversing gears are more robust, others have quite delicate parts. For example, the Maudslay gear of Cheddar engines seems very robust, but Stephenson gear has delicate parts. Graham's Hackworth gear also has some rather thin aluminium parts.

In my opinion, the best approach is stop steam and reverse, if the engine restarts reliably. If it doesn't, lower the rpm before reversing, do not reverse at full speed, especially in engines with delicate parts.

[DBS88]

Thank you for your contributions to the fwds/rev discussion, to summarise our shared experiences

• best practice is to stop the engine, change direction, start the engine
• following the change of direction, the engine may not always restart.
• Its possible to programme a transmitter to make the change by combining channels and using one stick
• Electronic mixers are available to combine the engine direction change and throttle into one transmitter channel.

Following Dereks suggestion, I have had a look at the Action Electronics and their P105 would appear to be a useful way of combining the engine direction change and throttle.  I have not used one and they are currently out of stock, but I would happily try one out if anyone has one that they are not using.


I have used the Dénes Design ECU (Engine Control Unit). At the time my Proteus Steam plant was not set up with servos so that I could change the engines direction and control the throttle so I set up the ECU on another steam tug with a Reeves Marcher engine and Stephensons link reversing linkage. The Dénes ECU was easy to set up. The ECU had been programmed so that when the transmitter stick was returned to the centre position (throttle closed) the engine direction change moved to a central/neutral position. This suits some engines, however it really did suit the Reeves Marcher with the Stephensons reversing linkage. The engine would not reliably restart with the linkage moved to the central position, here is a link to a video showing the issue with this engine [size=78%]https://youtu.be/wocHmwuAvCA[/size]


I spoke to Dénes about this and he responded by producing a 2nd version of the ECU that did not move the reversing mechanism back to the central position when the throttle was closed, it only made the change when the transmitter stick went past the central position to the new direction. Here is a link to a video of the 2nd version of the ECU [/size][size=78%]https://youtube.com/shorts/CYS56VDcWmk[/size]


As you can see, with the 2nd version of the ECU the changes of direction with the Stephenson linkage are now made easily and reliably, I have also tested it out on the lake without any problems. The ECU is now available in both versions from Dénes. I have since tried the 2nd version of the ECU out on the Proteus with the Maudsley reversing mechanism and the changes were also reliable.


To conclude, combining the engine direction and throttle with electronics (clever transmitter or electronic mixer) in this way also means that the engine cannot be put into reverse at high speeds so addresses some of the earlier thoughts expressed. Using the ECU was very intuitive, just push the transmitter stick forwards and the boat goes forwards, bring the stick back past the central position the throttle closes, the direction change is made, the throttle opens and the boat goes backwards.

[KNO3]

That's a nice system by Denes, very good to see it in action.

[Dainesh]

Have you seen my videos about the ECU?


At the beginning the servos were twitching many times, but thank you for Dave's and Richard's feedback I was able to reduce the number of the twitching.
Plus there are some extra features:

• You are able to set the Forward/Reverse servo maximum by the two potmeters. The forward position may be different than the Reverse.
• Middle set button (if you press it for 5 seconds you don't have to  search for the neutral position on the transmitter)
• It is able to remember the middle set position after power cycle, so you don't have to play with the neutral position just at the first time ( if you change the transmitter setup you have to set the neutral position again)
• If there is an issue between the transmitter and the receiver it is able to identify the problem and set both servos to neutral position. Other words if you loose the control on your boat after a couple of seconds the ECU stop the boat. If the connection setup again the control set up again. For example: your transmitters battery become flat until you change the batteries your model stop, after you change the batteries to a good one and switch on again everything goes back to normal.

[KBIO]

Hello !
You said it all !

Just to share my point of view concerning the reverse problem that we all have with the Stephensons gears .
The problem with Stephensons is the rattling that occurs after a while. Even with stiff connections and no play on the sliding sleeve, it comes a time (rapidly) where the slide , eccentrics and sliding sleeve get loose and the neutral is tricky to set.
It works fine for a short time after a good engine timing but everything goes "Tchic-tchic" then.
This is at least what I noticed on my engines, what ever the manufacturer. Saïto, Jmc and even some Stuart being the perfects examples.
Only with home made engines with thick linkages and a thick (slide-bow )?) and running at low RPM <400 , with a good oiling ,the reverse works good for long time.
That is why I favor the Maudslay which is the most reliable and that can be timed properly with the engine running . But it does not have the "charm" of the Stephensons !
A spécial Thank to DS88 for all those studies and informations that he shares with us and help us to understand. 
Have a good day !

