Motorised level crossing

[Topcat2018]

This may (or may not) be of interest. The last project I completed for my layout was a motorised traditional level crossing. The four gates move in sync and stop when the gates are either closed to road traffic or closed to rail traffic. To avoid trains crashing into the gates Signals from the limit switches that stop the gates in either position can be used to cut power to the rail tracks either side whilst the gates are either moving or closed to rail traffic.

This version is just a prototype and I intend to design a modified version that will be easier to assemble and have a lower profile. It will also have 3D printed gates that a friend has kindly made for me instead of the rather crude ones made from styrene rod.

[RDS]

That looks very good. I look forward to seeing the 'production' version

[The son of Triangman]

It can be done with the Hornby level crossings too. I have plans for a prototype unit to fit Hornby level crossings

[ColinB]

Will you be making them to Hornby spacing or Peco streamline spacing? That looks like something that would be really useful.

[Topcat2018]

@ The son of Triangman

I should be very interested to see what you come up with. I did look at the possibility of motorising a Hornby level crossing but apart from the initial expense of buying one there were some potential problems. The rails in the Hornby unit are already 5.2 mm above the base and you would have to build an additional base if you wanted to mount the motor underneath, or make a hole in the baseboard to accommodate the motor, or locate it off to one side.

At my age with arthritic knees I am averse to fiddling with wiring under the baseboard so all power wiring will be carefully hidden on the surface in routed out grooves and low-power wiring will be very fine gauge ribbon cable that can be glued flat and easily concealed.

The geared motor in my prototype is 10 mm high and is completely hidden within the base of the crossing (on the right-hand side of the photo) which is 12 mm deep. In my next version the base will be only 8 mm deep. This is determined by the width of the limit switches and the diameter of the worm gear attached to the motor. In the prototype I used some very tiny microswitches but these proved very flimsy and the smallest amount of over-travel would wreck them.

The top of the motor in the new version will protrude by about 2 mm above the base and will be covered by scenery. As the rails leading to the crossing are 4.5 mm high this means I will only need to build up the approach by 3.5 mm.

[Topcat2018]

@colinB

I'm not sure if your question was addressed to me. My level crossing will be used on a fairly rural railway line and narrow road. The gates on the Hornby crossing seem very long and out of proportion to the surroundings so I've reduced the inter-track spacing by 10 mm whilst keeping the distance of the track from the gates the same. There is still plenty of room for two trains to pass.

[Brew Man]

@ Topcat

I think Colin is referring to the fact that Hornby Set track spacing is 67mm, whereas Streamline spacing is 50mm, the latter being considered more true to scale. So his question was which of the two your model is built to?

[Topcat2018]

@ Brew Man

As I mentioned in my last reply my level crossing isn't built to a particular standard. Track to track spacing of the Hornby level crossing is 50 mm and the total length of the gates from pivot to pivot is 124 mm. As I also said the vehicular approach to my crossing will be a country road just wide enough for two cars to pass, and to widen this out to the size of the Hornby crossing would just look wrong, so the track-to-track spacing on my crossing is 37 mm and the gate length is reduced accordingly. Of course track-to-track spacing on curves would be greater, especially as I have some long coaches.

[Brew Man]

Also in your last reply you didn't seem sure of what Colin was saying or to whom he was saying it, so I was just clarifying.

[81F]

What period will your crossing be? If 3D printing you would have the option of representing some of the prefabricated units

See this googler map link

https://www.google.com/maps/@51.4149102,-1.5126702,3a,43.1y,100.23h,60.78t/data=!3m6!1e1!3m4!1sJT47ZUFJaTfVdHM8mdQAyw!2e0!7i16384!8i8192?hl=en

[Topcat2018]

@ 81F Thanks for the link but I'm not quite sure of the relevance as the photo is of a modern crossing with lifting barriers rather than gates.

As for the period it's pre-nationalisation as all my locos are in either LMS or LNER livery but it's of no particular date as there would be discrepancies as to what locos would have existed at the same time and their particular liveries. For example I have A4s with and without valances, ones with 4 -digit cab numbers and pre-war gold/red/black lettering, ones with four-digit cab numbers and silver lettering and ones with post-war two-digit cab numbers and silver lettering.

