The law of unexpected consequences

[LAandNQFan]

I thought that I had sorted my two complications - both vital to my layout. 
To work the EasiShunts without buying the expensive Dapol magnets, I used two flat rectangular magnets under the track and they uncouple beautifully.
To work the reed switches positioned on the sleepers beside the track I used small round magnets under wagons and they worked beautifully.
Now that I have enough of the layout complete to run from the storage sidings (with the reed switches to show track occupancy) to the stations (with magnets for uncoupling), I find that the wagons with the magnets leap off the track when they go over the uncoupling magnets!  If I decrease the magnets on the trucks so that they stay on the track they aren't strong enough to work the reed switches.  I'm reluctant to rip up my trackwork to remove the undertrack magnets and pay for the Dapol magnets, but what else can I do?

[zwilnik]

Can the uncoupling magnets be replaced with electromagnets? If so they can just be switched off unless you're uncoupling. The other option is maybe to fit the uncoupling magnets to a lever or a rod of some sort so they can be lowered away from or pulled away from the track when not being used?

[PaulCheffus]

I thought that I had sorted my two complications - both vital to my layout. 
To work the EasiShunts without buying the expensive Dapol magnets, I used two flat rectangular magnets under the track and they uncouple beautifully.
To work the reed switches positioned on the sleepers beside the track I used small round magnets under wagons and they worked beautifully.
Now that I have enough of the layout complete to run from the storage sidings (with the reed switches to show track occupancy) to the stations (with magnets for uncoupling), I find that the wagons with the magnets leap off the track when they go over the uncoupling magnets!  If I decrease the magnets on the trucks so that they stay on the track they aren't strong enough to work the reed switches.  I'm reluctant to rip up my trackwork to remove the undertrack magnets and pay for the Dapol magnets, but what else can I do?

Hi

Try turning one of the magnets under the wagons over so the magnetic poles are the different as opposites attract. This should stop them jumping, if not I would suggest a different method of train detection.

Cheers

Paul

[RailGooner]

.. I find that the wagons with the magnets leap off the track when they go over the uncoupling magnets! ...

Have you ruled out common polarity? If the bottom of the wagon magnets are the same polarity as the top of the uncoupling magnet, they'll naturally repel each other resulting in airborne wagons.

[PLD]

I find that the wagons with the magnets leap off the track when they go over the uncoupling magnets!

The issue is you have two sets of magnets which are doing exactly what magnets do half of the time and repelling each other!!
The only way to stop them repelling is to find a relative orientation for the magnets where they attract rather than repel...

I'm assuming the uncoupling magnets are correctly orientated with the North and south poles to the left and right as this is needed for the couplings to work properly; in theory the orientation of the magnets on the wagons shouldn't affect activation of the reed switches, so this is the one to experiment with.

Orientating the wagon magnets left-right should be OK with the wagon one way round but not if the wagons get turned.
Orientating the wagon magnets top-bottom may lead to wagons flipping over to one side.
Orientating the wagon magnets front-back may lead to lighter wagons twisting as they pass over the magnet, but I suspect may be the best option....

[PLD]

Have you ruled out common polarity? If the bottom of the wagon magnets are the same polarity as the top of the uncoupling magnet, they'll naturally repel each other resulting in airborne wagons.

The problem is in the way the dapol magnets have to be orientated with the poles left-right: effectively there is a north and south facing upwards...

Can the uncoupling magnets be replaced with electromagnets? If so they can just be switched off unless you're uncoupling

This is the solution for the majority of magnetically operated couplings where orientation of the magnetic field doesn't matter but Dapol Couplings need a left-right orientation which normal electromagnets don't give...

The other option is maybe to fit the uncoupling magnets to a lever or a rod of some sort so they can be lowered away from or pulled away from the track when not being used?

That might be a good idea - worth a try 

[LAandNQFan]

Thanks, everyone, for the suggestions.
I'm using two 20x6mm magnets side by side to get the left-right N/S effect, which means that going one way the wagon is attracted to the track, but when it goes round the reversing loop and comes back it will take off: each track magnet is rated at 1.6kg pull but is under the track, further away than the Dapols are supposed to be.  A major attraction  of this was that I would not have to cut the track and then fake sleepers as Caz does. 
I've tried mounting the wagon magnets vertically and horizontally without improving the situation.  Tomorrow I'll try two small cylinder magnets parallel to the side of the wagon to see if the N at one end and the S at the other neutralise the flying effect without losing the ability to work the reeds, PLD.
As I have minimum clearance between the upper and lower levels of the layout, Zwilnik, the trapdoor uncouplers won't work, sadly.

[zwilnik]

If they can't go up/down. What about a pull rod system to pull them across out of the way?

[Ian Bowden]

Reversing the polarity of one of the magnets would surely result in the magnets being attracted to each other causing stuttering or even stopping the wagon totally. Perhaps using a cheap servo to move the under track magnet away when not wanted might work

[LAandNQFan]

Orientating the wagon magnets front-back may lead to lighter wagons twisting as they pass over the magnet, but I suspect may be the best option....

Suspect no more, PLD!   You were correct!   

That was the idea which I needed.  Either two of the 5x1mm round magnets (0.3kg pull) or three of the 3x1.5mm (0.18kg pull) positioned with the N pole to the front of the wagon and the S to the rear works all the reed switches and the wagon stays on the track over the 20x6mm rectangulars.  The wagon is attracted to the track in either direction but not so much as to stop the engine or uncouple when it shouldn't.
   
Thank you, all who tried to help.  I can go back to laying the goods yard and putting motors on all those points! 

[mr bachmann]

Thanks, everyone, for the suggestions.
I'm using two 20x6mm magnets side by side to get the left-right N/S effect, which means that going one way the wagon is attracted to the track, but when it goes round the reversing loop and comes back it will take off .

That idea would be great for Thomas Tank layouts , keep the kids amussed at exibition's 

[PLD]

Suspect no more, PLD!   You were correct!