Using R/C servos on layouts

[RedgateModels]

This wasn't intended to turn out in a flame war about MERG membership.

There are lots of members on here who give , without charge , or even a thought of a charge, of their vast knowledge and experience in this forum and the charge is absolute zero.

My experience of MERG was simply they are there just for the fund raising and a very 'holier-than-thou' attitude. Its time they learned to come clean on just what they stand for.

 

I'm sorry, but I couldn't disagree more. Mike Bolton and Steve Perry are amongst the most approachable chaps I have had the privilage of contacting. Without their help Summat Colliery would not have block cut-outs at all.

[Guest baldrick25]

Each to their own view as to the why's and wherefore's of MERG, but this thread was started to try and provide some DIY approaches, and help in customisation of the electronics in model railways. MERG do not own the rights to all good ( or even bad ) ideas, and the help here was much along the lines of Bachmann/Hornby or whoever providing an RTR loco and you build the layout to your requirements to run it on.

It would seem more people are interested in stating their vested interests in MERG and their kits , than sharing their knowledge and coming up with some original ideas.

So be it , so why I should I spend my time and bother , just to be told its £4 for kit from MERG- Is that really what modelling has become these days?

I'll leave my tu'penneth at that.....

[Jol Wilkinson]

Each to their own view as to the why's and wherefore's of MERG, but this thread was started to try and provide some DIY approaches, and help in customisation of the electronics in model railways. MERG do not own the rights to all good ( or even bad ) ideas, and the help here was much along the lines of Bachmann/Hornby or whoever providing an RTR loco and you build the layout to your requirements to run it on.

It would seem more people are interested in stating their vested interests in MERG and their kits , than sharing their knowledge and coming up with some original ideas.

So be it , so why I should I spend my time and bother , just to be told its £4 for kit from MERG- Is that really what modelling has become these days?

I'll leave my tu'penneth at that.....

 

I haven't noticed anyone stating that they have vested interests in MERG.

 

I found this thread interesting, although when it started getting into electronic design and programming, etc. I started to feel a bit lost.

 

I have plenty to do at present building P4 track, locos, carriages, buildings, infrastructure, etc. etc. for my layout. So, while I would like to use RC servos, getting proprietory bits would make the difference between doing that or reverting to use more traditional point motors. In particular, servos for signal operation is of particular interest as I would like to make the signals removable for layout transportation but leave the electrics in place. A servo with a cam to drive the signal looks like a good way to do it.

 

I talk to quite a few people at shows who express an interest in starting to build etched kits. Quite often that means spending some time explaining the basics, what tools you need, etc. They don't all take it up (or at least they don't buy a kit from the business I assist with). It's sometimes annoying to spend time sharing your experience with someone only for it to be ignored, but there is little point in getting the hump about it.

 

Jol

[Kenton]

I found this thread interesting, although when it started getting into electronic design and programming, etc. I started to feel a bit lost.

 

I have plenty to do at present building P4 track, locos, carriages, buildings, infrastructure, etc. etc. for my layout. So, while I would like to use RC servos, getting proprietory bits would make the difference between doing that or reverting to use more traditional point motors.

Exactly my point. There are plenty of things that we can do to keep us more than busy with hrailway modelling.

 

I'm interested in these servos but only in as much as a simple alternative to the Tortoise that I currently use. I have no time or interest in struggling with them or learning a whole new world of electronics beyond what I know. The cost is insignificant though we may all look for areas to save money - for me this is certainly not it. In my limited experience with them they were a waste of my effort a step backwards from a robust off-the-shelf soltion to a somewhat heath-robinson affair.

That is not saying that they cannot be made to work or that I could not eventually get them to work but for me I'd rather spend my time on other things that do not have an off-the shelf alternative.

 

 

 

I talk to quite a few people at shows who express an interest in starting to build etched kits. Quite often that means spending some time explaining the basics, what tools you need, etc. They don't all take it up (or at least they don't buy a kit from the business I assist with). It's sometimes annoying to spend time sharing your experience with someone only for it to be ignored, but there is little point in getting the hump about it.

