Servo Motors & Servo Controllers

[Steve Hewitt]

I’ve started this topic in order to answer questions arising in mikemeg’s superb thread “More Signals at Hessle Haven & Scarboroughâ€.

 

I’ve been using servos to drive semaphore signals since seeing a demonstration on the Embedded Controls trade stand at a Wignal exhibition in the late 1990’s. In fact I was so impressed with what I saw that I volunteered to build the signals for our club’s “Oxenholme†layout. This was my first excursion into signal building.

Subsequently our club – Blackburn & East Lancs MRS – adopted the same techniqes for all semaphore signals on club layouts. I’ve now built operating signals for our layouts in 2mm, 4mm and 7mm scales.

Currently I’m building the signals for John Holden’s model of Liverpool Lime Street, which are also servo driven, but with bespoke controllers.

 

Before I go any further, let’s get one thing straight – I know almost nothing about electronics. Fortunately, I know a man who does!

 

The first question I’ve been asked is “which servosâ€.

Originally, I used the servos which came in the package with the Embedded Controls controllers.

These are quite substantial, with the following typical characteristics.

Dimensions (mm): 19.0 x 38.0 x 34.5

Weight (grams): 45.0

Speed (sec): 0.25

Torque (Kg.cm): 3.10

Ball Raced: No

They will definitely pull the skin off a rice pudding!

 

More recently, I’ve been buying controllers without the servos, and using the following.

These are what I’d call medium sized, with typical characteristics:

 

Dimensions (mm): 11.5 x 24.0 x 23.0

Weight (grams): 7.5

Speed (sec): 0.12

Torque (Kg.cm): 1.17

Ball Raced: No

This model is the SuperTec JP EN ER G Super Micro Digi 7.5g

The “Digi†refers to digital, and is reputed to give finer resolution of movement.

 

 

 

The smallest servos I’ve used are the SuperTec JP EN ER G Super Micro Servo 7.5g

which has the following characteristics:

Dimensions (mm): 8.0 x 20.0 x 19.5

Weight (grams): 4.7

Speed (sec): 0.12

Torque (Kg.cm): 0.60

Ball Raced: No

 

Prices from £5 to £8 approx, plus postage etc.

I have bought all my servos recently from http://www.servoshop.co.uk/index.php

No relationship other than a satisfied customer.

 

I know some have bought much cheaper servos direct from the Far East on eBay. However, the ones I have seen have lacked build quality.

They are a bit “sloppy†where the shaft is mounted. What we used to call “headache†when I was an apprentice. This leads to a loss of precision in signal movement.

 

You don’t need to spend a lot on high performance, ball bearings etc. for our application, but avoid the cheapest – you get what you pay for.

 

As a rule, I try to use the SuperTec JP EN ER G Super Micro Servo 7.5g wherever possible. It is very smooth runner and seems to do the job very well.

The smaller 4.4g models are useful where space is limited :

This twelve arm gantry is a case in point:

 

What about servo controllers?

I started using the Embedded Controls controller, and still do so today wherever I can.

Unfortunately, it isn’t currently commercially available!

I’m hoping that this will change in the fairly near future.

This gives a really good movement to your signal arm:

Slow pull to “Clearâ€; Slight return to at the end of the movement where the signalman has released the lever; Slight move of the arm as the signalman pulls on the lever to release it’s lock; Quicker return to Danger with a couple of small bounces at the end.

All that is seen at the servo quite easily! Whether the signal arm shows the same depends on how well you build your signals. Any slop or tightness in the operating linkages and the finesse is lost.

Just two adjusters - one for the Danger position, and one for the Clear.

If the Embedded Controls controller were available, it would probably be in excess of £15.00 each from the usual suppliers.

One unit required for each arm (servo motor) you want to drive.

 

I’ve experimented with the MERG “servo4†controller.

 

This is available from the Model Electronic Railways Group - MERG – an Internet group. To members only.

I joined for a couple of years to buy one or two of their kits, which are excellent quality and value.

Not really understanding electronics, I didn’t get any other benefit from membership, and let it lapse.

This easy to build kit will control up to four servos independently. The motion is much simpler. Danger to Clear at one speed, Clear to Danger at same or another speed.

The end positions and the speeds for each servo are set independently.

This can be done by using free software, download to your PC from the MERG website. Alternatively you can buy and build the MERG servo setting box kit.

Either your PC or the setting box plugs into the 9-pin “D†socket seen in the picture.

For a PC You will need a USB to Serial cable.

 

The third servo controller I have knowledge of is the “ESU switch Pilot servoâ€.

This is a dual DCC/analogue controller, which I have used on my demo. stand as an analogue device. (I know not much about DCC).