[ColinB]

Thanks Brewman for clarifying my question, that was exactly what I was asking. If you have an existing layout as in my case, where the spacing between tracks if 50mm then if the spacing on the level crossing is greater it causes issues, it means it just doesn't easily fit in. It is like using the Hornby station pedestrian footbridge, I have the Skaledale Goathland Station, but because of the difference in spacing between Hornby and Peco Streamline the footbridge is too wide, so where the footbridge sits I have had to widen the platform.

[81F]

@ 81F Thanks for the link but I'm not quite sure of the relevance as the photo is of a modern crossing with lifting barriers rather than gates...

 

 

Thanks for clarifying the period as such preformed units would not be applicable to you. However, modern barriers and modern crossings do not necessarily go hand in hand as there are some locations where track gets upgraded but the old gated barriers remain like this one on the Bicester Military railway:

https://www.google.com/maps/@51.8686023,-1.1259198,3a,89.8y,137.5h,61.44t/data=!3m6!1e1!3m4!1sw5l3qjsOvLvXZ0uOT8nXJA!2e0!7i16384!8i8192

However, I did not include this earlier as it was single track.

Also I have heard of people using a coil of memory wire to open gates. Although i have some I've never tried it.

[Topcat2018]

@ 81F Thanks for that link.

I've heard of different methods of driving level crossing gates, but never using memory wire. I wonder how that would work?

My system is quite simple, it uses four pulleys with a loop of plastic-coated jewellery wire wound round them so that the gates move in sync in the appropriate directions. A tension spring keeps the wire loop taut.

Each pulley only makes a quarter turn, so to prevent the wire slipping the rim of each pulley can be drilled at a suitable place and a wire loop fed through the hole and tightened around the drive wire and also secured with a blob of epoxy. The motor drives a lead screw attached to one leg of the wire loop and there is a microswitch at each end to act as a limit switch. One of the microswitches is fixed and the other adjustable so that the gates make exactly a quarter turn.

[96RAF]

@ topcat

Are you using the N20 geared motors with the long drive shaft.

I prototyped a point motor using one again with microswitches to cut power at the end of travel limits.

My problem was getting the switches to stop the motor accurately every time without destroying the points due to over-run, as the throw of the points tie-bar was only 3.5 mm. In the end I used a type of slotted cam plate which allowed accurate travel but also over-run space.

[Topcat2018]

@ 96RAF

Yes I use the N20 geared motors. I bought a load of them from China to use for point motors. The way I use them is to have the motor buried underneath the track between the rails. A piece of steel wire that goes through the motor shaft and projects up through the points tie bar.

As you know these motors have a lot of torque so I use a capacitor discharge unit to limit the duration of the drive pulse and avoid the need for limit switches. As the motors draw only tens of milliamps the capacitors can be quite small compared to those used for solenoid points and the wiring can be quite thin. I use very light gauge ribbon cable that can be laid flat on the baseboard and easily concealed.

Note that the LEDs are a guide to indicate how the points are supposed to be set, not necessarily how they are are set. As with solenoid points you don't know which way the points are set when you first power up the system and it's a good idea to set and reset the points a few times before setting them to your initial setup. I am looking at the possibility of an add-on that will allow all points in the system to be set to a known initial state at power-up.

[96RAF]

Thanks TC.

So you are just blipping the motor one way or t’other.

My pictures of the now abandoned project are on the other PC, but I will dig them out next time it is up.

I have a friend in Canada who has designed a torque sensing module that would in theory do away with the limit switches.

[Topcat2018]

@96RAF

A sketch showing how the N20 motor is mounted when used as a point motor (thicknesses of materials not to scale). It is mounted in a cradle made from 0.2 mm tinplate. To hide the hole in the baseboard and prevent debris falling into the exposed gears a piece of thin black card or plastikard is used to cover the gears and motor.

I originally tried to fix the cradle using the original tab holes holes intended for solenoid point motors but tabs made in the tinplate are fiddly to make and quite flimsy so I used very small nuts and bolts instead.

[Topcat2018]

@ 96RAF Yes I am just sending a short pulse of current to the motor as you would using a capacitor discharge unit with a solenoid point motor, but with two advantages:

1. As the motor only draws a small current, a smaller capacitor and thin wires can be used.
2. as the motor is reversible only two wires are used, unlike a solenoid motor where three wires are needed.

I guess when you say "torque sensing" your friend's design is measuring the stall current of the motor. I don't think it would offer any great advantage in terms of reducing wear on the points as they would have already switched over before the stall current was detected and the current was switched off. It also wouldn't guarantee that the points had actually switched over, they could just be stuck. This can only be achieved with limit switches and like you I had abandoned them for various reasons.

