Servo Controlled Points

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gregh
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Re: Servo Controlled Points

Post by gregh » Wed Mar 17, 2021 7:21 am

big-ted wrote: Tue Mar 16, 2021 10:58 pm I think a while ago someone on here had used an Arduino or similar to program servos to mimic the bounce and heavy motion of a semaphore signal. It looked really impressive, but as you say, more gubbins outside to go wrong, for sure.
That was me. Using a Picaxe control.
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Re: Servo Controlled Points

Post by GAP » Fri Mar 19, 2021 3:27 am

I have modified all 12 of my Servo Testers, so now I am ready to set them up on the layout.
I will be putting each one next its relevant point so that way I can adjust with a bit of ease.
They will be housed in plastic food containers, with a seal-able lid under the baseboard, we have had torrential rain this week and where I am planning on putting is still dry so they should be OK, the only water that gets under there is from the irrigation and it is only a fine mist anyway.

I added a On/Off switch for the 5V bus that I had in a box it is rated at 500V and 30A so I think it should handle a 5V 3A bus OK.

I did consider a "service" switch in line with the main switch that would isolate it while I made adjustments so that I do not have to walk back and forth to the control panel while adjusting, I may still retrofit one if the becomes necessary.

I also considered a 1ohm resistor in line with the servo +ve line so I could put a voltmeter across it to measure the current while adjusting but at this stage, I'll just listen for the servo buzzing to indicate over driving of the motor.

Edit; added enclosure to picture.

A picture of the way I modified the testers and mounted them in an enclosure, Power on the Right, Servo on the Left and switch input at the bottom, all cables will come in from the bottom through a piece of cut down irrigation fitting.
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Last edited by GAP on Mon Mar 22, 2021 1:50 am, edited 2 times in total.
Graeme
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Re: Servo Controlled Points

Post by gregh » Sat Mar 20, 2021 4:01 am

A great solution. I'm impressed and will use this method when/if I add any more turnouts.
Greg from downunder.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm

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Re: Servo Controlled Points

Post by GAP » Sat Mar 20, 2021 9:01 pm

I had a thought about how I could control them via radio control by replacing the toggle switch with one of these https://core-electronics.com.au/pololu- ... mbled.html and a 2.4GHz receiver at each point.
Would get expensive and defeats the purpose of doing it on the cheap though, plus I would need 12 radio channels.
Graeme
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Re: Servo Controlled Points

Post by ge_rik » Mon Mar 22, 2021 9:49 am

Hi Graeme
That all looks very elegant.

Can I just clarify how it all works?

Am I right in thinking there will be a servo tester assembly close to each turnout, so you can tweak the amount of throw?
Will the switching for each turnout be done from a central control panel, using hard wired connections, or will you have a series of smaller control panels for doing the switching at various locations?

Rik
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Re: Servo Controlled Points

Post by GAP » Mon Mar 22, 2021 8:01 pm

ge_rik wrote: Mon Mar 22, 2021 9:49 am Hi Graeme
That all looks very elegant.

Can I just clarify how it all works?

Am I right in thinking there will be a servo tester assembly close to each turnout, so you can tweak the amount of throw?
Will the switching for each turnout be done from a central control panel, using hard wired connections, or will you have a series of smaller control panels for doing the switching at various locations?

Rik
Rik,

Am I right in thinking there will be a servo tester assembly close to each turnout, so you can tweak the amount of throw?
Yes, I can break the control switch line and insert a "service" switch and tweak the throw.

Will the switching for each turnout be done from a central control panel, using hard wired connections.
Yes all switches are on a central controls panel on the fascia. I did consider a switch at each point but decided against it because I would still be walking back and forth to set the points.

I am going to use the a line attached to the servo horn to move a semaphore type signal similar to what gregh suggested.
Graeme
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Re: Servo Controlled Points

Post by GAP » Fri Apr 09, 2021 8:31 am

I installed one tester and servo onto a set of points and when I powered it up the servo did a setup of moving to both extremities of travel.
This did not happen with the mock up tester, but I did note that there appears to be 2 variants of the tester in my order (one on a red board, similar to what was on the website and one on a green) and the mock up one is a lot older, over 7 years.
Looks like I will have to investigate if the 2 different variants do something that the older mock up does not further.

I am not sure whether the servo (it is different to the mock up) is the issue or the tester

Meanwhile I bought some things called "linkage stoppers", from HobbyKing an R/C model supplier, that allows the servo horn to go over centre at power up and return to the preset position so the servo does not try to overdrive the point blades as there is enough sideways "slop" at the throw-bar end with the clevis pin being able to 'float in the end slot', so this may be a work around.
It seemed to work with preliminary testing.

Linkage Stoppers;
Aust warehouse
https://hobbyking.com/en_us/linkage-sto ... s_products
Global warehouse
https://hobbyking.com/en_us/linkage-sto ... ?wrh_pdp=3

To fit them all that had to be done was drill the servo horn holes out to 2mm and push them in, they come with a circlip/washer to hold them in place but I have not needed them as gravity hold it in place so far plus they allow transverse adjustment of the control rod.
Graeme
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https://ringbalin-light-railway.blogspo ... -page.html

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Re: Servo Controlled Points

Post by gregh » Fri Apr 09, 2021 9:49 am

Murphy strikes again. Hope you sort it out.

