Lower quadrant semaphore 'bouncing' operation

gregh

gregh

electronics, computers and scratchbuilding
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I don't have much knowledge of signalling, but a friend mentioned it would be nice to operate semaphore signals with a servo motor and ADD THE BOUNCE FUNCTION.

Now from my limited observation, UPPER quadrant signals had a motor on the signal head and operated pretty smoothly.
But LOWER quadrants were usually operated by a wire to pull them clear and then 'fell' back to Stop when the wire tension released. I've never seen one operate, but a trawl of Youtube, found a couple of example of one going from clear to Stop with lots of bouncing.

https://www.youtube.com/watch?feature=player_detailpage&v=V31E8pmml3Q#t=40

Does anyone know if they also 'bounced' when going from Stop to clear??? Any videos showing this??

From the youtube video I examined every frame and determined the following timing for the bouncing from clear to Stop:

Initially 'clear' at 50deg down.
Takes 0.56 sec to rise to horizontal
Then bounces down 18 degrees in 0.40 sec (0.98sec)
Stays there for 0.08sec, then (1.06s)
Rises to horizontall in 0.48sec (1.52s)
Bounces back down 6 degrees in 0.18s (1.76)
Waits 0.08s, (1.84s)
then bounces back up to horizontal in 0.32sec (2.16s) and stops.

Any comments???
 
In the U.K. many, if not most, upper quadrant signals were also wire, lever and counterweight operated so bounced when returning to danger. From memory and the odd film clip they didn't bounce as much as the one in your link but I suspect many lower quadrant examples similar to it also had less bounce
 
Gregh, from my knowledge of LQ (Lower Quadrant) Signals and that is mainly GWR (former Great Western Railway UK) I cannot remember them bouncing. That is of course not to say that they did not, no doubt people with other or better memory will shoot me down on this.

UQ (Upper Quadrant) ones tended to Bounce Sometimes on return to Normal. People in 00 and other predominantly indoor scales have worked hard to achieved the effect and have done so very well with arrangements of cams and things. However to my mind the effect is probably a bit over done, as the signal does not always bounce out there in the real world. I suspect the effect is caused by things such as heat and cold effecting tension on the wire etc.

So if you want it anyway just do it and enjoy. After all it is your Railway and Rule 1 applies. I look forward to seeing your efforts. Sure it will be good.
JonD
 
I'd be interested in the results and how to do it. I think it was all to do with wire stretch, so the further from the s/box the more would be the bounce.
 
There's a sort of extra flick when pulled off on this video. Mind you, not sure if this is typical as they are trying to repair a fault (later on they discuss it hitting the end stop and bouncing back)

http://youtu.be/nQ-PQrq3Qko?t=3m5s

There's a less perceptible 'bounce' at the start of this video, though not as much as when set to danger
http://youtu.be/wAO3JbXYRnI?t=14s


Rik
 
bobg said:
I'd be interested in the results and how to do it. I think it was all to do with wire stretch, so the further from the s/box the more would be the bounce.
Click to expand...
Hm looking at the Vids from Rik, it is just the flexibility of the wire between the Counter Eight and the Signal Arm. Very interesting to see it replicated by Hand as it were.
JonD
 
That would depend on if the run from the box was wire or point rodding, Not a lot of noticeable stretch in point rodding, but wire was often used for fair distances, though the counter weight could easily damp out some of it.
 
ge_rik said:
There's a sort of extra flick when pulled off on this video. Mind you, not sure if this is typical as they are trying to repair a fault (later on they discuss it hitting the end stop and bouncing back)
http://youtu.be/nQ-PQrq3Qko?t=3m5s
There's a less perceptible 'bounce' at the start of this video, though not as much as when set to danger
http://youtu.be/wAO3JbXYRnI?t=14s
Rik
Click to expand...
from the 1st video it looks like ALL the bounce is in the signal arm+head. It bounces but the weighted arm doesn't. Interesting.
Anyhow, looks like I could make the movement to clear go past it's usual position and then bounce once back to its rest position.
Haven't had a chance to look at the long video yet.

I've written the picaxe program to do the bounces at stop.
 
Greg,

From memory NSW lower quadrant signals also bounced a bit on being cleared although not nearly as much as when returning to danger, but that memory is years ago when I was a volunteer for AHRS. I seem to remember that it had to do with the elasticity of the wires. I may have video of it, I'll have a look when I get home, but I'm not confident.

Steve
 
I've spent too much time programming a picaxe to try to simulate the arm movement with a servo. Initially I assumed the arm movement was a constant speed but it didn't look quite right. So I rewrote it to move the arm under a constant force (gravity) when going to stop. This means the arm starts of slow and accelerates. I left the movement to clear as const speed,. I've added some bounce to this movement too, but will investigate further if it's needed.
Anyhow, here's a video of a simulation of a mock-up showing my simulation and the prototype.

http://youtu.be/-3EBrW2ZuWk
[youtube]http://www.youtube.com/watch?v=-3EBrW2ZuWk&feature=youtu.be[/youtube]
 
I reckon that's pretty close. Well, close enough, any road! [e]339[/e]
 
I hadn't realised that anyone had ever simulated the 'bounce' which together with the clanging sound of some was so characteristic. :D :D
An essay at school once got me an A+ for an onomatopoeic (Ooh 'ark at him) description of a WD 2-8-0 clanking to a stop at a Home signal with clattering buffers on a loose coupled freight and then the sound as the signal dropped and it wearily heaved itself away. Incidentally, the last DubDee I ever saw or heard in BR service. :(
 
Back in my first post I mentioned I had originally programmed a 'constant speed' movement, but abandoned it for a constant force movement.
I was trying to rewrite the program to make it more 'general' ie the amount of movement , speed etc could be varied. It turned out to be pretty complicated for the const force program. So I thought I'd revisit the const speed version.
So here's a short video that compares the const speed, const force and real signals. All version take the same time to complete the raising sequence.
I still like the const force version. What about you??

[youtube]http://www.youtube.com/watch?v=oy_hwS1T5Ks&feature=youtu.be[/youtube]
 
Wow Greg....that is nigh on perfect!
Well done that man.
You will have to give a tutorial on picaxe programming.......
 
Constant force it is. My take would be that if the bounce is caused by elasticity in the signal wire, so there will be acceleration & deceleration, and therefore not constant speed.
 
I'd vote for constant force too. Fascinating project and visually very effective. Just wish I knew more (a lot more) about electronics.
 
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