Servo size, distance of operation and reliability of throw.

[Dave S]

Servos do not have any switching ability but you have a couple of choices. First you can use the movement of the servo to switch a separate micro switch. Some servo bases cater for this.
Secondly, as you are using a micro computer to drive the servo you can also drive a relay at the same time.

Thank-you TDD.

Second option:
I'll likely have around 40 points, so that sounds like £200 plus and extra hassle and more that could go wrong.
I don't like the answer, but mustn't shoot the mesenger.

First option>
Could you post a link of the type of micro switch that could be used.
I'm struggling to imagine 1 servo with 1 defined action for point throw and somehow also pushing the button if this is the sort of thing:
https://www.ebay.co.uk/itm/233246029175 ... SwRkJc9PVW
Can the type of micro switch you have in mind, are they lower lost cost to 2nd option if I bought in bulk?

Edit, just found this. Doesn't look too elegant.
https://www.ebay.co.uk/itm/334183473919 ... SwX8ZhaqV-

[teedoubleudee]

TBH, my preferred option (and how mine is configured) is to go for the second option and use an output from the micro processor to drive a relay to switch the frog polarity. If you use a relay module like these below, they have 5v logic inputs so can be driven directly from the MPU. They are available in 1, 2, 4, 8 and 16 relay modules. https://www.ebay.co.uk/itm/262722739443 ... 1656561190

[Dave S]

That seems like much work to make a shelf product work smoothly.
My foggy understanding is getting foggier and the assumed advantage of servos over solenoid diminishing.
It would appear simpler to use these
https://www.gaugemasterretail.com/magen ... c-pm1.html
Don't know if unit cost is worse/better/same for solenoid type and what PCB's are needed for them to be PC driven.
Unfair question to you, but that's currently a fog for me.

[teedoubleudee]

Dave, your original question and indeed the title of this thread was regarding the use of servo motors to change points. All the replies you have recieved so far have addressed this subject. If you now want to widen the subject to alternative methods of point switching you need to re write your question in order to attract a different audience.

My personal experience of the seep motor are that the positioning of them has to be precise,, they are noisy and the switching element is notoriously unreliable. However they are cheap and popular and can be computer driven.

I wish you luck in your quest.

[Dave S]

Thank-you TDD.

On the aspects of threads, "On a sliight tangent, but still relating to servos...", I realised I was going off core topic but was reluctant to start new thread.
I have been thinking about this over night.
I am currently seeing more barrirers to entry.
IOT should simplify implementation and and reduce cost of required comms, yet currently swimming upstream.

Reiability of throw. On topic.
With regard to point blades (distinct from frogs) I note your comment TDD " It's important to remove the point springs to remove any resistance and give a nice smooth quiet transition." .
That seems sensible, so as not to provide resistance to the servo. But... upon seeing comments re poor blade conductivity on youtube, I am wondering if leaving springs in may be better. It may make them work a bit harder, but they are only on for a few seconds, or do they completely lack the torque?

[teedoubleudee]

Think of Solenoid operation as a hammer blow, swift and hard but no lasting pressure, hence the need for built in spring. Then think of servos, cobalts etc where there is a gentle but continuous pressure (provided by the springy actuator wire).

TWD

[Dave S]

That is how I think of servos versus solenoids.
I believe once servo thrown, it is not powered to maintain position. I'd assumed point blade could easily lose contact with stock rail and the tie bar linking it to servo would, action and reaction etc, mean the servo motor is free to turn a few degrees out of position, with no resistance, as unpowered.
So unsure where how continuous pressure can be maintained?
If practice is different to theory, good.

If continuous pressure is maintained, that would imply no extra wiring required to ensure switch blades are powered (live frog seperate question).

[Tricky Dicky]

Reiability of throw. On topic.
With regard to point blades (distinct from frogs) I note your comment TDD " It's important to remove the point springs to remove any resistance and give a nice smooth quiet transition." .
That seems sensible, so as not to provide resistance to the servo. But... upon seeing comments re poor blade conductivity on youtube, I am wondering if leaving springs in may be better. It may make them work a bit harder, but they are only on for a few seconds, or do they completely lack the torque?

TWD is correct about the operation of servo and stall motors but no matter which type of motor is used dirt, paint etc. between the blades can cause continuity issues. The are modifications that you can make to the points to overcome the problem. Often wrongly termed DCC point modification but it applies to DC as well. Brian has details on his website and in his book,

https://www.brian-lambert.co.uk/Electrical-Page-2.html



Richard

[Dave S]

Thank-you Tricky Dicky.
I couldn't find it thinking it was part of this forum but think I have found it in my history, on his own website.
Better not post link here as unsure of forum rules re third party sites and seem to have had 2 of my posts deleted from yesterday.

[Tricky Dicky]

Better not post link here as unsure of forum rules re third party sites and seem to have had 2 of my posts deleted from yesterday.

I am sure Brian will make an exception for his own website and book on his own forum

Linking to a website if the the information is pertinent to the thread is acceptable it is mainly links to websites to advertise their products that fall foul of the moderators.

Richard