Author Topic: Not Dead Yet  (Read 2504 times)

Offline Captain Jerry

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Re: Not Dead Yet
« Reply #15 on: October 22, 2022, 01:50:16 AM »

Thanks for taking a look, Per.  It is hard to follow from a still photo but J will attempt a simple explanation. 


A double acting steam engine works by applying steam alternately to opposite ends of the cylinder to drive the piston back and forth.  Most simple engines operate with a simple steam valve that opens and closes the steam valve in a sinusoidal mode which works but is not using the steam very efficiently. This becomes more important as engines grow larger.  A more efficient use of the steam occurs if the closing of the steam valve occurs earlier in the cycle, based on engine load, and if occurs sharply so that power is supplied by expansion of the steam rather than just blowing it out of the exhaust port. There have been numerous mechanical linkages designed to do that and I cant remember all of their names and I am sure that I have not seen them all but the all have a common feature which I call a latch, and some beans to disengage that latch. A governor is used to control when the latch is disengaged. Each steam valve is independent of the other and the timing of each valve can be adjusted individually.


I have built and tested at least 8 different early release mechanisms and some of them worked. Most never saw the light of day.  The problem is scale.  I guess that I am not as much concerned with building historically correct models as I am in designing model mechanism that work and have an interesting appearance.  The most common cause of dissatisfaction is what I call "the wobblies." The number of parts and joints increases the wobblies so I keep trying new designs.  Animation in Alibre' never suffers fro the wobblies.  All fits are perfect on screen but I now recognize the contributing factors.  Keep parts counts low and keep all forces on the same plane,


In this design the latch mechanism is at the connection of the rocking plate and the push bar.  The push bar is the ONLY part in the linkage between the rocking plate and the valve control arm. The unlatching mechanism is the round red pin that the pushbar encounters causing it to lift out o the driving notch. When out of the driving notch, it is completely disconnected from the valve linkage. The dashpot that is connected to the other arm of the valve pulls that arm down sharply. closing the valve. The pushbar is completely free of the rocking plate until it is time to open the valve on the next stroke. It is resting on the top edge of the rocking plate but transmitting no force.  The weight of the push bar is all that is necessary tto reset the latch, no springs.  There are two small ears on the push bar that keep the bar and plate in line but transmit no force. The other valve latch will disengage before this one reengages.


I have uploaded a video of the rocking motion and a backside video showing the rocking action front and back and a snapshot of the disengaged latch.  I don't think Alibre or any other design CAD can animate the action without a lot of video editing.


I am going to save this post before I try to upload the video so I don't lose it so if they are not there, check back in a few minutes.


Jerry

« Last Edit: October 22, 2022, 02:03:13 AM by Captain Jerry »
NOTARY SOJAK

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

Offline Admiral_dk

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Re: Not Dead Yet
« Reply #16 on: October 22, 2022, 11:47:13 AM »
Thank you for the more 'Zoomed In' drawings + explanaiton of the DashPots - the later working as what I would consider Counter-Weights (though not for linear, but rapid motion).

I can see why this should work as intended - and only wonder about Friction + Wear of the Latching Edges + Pins .... This is probably nothing to worry about in a small model ....

Per

Offline Captain Jerry

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Re: Not Dead Yet
« Reply #17 on: October 22, 2022, 02:34:41 PM »
I adree completely with your observation regarding wear on the latching faces and if I were designing for full size manufacture, I would probably use bolt-on replaceable faces  but the actual load on the mechanism is small and lubrication js easy.. Material choice is a consideration. I will probably use brass but cast iron is a possibility.


I have some animated video of the operation but I seem to have forgotten how to post  .avi files. I am working on it


Jerry

NOTARY SOJAK

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

Offline Bearcar1

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Re: Not Dead Yet
« Reply #18 on: October 23, 2022, 06:44:49 AM »
Capt', I have always enjoyed your designs and interesting, eye-catching mechanisms. They get my mind going and provides many hours of concentrated arm chair engineering..... Thank you for that. :wine1:


BC1
Jim

Offline Charles Lamont

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Re: Not Dead Yet
« Reply #19 on: October 23, 2022, 08:40:30 AM »
I don't think I have seen a trip gear any simpler than that. You might need light springs to ensure the latches engage quickly. If possible, I would use hardened steel latch parts.

Offline Captain Jerry

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Re: Not Dead Yet
« Reply #20 on: October 23, 2022, 06:52:29 PM »
Thanks for looking in and commenting.  I hope to avoid springs but I have considered the possibility. I will probably use cast iron for the push link and hope that the weight will be enough.  If not, I can add weight to the bar over the latch point.  The rocking plate will be either brass or aluminum and I can add an insert of either cast iron or tool steel to the top for wear.


Jerry
NOTARY SOJAK

There are things 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: Not Dead Yet
« Reply #21 on: October 26, 2022, 03:52:52 AM »
Does this work
I guess it does!




This is the inside and outside action on my latest design.  It does not show the actual release and early valve closing but That can only be done with some fancy video editing which I cant do yet.


[youtube1]https://youtu.be/yeroAY03nwU[/youtube1]
« Last Edit: October 26, 2022, 04:24:52 AM by Captain Jerry »
NOTARY SOJAK

There are things 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: Not Dead Yet
« Reply #22 on: October 30, 2022, 01:41:52 AM »
My shop time is turning into armchair design time so I am posting this update of my latest design.  This is a revision of the governor control method.  The wedge design show in previous versions is easy to understand but it has a few drawbacks. It lacks full control of the knockoff pins as the wedge is retracted to reduce early cutoff it relies on gravity to drop the pin bar.  Alib' does not recognize gravity so it would need some kind of spring or counter weight.  The current design replaces the wedge design with an eccentric that more precisely controls the position of the knockoff pins in both up (earlier cutoff) or down (later cutoff) directions.  It is only slightly more complicated but overall more reliable.  The green bar causes the eccentric to rotate around the red pin under control of the governor
 
« Last Edit: October 30, 2022, 01:13:09 AM by Captain Jerry »
NOTARY SOJAK

There are things 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: Not Dead Yet
« Reply #23 on: November 02, 2022, 06:26:54 PM »
I think that I want to build this but my shop time may be more limited than I had anticipated. I am able but it seems that I am needed in the house most of the time. So I'm going to close this re-intro and open a new one under the "Your own Design" tab in the near future.
NOTARY SOJAK

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

 

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