Using Servo's as point motors

[Scottish Modeller]

HI all,

 

OK - currently in the process of building some fiNetrax points and also working out how to power them.

 

All of the solonoid types are out as they are far to abrupt in the way they operate and smash tiebars etc as a result.

 

Tortoise or similar are out as well - due to the limited underboard height that is available (30mm).

 

For motorised points this takles me to Servo type mechanisms.

 

Plan, (if can be made to work) will be to use mini sservos in brackets under the board.

 

Problem is that there do not seem to be horizontal mounts available at a reasonable price (compared to vertical mount types).

 

Does anyone know of any of the horizontal type at a reasonable price?

 

THanks

Phil H

[davetheroad]

Look at these, Micron Radio Control specialises in RC but as far as I understand, a servo is a servo and as long as the correct voltage is applied the control signal is the same

 

http://www.micronradiocontrol.co.uk/servo.html

[adriank]

Problem is that there do not seem to be horizontal mounts available at a reasonable price (compared to vertical mount types).

 

Does anyone know of any of the horizontal type at a reasonable price?

 

THanks

Phil H

 

Dave at Megapoints uses aluminium channel. Have a look at the video on the Megapoints site.

 

Adrian

[Suzie]

The Signalist servo point motors are about 40mm high.

 

 

They fit in the same footprint as a Peco PL10 solenoid on a PL9 or PL12 base and have the provision for two microswitches for end position feedback or frog switching.

[njee20]

Their base looks good, shame they don’t do those separately, as I don’t need servos and I’m not paying £11 a throw.

 

I use the Megapoints boards with aluminium channel as per Dave’s recommendation. The boards are great and the mounting’s not bad. The servos can move in the channel, but I admit I’ve just used an interference fit, and because the motion of the actuation rod is an arc you can find some stock clips the top of the rod. Dapol silver bullets and Megafrets are bad for it. I’ve not found any mounts I like enough at a price I want to buy 50! You can obviously set the motors up in such a way that the rod is ‘high’ when furthest from the rail. I lacked that forethought.

 

I’ve not looked at the Finetrax points too closely, are you using a secondary tie bar under the board? May mitigate the ‘arc’ motion if the actuation rod is below board level.

[Miss Prism]

The Signalist servo point motors

 

Nice. Source?

[Suzie]

Nice. Source?

 

Peedie Models

 

https://www.peediemodels.com/proddetail.php?prod=SB1

[njee20]

Slightly cheaper from Coastal DCC, albeit not in stock. I see they do also do the mount on it's own, still £8 though. Not sure I can stomach £400 to change!

[Crosland]

Nice. Source?

 

Manufacturer's website is http://signalist.co.uk/index.html but some of the links are broken/wrong.

Edited January 9, 2019 by Crosland

[Grovenor]

Does anyone know of any of the horizontal type at a reasonable price?

 

THanks

I metre of allumnium angle from B&Q and you can make a lot of mounts for pennies.

See example here, https://youtu.be/f4MGyCEL5XA

and https://youtu.be/_4T8xw0ibvc

Regards

Keith

 

PS, Someone seems to have added a soundtrack to my videos, I never heard that before!

Edited January 9, 2019 by Grovenor

[njee20]

That's a neat tie bar mechanism you're using, is that homemade? 

[Harlequin]

See also: http://www.rmweb.co.uk/community/index.php?/topic/133913-burton-on-trent-south-some-progress/&do=findComment&comment=3346777

 

Where Ian (ISW) is using the aluminium channel technique and has some great construction drawings.

[Grovenor]

That's a neat tie bar mechanism you're using, is that homemade?

The grey plastic parts are from an Exactoscale tortoise adapter which was to hand. Not worth buying them specially though as its easy to duplicate with styrene sections.

I agree that the use of channel to mount servos works well but will be a very tight fit in 30mm. Using the system I illustrated only takes about 12mm depth. It was tried out specifically for a similar request a coupke of years ago.

Regards

Edited January 9, 2019 by Grovenor

[Scottish Modeller]

Hi all,

 

Thanks for the pointers and links.

 

Now sorted with Servo Mounts!

 

Just need the servos and microswitches and operating switches!

 

The list seems endless!

 

Grows longer every time I look at how to do things.

 

Anyway - more as I progress things.

 

Thanks

Phil H

[Ron Solly]

And if you didn't want to use servos, then these top mounted units may do the trick   Cobalt SS

https://www.dccconcepts.com/product-category/the-cobalt-collection/cobalt-point-motors/cobalt-ss/

[njee20]

SG90 9g servos are the ‘standard’ choice, buy from China via Ali Express and you can pay around £1 each, but they’ll take a while. UK sellers charge up to £6 or £7 for exactly the same item.

[Scottish Modeller]

SG90 9g servos are the ‘standard’ choice, buy from China via Ali Express and you can pay around £1 each, but they’ll take a while. UK sellers charge up to £6 or £7 for exactly the same item.