[DBS88]

Thank you for sharing your experiences with reversing mechanisms and twin cylinder engines not always being self starting, we are all wiser now.


So why did I put the second proteus steam plant the Tug in and why now?


During the experimentation with the engine direction changing, both with and without the Engine Control Unit a number of conversations were had with different people in January and February. One of these conversations inspired me and it set the wheels in motion to get the Boat finished. It transpired that in just over a month, a friends Model Boat Club would be holding a challenge event (Mid April), most laps in one hour and still be running. The bit that inspired me was that the event had not been done by a steam powered boat. So I now had a target date and about five weeks in which to repair and refurbish the hull (at this point in time it had not been started) and get the steam installation done. So that was the reason and the motivation for why this project got under way now.


The reason for selecting and installing the second proteus steam plant was it already had a servo installed for the engine direction selection and amongst all the bits that came with the steam plant were some nice water tanks, piping, and an oil separator, so at the time, I thought it would save me time! Heres a photo of the servo for changing the engine direction with the Maudsley mechanism.


So with the target date set in the calendar, I ordered the additional parts I needed and set about my first installation of a steam plant complete with the electronic controls. The event rules, for safety reasons, did allow steam boats to return to the bank to stop and take on additional water and oil and to empty the oil separators, they were not allowed to take on extra gas though. As I said at the beginning, I want to build a steam boat that will run for an hour and this was an opportunity to put into practice all the recent months research that we have been discussing and to be my practice project, with the lessons learned being transferred to the new build Black Swan Sloop. So my aim for the Bustler Tug became to run in the event and to run for the whole hour without returning to the bank.


This then threw up a few challenges, what were the limiting factors?

• How much oil would be needed in the displacement oiler to run for an hour?
• How large did the oil separator need to be so that it did not need to be emptied?
• How much gas would it take to run for an hour?
• How much water would I need to run for an hour?
• Where would I get the water from, the lake or an onboard tank?

[derekwarner]

An interesting challenge .....'most distance covered & still be steaming after 60 minutes, but no additional gas ' ....leads to some assumptions and quite a bit of due diligence in extensive pre-race tests with an engine at operating temperature, with a final speed test set for an arbitrary 15 minute duration
---------------------
1. A higher speed boat will cover a greater distance than a slower vessel, however what type of higher speed vessel could complete the time requirement considering the greater water capacity and gas capacity requirement to maintain the higher speed for the required time?
Or does a high speed boat only need to achieve say 2 laps lead, then slow down to the speed of the balance of the Fleet?...and simply maintain this lead, so maintaining water & gas?

2. Displacement lubricator capacity?....[adjustable type?].....the answer is that a minimum amount of lubricating steam oil is required for cylinder lubrication....it is easy to use too much, but not so easy to check & determine successive tests with a reduced oriface valve setting & reduced flow.
However, from there, it is easy to confirm the volume of steam oil consumed, by determining the volume [weight] of oil required to replenish the lubricator body after the 15 minute test and understand if the lubricator body is of sufficient size for the 60 minute run. The position/location of the displacement lubricator relative to the boiler will also alter the viscosity of the 460 Grade steam oil, so another requirement of operating temperature tests
A displacement lubricator with an internal blowdown valve [as shown] will allow for quicker removal of condensate and refill with pre-warmed steam oil, naturally both boiler and engine isolation valves are required 

3. Oil seperator volume?.........so after the displacement lubricator setting is achieved, the volume of waste oily condensate can be collected and weighed after the final 15 minute test..........this will the determine the total volume required to contain the waste for the 60 minute run . A temporary plastic overflow container could be considered and so tubed up to catch cooled oil as opposed to providing a larger capacilty separator body

4. Gas requirement……easily confirmed with a set of kitchen digital scales……weigh the full tank [record tank temperature] at the commencement and end of the 15 minute final test, then understand if the tank holds sufficient gas for the 60 minute run……[gas tank temperature {variations} during the 60 minute could also influence the requirement]
Without seeing the Rule Book, and whilst you note that gas refilling is not permitted, are dual or multiple gas tanks allowed?