Whatever type of point motor is used there is going to be wear of the hole in the tie bar. This should be less with a geared motor than with solenoids because the motor moves much more slowly and with less kinetic energy, although the operating pin does rub against the sides of the hole as the motor turns. As the hole wears the motor will just turn through a greater angle. Just make the pin long enough that it doesn't come out of the hole in the tie bar as wear occurs but short enough that it doesn't foul anything above.

[Topcat2018]

Just some final, slightly esoteric comments as to why a motorised point motor is probably kinder to your points than a solenoid one.

The energy stored in a capacitor is E = 0.5 x C x V x V, where E is the energy in Joules, C is the capacitance in Farads and V is the voltage to which the capacitor is charged.

Some commercial capacitor discharge units have capacitors as large as 10,000 uF, so the energy stored when charged to 12 V is 0.72 Joules. I don't know how much of this is converted to kinetic energy as the solenoid slams the points from one side to the other, but it's certainly a lot more than that of my point motor, which uses a 1000 uF capacitor, so the energy stored is only 0.072 Joules.

An unimportant but amusing point is that my point motor uses the same charge twice. If S1 is set to MAINLINE in the circuit diagram above then C1 is uncharged. Switching S1 to BRANCHLINE now charges C1 and operates the points. Setting S1 back to MAINLINE discharges C1 and sets the points back to the main line. So it's not strictly a capacitor discharge unit but a capacitor charge/discharge unit.

I think I need to get out more.

[96RAF]

@TC

The forum needs an electronics guru, who understands the design theory beyond the practical application.

Chris was our previous go-to theory man, but along with his passing we also lost a wealth of his legacy illustrations during the recent forum ‘update’.

We remain ‘stumped’ trying to find an on-site way of cataloguing such communal knowledge against similar loss in any future update event.

[Topcat2018]

@96RAF

I'm always happy to share my electronics knowledge. I have 44 years experience working in the electronics industry. After leaving university I first worked for Rank Wharfedale in Bradford designing automatic test equipment for audio amplifiers. This was when integrated circuits were just coming into use and the largest memory IC was 64 bits, so all the test parameters and which inputs/outputs of the amplifier signals were fed to/from, signal levels and frequencies were stored on punched tape. That was my dream job as I love music and at the time British hi-fi was some of the best, and a lot of it designed and made in Yorkshire (which is the second best county - after Lancashire).

Since then I have worked for several companies including as UK editor of Elektor, a Dutch electronics magazine, Ferranti Semiconductors, Analog Devices, Brother, and finally as a technical author and freelance design consultant, when I designed various things for an electronics contractor who made equipment for various organisations such as an exhaust gas analyser and oxygen sensor tester for independent garages, a fingerprint entry system and various pieces of equipment for British Rail (which all dried up after privatisation).

I am quite experienced in analogue and digital circuit design and in microcontrollers to a certain extent (the brand I always used was Microchip) but as far as PCs are concerned I am just an average user.

I did have a website that I used in connection with my work but haven't used it for years although I still keep up two domain names, so I suppose I could resurrect it and upload information to it.

[96RAF]

That was where we fell into a trap with Chris’ stuff TC, it was all lodged on his personal BT Drive to which access was lost upon his demise. My own website will suffer the same fate when I am gone. Our moderator IT guru also has a personal Railmaster help website, linked to from the Hornby forum, which comes with the same pitfall, as will any private external site.

These collective info caches need to be lodged on Hornby’s servers, but disassociated from anything that will change upon update, such as a forum database if there is such a thing.

The forum moderators (for all Hornby Hobbies brands) are working with Hornby IT to establish better future forum facilities even if this means opting for a mast-headed commercial based forum set rather than bespoke written forums as at present, but integrated with their main web site. Early days at present as it all has to be tied into shopping accounts, personal lodge areas, cross brand functionality, etc.

However, interesting though it is, we seem to have drifted well off topic.

[Topcat2018]

@96RAF

Yes we have drifted off topic. I guess we need some sort indexed, easily searchable knowledge base.

[96RAF]

@TC

Your topic.

At present we have a set of FAQs on various topics and a few comprehensive guides, but what is lost are the many individual question directed illustrations that Chris did on the old forum that didn’t carry across. These appear in post as image place holders and Hornby IT is struggling to find them - likely will never do so.

The logic at the time was to provide a comprehensive FAQ searchable knowledge base, such as currently found in Railmaster.