Jacobs Ladder---

[Brian Rupnow]

I am really surprised about the "delicacy" of timing between the two shafts. Even the slightest bit of slack in the chain, and the non-driven shaft wants to flip around and travel backwards, locking up the mechanism. Tomorrow morning I am going to but an outboard link between the two shafts 90 degrees out of phase with the center staircase. That will absolutely keep things from getting "out of time",and may do away with the necessity of having a chain and sprockets. I am learning new stuff here. In 46 years of designing just about every conceivable type of industrial machinery, I haven't ran across something quite like this. It is reminding me more and more of the solid links between drive wheels and non drive wheels on steam trains. John Bogstandard tried to explain this to me in a much earlier post, but I didn't understand what he was getting at, however it is becoming clearer as I progress.

 

[tel]

And then, of course, the situation may well change when it is running under power and inertia is tending to push the driven wheel 'forward' as well.

Meanwhile I'm still thinking gears, with an idle wheel space - but heeeey! I like cutting gears!

 

[rleete]

but heeeey! I like cutting gears!

And here I thought I was weird.

 

[tel]

And here I thought I was weird.

I find it very ... erm .... therapeutic!

 

[Brian Rupnow]

Well, at this point in the game, all I have to report is a complete and total FAIL!!!!! I got up early this morning and made the modifications to add a second arm on the outside of the pulley. I even took the inner staircase, the bearing support, and the added link which all have to have identical hole centers and put dowels through all 3 at the same time to convince myself that I hadn't machined something wrong. The net result of adding the second link was that it locked things up tighter than ever. I am somewhat bumfoozeled at this point, so will take a break from this and read for the afternoon. My next plan is to remove the second link, go back to the chain and sprockets, and open the lower hole in the staircase out to .030 oversize. Maybe if I engineer a bit of "float" into the system it won't lock up like it currently does when all the holes are a "reamed fit"

 

[GailInNM]

Brian,
On model locomotives, it has been a rather standard practice to elongate the holes in the rods to correct or any position errors and for quartering errors. Quartering is the setting of the cranks at exactly 90 degrees to each other. Either error will cause things to lock up. It is not a bad a practice as it seems as neither rod is contributing any thing when a line between the rod ends passes through an axle. Actually quite a bit of slop can be introduced this way and it is not evident. Even making the rod end holes oversize rather than elongating does not show up.
Gail in NM

 

[coopertje]

Brian, first of all compliments for your build, very interesting!

I am not sure if I start to repeat Gail, but maybe the problem is not the exact fit but the fact that the 2 levers operating the inner staircase travel the exact same way during the rotation. I believe that if you give them an offset (turn on a little CW and the other one a little CCW) they will never line up and most likely not stall anymore. If the offset is kept reasonable it probably will not be visible in the movement of the inner case.

Good luck and hang in Jeroen

 

[Brian Rupnow]

I'm going to make this statement while firmly grasping my wooden chair, but the oversize hole in one end of the staircase SEEMS to have gotten rid of the bind. I think that with a swing arm chain tensioner, the problem may be solved.

 

[rleete]

I'm interested in seeing what you have in mind for a tensioner system. Torsion spring? Gas pressure piston? How are you determining the force neccesary to maintain tension, without putting too much drag on the system?

 

[Brian Rupnow]

It works!!!!---BUT---The trick is going to be slowing it down enough. I had a 1.5" pulley on the mill to test drive it with, and the moving center staircase wanted to run at warp speed. I kept putting the 1" steel ball on it and then slowly advancing the mill speed from zero to see it elevate the ball. The device wouldn't run at all, then would take off and bounce that friggin steel bearing ball around like a ping pong ball. I didn't have my chain tensioner on a spring loaded swing arm, just had it bolted onto the bearing support, but that isn't going to do it. The sprockets are not perfectly concentric to the hub bores, and the load imposed by the center staircase varies quite a bit through its 360 degrees of travel, causing the chain to "whip" and jump sprocket teeth, which of course threw things out of time and caused it to lock up repeatedly. At any rate, it works. all I have to do is slow it down a lot.

 

[Brian Rupnow]

And I know how I'm going to do it. In the foreground of the attached picture is the pump that I built a couple of years ago, and I am going to reclaim the timing belt pulley from it. In the background is a gear reducer system that I had on the Doodlebug, which has the mating timing pulley on it, as well as a pair of nylon meshing gears. I am going to "reclaim" these components and build them into the Jacobs Ladder, to get it running at a more manageable speed.

 

[Brian Rupnow]

My dozen wooden balls showed up in the mail today. Good quality and a very fast turn around. In spite of all the crude remarks that I thought of before posting this picture, I'm going to be the good clean living boy my 91 year old mother expects me to be and say nothing, just post the picture.

 

[rleete]

What? You've lost so many marbles that you had to go buy wooden replacements?

 

[Brian Rupnow]

I was right at the point of giving up on this project. It kept locking up, the balls kept falling off when they were almost to the top----it was ugly!!! I was setting here thinking "What haven't I tried, that might have some positive effect on the way things worked." The only obvious thing was to try the pulley on the lower shaft, so just for a giggle, I did.---and EUREKA!!!! It made a big difference in smoothness of operation and how the balls stayed on the operating ladder. With all the gears, timing belts, etcetera, it is starting to take on a Rube Goldberg/Steampunk appearance, and I like that!!! Time is at a premium right now, but once we get thru christmas I will be hooking this up to my overcrank single engine and beginning to take a serious look at a ball return. Merry Christmas everyone, thanks for looking.---Brian

 

[Path]

Merry Christmas and a Happy New Year to you and your family.

Looking forward to seeing your finished ladder. :big:

Pat

 

[Brian Rupnow]

Here we are guys. Large as life and twice as ugly!!! First succesful run!!!

 

[Harold Lee]

Now that is cool!!!!!! That would be a good stress buster, watching that while having a cup of coffee. Glad you persisted on it.

LOVE IT BRIAN!!!!

Harold

 

[lee9966]

Very nice Brian. I love watching as you solve design puzzles, very educational.

Lee

 

[90LX_Notch]

Brian,

That is very cool. I like it very much.

Bob

 

[larry1]

Brian, As usual great job, Thank you. larry