Chris's Build of Steering Engine

[crueby]

Got the valve assembled this morning and it is working quite well. I was wondering how to show the air coming out of the proper outlet pipe, and since the shop elves broke their air canons in a war with the local squirrels, the next best thing was to stick bits of tissue paper in each pipe and move the valve from center (off) to either side to show the operation. Here is a very quick video (doubt it will win as Oscar)
[youtube1]https://youtu.be/IfKFAvn6y0Q[/youtube1]

Next up is to get it mounted on the engine and make the links up to the crank arm to test it for real.

[Kim]

Looks pretty good!  Not getting much leakage when they're closed, and that's important. 

When you get it mounted you'll have much finer control over moving the valve too. That will be helpful in testing.

Kim

[cnr6400]

Hi Chris, the control valve works great! Liked the video too. 

[Michael S.]

Very good Chris,

on the large machine, the valve is not 100 percent tight in the middle position. I then hear a very faint noise.
It is important that the machine goes to STOP.

Michael

Prost 

[crueby]

Very good Chris,

on the large machine, the valve is not 100 percent tight in the middle position. I then hear a very faint noise.
It is important that the machine goes to STOP.

Michael

Prost 

I could hear a tiny hiss on mine (had to check since the compressor hose connection was leaking a little too), there is a very very slight leak at the one port. I doubt it will be a problem since I've never made a model sized piston valve (which will be at the cylinders) that didn't have a little bit of leakage too, so it shouldn't be able to build up enough pressure to move the engine. I hope!

[Michael S.]

I've often thought about how to build the cylinder block.
I could remember how I once built a horizontal steam engine with piston valves. There was a blueprint for it at the time. The block is made of six parts. Two pieces of pipe, two connecting pieces with channel and two flange plates. Everything is soldered.
Maybe it is an inspiration for you.
Something needs to be changed. But the flange plate at the top would be possible and have a different shape at the bottom. With two holes for the columns.
But you might already have your own plans.

Michael

[crueby]

I've often thought about how to build the cylinder block.
I could remember how I once built a horizontal steam engine with piston valves. There was a blueprint for it at the time. The block is made of six parts. Two pieces of pipe, two connecting pieces with channel and two flange plates. Everything is soldered.
Maybe it is an inspiration for you.
Something needs to be changed. But the flange plate at the top would be possible and have a different shape at the bottom. With two holes for the columns.
But you might already have your own plans.

Michael

Hi Michael,
I haven't given the cylinder blocks much thought yet, other than how to get the top/bottom passages to be in the right place in the valve opening, since they need to be at a known distance apart to get the spool valve dimensions to match. I was thinking of drilling vertical holes from the top/bottom between the cylinder and valve openings, and drilling horizontal holes from the outside of the valve side, then plugging the outside of those holes. That would get the holes to all line up without having to get angled holes in exactly the right place/angle.

I hadn't considered making the valve and cylinder halves seperately - that would work out easy as well.  More thinking to do!   
 
Chris

[crueby]

And first test of the control valve in place on the engine! I made up the links from the crank arm to the valve rod, and got it installed this morning. Turning the wheel either way opens the valve to run the engine the other way, which re-centers the valve and turns it off.  Took a short video of it in 'action', which consists of hearing the air coming out one of the two control ports. Since the engine is not built yet, I was turning the front gear wheel manually to simulate it. There is some slack in the crank arm connection to the upper shaft which makes for some play in the wheel before the valve moves - looks like that is almost all in the Acme screw and nut. Very small slack, but enough to notice on the wheel. I'll have to investigate to see if I can tighten up that motion somewhat, or if that is just a 'feature' of scaling down.
Here is the video:
<a href="https://www.youtube.com/watch?v=QT7hJQIPUdQ" target="_blank">http://www.youtube.com/watch?v=QT7hJQIPUdQ</a>

[cnr6400]

Cool! 

[Michael S.]

In principle it will work, very well demonstrated.
And now for the first time I can see with your hands how big the model has become.
Unless it was the hands of the workshop elves! 😁

Greetings Michael

[Kim]

Very nice demo there, Chris! 

Kim

[crueby]

Thanks guys!!
Looks like next I can start on the actual 'engine' part of the steering engine, with the crankshaft!       It will be built up from bar stock, with the center section having a length of the Acme threaded rod forming the worm gear - I'll dirll through the section of threaded rod and pin it to the crankshaft center section

Thanks for following along and chiming in!   

[crueby]

I just wandered back into the shop to look at the issue of too much play in the wheel/linkage on the control valve, and have found where the extra movement is coming from:

In this picture, the two red arrows point at the crank arm on the left and a straight arm on the right, which suspend the bronze follower pointed at by the green arrow. Both arms are just a sliding fit on the crossbar, and they fit over posts on the sides of the follower. The fits on the bar and posts is pretty close, but there is just enough movement that the follower can twist as the screw is turned. It didn't show before, but now with the resistance of the valve rod packing, the crank arm gets resistance from the valve rod, and the straight arm rotates first, letting the follower rock, and delaying the first movement on the valve rod. Hope that makes sense!  The follower is a little loose between the lips on the inner screw fitting, which was not a problem if everything moved together.

So, two things I can try:  1) either (A) connect the crank arm and straight arm with another crossbar to only let them rotate together, or (B) fix them to the crossbar so the crossbar has to rotate. That second option would make it a lot harder to assemble/disassemble, since I'd have to un-fix one of them from the crossbar to get the arms over the posts. That could be done with a removeable through-pin on both thought.  2) in addition to the first thing, also shimming the follower sides with some thin shim stock to get a tighter fit in the screw fitting, though I don't think that will help as much, and I dont want the follower to bind up.

So So, I think I'll give one of the first options 1A or 1B a try tomorrow. Right now there is over half a turn of nothing happening on the steering wheel, which is just too much - it functions, but its too much play for my liking.

[Kim]

Good sleuthing, Chris!  Knowing the issue is the big half of the problem.  Once you know what it is, you can devise a solution for it.  Looking forward to seeing what the final call will be.

Kim

[crueby]

Success!  I drilled/tapped through the crank and straight arms and the cross shaft for 1-72 screws, which got rid of the slack in the movement of the crank arm and valve rod.


There is still a little bit of wheel movement needed before the valve opens when turning the opposite way, but that is due to the overlap on the ends of the valve slider over the port openings. I COULD trim back the valve slider length to eliminate that, but until I have the engine built and running I am not sure that is a good idea - too small an overlap, and its possible the engine could over-run the off position and cause the mechanism to hunt back and forth at the 'stop' position. Better to wait and see how it behaves, and trim the slider at the end if desired.

Happy with that fix, so its on to the crankshaft!