5. Boiler water requirement…..again easliy confirmed with a hand pump installed into the boiler feed line…..accurately mark the water level on the boiler gauge glass, bring the boiler & engine to operating temperature, pump up the water consumed to the set mark, with the refilled gas tank complete the 15 minute test, then determine the water required [by tank volume change] to return to the set point and then calculate the total requirement for the 60 minute run
This the will at least confirm minimum makeup water pump displacement to suit the crusing speed conditions for the 60 minute duration

I have not considered boiler makeup water source requirement, however similar considerations & tests of engine driven or electric driven pump displacement/reliability and volumes location

Do you have that crystal water that Jerry C steams in?.... or that brackish liquid called water of the Thames?……. this itself would determine the source of makeup water

   
One further area of consideration or concern would be the external lubrication of engine journals & linkages etc, together with the stern tube lubrication for 60 minutes


[sorry to be getting back to the 5” Gauge ……but on Public running days, & my time on the station, I see these drivers manually oiling the engine external linkages & journals every 15 to 20 minutes at the station when the outgoing passenger’s alight and a new group board]


Are your Tx & Rx batteries OK for 60 minutes?
Are you OK to sit/stand in one spot for the same 60 minutes?
Do you have an impartial Lap Counter prepared to sit/stand for 60 minutes?

Derek
 Have you an imvent?
Derek

[KBIO]

Hello!
First of all:
- Is it a speed race for one hour or a challenge to sail for one hour without refilling ?
Moving the boat  slowly forward for one hour claims a lot less steam &  gas than speeding full blast with an heavy tug !
Also, you should be able to save a lot of steam and gas with your electronic controller.
I hope that I answer to some of your questions below.   
Not sure that I am right though !


An interesting post that answer almost your questions without any calculation:
https://www.modelboatmayhem.co.uk/forum/index.php?topic=65437.50


Concerning the gas needs,  first , you need to know the size of your jet.
N°5 = 55 g/h  = +/- 100 cc + 25% safety factor = 125 cc + 25% available gas voulume on top = 160 cc tank >>>> I would suggest a 3’’x 4’’ tank to have a good top.
N°8 = 95 g/h Double the size.
You cannot install liquid phase on the Cheddar burner but you’ll make it without.

Concerning the oiler , I agree with Derek ! You just need to reduce the frictions to give more engine efficiency. For example, a standard Stuart adjustable oiler last 40 min with a small opening.
The lubrication is not related to the engine size but to the time needed . I wouldn’t worry too much about external lubrication for 1 h sailing. the worst that can happen is losing  a bit power due to the lack of lubricant. But , doubtfull on a Proteus or others.

If you are confident in your water supply with the pump, I would suggest that you take the water from the lake (if clean and netral Ph) through a good and large screen to avoid plugging. If the boiler swallows some shrimps, the engine will chew it ! So the challenge will be to be over before that you empty the lake !
Normally ! ;-))
I would not even consider to warm it up if it needs a complicated installation.The energy needed to  rise the temp from 10°C to 120°C is neglictable compared to what it needs to vaporize it ( >7 time more)

Steam consumption:-The Proteus is given for 4,1 cc ;
Now it all depends on the RPM you need to move your boat =
- Wide open = +/- 800 RPM
- small opening to last longer = 250 RPM
Below is a simulation with 800 rpm for 70 min and a 60 mm propeller.
(The weight of the boat and its speed is not taken into consideration)

De-oiler :
- What comes out of the boiler comes in the de-oiler , … theorically!  So it will be the boiler consumption less the evaporation escaping through the steam outlet .
Depending on the shape of the de-oiler  (cyclonic) , you may be left with a very small amount of condensate at the bottom and the injected oil at the top. I would not worry too much about it as when the engine is hot, there is very little condensate and most of the steam comes out.

That a quick answer but it should be close to fit your requirements !
I hope so … :—I

[DBS88]

Thank you for such comprehensive and helpful replies. Re the endurance event, at first glance it seems easy, but as you have realised, the more you think about it, the more there is to it. I am loving Dereks tactics of racing into the lead, then slowing down to keep pace with the following pack. The winner of the event is the boat that has completed the most laps and is still moving, so its about going as fast as you can without running out of power (steam, batteries, etc).


