Using Servo's as point motors

[Nigelcliffe]

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

 

The timing issue is only a factor with poorly wired turnouts (eg. Peco N electrofrogs where the user feels the need to add additional electrical switches to the frog). With those the blades act as crossing (frog) switches.  If adding an external switch for the crossing (frog), it is necessary to either get the timing of the switch movement correct, or modifying the turnout.   But other turnout electrical arrangements don't have this issue.

 

 

The thread started with FiNetrax turnouts, they are built with "proper" wiring, in that the frog is electrically separate from the blades, and the blades are bonded to the fixed rails, so there is no short circuit if the blades move at a totally different time to the frog switching.    So, the relay approach I outlined will be reliable (*). 

 

 

I find that decent motors are reliable, the most common failure I see in models is the turnout blades detaching from tiebars, and with that fault a microswitches on the tie-bar movement doesn't tell you the blade has detached. 

 

 

(* its not N, but I'm helping build a large EM layout, DCC so track is under power at all times.  Hand laid turnouts.  Tie bars moved by servos with parallel relays for frog switching.  The first dozen or so have been installed for some time, they are reliable and the difference in timing of relay and servo tie-bar movement does not, and cannot, cause short circuits.   I'd not have used that arrangement had there been a short circuit risk.   )

 

 

- Nigel

[Ron Solly]

I do agree that if the turnouts have been modified for DCC or hand built, then shorts between timing of  blades & relay contact  will not occur but many I know use the turnout as it comes out of the box - no modifications done at all.

I have no problems with frog switching - I use either Hex Frog Juicers or have dead frogs ( similar to Unifrog but not wired at all) , It is the contacts required for panel indication of turnout direction when using side mounted motors & no room for microswitches. At times I have found that some solenoid does not move even with a good CDU kick.

[WIMorrison]

Take a look at these, very cost effective and easy to surface mount, or even if you have limited depth under the board they fit easily.

 

https://dcctrainautomation.co.uk/point-motors/4447-mp1-point-switch

 

Plus you don't need anything special to drive them and stop them in the right place, unlike servo motors

[Junctionmad]

On 16/01/2019 at 21:17, Ron Solly said:

I do agree that if the turnouts have been modified for DCC or hand built, then shorts between timing of  blades & relay contact  will not occur but many I know use the turnout as it comes out of the box - no modifications done at all.

I have no problems with frog switching - I use either Hex Frog Juicers or have dead frogs ( similar to Unifrog but not wired at all) , It is the contacts required for panel indication of turnout direction when using side mounted motors & no room for microswitches. At times I have found that some solenoid does not move even with a good CDU kick.

Eh , but people using “ out of the box” turnouts don’t need to switch frogs , so your issue of shorts never crops up. 

 

The most reliable way , to switch frogs , where you have wired them properly , is to use a relay triggered by the servo movement or failing that’s by the actuating switch. 

[ikcdab]

using relays as polarity switches for servo point activation.

Is it acceptable to use the point switch circuit in series with the relay to trigger the relay?

as per this diagram?
in practice, the relay board (Megapoints) has 12 positive on/off inputs for each of 12 servos and a single common negative,

 

[Happy Hippo]

20 minutes ago, ikcdab said:

using relays as polarity switches for servo point activation.

Is it acceptable to use the point switch circuit in series with the relay to trigger the relay?

as per this diagram?
in practice, the relay board (Megapoints) has 12 positive on/off inputs for each of 12 servos and a single common negative,

 

If you are using the Megapoints servo control board, you cannot just wire a relay into the  circuit.  It will need a separate relay control board, which Megapoints also make as part of their system. You can also get the correct relays from Dave, and he tests them to make sure they work before despatch.

[AndyID]

41 minutes ago, ikcdab said:

using relays as polarity switches for servo point activation.

Is it acceptable to use the point switch circuit in series with the relay to trigger the relay?

as per this diagram?
in practice, the relay board (Megapoints) has 12 positive on/off inputs for each of 12 servos and a single common negative,

 

 

 

 

Hi,

 

No, I don't think the relay will pull in when you close the switch, and if it did it could conceivably damage the input on the Megapoints controller.

 

I think what you would like to do is have more things activated when you close the switch? If that is correct what you could do instead is use the control panel switch to control the relay only then use one of the relay's contacts as an input to the Megapoints controller. You'll probably need a relay with more contact pairs for that, but not necessarily.

 

If you can give us a better idea of what you'd like to be able to control we should be able to help.

 

Cheers!

Andy

[Suzie]

Ikcdab, What you have proposed will not work. I think you would be best either:-

• Use a double (or more) pole switch - the extra contacts in the switch replace the relay contacts.
• Use a pole of the relay to activate the servo driver board.

There are other ways around that you can switch the relay and servo controller with a SPST switch but the isolation circuitry and power supply requirement gets a bit out of hand and is really not worth the effort.

[ikcdab]

1 hour ago, Suzie said:

Ikcdab, What you have proposed will not work. I think you would be best either:-

• Use a double (or more) pole switch - the extra contacts in the switch replace the relay contacts.
• Use a pole of the relay to activate the servo driver board.

There are other ways around that you can switch the relay and servo controller with a SPST switch but the isolation circuitry and power supply requirement gets a bit out of hand and is really not worth the effort.

Thanks for the replies. On my current layout there are 10 turnouts and two semaphore signals worked from a twelve unit megapoints controller. I switch crossing polarity with microswitches. I have a route setting diode matrix  for the turnouts. This layout has been a testtrack and I am now moving onto the "main event". Reading about it, relays seem better than microswitches and I have had to replace a couple of microswitches as well as making the servo mounts more complex. 

I was just trying to figure out how to fire the relays. I see that megapoints supply relay drivers, but I am always looking to do it myself. 

I'm not sure I'm going to do the route setting again as the new layout is more complex and has exponentially more routes (but i might do). So I guess the answer is to use DPDT switches on the control panel. 

as per this sketch:

 

 

Edited May 28, 2020 by ikcdab
added diagram

[ScRSG]

9 hours ago, Happy Hippo said:

If you are using the Megapoints servo control board, you cannot just wire a relay into the  circuit.  It will need a separate relay control board, which Megapoints also make as part of their system. You can also get the correct relays from Dave, and he tests them to make sure they work before despatch.

 

I agree re the Megapoints board, the switch is merely a route to earth and does not carry any voltage as such so can't be used to power the relay. The most common method is to use a microswitch on the point motor activated by the servo arm. This is, of course, a mechanical solution. 

 

If you don't mind loads of extra wires (!) then you could use a DPDT switch on the panel, one side of the switch wired as the trigger for the board and the other side to carry the +v for the relay, with the relay sited close to the point to minimise the frog wires - hope this makes sense, and I will certainly bow to the knowledge of more electrical savvy members than me!

[Dave-5-5-7]

I run mine through an arduino. Simple program, set the angles and you're done. Toggle switch control, cheap as chips. Arduino Uno is about £6. I use Dingo servo mounts. This was the test rig. 

[Nigelcliffe]

1 hour ago, ScRSG said:

 

I agree re the Megapoints board, the switch is merely a route to earth and does not carry any voltage as such so can't be used to power the relay.

 

 

A bare relay coil, yes I agree.  

But, a relay module board, which is also triggered by closing contact to ground will work  (built relay module boards are cheap on Amazon, Ebay, etc..  plus other sources).  

All subject to the voltages been appropriate, common reference 0v between both relay and servo controller board, etc...  

 

- Nigel

Edited May 28, 2020 by Nigelcliffe

[Junctionmad]

MERG has a little servo board that can use the servo signal to switch a relay , you set the switch over point