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Fitting TOUs


Fen End Pit

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I spent a few hours today fitting the TOUs and servos which I built yesterday. I'm hoping a step by step guide might be useful to some people.

 

The first step is to drill the holes which the TOU will go through to connect to the switch blades. If you are sensible and have planned ahead you will of course have drilled these before you stuck the point down or at least before you fitted the rails! However all is not lost as you can carefully drill a couple of pilot holes in the right place about 5mm from the end of the switch blade. Having drilled these I then VERYCAREFULLY opened the holes out to 8mm in several stages, making sure that the drill bit didn't go to far and touch the rails! A decent electric drill helped here (good to know I got something useful for working with my current employer for 5 years!). Designing the bracing on the board so it won't foul the TOU is obviously a must (spot the deliberate mistake).

 

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The TOU and servo mount were positioned under the board, It is a bit tricky to see both sides of the board at once and I found that putting some double sided tape on the units helped me stick them to the board while then allowing me to adjust a bit. It provides enough hold to them allow me to get a pilot hole drilled prior to putting the screws in.

 

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Then the length of .8mm brass wire can be bent up. I usually go for a short right angle bend and then bend that slightly to one side so that the short section will sit into the web of the bull-head rail. The wire can then be threaded down through the brass tube and soldered to the rail. Once both sides are done the TOU should move the blades smoothly. There is space for a little bit of tweaking if the blades aren't quite the right distance apart, the tube will take a little bend if you need 1/2mm of extra or less movement.

 

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Next job is to link the TOU to the servo, and this is where the real advantage of the servo comes into play. Because you can adjust the throw so easily you don't have to fiddle about making the linkage exactly the right length. I simply made a short length of steel wire by eye the distance from the hole in the TOU operating arm to the centre of the servo drive. Then I fitted one of the smallest servo arms (the servos have a variety of shapes and sizes supplied) and threaded the wire linkage between the two units.

 

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The downside of servos of course is that they need some electronics to make them work, but the 4 servo unit produced by the MERG (called a Servo4) is very easy to build and cheap at GBP 5.50. This unit has 4 double-pole-double-throw switches connected to it, one pole switching the frog polarity and the other switching the input on the Servo4. To set the board up you can either build and use the purpose built programmer which the MERG sell (probably a good idea to get one to take to exhibitions if you need to do any adjustment) or use a serial cable to a PC running the ServoSet application.

 

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The Servoset application runs on windows (there is a java based version available I believe for linux users). The left hand side of the display shows which servo you are programming and where it is connected on the Servo4 board. In the centre are the sliders which you move up and down to set the on and off positions and the speed you want the servo to move at. Once happy you just write the data to the board and you can disconnect the PC.

 

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The servos make a noise if you push them too hard so it is easy to get a feel for where to set the end points, you shouldn't need so much torque that the servo buzzes. The servo controller switches off the power to the servo after 5 seconds so that they are completely silent once changed (unlike some of the alternatives which stall a motor and can hum gentle to themselves).

 

If you are offended by a brief plug for the MERG please stop reading now!

 

Just to finish, a few thoughts about cost. A quick internet trawl shows a typical Tortoise point motor at about GBP 14.50, a Cobalt point motor at GBP 17.50 and a typical Servo at under GBP 3 and the MERG's Servo4 board at GBP 5.50. So, four points driven by Tortoises would cost GBP 58.00 while four driven by servos comes out at GBP 17.50. I think the difference pays for the MERG membership fee several times over.

 

David

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What you say about cost is true although you've overlooked the "price" of building a TOU, adding a microswitch for crossing switching, etc. Speed/ease of installation is a factor that cannot always be costed.

 

I've opted to use Cobalts for turnouts on the new layout section that I am building, but will be using servos and MERG Servo4s for post, bracket and ground signals.

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What you say about cost is true although you've overlooked the "price" of building a TOU, adding a microswitch for crossing switching, etc. Speed/ease of installation is a factor that cannot always be costed. I've opted to use Cobalts for turnouts on the new layout section that I am building, but will be using servos and MERG Servo4s for post, bracket and ground signals.

 

Point taken, but you would have needed some kind of TOU to get a Tortiose/Cobalt to drive a handmade turnout (ok, so you can just stick the wire through a Peco streamline point). Also you'd need a switch to operate the Tortiose and the difference in cost between a SPST and a DPDT is pence. I would cost the TOU at around 50p each in parts.