Thank you for the link to a previous Mayhem thread, you are right there is a lot of relevant information there.


Testing on the bench shows that a large portion of the steam oil is lost from the displacement lubricator at the start of running, so once the engine is hot, its worth shutting the steam off, topping up the displacement oiler and then running.
The same thing happens with the oil seperator, so again once the engine is running and hot, empty it, then it seems fine.
The engine has been running at 4 bar but is rated at 6bar, the boiler has a steam drying loop that drops into the fire box and back out to the engine. The gas jet fitted is a No 8 and having weighed a gas tank before and after a bench test run, 100g/hr is what it is using. I agree the controls will help with minimising the gas consumption.

Re Oiling the moving parts I will look into fitting a tank with small pipes that drip oil on the relevant moving parts - old school style, since its not easy to reach the engine with a syringe to oil it. Any advice or experiences with this method would be most welcome.


The prop fitted is the largest I could fit without modifying the hull, its from PropShop, its 80mm by 1.5 pitch 4 Bladed Prop, it is a thing of beauty. The hulls waterline is 125 cm long, its breadth is 25cm and its depth is 13cm


Re the water supply, what I have learned from the bench testing and previous experience with my first tug, is that the water is used in the boiler until the water level drops to sight gauge sensor level, it then never gets lower. So if this is set at 2/3 and the boiler capacity is 0.6 litres, then only 0.2 litres maximum of water is used from the boiler, as soon as that has been used, the rest of the time the water used by the boiler is coming from the external supply (tank or lake). So to get the best run times when using on board water tanks, the sensor needs to be a bit lower in the boiler. The Boiler controls then take over to fill the boiler until the water level goes above the sensor, then for a further 15 seconds, the controls keep cycling in this way to maintain a more or less constant level of water in the boiler.

[KBIO]

Hello !
N°8 jet = 100 g/h as per the book. So you know the tank that you need.

I like steam about 4 b ! That's hot & efficient !

As you are interested to understand what you are doing , it would be great to be able to measure the RPM of your propeller @ 800 RPM.
But also at different engine's speed and with different types to make a spread sheet ...
This is the kind of information that I miss to complete our calculation sheet. Your clever partner could easily think of a device to install in the boat and give the informations !
I know that someone did something on that , with the RPM information sent to the RC . But I cann't find it anymore to contact him .
Always instructive to follow your post ! Thanks Dave!


Note ; If you definitely want a permanent lubrication on the external moving parts , the crankshaft being the most important, you can consider using a wick lubrication. That last long !

[Dainesh]

Hi KBIO,


Sorry for the OFF topic, but...


The measurement of the RPM is not as big issue, but how can I send the information back to the RC.
I'm really interested in this.
I try to find descriptions or books about but I couldn't find any useable.
Just it can be a direction of the development of my products...

As you are interested to understand what you are doing , it would be great to be able to measure the RPM of your propeller @ 800 RPM.
But also at different engine's speed and with different types to make a spread sheet ...
This is the kind of information that I miss to complete our calculation sheet. Your clever partner could easily think of a device to install in the boat and give the informations !
I know that someone did something on that , with the RPM information sent to the RC . But I cann't find it anymore to contact him .



Note ; If you definitely want a permanent lubrication on the external moving parts , the crankshaft being the most important, you can consider using a wick lubrication. That last long !

[KBIO]

Hello Daynesh !


I cannot find anymore the topic describing this item. Don't even know if it has been to its term !
Since, though, things have changed and the best and most reliable for an affordable price I have found , is the following:


Radio Graupner MZ12 PRO 2,4 GH        185 €
Receiver  Graupner GR12-L Hott.            46 €
Optical probe for RPM                            18 €
Magnetic probe for RPM                         19 €
Temp sensor 200 °C HoTT                      19 €

It does not replace your Electronic control but both can be considered !
Thanks for sharing
Regards.


Note: when everybody will be able to tell the RPM and boiler pressure, we shall have a big improvement in knowing what we do .... and what we need !