It again will control up to four servo motors.

The motion control is even more basic.

Each servo can have its end positions set. The speed of movement can also be set, but it is the same in each direction per servo.

This controller is more suited to point control than signals.

Besides the motion control, the control principle is akin to a solenoid point motor, i.e. a passing contact or momentary switch is used. The controller will also only allow one servo to operate at any one time, so it isn’t suitable for simulating a “slotted†signal, where you may or may not want two arms to move simultaneously.

The unit on my demo stand was kindly donated for evaluation purposes by “South West Digitalâ€

 

I know there are other servo controllers available, but I do not have first hand knowledge of them. In one case not for the want of trying!

 

If you wish to see these demo items for real, I’ll be at the ALSRM’s Bolton event on February 26th, and at Warley again in November.

 

I look forward to your further questions………..

 

Steve Hewitt.

[ScRSG]

We too used the Embedded Controls system for our "Alloa" layout, and, having now tried both the Heathcote version (which are ok) and the modules from MUTR (which are NOT ok), I wish the Embedded Controls modules were still freely available as they are vastly superior to any of the others due to the subtle movements available such as bounce etc. I have tried to persuade the former manufacturer to re-introduce these but to no avail (as yet). Not cheap but definitely the best!

[Grovenor]

This easy to build kit will control up to four servos independently. The motion is much simpler. Danger to Clear at one speed, Clear to Danger at same or another speed.

The end positions and the speeds for each servo are set independently.

MERG now has firmware available for the serv4 designed for signals. This provides for up to 3 individually adjustable bounce positions at each end of the travel. Each of the 4 servos can be adjusted separately. The original version was designed for points where bounce is not usually wanted.

Regards

Keith

[Fen End Pit]

Best source of Servos I've found so far is Giant Cod , they seem to have a large range at very good prices. I had several for less than £3 each which have been fine for model railway use.

no connection except satisfied customer.

 

David Barham

[Stephen Freeman]

The recommended servo for the MERG Serv4 is, I understand, the TowerPro SG90 9G, currently available from Giant Cod at £2.86 plus carriage. If it's DCC control you're after have a look at Tam Valley Depot , they appear to have a DCC/Conventional 3 position servo for 2 arms with bounce as well as others without. Unfortunately the Serv4 kit is not available at the moment as it is being re-designed.

 

Keith forgot to mention that to access the Sema4 code, you need to be a member and to use it, have, or know someone who has, the means to program the PIC firmware.

[ScRSG]

The recommended servo for the MERG Serv4 is, I understand, the TowerPro SG90 9G, currently available from Giant Cod at £2.86 plus carriage.

 

If you do a bit of a search on Google for these servos you can find, as i did, from Hong Kong direct, four SG90's for SIX QUIDIncluding postage and they arrived in less than ten days! (last December snow and ice and all!)

[Worsdell forever]

Hi Steve,

 

I have a Switch Pilot Servo to operate my signals in analogue and I see you have a variety of different switches on your demo. The instructions mention push buttons and I see you have these in the centre, does the 'lever' have to be turned off or can the system cope with on/on toggle switches like the type you have on the left, I already have these in the 'frame' in the control panel (I want to keep the 'Frame' feel to the panel) and I was hoping to just have to add some more wires as I was originally going to use memory wire (simple on/off) but gave it up due to reliability problems when exhibition halls warmed up.

[Grovenor]

Keith forgot to mention that to access the Sema4 code, you need to be a member and to use it, have, or know someone who has, the means to program the PIC firmware.

But to buy the Servo4 kits in the first place you have to be a member or be a friend of one, so if you are in this position you will also have access to the Sema4 firmware and reprogramming service if needed.

Regards

Keith

[Steve Hewitt]

Hi Steve,

 

I have a Switch Pilot Servo to operate my signals in analogue and I see you have a variety of different switches on your demo. The instructions mention push buttons and I see you have these in the centre, does the 'lever' have to be turned off or can the system cope with on/on toggle switches like the type you have on the left, I already have these in the 'frame' in the control panel (I want to keep the 'Frame' feel to the panel) and I was hoping to just have to add some more wires as I was originally going to use memory wire (simple on/off) but gave it up due to reliability problems when exhibition halls warmed up.

 

Hi,

 

The demo is to show alternative switch types all doing the same sort of thing.

The switch on the left is a "centre off" switch, with a centre bias. i.e. it springs back the "off" when released.

Pull the lever towards you and release, moves the servo to the "clear" position.

Push the lever away and release, moves the signal back to "danger".

 

The push buttons in the middle work as you'd expect.

Press and release the green button, the servo moves to the "clear" position.

Press and release the red button, the servo moves back to "danger".