Couldn't agree more - as the saying goes if I had a penny ... I'd be a rich man - but wealth and happiness can be more than just counting pennies ... if only a few listen to experience isn't that rewarding enough? Besides even those with experience rarely agree on everything.

[Suzie]

The problem is that the omega loops will be in compression, more so as the servo moves anti-clockwise in this example, and the servo will be fighting against them. This can lead to noise form the servos and a much higher power consumption than expected. One solution is turn off the control pulses once the servo reaches the desired position. The friction in the servo gear train is enough to hold it in place.

 

Andrew Crosland

 

I do put omega loops in my linkages, but I adjust the linkages so that the full servo movement matches the required throw. The omega loops are just there in case something gets in the way (flange in the point if it gets thrown when it shouldn't!). Gearing it down in that way puts less load on the servo, unless you stall it of course when the load will be the maximum. The mechanicals and electricals get a lot simpler if you just use one servo for one movement, e.g. two servos for a three way point or slip rather than one.

[Suzie]

You can buy the servos off the shelf and you have a wide choice in terms of cost and performance to choose from. You can buy controllers either as DCC decoders or kits if you don't want to make your own. What is really lacking off the shelf is a handy unit to mount the servo under the baseboard and provide a suitable linkage with simple mechanical adjustment to adjust the throw and offset. That is all that is required to make using a servo as easy as using solenoid or tortoise.

[buffalo]

...What is really lacking off the shelf is a handy unit to mount the servo under the baseboard and provide a suitable linkage with simple mechanical adjustment to adjust the throw and offset. That is all that is required to make using a servo as easy as using solenoid or tortoise.

 

Well, there is the mounting made by South West Digital but, by the time you've bought one of those, the cost is probably more than a tortoise (or one of those new ones discussed in another thread).

 

Nick

[buffalo]

Just finished putting this one together, it wasn't ready when I posted the previous comment on the SWD mount. Its a piece of 40x15x1.5mm aluminium angle with suitable holes and slots drilled and milled. Servo and microswitch are mounted on 4mm ply spacer blocks and the operating wire is a spare borrowed from my Tortoise bits collection. What it could really do with is those little clamp thingys to hold the wire as on the SWD mount, rather than my ad hoc brass strap. Maybe there is something available from one of the RC aircraft suppliers?

 

 

The intention is to drive these from MERG Servo4 boards and control them via DCC. I could build my own controllers and program my own PICs, but I just prefer to spend my time on the mechanical and artistic side of modelling rather than the electronics. Each to his own...

 

Nick

[Jol Wilkinson]

When I built R/C boats and planes many years ago, double sided foam sticky pads were often used. Provided these are stuck onto a smooth surface (chipboard or ply might need a coat of gloss paint) then this worked very well. The exact positioning of the servo may not be too critical, as the design of controllers available - whether as outlined before in this thread, DCC or MERG - all seem to have end/throw adjustment. The flexibility of the foam mount would also give a small amount of "spring" similar to the effect of an Omega loop.

[buffalo]

Yes, sticky pads would be a much simpler solution and would probably be fine for situations where the servo is mounted remotely (as in baldrick25's OP) or, perhaps, for mounting directly under a signal. For turnouts, though, there is still the issue of mounting microswitches for frog switching. I wouldn't expect to be able to achieve reliabilitiy and repeatability of operation if using a flexible mounting for these.

 

Nick

[Suzie]

I did not realise that the SWD device was available. I think that what is really required though is something a bit simpler that is geared down with a fixed fulcrum that will reduce the load on the motor when it is at the end of travel and applying a bit of pressure.

 

I prefer to use the full 180 degree range of travel of the servo rather than just a few degrees - it makes smoother operation much easier when you only have a thousand steps to play with for the full 180 degrees - about five steps per degree. I have not seen how smooth any of the other solutions are. I know from motorising a level crossing that 250 steps from end to end was far too jerky, the servo has to be updated with a new position fifty times a second and the new positions have to be accurate or the servo will growl a bit if nothing else.

 

 

[buffalo]

...

I prefer to use the full 180 degree range of travel of the servo rather than just a few degrees... I know from motorising a level crossing that 250 steps from end to end was far too jerky...