[DocMartin]

As you are interested to understand what you are doing , it would be great to be able to measure the RPM of your propeller @ 800 RPM.

Would not the RPM of the propeller be the same as the measured RPM, say of the flywheel??  [Assuming a direct drive system]
Measurement of the flywheel's RPM should be easily accomplished with any modern telemetry-equipped transmitter/receiver combined with either optical or magnetic sensors (similar to KBIO's example).

[DBS88]

Fascinating discussion, it really would be interesting to have live data, so I will watch with interest as telemetry is developed for use in model boats.


Towards the end of March, the work on the hull was complete and the prop installed. The Endurance event was now about three weeks away, time was running out, so I made some quick decisions about the steam plant installation in the Bustler Tug.
I went with onboard water tanks - I already had some.
I positioned the steam plant in the hull and decided to have the steam plant with the boilers flue running straight up and out of the models funnel. I did consider moving the steam plant further forward which would have meant bending the boilers flue - which as it happens may have been better.


With the position of the steam plant decided, I measured the space between the bulkhead and the engine and tried to install the water tanks I had - no they were not going to fit, so back to the drawing board. I found some fuel tanks made by Dubro. I selected two 16 ounce tanks, 1/2 litre tanks to provide an additonal 1 litre of water for the boiler. I went with two tanks, position lengthways, since they are not baffled, to minimise the effect of water rushing from one side of the boat to the other, so I ordered them and some silicone fuel line to connect them and waited 48hrs for them to arrive. The soft silicone was fine to use on the suction side of the pump and on the bypass circuit, since there is hardly pressure in them. The water line from the pump to the boiler must be in hard pipe so that it does not expand and reduce the pumps efficiency in terms of delivering water into the boiler. The photos show my first plumbing arrangement for the tanks.

[KBIO]

Helloo!
Would not the RPM of the propeller be the same as the measured RPM, say of the flywheel??[/size][size=78%]quote][/size]
[/size]
[/size]Exactly ! The flywheel has to be painted in black and a small piece of reflecting silver paper sticked on the edge.
[/size]Right now my measurements are made by hand with the steam plant and the propeller that I intend to use . All this is a water tank. But it is static and the RPM must different when the boat is sailing.
https://youtu.be/zNQK1VZ0flA


Have a good and sunny day !

[rhavrane]

Bonjour Yves,

Quite interesting video indeed.

I don't understand how you can loose 2 bar in less than 10 cm of pipe, it doesn't make sense.

Why a pressure measure in the steam flow be different of a static one ? That is the question and it is not elementary...

I would also suggest that the measurement is distorted by the fact that the steam valve is not fully open.

About the piston measure, I think it drops naturally because by definition, the piston descends, the volume increases when the steam arrives and the manometer has no time to operate correctly.

[KBIO]

Hello !
This is the diffrence between steam and compressed air.
The detent of the steam starts when coming out of the boiler. The pressure drops but the temperature is the same. The line is too short to cool down the steam flowing toward the engine.
So we have a steam which is over heated compared to saturated steam. This is (if I am not wrong) what is called "detent adiabatic «  . detent without work production at this stage.
The litterature and L.SUYKENS (Compilation des cahiers- I suggest that you read it) calculations give average 30% pressure drop between the boiler and the engine inlet . The video shows 50% loss because my engine is too big for the boiler capacities.
i certainly do have the needle valve not totaly opened and I am « laminating » a bit. It explains also part of the pressure drop.
Steam is magic but trying to understand it drives me nut. There is more qualified peoplethan I  able to explain all this clearly.
Have a good day.

[DBS88]

I really do look forward to trying out the next developments with telemetry, although from my early trials with a camera on board the boat transmitting real time video back to the bank to be able to see the boiler pressure and water level, the equipment involved takes up a lot of room. Here is a video link showing the images from onboard. https://youtu.be/A0W8UeumhRs


With the water tanks installed, filling them is easy, its done through either one of the two vent pipes that terminate high up at deck level. Also installed in one tank is a water level probe connected to the automatic boiler controls, this turns on the high intensity red alert LED to warn the user when the tank is near empty and it turns the gas down to the pilot light setting, this gives the user time to return the model to the bank before the water level in the boiler drops too low.


