Self starting small steam engines

With twin single acting cylinders a 180 degree crank will mean that one cylinder is almost always on a power stroke, if you have a 90 deg crank then there will be a period where both cylinders are on the exhaust stroke which does not give as smooth running and a larger dead spot where it won't start

Your plunger could be held out the way by steam pressure, only engaging when steam pressure is removed from the feed.

Hi Mick,

The intention is really just to build a beginner engine, not particularly to install into a boat. I seem to spend a lot of time doing other stuff, tooling, making good the machines I've bought etc. This is my very first engine build and I wanted to do something that would be a bit of a challenge.

Regards,
Ed.

At the risk of boring the forum to death on this subject, I have had some further thoughts overnight (dangerous territory). I intend to make a boiler feed pump which will be actuated by a drop link from the rotary valve at the flywheel end of things. The pump will obviously be a load on the engine especially at the beginning of the delivery stroke. If the links were adjusted appropriately would this provide the necessary "brake" to stop the engine at the required place? Is there a method of calculating this or is it a trial and error exercise? As ever, your thoughts are valued.

Mick

Do some calculations of the expansion of water to steam to see what volume the pump needs to be. Often best to gear it down anyway which rather defeats that idea but otherwise probably has the right effect.

Further to the idea of a spring loaded roller pressing on a cam, I have an old bound copy of the engineer which has a report of just such an arrangement on full size single cylinder engines. The engines were fitted to the machines they drove, one engine per machine instead of one very large central engine. There is no arrangement show to lift the roller from the cam once the engine is running! The noise and waste of power must have been horrendous. I think that a small cylinder could be arranged to take steam at the same time as the engine valve is opened, to just lift the roller clear of the cam. It would of course also need some sort of pressure release for when the engine is stopped, to allow the roller to drop onto the cam.

When someone comes up with an idea, I'll be interested, I would like a starting system for Hot Air / Stirling Engines.

I often read that one of the disadvantage of the hot air motor is that it is not self starting, but neither is an IC engine. Among prime movers only steam seems to be able to be designed to self start, unless you count in electric motors.

Ian S C

I was up late last night modelling the valve linkage and thinking about the 'assisted-start'.

Had an idea of using a mechanism similar to a pull-cord start on petrol engines - with a couple or even one pawl that flies out and engages with a fixed internal cog on the crank shaft.

The pawl mechanism could be driven by a freely rotating bush around the crankshaft which is turned by a lever or an RC actuator. Although this would only be any good for forward direction of the crankshaft.

Ed.

Nearly a year later I think that I have solved the problem with this steam engine........or more accurately I have found a way round the self starting difficulties if the motor stops with the cylinders at BTC and TDC.

This involves the use of a needle roller one way clutch bearing which is fitted on the crankshaft. I have made up a collar with a drop link, which is a close fit over the bearing. The second item required is a miniature push pull solenoid. This is linked to the drop arm of the bearing collar. On application of 12 volts, the solenoid, which has a movement of 10mm, pulls the crankshaft round approximately 50 degrees which is enough to enable self starting when the steam is turned on. With the motor running the crankshaft turns freely inside the bearing. The solenoid and bearing came to about £6 and in this case was money well spent. The requirement for a battery is no problem because the boat needs one anyway for remote control.

If this is of any use to anyone else please feel free to PM me for details.

Mick

Nice to hear of a conclusion to the story. Use of the roller clutch is clever.
Do you use a separate channel to activate the solenoid or a crank shaft position detector, or flip it anyway when applying throttle?
It occurs to me that a regular servo would do and would be 5v like the radio. Then again a link from the throttle or rudder servo could also be brought into play just an extra waggle until it starts. It's almost making me want to take up the challenge of a single cylinder boat as I have such an engine somewhere which I had discounted as useless.

Hallo Bazyle. I like the idea of using a regular solenoid. I must confess it had never occurred to me. I have used the push pull solenoid because I already had it for a previous (abortive) experiment. As you suggest, it would allow for a single 6v battery on board.

The motor is still on the bench whilst I get the mechanicals spot on. The remote control, of which I have no experience is yet to be fitted up and will no doubt provide fertile material for another thread when I get stuck. I could see no point in investing time setting up the radio control until I had a reliably working motor which would not get stuck in the middle of the pond.

I think though that the "flip it anyway" approach will be adopted.

Mick

There are single direction bearings which lock when driving, but turn freely when driven, commonly used for auto-rotate systems in RC helicopters.