Placement of uncoupling magnets

[RobinofLoxley]

I'm going to bury some Kadee magnets in the track beds of the Terminus stations of my layout, way before I have any intention of operating with them. I would like to know in people's opinion who have done this, how much space to allow between the magnet and the buffers. The longest loco that I have is a Duchess - my stock is all steam at the moment, so if say the Duchess loco + tender is 30cm, how much room should I leave for uncoupling and easing the loco away from the carriage rake so the carriages can be coupled from the other end, where the pickup manouvre will push them slightly towards the buffers as well. My platforms are reasonably long (5/6 carriages plus loco) but I do eat into the space the more gap I leave from the buffers to the magnet. After uncoupling I can run the uncoupled loco right up to the buffers to create a little more space. Ideas?

[WIMorrison]

You will need to allow enough space for,

 

a) train overrunning stop position - 25mm?

b) action of uncoupling and moving away - 25-50mm?

c) distance coaches will move when loco couples at opposite end - 25mm?

 

total - around 100mm?

[Dungrange]

36 minutes ago, WIMorrison said:

You will need to allow enough space for,

 

a) train overrunning stop position - 25mm?

b) action of uncoupling and moving away - 25-50mm?

c) distance coaches will move when loco couples at opposite end - 25mm?

 

total - around 100mm?

 

I don't see a need to add each of these.  If the train overruns the stop position (ie where the coupler is mounted), then the locomotive will have to be set back to the point at which the coupler is situated before it draws forward again after uncoupling.  As such, I think you can eliminate a).  As for b) and c), provided b) is greater than c) then the rake won't couple to the locomotive even if it is pushed back by whatever distance you assume for c).

 

If we assume c) is correct, then as long as a bit more than that is provided it should be okay.  However, it's perhaps worth pointing out that locomotives are not supposed to be driven right up to the buffer stop and are, I think, supposed to stop approximately 2 m short, which in model form is about 25 mm on a 4mm scale model railway.  I'd therefore be tempted to go with a distance of about 60 mm.  That is, stop over the magnet and uncouple.  Draw the locomotive forward about 35 mm stopping about 25 mm before the buffers.  That then means that any locomotive coupling on the other end would have to shunt the coaches back 35 mm before it would recouple, which is quite a lot given that you should be trying to couple up without the coaches moving at all.

[Nigelcliffe]

If you're fitting permanent magnets, and using cheaper rare-earth ones (one row towards each side of the track, N pole upwards one side, S pole upwards the other side), then place a long string of them along the track from where you want to uncouple until the furthest point the shortest loco might stop.   Then, having uncoupled, the loco and stock will remain with its coupling open.   Should the station pilot accidentally push the train up to the loco, it remains uncoupled.     

This only falls apart if your coaches are shorter than the length of this magnet area, then the first coach could be uncoupled from the second coach.  

 

 

 

 

[BR60103]

Caveat:

Don't place the magnets one coach length from the buffer stops. This will uncouple the last coach of a departing train and make re-coupling impossible.

Also with multiples of wagon lengths.

You can bring the train in and stop with the coupling over the ramp and pull the coaches out with the station pilot. If you uncouple and move the loco forward, some cowboy (guilty) will push on the back and couple them up again.

 

[RobinofLoxley]

9 hours ago, Nigelcliffe said:

If you're fitting permanent magnets, and using cheaper rare-earth ones (one row towards each side of the track, N pole upwards one side, S pole upwards the other side), then place a long string of them along the track from where you want to uncouple until the furthest point the shortest loco might stop.   Then, having uncoupled, the loco and stock will remain with its coupling open.   Should the station pilot accidentally push the train up to the loco, it remains uncoupled.     

This only falls apart if your coaches are shorter than the length of this magnet area, then the first coach could be uncoupled from the second coach.  

 

 

 

 

I have obtained Kadee magnets, the specification designed for under-track placement. I dont know which of your categories they are in. Kadee magnets are 50mm in the run direction so cover some of the positional variation that might arise. I dont know if I want to install things that are to cater for accidental events though.

 

5 hours ago, BR60103 said:

Caveat:

Don't place the magnets one coach length from the buffer stops. This will uncouple the last coach of a departing train and make re-coupling impossible.

Also with multiples of wagon lengths.

You can bring the train in and stop with the coupling over the ramp and pull the coaches out with the station pilot. If you uncouple and move the loco forward, some cowboy (guilty) will push on the back and couple them up again.

 

A good point. Most of my trains will run with a loco at the front arriving, but I hadnt thought about what will happen if I shunt in a rake of carriages. The magnet has to go somewhere and inevitably it will cover the position you refer to. However, most of my carriages are likely to run in fixed rakes. So while I wouldnt need to have Kadee couplings everywhere, it was certainly my intention to throw out all the standard ones that I have over time. But if there was no option I could leave tension locks or similar in 'vulnerable' locations.

 

10 hours ago, WIMorrison said:

You will need to allow enough space for,

 

a) train overrunning stop position - 25mm?

b) action of uncoupling and moving away - 25-50mm?

c) distance coaches will move when loco couples at opposite end - 25mm?

 

total - around 100mm?

I was thinking the same total but purely to be able to create a decent (prototypical?) separation between loco and coach for the recoupling operation.

 

I think that (a) and (c) are basically the same error? Arising from the carriages not being in their calculated position.