 

The switch on the right is an old H&M "Flash" switch.

Pull the switch, (quite slowly) and the servo moves to "clear".

Push the switch, (again quite slowly) and the servo moves back to "danger".

If you move this switch too quickly the contact is too brief to be recognised by the controller.

 

They are just alternative ways of giving the "momentary" switch contact required by the Switch Pilot Servo.

 

regards,

Steve.

[Worsdell forever]

Thanks Steve, I'll probably replace the signal 'levers' with the centre sprung ones.

[Steve Hewitt]

I've recently completed a 7mm scale Home and Distant signal which uses servo motors and Embedded Controls units very effectively.

Here are a couple videos which show the results.

 

The servos in action.

 

The resulting movement of the arms.

 

If the Distant is pulled off first, the arms don't move until the Home is also cleared:

 

You can see the Distant arm tries to move when it is pulled off, but is prevented by the mechanical slotting, as in the prototype.

 

Steve.

[Donw]

Great stuff. We just need a sound chip for the noise now Steve!

Don (tongue firmly in cheek)

[beast66606]

Great stuff. We just need a sound chip for the noise now Steve!

Don (tongue firmly in cheek)

 

I've got semaphore sounds on my videos, so not as tongue in cheek as you imagine.

[ghisere andy]

At last! I can plan to use the correct semaphore signals for my about (permanantly about!) to happen LNER/M&GN layout. Trying to justify colour lights on the Loop line in 1948/9 was becoming tiresome. Now to recruit my son-in-law to utilise his aeromodelling skills....!

[ScRSG]

Anyone have any comment on the circuit diagram in MRJ 205?

[Suzie]

Anyone have any comment on the circuit diagram in MRJ 205?

 

Has anyone got a link to it?

 

 

 

[ScRSG]

Has anyone got a link to it?

 

Afraid that the Model Railway journal does not seem to go in for that sort of thing! The circuit was submitted as part of a letter to the magazine, and if the writer should be a member of RMWeb perhaps he could post a copy on here. Don't want to infringe any copyright issues by scanning and posting myself unless any one can tell me it is ok.

 

Or hope you can buy, beg, acquire a copy of the mag!

[Steve Hewitt]

It's quite a while since I started this topic, and it's been quiet for a while now.

There has recently been a new development coming onto the market for servo controllers...

 

For a long time now I've been working with John Holden's team on his Liverpool Lime Street project. Besides being operator, I've built all the semaphore Signals.

One member of the team, Geoff, has developed all the electronic control systems for it.

These include the Route Setting computer, the sector plate and turntable controllers etc. etc.

 

His latest development has been the servo control system for the semaphore signals.

 

On the Lime Street project this has been developed as an integrated system, with capacity for up to sixteen servos per control board, fully integrated with the Route Setting computer.

 

However, as a spin off he has developed a two-servo controller for the general market.

 

This is a picture of it:

 

The main features are:

1. 12v dc power supply required.

2. Two independent controllers.

3. Each controller switchable between "simple" and "bounce" modes.

4. Switchable "Safe" mode sets both controllers to "mid position".

5. "Joggle" controls for adjusting each controller's position independently.

6. Fully digital technology. i.e. No analogue adjusters.

Simple mode moves the servo from Danger to Clear at a slow steady pace, and from Clear to Danger at a faster pace.

Bounce mode moves the servo from Danger to Clear at a slow pace, with a short pause mid-way. At Clear the servo overshoots a small amount before coming to rest. Moving from Clear to Danger, the servo first moves slightly towards Clear then returns to Danger at a faster speed, with a rapidly decaying bounce.

The Safe mode is designed to assist in the servo installation process as follows:

Remove the Horn from the servo, connect it to the controller and set the switch to Safe to centralise the servo.

Refit the Horn and the signal connections, with the signal arm also set in a "mid" position.

Unset the Safe switch, and use the adjuster to set the signal positions.

At any time the controller is in use, the adjuster can be used to adjust the arm position. Any position set will be automatically retained by the controller after a short delay of a few seconds. This means it is a true adjustment and not a re-set as in the case of some controllers.

Each click on the joggle wheel adjusts the bandwith of the servo control signal by 3 x 1,000,000ths second. The full range is adjustable between limits of 1,000th to 2,000th seconds which is quite fine.

 

 

These Servo Controllers, and a Turntable drive unit using stepper motor technology again as used on Lime Street, are marketted by G F Controls. See their website : http://www.gfcontrols.co.uk/

 

I apologise if my reporting this new product is in any way biased, but having been involved at the edges of its development it is natural I suppose.

 

Steve.

