Reed switches and magnets etc

[philipy]

Okey doke, I need some help please.

I'm attempting to set up an auto-shuttle on my Faller Railcars, using a Micron 603b, reed switch and magnet. Upside down on the bench waving a magnet near the reed switch causes it to operate and the auto-shuttle routine runs as it should do, although the magnet ( an N52 bar) seems to need to be nearer than I would have expected.
Put it on the track and I can't get it to work at all, even though the magnet is only about 5 or 6 mm from the switch. I've tried all sorts of different orientations of magnet and switch, but one thing I have noticed is that the magnet seems to be much more interested in trying to stick to the adjacent rechargeable battery pack than operating the reed switch.
I know very little about magnetics but I'm wondering if the attraction to the batteries is weakening the magnetic force available to operate the switch, if that makes sense?

Thoughts anyone?

[ge_rik]

Hi Philip
I've not tried the auto features on the MR603b but I have used both shuttle and station stop on the Deltang Rx65b.

I seem to recall having similar problems with auto station stop. I tried two or three reed switches before I got one to operate reliably and I also put another magnet on top of the one between the rails - I didn't fix it in place, just used their mutual attraction. This not only raised the height of the magnet I think it also increased the magnetism.

Rik

[philipy]

Hi Philip
I've not tried the auto features on the MR603b but I have used both shuttle and station stop on the Deltang Rx65b.

I seem to recall having similar problems with auto station stop. I tried two or three reed switches before I got one to operate reliably and I also put another magnet on top of the one between the rails - I didn't fix it in place, just used their mutual attraction. This not only raised the height of the magnet I think it also increased the magnetism.

Rik

Thanks Rik.
Yes I've read your various blogs on the subject.
I must admit that I don't understand how putting magnets on top, N-S & S-N, would increase the pull? I'd have thought exactly the opposite since you are completing the magnetic loop, rather like putting a keeper plate on an old fashioned horseshoe magnet.

However it does seem to be extremely critical. I did a lashup on the track in the garden and had it running back and forth round the loop half a dozen times. Then moved the same magnet 10ft round the corner into the station and it refuses to work, the train just runs straight over it.

[Phil.P]

Hi Philip,
The reed switch is also a magnet, albeit a tiny springy one!

Have you tried turning your bar-magnet over?

Two magnets on top of each other, will create a more focused effect.

Modern cells have steel outer-cases, in our youth, we all had zinc-carbon batteries, and the outer-case was zinc.

The type of Reed-switch, and orientation of the magnet and switch, will have an affect on each other.

I use a plastic encapsulated reed, where the contacts come out of one face.. This gives me the orientation of the reed in the housing, which makes results much more repeatable.

Phil.P

[philipy]

Interesting Phil, thanks.

To answer your question; Yes, I've tried the magnet in every possible orientation.

On the question of double stacking to increase attraction, I found this link https://www.first4magnets.com/tech-cent ... 9#anchor23 which seems to be very informative on all things magnet. In the "Performance" section it says that doubling up does significantly increase attraction but not by as much as simply using a magnet that is twice as thick.

[GTB]

You'll get more 'bang for your buck' by reducing the the separation between magnet and reed switch, than by adding more magnets. Magnetic field strength follows an inverse square rule as the distance varies, halve the separation and the field strength quadruples.

Apart from magnetic materials like steel, a moving magnetic field can create eddy currents in other metals which can distort/disrupt the field. I have no idea how much metal, if any, is in those railcars, but diecast zinc is common in rtr models and it can screw around with magnetic fields. Electrical wiring also creates magnetic fields when energised, the field strength depending on the amperage.

To put some numbers on using reed switches.... Some years ago when I was still modelling in HO, I built a speedometer car to measure loco speed while setting up DCC decoders. The speed sensor was a reed switch with a small magnet on an axle, driving a cheap bike computer. A 5mm disc magnet had to be within 2mm of the reed switch to turn it on and at least 5mm away to turn it off, which is about a factor of 6 change in magnetic field strength between on and off. At a scale 50mph, the switch was operating at about 450 times per second. As I recall it took a lot of experimentation on the bench to get it to work at all in the limited space and I think the design was up to Mk.4 before it worked reliably.

If only one of those railcars is powered, it may be that the reed switch would be better off in the unpowered trailer, underneath the floor, away from metals and wiring and as close as possible to the track magnet.

Regards,
Graeme

[philipy]

Well, here we are, 4 weeks on from the last post on this thread ( thanks Graeme) and It's working, finally! It hasn't actually taken all 4 of those weeks, I was away for 2&1/2 of them and then Phil.P ( RC Trains) was away when I got back. so I had to wait for a new reed switch and magnets which arrived a couple of days ago. Plus I also had to do some terraforming in the garden to keep the Planning Authority happy!
I must thank Phil for his help and advice, which has definitely paid off.

The reed switch is still closer to the track than I would have liked but it does clear, which is all that is really required. The magnets are small round ones, 5mm diameter, and I've used a stack of 6 laid sideways, parallel to the sleepers. I printed a housing for them which is screwed to a sleeper and makes for easy relocation if required at some point in the future.

Screenshot 2023-08-18 13.12.36.png (9.64 KiB) Viewed 3084 times

Inbetween the downpours this morning I managed to nip out and fix the magnets, and the railcar then spent half an hour trundling from Elderbury station along to the new loop, round it and back to the station. Stop, wait, reverse and repeat.
It does seem to be speed dependant though, too fast and it sails straight over the magnet without stopping, but I guess that makes sense. I may try experimenting with two sets of magnets in parallel, to see if that allows it to 'bite' for longer.

[GTB]

It does seem to be speed dependant though, too fast and it sails straight over the magnet without stopping, but I guess that makes sense. I may try experimenting with two sets of magnets in parallel, to see if that allows it to 'bite' for longer.

That was what I found with my HO speedometer car, as the actual speed increased, the displayed speed decreased, because the chip in the bike computer started missing pulses and lost count.

You may get more reliable results by orienting the magnet longitudinally along the track, rather than transversely.

A 2' gauge railcar shouldn't be travelling at much more than 20 scale mph anyway...........

Graeme

[philipy]

You may get more reliable results by orienting the magnet longitudinally along the track, rather than transversely.

A 2' gauge railcar shouldn't be travelling at much more than 20 scale mph anyway...........

Yes. Phil recommended putting the magnets at an angle to allow for any gauge slop. That's on the list to try as well, but for the mo I'm just happy that it works.
The speed will be kept low, the loop is 3ft off the ground and the boards are narrow!