Author Topic: Recently Rediscovered Drawing of the TTNW Valve Release  (Read 873 times)

Offline Captain Jerry

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #15 on: August 13, 2019, 01:20:24 AM »
It took me a day to knock up something as an example of what might be done. I say might because until there is a governor attached, I cant be sure what will work.  The length of the levers on the crank are the critical element. The corresponding crank at the governor and the power developed by the governor will be part of the final design.


From this example, it seems to need either a longer lever arm or a slotted connection where the lever connects to the lift rod.  The lift rod is a close fit in the guide for stability of the ramps and that constrains the travel to a straight vertical path and the curved path of the lever arm causes some binding.  A slotted connection will probably be the best solution.



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Offline ChuckKey

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #16 on: August 13, 2019, 08:37:25 AM »
Seems to be coming along nicely. One problem I see is that the tripping force will be transmitted to the governor, but, having only just read up to date, I have not thought how to avoid or minimise that yet. It probably relates to clock escapement design.

Offline Captain Jerry

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #17 on: August 13, 2019, 01:44:29 PM »
Governor feed back is always a consideration and I have done what I can to minimize it with this design.  As far as I can see, every cut off design faces the same problem. The design consideration comes down to how long the sensing mechanism is in contact with the cutoff control surface as it moves the latch faces until they separate. One factor is the depth of the latch faces or how far  the moveable face must move from latched to released. The other factor is how much force is applied to the moveable face, usually a spring.


On the toggle release, the force that is applied is a fraction of the weight of the toggle itself and a fraction of the weight of the arm that links it to the valve,  The depth of the contact faces is a bit harder to describe.  It involves two lines. Line one is the line between the pivot at the small end of the toggle and the pivot at the valve end of the link arm. Line two is the line between the two pivots on the toggle.   For the toggle to latch the second line must be below the first. when the knob on the toggle contacts the ramp, it begins to raise the second line and it remains in contact with the ramp untill the two lines become one (and a little bit more).  At that point the toggle releases and the knob flies away from the ramp.


Aha!  I see what you mean. With the method that I have shown, during the time that the knob is in contact, there is a reaction force applied to the ramp and transferred to the lift rod, the lift crank and ultimately to the governor. It helps to have questions like yours and it helps to talk about the problem.  I have an answer!  That answer also solves the problem that I found with the crank binding as it raised the lift rod.


If I get time in the shop today, I will post a revision of the lift mechanism that relies on a cam to raise the ramps.  There will still be some feedback but it will be greatly reduced. 


What do you think? Cam shape not yet final.
There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.

Offline Captain Jerry

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #18 on: August 13, 2019, 11:40:59 PM »
OK, no cam, unless you consider a wedge to be a flat cam. I think it works better, with less slop than a cam and I think it completely handles the backfeed issue.



IMG_0195 by captain.jerry Ginn, on Flickr


Jerry
« Last Edit: August 13, 2019, 11:58:13 PM by Captain Jerry »
There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.

Offline ChuckKey

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #19 on: August 14, 2019, 01:21:35 AM »
That works. Just an idea: instead of raising and lowering the trip ramps, how about having them separate, sliding in a track on the shelf, and moving towards each other for shorter cutoff. That way it might be easier to have a ramp each side of the toggle, which will avoid the twisting force that would induce wear in the single-sided mechanism (which I realise you are only using for trying out the idea). Rasing the ramps also precludes the use of the curved tripping surface I suggested earlier, but of course I am not saying you are obliged to like that idea.

Offline Captain Jerry

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #20 on: August 14, 2019, 02:05:15 AM »
I see you are doing a little design thinking. Great! The idea of separate ramps, moving opposite to each other is a good one and I also considered separate ramps tha pivoted rather than lifted but the linkage involved to keep them in sync was more than I wanted to deal with.  Balancing the twist with a matching ramp on the outside is also a good idea and it might be possible to do that with a one piece lifting mechanism.  On a larger model where it could be done without looking so out of scale it might be possible to do that by lifting the ramps from the bottom.  That is the way it is done on the Greene Engine.


Keep on thinking and thanks for posting,


Jerry
There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.

Offline Captain Jerry

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Re: Recently Rediscovered Drawing of the TTNW Valve Release
« Reply #21 on: August 16, 2019, 02:42:20 AM »
I may be beating this to death but I'm having fun with it.  I see that it is getting a few views but not much conversation.


The current condition is the result of some refining of the design.  The general principal works but since the pieces have been hacked out of scrap with no real plan, just a general idea.  Everything has been a "Make to fit", eyeball measured, do it over effort and there has been a lot of slop in the linkage so some of that has been improved.  Clearances and unnecessary spacing and oversized components have been tightened up and still more is needed.  The most important feature on this version is a greatly stabilized knock off ramp design and the first effort to locate the governor control link to the bottom of the mechanism.  It works,  It needs smoother action and finer control and can be reduced in size.


More to come.  I hope you enjoy the video.


There are thing that you can do and some things you can't do.
Don't worry about it. try it anyway.