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RC Model Steam Project

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kvom:
As a mechanical engineer by training, if not by prefession, I have found it interesting to see how the piston valve works on John's engine. 

One aspect that I have not examined is that optimal phasing of the valve and piston.  Assuming that the engine runs at a constant RPM, then the positions of the piston and valve plotted against time will be sinusoidal curves that are out of phase by some amount.  I would expect that the engine will run over a given range of phase difference, but that one phase would be optimal.  I am now wondering if the phase setup given by the tuning instructions yields the optimum operation.  Obviously it is pretty hard to adjust the eccentric angle by just a few degrees on a model, so this is mostly an academic question.

However, I have read on this forum that piston valves were used on real steam trains in the past, and I'm sure the phase would have been adjusted for peak performance.

Bernd:

--- Quote from: kvom on June 17, 2009, 08:27:34 AM ---However, I have read on this forum that piston valves were used on real steam trains in the past, and I'm sure the phase would have been adjusted for peak performance.

--- End quote ---

kvom,

Your right. The steam locomotives built in the later years used piston valves. But I believe the piston valves worked more on the principle of the D-valve since they had linkage to reverse the engine and not a valve such as is used in the Paddleducks Engine.

Well I've got material that I think I can use to start the chassi and wheels. So look forward to a new "Projects" thread soon.

Regards,
Bernd

bogstandard:
I think you will find that on model engines, it doesn't make much difference, but on larger engines, where they use a lot more steam (not air) the timing and duration was altered as the engine speeded up to allow a more efficient use of the expansion of the steam.

Imagine the engine running at full wack, to keep it running at that speed only needed the pistons to be nudged at a specific time, for a shorter duration, rather than having the full charge of steam admitting into the chamber.

The same principle as you use when driving your car on a motorway, foot to the floor to get you up to the required speed, then gently back off on the accelerator, so the car stays at the same speed, but uses less gas.

Only laymans terms, but explains the reasoning behind it.

Bogs

Bernd:
John,

I've been eyeing that engine you posted a pic of at the begining of this thread. It looks simular to the one on the French web site given here somewere. I was wondering if it would work with say 3/16" bore by 3/8" stroke. Then connecting it through one of these Tamyia Gear Boxes. I'm looking at using this for a steering engine. Still working (pictureing in my mind) on the components for making it steer. I want to start with the engine first. It needs to be compact.

Your thoughts?

Bernd

rleete:
Bernd, search Craigslist (or post a want ad) for a cordless drill with a dead battery.  You ought to be able to get one cheap.

Same type of gearset in the nose, and built to withstand quite a bit of abuse.  Heck, I have an old sears one you can have, if you're willing to come get it.

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