Hi there,

 

Yes - seen the same situation on prices.

 

Agreed 9g Servos are a standard but still looking and not sure, but think will be bought from China.

 

Thanks

Phil H

 

edit - an after thought...

Is there a write up somewhere about converting servos to stall motors?

[Suzie]

There are fake SG90s on the market, so if you really want an analogue servo (some controllers muck about a bit with digital ones) you probably want to find a reputable source. The fake ones are digital due to being cheaper to make.

[Izzy]

Hi there,

 

Yes - seen the same situation on prices.

 

Agreed 9g Servos are a standard but still looking and not sure, but think will be bought from China.

 

Thanks

Phil H

 

edit - an after thought...

Is there a write up somewhere about converting servos to stall motors?

 

I think there are quite a few threads on RMweb about using servo's as stall motor devices. I have used them like this in a few different ways, generally called 'hacking servos', but this is one configuration that I did a thread on;

 

http://www.rmweb.co.uk/community/index.php?/topic/112916-hacked-servo-point-control/

 

This version has the advantage that the switch controls/limits the travel and also switches the crossing polarity but aren't what some people like of really slow motion as it needs a minimum voltage for the servo to have the power to move the switch so moves quite fast. But still gentle enough to work 2FS pointwork tie-bars without breaking them. The key is in choosing the size of the steel acutating wire for the length needed, whether the acutator needs to go through a deep baseboard etc. I find steel piano wire the best type because thinner stuff will bend quite easily yet retain it's spring tension even if set in a very bent position for a long time.

 

Izzy

[AndyID]

 

Is there a write up somewhere about converting servos to stall motors?

 

Not exactly a stall motor but.... http://www.rmweb.co.uk/community/index.php?/topic/96929-no-stall-servo-point-motor-servo-hack/?hl=%2Bservo+%2Bhack

 

Then there is this, but I have not got very far with it   http://www.rmweb.co.uk/community/index.php?/topic/139521-load-sensing-point-motors/

[Junctionmad]

You can join MERG and get 3D printed servo mounts cheap

 

Dave

[Ian Morgan]

HobbyKing is a cheap source of servos, and quick delivery from warehouses around the world too. I usually go for HK15168 as a straight analogue SG90 replacement. Some people prefer metal geared ones.

 

Digital servos carry on trying to keep the last position even if the control pulses are switched off, where analogue ones stop trying, and friction in the gear train, etc. is used to keep it in place. Several servo controllers for model railway points now switch off the pulses after a second to cut down on servo 'chatter' (and current draw/heating) after the point has been thrown.

[Nigelcliffe]

Hi all,

 

Thanks for the pointers and links.

 

Now sorted with Servo Mounts!

 

Just need the servos and microswitches and operating switches!

 

 

Depending on your chosen control method (ie. the panel switches), it may be simpler to use the switch to operate two things at the same time - a servo control board and a relay board.  The relay board can switch the frog polarities. 

 

Off the shelf relay boards for running on either 5v or 12v DC are available cheaply from Ebay, Amazon, various electronics suppliers, etc..   Depending on the servo control board in use, you may be able to use the same wire from the switch to operate both items.    Relay boards may be a lot less hassle than mounting microswitches unless your chosen servo mounting method includes attachment for microswitches, and adequate control of the throw of the servo to operate both tie bar and microswitch. 

 

I've used both microswitches and relays, and will continue to use both, picking the one best suited to the situation.

 

- Nigel

[Ron Solly]

Depending on your chosen control method (ie. the panel switches), it may be simpler to use the switch to operate two things at the same time - a servo control board and a relay board.  The relay board can switch the frog polarities. 

 

Off the shelf relay boards for running on either 5v or 12v DC are available cheaply from Ebay, Amazon, various electronics suppliers, etc..   Depending on the servo control board in use, you may be able to use the same wire from the switch to operate both items.    Relay boards may be a lot less hassle than mounting microswitches unless your chosen servo mounting method includes attachment for microswitches, and adequate control of the throw of the servo to operate both tie bar and microswitch. 

 

I've used both microswitches and relays, and will continue to use both, picking the one best suited to the situation.

 

- Nigel

 

Nigel, using relays in parallel with the servo ( or even other means of operating the tiebar) assumes that both will work at the same time. I have known solenoids not to move but separate methods of frog switching/ direction indication does , so either a short on the frog or incorrect indication. To me, the only real way to get correct indication / frog switching is based on tiebar movement meaning some form of switching from thet iebar = micro switches

[Crosland]

Nigel, using relays in parallel with the servo ( or even other means of operating the tiebar) assumes that both will work at the same time. I have known solenoids not to move but separate methods of frog switching/ direction indication does , so either a short on the frog or incorrect indication. 

 

If the points are correctly modified for frog switching (i.e. frog isolated and switch rails connected to adjacent stock rails) then a short cannot occur.