 

David

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I like the simple design of the TOU's and the way you are operating them via servo. As a newbie to this way of doing things, and appreciative of the clear way you have shown how you made and programmed it all, could I just ask how the servo's are actually powered and operated. By ordinary switch, or via DCC perhaps?

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Hi Izzy

For this little section of board the servo4 board is powered by a 12v DC input. The board has a connector with 0v on one pin and then 4 other pins, one for each servo. A switch simply connects the appropriate servo pin to the 0v, nothing clever there at all. As I said I use a double-pole-double-throw switch so I can use the other pole to switch the polarity of the frog. On the main section of the layout I use the MERG CBUS modules to switch double-pole relays which have exactly the same effect, however for this little section of yard I was happy to just leave it with 4 simple switches.

 

Hope that helps.

 

David

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Thanks for a very clear and easy to follow "How to"

 

Servos may feature on some of my future projects after reading this.

Are the bits available to non MREG members or do you have to join to get hold of the PCB and programming software?

 

Cheers!

Frank

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David,

 

It looks like we were doing some similar things over the Christmas break but adopted some different approaches. I will put a posting up on my workbench thread later (its called a Highland Miscellany and is repeated on the Scalefour Society forum).

 

Not saying my approach is better but it is more "me"!!!

 

And I seem to have b******red my Servoset, so have to buy a lead and try my hand at the PC method!

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Thanks for a very clear and easy to follow "How to" Servos may feature on some of my future projects after reading this. Are the bits available to non MREG members or do you have to join to get hold of the PCB and programming software? Cheers! Frank

Hi Frank

The MERG components are only on sale to MERG members, this is for a variety of reasons but partly because if they were on sale to the general public they would require things like CE certification. The MERG are a pretty friendly bunch though and accept that a single MERG member might buy items for a club layout. Membership is currently £14 per year with a £4 joining fee.

David

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David, It looks like we were doing some similar things over the Christmas break but adopted some different approaches. I will put a posting up on my workbench thread later (its called a Highland Miscellany and is repeated on the Scalefour Society forum). Not saying my approach is better but it is more "me"!!! And I seem to have b******red my Servoset, so have to buy a lead and try my hand at the PC method!

 

Hi Portchullin Tatty

I look forward to seeing that later. I'm sure there are multiple methods to do this and will be interested in seeing what you've done differently (and probably better!)

David

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Hi Izzy For this little section of board the servo4 board is powered by a 12v DC input. The board has a connector with 0v on one pin and then 4 other pins, one for each servo. A switch simply connects the appropriate servo pin to the 0v, nothing clever there at all. As I said I use a double-pole-double-throw switch so I can use the other pole to switch the polarity of the frog. On the main section of the layout I use the MERG CBUS modules to switch double-pole relays which have exactly the same effect, however for this little section of yard I was happy to just leave it with 4 simple switches. Hope that helps. David

 

Thanks, it does. As someone electronically limited, I get there eventually but it takes a while, and this helps me understand things now. Obviously the MERG board takes the 12v dc and puts out just what the servo's need.

 

Having tried a Colbolt recently and not been over-impressed with it's limitations, larger and more expensive than I'd like, and like the similar but even larger Tortoise not particularly adaptable in limited space situations, the servo answer seems a rather neat solution.

 

Having gone down the DCC route for Loco control I'm not sure how much further I want to go with point/signal/electromagnet control(for couplings), and something like this could be part of the solution I adopt.

 

cheers,

 

Izzy

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Thanks, it does. As someone electronically limited, I get there eventually but it takes a while, and this helps me understand things now. Obviously the MERG board takes the 12v dc and puts out just what the servo's need. Having tried a Colbolt recently and not been over-impressed with it's limitations, larger and more expensive than I'd like, and like the similar but even larger Tortoise not particularly adaptable in limited space situations, the servo answer seems a rather neat solution. Having gone down the DCC route for Loco control I'm not sure how much further I want to go with point/signal/electromagnet control(for couplings), and something like this could be part of the solution I adopt. cheers, Izzy

Hi Izzy

Yes, I've always been a bit sceptic about the benefits of point control with DCC. The classic 'loco goes against a point the wrong way, shorts out the DCC and the operator can't then change the point as it is DCC controlled' problem just being the most obvious example. I've opted for the MERG CBUS method on the main part of the layout which uses a seperate 'control bus' to connect a number of circuit boards together, these boards can have things like a complete control panel with 128 switches attached to them or a simple board which drives 8 servos or relays or an option that can drive 4 solenoid based point motors. The advantage of this system is that only need 4 wires between the boards.

David

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