[Jon Fitness]

Looks a nice bit of kit Steve. May be tempted myself for further developments on "Saltney". It would be easier than using the MERG setting box and the bounce / lever pulling effect...lovely.

Jon F.

[Gordon H]

Looks a nice bit of kit Steve. May be tempted myself for further developments on "Saltney". It would be easier than using the MERG setting box and the bounce / lever pulling effect...lovely.

Jon F.

Can't disagree that it looks the part, but the downside is the price you pay to have joggle controls permanently fitted - which theoretically you would only ever need to use once during installation.

The resulting £12 per servo control (excluding the servo itself) seems a bit over the top.

Interesting also that there seems to be a facility for connecting a setting box to it, going by the board legend.

[Grovenor]

The MERG Servo4 comes in at £1.50 per servo for the electronics so you have a significant saving on the first four signals even including the first years' subscription to MERG. The electronic assembly for these kits is IMHO easier than building the working signals to go with it.

Regards

Keith

[Jon Fitness]

The MERG Servo4 comes in at £1.50 per servo for the electronics so you have a significant saving on the first four signals even including the first years' subscription to MERG. The electronic assembly for these kits is IMHO easier than building the working signals to go with it.

Regards

Keith

 

Agreed! I have 5 boards in use on Saltney (so far; I'll need another 6 or 7 by the time I'm finished) and they're generally trouble free. The only time I have to tune them is if I have disturbed the mechanical linkage or something has come undone!

Having said that, for future board builds I'll be looking into making the connection for the setting box on a lead to the baseboard edge. Beats grubbing about under the board looking for the socket to make adjustments. I don't think this would be an option with the GFcontrols board.

I was thinking more on the lines of having a sort of "favourite" signal, maybe in a prominent place, that I could treat to one of these boards.

I think upper quadrants lend themselves to the sort of action that the GF board provides so I'l definately treat myself to at least one.

Wouldnt mind one of those 16 way boards thats been made for Lime Street though

JF

[Steve Hewitt]

Can't disagree that it looks the part, but the downside is the price you pay to have joggle controls permanently fitted - which theoretically you would only ever need to use once during installation.

The resulting £12 per servo control (excluding the servo itself) seems a bit over the top.

Interesting also that there seems to be a facility for connecting a setting box to it, going by the board legend.

 

 

The leading servo controller for semaphoire signals has for many years been the "Embedded Controls" unit, which had a good representation of the signal movement, and control of the limits of movement by two analogue potentiometers.

When last available on the market, these were bringing prices up to £15.00 each, without servo.

Each unit controlled one servo.

 

You're correct that the board is designed to eventually take a socket for connecting a setting box.

This is intended to allow user control of all the movement parameters, which are currently pre-set variables in the software in the PIC. I cannot say when the setting box will be available as its development is totally outside my control.

 

Steve.

[Steve Hewitt]

The MERG Servo4 comes in at £1.50 per servo for the electronics so you have a significant saving on the first four signals even including the first years' subscription to MERG. The electronic assembly for these kits is IMHO easier than building the working signals to go with it.

Regards

Keith

 

I agree that the MERG unit delivers the lowest cost option to someone seeking a servo controller for semaphore signals.

I've had one for a few years and demonstrate it regularly at exhibitions.

 

It is limited in two aspects:

1. The relatively un-sophisticated movement of the signal.

2. The requirement to have a Setting Box, to make adjustments. The cost and investment in time to build one of these must be considered when comparing costs.

 

The setting box kit from MERG is not quite so straight forward as the servo controller kit to contruct!

The alternative of linking up a PC via a serial cable connection and downloading software from the Internet is even less user friendly.

 

The G F Controls unit is particularly suitable for customers who don't wish to construct their own controllers for whatever reason.

 

Steve.

[Steve Hewitt]

 

Having said that, for future board builds I'll be looking into making the connection for the setting box on a lead to the baseboard edge. Beats grubbing about under the board looking for the socket to make adjustments. I don't think this would be an option with the GFcontrols board.

 

......snipped.....

 

Wouldnt mind one of those 16 way boards thats been made for Lime Street though

JF

 

Hi Jon,

 

I'd suggest mounting the G F Controllers near the baseboard edge, possibly on a drop down sort of mount.

I believe from RC users that you can safely use extensions of the servo cables up to 2 meters to facilitate this.

You can then twiddle the controls whilst watching the signal in relative comfort.

 

(Learnt this lesson years ago using Embedded Controls units on our clubs 00 layout "Oxenholme"

Lying under the baseboard whilst someone shouts "up a bit, down a bit" isn't a pleasure, particularly when you can't remember which way is "up".)

 

If you want a special board building, I suggest you contact Geoff at G F Controls directly, via their website.

 

Steve.