I don't follow how those linkage stoppers work. Do you have a pic (or video) of how they are fitted and work?
Greg from downunder.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm

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Re: Servo Controlled Points

Post by ge_rik » Fri Apr 09, 2021 2:24 pm

gregh wrote: Fri Apr 09, 2021 9:49 am I don't follow how those linkage stoppers work. Do you have a pic (or video) of how they are fitted and work?
Exactly my question. I too can't figure out how they work. They look to be good value though.

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Re: Servo Controlled Points

Post by GAP » Fri Apr 09, 2021 10:31 pm

gregh wrote: Fri Apr 09, 2021 9:49 am Murphy strikes again. Hope you sort it out.

I don't follow how those linkage stoppers work. Do you have a pic (or video) of how they are fitted and work?
The small pin goes through the holes on the servo horn and the control rod goes through the hole on the side and is held in place by a grub screw.
This provides a pivot point for the rod on the horn. They are an alternative to the traditional "Z" bend and provide mechanical adjustment of the control rod to throw bar length.

Pictures show;
L top point blade set to straight
L bottom point set to curve
R top servo horn at max extremity to right which is where it travels to at power up
R bottom shows a side view of the stopper mounted on the horn and the clevis pin on the throwbar.
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I understand these are mostly used by the model aircraft folk to attach their aileron controls so they can fine tune them.

I will now have a play with the servo position setting pots and the mechanical adjustment to fine tune the blade positions, I'll update my blog when I have them working to my satisfaction.
Bit of testing to be done.
Graeme
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Re: Servo Controlled Points

Post by gregh » Fri Apr 09, 2021 11:23 pm

GAP wrote: Fri Apr 09, 2021 8:31 am
Meanwhile I bought some things called "linkage stoppers", from HobbyKing an R/C model supplier, that allows the servo horn to go over centre at power up and return to the preset position so the servo does not try to overdrive the point blades as there is enough sideways "slop" at the throw-bar end with the clevis pin being able to 'float in the end slot', so this may be a work around.
It seemed to work with preliminary testing.
Sorry for my ignorance, but I understood from the above that the linkages allowed the end-to-end servo movement without stressing the point blades. But from your last post (thanks for the pics) I still cannot see how they do that. They are just a solid rod. What have I missed?
Greg from downunder.
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Re: Servo Controlled Points

Post by GAP » Sat Apr 10, 2021 12:37 am

gregh wrote: Fri Apr 09, 2021 11:23 pm
GAP wrote: Fri Apr 09, 2021 8:31 am
Meanwhile I bought some things called "linkage stoppers", from HobbyKing an R/C model supplier, that allows the servo horn to go over centre at power up and return to the preset position so the servo does not try to overdrive the point blades as there is enough sideways "slop" at the throw-bar end with the clevis pin being able to 'float in the end slot', so this may be a work around.
It seemed to work with preliminary testing.
Sorry for my ignorance, but I understood from the above that the linkages allowed the end-to-end servo movement without stressing the point blades. But from your last post (thanks for the pics) I still cannot see how they do that. They are just a solid rod. What have I missed?
To set the blades;
I position the on board pot so that the blades are set to straight through.
The control rod is then set so that the clevis pin is pushing on the throwbar at the edge of the slot closest to the rail.
I then make the switch and the servo moves its set distance, I then adjust the added pot till the blade is against the stock rail and the clevis pin is against the edges of the slot furthest from the rail.
When the servo moves the control rod transfers that movement to the throwbar the stopper pivots in the hole on the horn when the horn moves.
The setting of the 2 pots determines the amount of pressure is applied to the blades.

If you bent a piece of wire at 90 degrees and fitted it through the servo horn (the plastic actuator bit) so that you now have a straight length of wire extending away from the servo when the servo moves the amount of travel at the horn and at the end of the wire will be the same.
The piece that went through the horn is able to pivot the stoppers just replace the bent wire.

After a bit of testing I found that bloody Irishman Murphy had taken up residence on my setup.
The tester causing the issue is one of the 2 out of 12 that came with the order (green circuit board as opposed to red circuit board) it appears that the micro-controllers have different programs in them.
At power up it drives the servo a full 90 degrees before settling at the position determined by the pot, the other 10 just move to the position set by the pot.
Guess I am lucky I used that one first.

I replaced the offending tester with one of the others and it is working fine, the points change as advertised and there is no annoying overdriving at power up.
Now I am 2 testers short but I am looking at a work around of driving 2 servos off the one tester as the points I am working on are part of a crossover so that may work.

Edit;
I installed a second servo running of the tester and now have 2 sets of points on the crossover that change when the one switch is made. This overcomes the shortage of testers.
It took a bit of adjusting, considering I had 4 adjustment points, but after a bit of fiddling it now works well and neither of the servos overdrive.
I will duplicate this on the other sets of points on the crossover.

Picture of the linkage and control rod.
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Re: Servo Controlled Points

Post by GAP » Wed Apr 14, 2021 9:50 pm

I have published a page on my blog which shows the whole install of the servo controlled points, it contains links to the original article and the components used.
https://ringbalin-light-railway.blogspo ... oints.html
Graeme
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https://ringbalin-light-railway.blogspo ... -page.html

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