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More work on lever frame

Fen End Pit

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I realized that the spring on the lever was effectively duplicating the one in the micro-switch so in the best traditions of trying to keep things simple I tried to build a version which doesn't bother using it. The revised lever arrangement is a bit simpler but it takes a little bit of adjustment to:-

  1. get the springing in the lever right,
  2. the micro-switch to change correctly as the catch handle is pulled and also
  3. the screw which fastens the attachment to the lever not to foul the micro-switch on the lever.

blogentry-7212-127886851892_thumb.jpg

 

 

The resulting modules fasten on the levers quite well. (though I realized after I took this picture I'd got the one on the end with the mounting bracket upside down.

 

blogentry-7212-127886857437_thumb.jpg

 

Then I thought I'd turn to the locking bar. This is very much option 1 so I'm expecting to have a load of different arrangements before I settle on the best way of working. This version using the push rods on the frame which pass through a 'key hole' shaped hole. A piece of brass tube will only go through the large part of the 'key hole'. I used a piece of square brass tube as the basis of the locking bar as it is stronger than a sheet material. I drilled 2 1.2mm holes 5mm apart for each lever and then opened both the holes out to 4mm on one side and one of them to 4mm on the other. The I joined the holes up with a piecing saw and a dremel to make the shape required.

 

The photos below show the operating sequence.

 

Initially all the levers are locked as the piece of tube around the push rod is trapped behind the lock in the small part of the 'key hole' shape.

 

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The lock moves the the left aligning the large part of the 'key hole' with the push rod.

 

blogentry-7212-12788693375_thumb.jpg

 

A lever (in this case lever 2nd from the left is reversed, pushing the piece of tube through the larger part of the 'key hole'.

 

blogentry-7212-127886969875_thumb.jpg

 

Finally the locking bar slides back to the right locking the push rods again, in this case with the piece of tube on lever 2 on the other side of the lock.

 

blogentry-7212-127886935402_thumb.jpg

 

It works in theory, I just need to try and connect a servo to the locking bar now!

 

I think I'd like to make the locking 'spring loaded' so the servo pushes the locking off, but a spring pushes it back. That way if you release the catch handle, but the lock isn't quite aligned exactly the servo can just go back to the locked position but a spring actually does the work.

 

Any one got any better ideas?

 

 

David



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I assume the microswitch switches only while the catch handle is in the pulled position?

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Yes, there is a separate switch on the frame that is closed when the lever is reversed. The intention is that the switch on the catch handle is used to tell the control system that the signalman wants to pull a lever. The electronics will then clear the locking bar if the lever should be free.

 

David

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Ah yes. Sorry, I should have read your previous 'framework' blog.

 

What do you estimate the unlocking and locking cycles to be timewise?

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Well the electronics seem to work pretty instantaneously. On the test rig I can't sense any time between my pulling the catch handle on a free lever and the light indicating the locking is clear going on. So the delay will be how fast I can move the locking bar out of the way. It has been pointed out on the MERG forum that I might be better off with a solenoid but I'm going to have a go with a servo for a start. I reckon I only need a few millimetres of movement which would only be a few degrees of turn on the servo. To be honest until I build it I don't know whether it will feel quick enough. I don't really want the operator to have to think 'catch handle - PAUSE - pull'.

 

David

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I suspect you will become quickly attuned to the characteristic. I'd never really considered wholeframe locking/unlocking before, but for a 'one signalman in steam' box I can't see a disadvantage.

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Another thought I had was that if the locking was actually 'spring loaded' on a per lever basis then the electronics could be made to automatically return the lock to 'locked' in the event that a second catch handle was pulled. That way only one lever would ever be free at a time.

 

David

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I love mission redesign statements! How's about the locking being initiated only when the microswitch reversion (confirming the locking) is checked to be the same one that initiated the unlocking?

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I love mission redesign statements! How's about the locking being initiated only when the microswitch reversion (confirming the locking) is checked to be the same one that initiated the unlocking?

 

The point here is that with 'whole frame' locking it is possible to pull the catch on lever 1, unlock the frame, then pull the catch on lever 2 and pull lever 2. In order to avoid this pulling a second catch handle should result in the frame being locked. However if in this case lever 1 was 'half pulled' it could prevent the locking bar from locking the rest of the frame unless there is some kind of separation between the locking bolts. I think this is probably achievable. As to mission redesign, well I'll fix it in the documentation for the next release!

 

David

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As I see it, there are several parts of the logic:

 

- preventing two catch handles being pulled within a single locking 'cycle';

 

- ensuring that once a lever has been selected for movement, that lever is either moved completely or is not moved at all, i.e. not half-pulled;

 

- in the case where one wanted to move lever x but instead mistakenly pulled the catch on lever y, and then released the catch on lever y without moving lever y, the frame should still unlock (provided of course that lever y was 'releasable' according to the locking table) and re-lock.

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David, Following your lever Frame building with interest. Your latest version is an excellant design, my only concern is the Micro switch attached to the lever may cause premature failure of the wiring due to lever movement. I wonder if you'd cnsidered something along the ines of Leslie Bevis-Smith (MERG) design where the micro switch is fixed? I'm sure that your current design could easily be adapted.

 

regards

 

David (Pannier Tank)

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David, Following your lever Frame building with interest. Your latest version is an excellant design, my only concern is the Micro switch attached to the lever may cause premature failure of the wiring due to lever movement. I wonder if you'd cnsidered something along the ines of Leslie Bevis-Smith (MERG) design where the micro switch is fixed? I'm sure that your current design could easily be adapted.

 

regards

 

David (Pannier Tank)

 

I can understand your concern but I think it will be ok when I feed each pair of wires through a hole in a baseboard. Another possibility is to half the number of wires by using the frame as the return. This would work with the CANACE8c I'm using now but not if I extend the frame and use the CANACE3 instead as this needs the different signals to have different returns with various diodes in the way.

 

David

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