The first test run of the boat and the steam plant on the lake took place just 7 days before the endurance event. The water in the water tanks was being drawn by the pump from both tanks and I wrongly assumed that the this would happen evenly from each tank. The first test run of the boat showed that this was not the case. To resolve this I ordered some fittings and more pipe so that I could install a balance pipe, low down in the tanks, to enable the level to remain the same in each tank. Once they arrived, the water tanks had to be removed. Fitting the balance pipe was  easy, the plastic of the tank was drilled out tapping size for M6, the holes were tapped M6 and the M6 threaded fittings fittings were screwed directly into the thin plastic, they sealed perfectly water tight.


The first test run also revealed the ballasting was not right, a bit too much weight in the bow, it also revealed that the boat was not performing as I had hoped, the engine was not revving as it had on the bench, it seemed to lack power. When I got home and re ran the boiler and engine I realised I had made another rookie error, I had only opened the steam valve on the boiler about half a turn. I usually open it about 1/2 a turn at about 2 bar, to let some steam through to start warming the engine and get it turning over slowly, in my excitement to run the boat I had clean forgotten to open the steam valve further, so had inadvertantly starved the engine of the steam it needed.


A lot had been learned from the first run, and a lot needed to be done before the second test run, which would be 4 days before the Endurance event.

[KBIO]

Nice !
I Cann't wait to hear the end of the story ! with the big trophy going along !

[DBS88]

To get the Bustler Tug ready for the next run, I removed the water tanks and removed the steam plant. This allowed me to reposition two of the 450g lead ballast blocks from the front and shift them towards the rear. Next I was able to carry out the work to the water tanks to fit the balance pipe described above. I then reinstalled the steam plant and ran it again on the bench, all appeared to be OK, so I charged the batteries, oiled everything and got ready for the second trial run.


On the Wednesday before the Endurance Event, I took the Boat to the lake and prepared it carefully, fired the boiler and waited for the pressure to build. As I warmed the engine I noticed that for some reason the throttle was not closing properly so the engine was always turning, I messed about for a few minutes trying unsuccsfully to resolve the issue, then decided to run the boat. Here are the photos from this the second test run and a link to a video of the Bustler Tug running on the lake https://youtu.be/jM7NhrXsch4 As you can see the performance was much better.

After a while during the test run, the high intensity warning LED form the automatic boiler controls was illuminated telling me there was an issue and that the model should be returned to the bank for further investigation. The problem was that the under running conditions the boiler had not been filled sufficiently with water, the warning LED was correctly telling me that the boiler had insufficient water in it and that after a period of time rechecking and allowing the pump to run on to make up this situation, the water level was still to low, so the system was now showing the full alert. Frustrated and disappointed I packed up the model and returned home, pleased with the performance, but disappointed that I had not got the bypass valve set up correct,  which meant insufficient water entered the boiler.

Time was running out now, I had three days left, I was doubting whether I could get the Bustler ready in time.

[DocMartin]

Also installed in one tank is a water level probe connected to the automatic boiler controls

Can you describe the construction of the water level probe you have installed??  Any pictures of it prior to installation??

The instructions for the ABC unit Denes designed make mention of the water probe but the actual design is not elaborated upon.  Any information you could provide would be appreciated.

Thank you (everyone) for this most informative topic thread! 

[Dainesh]

Hi DocMartin,


Unfortunately I do not know where to purchase any water probes, but if you see my videos on www.denesdesign.co.uk you can see that I use two pieces of bare copper/brass wires, I just have to clean them regularly, stainless steel may be better.
If you don't want to use the feeder tank sensor option you just have to connect the Cold tank input to one of the GNDs.


I hope somebody can help you from here.


If I can help you just send a personal message. 


Denes

[DBS88]

As requested, here are some photos of the water level sensor used in the onboard water tanks, this one is the sensor that came with the original Cheddar ABC. It appears to be a piece of copper pipe with one wire soldered to it and another insulated wire passing through it, the end of the second wire is bare. I assume that when water is present there is a flow of electric current and when no water is present, no current flows - as I said previously the electrics are a dark art form to me, hopefully someone with a better understanding will be able to offer a better explanation. Any way from the photos it looks easy enough to make one.

[DocMartin]

Thank you very much!  That was exactly what I was looking for. 


Cheers!!