Chris's Un-Ransome Tree Feller

[crueby]

Got the little adjustable bit made (some trial and error, may make a cleaner one later) and made a short video of it in action, moving the piston back and forth by hand. Awkward to do that and hold the camera!  You can hear the snap of the shuttle moving back and forth as the tone of the air changes. I had to add a clamp over the openings for the pipes to the cylinders (which dont exist yet) to restrict the air flow somewhat, otherwise there was no pressure left to operate the shuttle! That took a few minutes to realize what was happening.
<a href="https://www.youtube.com/watch?v=wu5g01jXXT0" target="_blank">http://www.youtube.com/watch?v=wu5g01jXXT0</a>

[crueby]

I made a cutaway view of the CAD model and added some colors to make it clearer what I did in the valve chests. First, here is the diagram:

The parts: At the top the red bar is the valve rod moved by the linkages to the pistonThe dark blue on that rod is the smaller D valve.
Around it, and in the chest down lower, is the compressed air or steam in yellowThere are passages, in green and purple, under that d valve that lead down to the lower steam chest. When the blue valve is shoved all the way to one end, it opens one of those passages, sending pressure down to push the orange shuttle rod to the other end. When the blue valve is in the middle, no pressure is sent, so the shuttle rod stays in place by inertia and friction.The orange shuttle rod moves the darker orange D valve, which connects the ports at the bottom, in pink and light blue to either the yellow pressure or the light blue exhaust, just as normal in a steam engine.


Hope that helps!

[cnr6400]

   

[Kim]

Ah.... Now I see!  That shuttle rod (the orange thing) gives it some hysteresis.  It's either one way or the other.  You don't have any of those problems with transitioning valves or anything.  Clever!

Kim

[crueby]

Ah.... Now I see!  That shuttle rod (the orange thing) gives it some hysteresis.  It's either one way or the other.  You don't have any of those problems with transitioning valves or anything.  Clever!

Kim

Yup!  A lot like a toggle light switch on the wall - you can move it quite a ways across the middle before anything happens. This was key to fixing the problems I was having with the original Ransome twisted-bar design, since as the saw moved it was moving the valve the whole time. That was probably okay with steam at full size, but at model size with compressed air it would stall out and wobble in the middle. Probably other ways to fix that with slack in the links and such, but it got too fiddly and I gave up. This should work much better. I hope!!

[crueby]

Thanks Jeff!!
 

[bent]

"Piloted part of the shuttle valve term, what does that mean?"

A pilot valve is usually a direct acting (manual or solenoid control), small, low-force valve that controls a small pilot flow to push a larger piston/shuttle and thus control a larger flow that needs more force to actuate.  Using the hydraulic "leverage" to your advantage.  Or, as in your case and more importantly, to create the hysteresis you want.  I've only learned recently about hydraulic shuttle valves and valve stacks...and the range of what can be done with them is staggering.  We are using some ancient Vickers parts for an actuator we build at work.

[crueby]

"Piloted part of the shuttle valve term, what does that mean?"

A pilot valve is usually a direct acting (manual or solenoid control), small, low-force valve that controls a small pilot flow to push a larger piston/shuttle and thus control a larger flow that needs more force to actuate.  Using the hydraulic "leverage" to your advantage.  Or, as in your case and more importantly, to create the hysteresis you want.  I've only learned recently about hydraulic shuttle valves and valve stacks...and the range of what can be done with them is staggering.  We are using some ancient Vickers parts for an actuator we build at work.

Gotcha!  There's  an amazing variety of  combinations of  valves and linkages, feedback methods, etc.Fun to learn about!

[Admiral_dk]

Thank you for clarifying how your new design functions - really helps the olde grey matter 

Per       

[crueby]

Thank you for clarifying how your new design functions - really helps the olde grey matter 

Per       

Glad it helped!  Though the grey matter must really be getting old if it spells it 'olde' ...   

It did spark a thought in my graye mattere, the position of the pivot on the lengthwise bar parallel to the piston rod ought to be farther out from the center of the piston travel than it is. If it was the same distance out from center as the length of the short bar atached to the piston, then the arc of the next bar would be centered crosswise. In the video, you can see that it arcs farther to one side than the other. That could make the travel adjustment trickier, all I need to do is redrill one hole and make the final bar to the clevis a little longer.

 

[crueby]

No shop time today,  long lunch with friends  then out canoeing, perfect fall weather!

[crueby]

Catching up with progress from yesterday and today, got the new linkage rods made and installed, this time with the fixed pivot point moved out like I mentioned the other day. This makes the lever angle symmetric across the axis, and the new link allows easier adjustment of the throw.

Also drilled/tapped for the pipe fittings at the ends of the cylinders, and got the pipes made up (after taking this picture)

While its all apart, I've gotten the piston head made, with Viton o-ring. Before putting it all together I'll make the gaskets and get the valve faces lapped smooth. Might be testing on compressed air tomorrow or Monday (at the pond Sunday).

[cnr6400]

 

[crueby]

This morning I made the cylinder end cap gaskets, ran some oil into the cylinder to lube the o ring, and got it assembled. Before taking the steam chests apart to make those gaskets and lap the valve faces, decided to give it a test.  After realizing that one of the links was on backwards and a couple experiments to find the right setting for the length of the connection on the middle link, it took off! I had put an off-the-shelf plumbing needle valve in line in the air hose, so I could run the pressure up to about 30 psi and adjust the speed with the needle valve - that was key I think to adjusting it. With a moderate flow, the speed of the piston stayed down but there is still enough pressure available to give it enough force for sawing.

Grabbed the camera, and got this video of it ticking over. If I run the speed up too high, it over-travels the piston slightly, but that should not be a problem, since the saw blade wouldn't like too fast a speed anyway.
<a href="https://www.youtube.com/watch?v=t2fiGmR9_t0" target="_blank">http://www.youtube.com/watch?v=t2fiGmR9_t0</a>
And yes, the shop elves are in hiding!!   

Next up will be to take the steam chest apart and do the gaskets/lapping there. Then, on to making the base frame!!

[cnr6400]

  She's a runner! works well Chris, congratulations!

(and I think the shop elves showed good judgement by hiding)