 

Videos of coupling on u-tube always show a successful outcome but I wondered what the reality was; how many total misses in coupling up, etc.

 

Thanks for all the replies.

Edited May 7, 2021 by RobinofLoxley

[Geep7]

What I usually do is measure my longest locomotive over the couplers (usually a Class 47 in my case) and then add another 1-2 inches. This allows the locomotive to draw forwards away from the coaches, and leave enough room to the buffer stops, but also means if you reverse the coaches over the magnet, the likelyhood of an inter-coach coupling being directly over the magnet is reduced.

One thing I have done on my latest layout (albet Spanish outline) is to cut the kadee magnets in half (the metal plate is the difficult bit, score and bend in a vice, the magnet itself is a soft rubber like material which can be cut with a knife), which A: doubles the number of magnets you have, and B: reduces the operational area the magnet will work by half. The latter meaning that you're less likely to accidently place a coupling over the top by mistake.

[RobinofLoxley]

On 07/05/2021 at 09:52, Geep7 said:

What I usually do is measure my longest locomotive over the couplers (usually a Class 47 in my case) and then add another 1-2 inches. This allows the locomotive to draw forwards away from the coaches, and leave enough room to the buffer stops, but also means if you reverse the coaches over the magnet, the likelyhood of an inter-coach coupling being directly over the magnet is reduced.

One thing I have done on my latest layout (albet Spanish outline) is to cut the kadee magnets in half (the metal plate is the difficult bit, score and bend in a vice, the magnet itself is a soft rubber like material which can be cut with a knife), which A: doubles the number of magnets you have, and B: reduces the operational area the magnet will work by half. The latter meaning that you're less likely to accidently place a coupling over the top by mistake.

I understood that cutting magnets in half was a feasible technique. However I am looking at automatic uncoupling in the distant future and doing necessary preparations now. For automatic to work the train has to stop over the magnet and cutting it in half would have a proportionately greater effect on the size of the sweet spot where uncoupling would take place. So are you uncoupling manually in terms of setting loco position or using another method to ensure the train stops in the right place., or auto is working perfectly with the cut down magnets - as it might with everything spot on.

 

I analysed the possibility of an accidental uncoupling based on a probablility of where couplings would fall in a terminus situation depending on the rolling stock. Given the range of stock lengths I have there is quite a large zone where the probability of a resting coupling over a magnet is zero. This is with a 5cm span of stopping position in automatic. With other stock this might not be the case.

[BR60103]

Sometimes you have to back up with the train, push the coach hard against the buffer stops, move the train out quickly and hope that the spring in the buffer stop propels the coach out past the magnet.

 

[MartynJPearson]

One other thing to consider is the effect of the magnet on steel wheels. I fixed Kadee magnets on my layout and whilst coupling works fine, my small TAA tankers lurch when you go over them slowly. If you think that might be an issue, pivoting them so you can move the magnet away from the track when not needed might be an idea. 

[Geep7]

12 hours ago, RobinofLoxley said:

I understood that cutting magnets in half was a feasible technique. However I am looking at automatic uncoupling in the distant future and doing necessary preparations now. For automatic to work the train has to stop over the magnet and cutting it in half would have a proportionately greater effect on the size of the sweet spot where uncoupling would take place. So are you uncoupling manually in terms of setting loco position or using another method to ensure the train stops in the right place., or auto is working perfectly with the cut down magnets - as it might with everything spot on.

The magnet is 1.5" in length once cut in half, long enough to effect both couplings, so auto-uncoupling is working perfectly as always, just that the length of track over which the magnet is effective is halved. I have to be pretty spot on where I stop to uncouple in this case. However I usually mark where the centre of the magnet is, either with a paint mark on the side of the track, or a convieniently placed object. Also, I tend to remember where they are after a while, and also have them marked on the control panel for other operators.

[RobinofLoxley]

1 hour ago, Geep7 said:

The magnet is 1.5" in length once cut in half, long enough to effect both couplings, so auto-uncoupling is working perfectly as always, just that the length of track over which the magnet is effective is halved. I have to be pretty spot on where I stop to uncouple in this case. However I usually mark where the centre of the magnet is, either with a paint mark on the side of the track, or a convieniently placed object. Also, I tend to remember where they are after a while, and also have them marked on the control panel for other operators.

Sorry I think we're slightly at cross purposes here. I am talking about automatic positioning of the loco stop, using iTrain or similar. So this is achieved by calibration of loco speed, the accuracy of this and several other factors detemine if the loco stops exactly where required or some distance from it. Not whether the Kadee shuffle or whatever is performed afterwards, theres quite a bit of public domain stuff around suggesting it works with half magnets. Im with you on marking the magnet location.

[Geep7]

33 minutes ago, RobinofLoxley said:

Sorry I think we're slightly at cross purposes here. I am talking about automatic positioning of the loco stop, using iTrain or similar. So this is achieved by calibration of loco speed, the accuracy of this and several other factors detemine if the loco stops exactly where required or some distance from it. Not whether the Kadee shuffle or whatever is performed afterwards, theres quite a bit of public domain stuff around suggesting it works with half magnets. Im with you on marking the magnet location.

Ah, I see what you mean. In which case, I would use the full magnet, so it gives you some extra tolerance. The other possibility is the under track electromagnets, but i'm not sure how these would interact with any automated system.