I can see that the stepping might be a problem with crossing gates, particularly given the lack of frictional or other damping and the presence of undamped springs like omega loops, but I don't see it being a problem with turnouts where the need is only for a few mm travel. What I don't yet know is how noticeable it might be with directly driven signals. I haven't noticed anyone else raising it as a problem.

 

Ideally, the friction in the servo gear train should be sufficient to hold most things in position at the ends of travel, so a controller could/should remove power and pulses once the end point is reached. I haven't yet looked at the PIC code for the MERG controller, and I'm trying to avoid doing so Does anyone know if it does switch off at the ends?

 

Nick

[Crosland]

Ideally, the friction in the servo gear train should be sufficient to hold most things in position at the ends of travel, so a controller could/should remove power and pulses once the end point is reached. I haven't yet looked at the PIC code for the MERG controller, and I'm trying to avoid doing so Does anyone know if it does switch off at the ends?

The standard code doesn't at the moment. I seem to recall a message on the MERG group that someone would look into it.

 

There are some who will not accept that the servo friction is sufficient.

 

The code I wrote to turn the MERG CBUS ACC8 into a servo driver does remove the control pulse at the end of travel.

 

It is a particular issue with some of the cheaper servos that can buzz annoyingly as they hunt around the set point and fight the resistance of the mechanism.

 

Another issue to watch is twitching when first powered up. This is usually solved by a resistor between the control signal and either power or 0V. It varies between servo types.

 

Andrew Crosland

[buffalo]

Thanks, Andrew

 

The standard code doesn't at the moment. I seem to recall a message on the MERG group that someone would look into it.

I hope they do. As I said, I don't really want to get into PIC programming as I know I could 'waste' a great deal of time once I'd started

 

There are some who will not accept that the servo friction is sufficient.

For the moment, all of my turnouts are loose heeled so I doubt if there'll be a problem. Perhaps sprung blades in larger scales might be problematic, though...

 

Another issue to watch is twitching when first powered up. This is usually solved by a resistor between the control signal and either power or 0V. It varies between servo types.

Yes, I've seen that happening and had read the discussion about it on the MERG forum, so was planning to try the resistor fix.

 

Nick

[Suzie]

The friction in the gear chain does vary widely. Generally the better quality the servo the less friction. I have some where it is very easy to turn the motor by turning the horn with quite light pressure, but others where I know I will strip the gears before the motor will turn. Not all servos like having the pulse stream switched off, some will tend to drift off or twitch.

 

Again the hunting is more likely in a cheaper servo where there is not enough resolution in the poor quality feedback pot to exactly match the requested position, and there can often be a lot of backlash in the gears, but hunting should not be a problem in any model application - if it is excessive the servo is faulty or needs its feedback pot cleaned (often not an easy task).

 

 

[phlyfifer]

Have the 555IC servo motor control circuit drawings been removed from the thread -- what was in the missing photos (or is it just me that ahs them missing !!)?

[melmerby]

Have the 555IC servo motor control circuit drawings been removed from the thread -- what was in the missing photos (or is it just me that ahs them missing !!)?

 

You are not alone. My browser says "photos have been deleted or moved"

 

Keith

[57xx]

You are not alone. My browser says "photos have been deleted or moved"

I got this from day 1 of the thread

 

 

 

 

[stewartingram]

Am I glad I saved this to my hard drive!

[Kenton]

Why not PM baldrick25 and ask ? He may not know.

They may have been taken down for a reason or it may just be Photobucket blocking images again.

 

Of course the old motto is if youo find a thread interesting on RMWeb - make a copy - as simple as pressing Ctrl+S

[kipford]

These controllers work Brill and are so cheap, its not worth geting out of bed to build them!

Controller

 

I use these servos (at £2.50 a pop they are a bargain) with the controller

 

Servos

 

The controllers are mounted on special circuit board designed by one of my club mates, These boards allow a common power bus to be run for the point motors and single signal wire to each servo, It also has variable pots to allow precis set up of the servo throw. Full details will be given shortly in my layout thread.

Brighton East

 

There is already a picture of one the servo powered TOU's I am building at the bottom of the thread.

[Guest baldrick25]

Why not PM baldrick25 and ask ? He may not know.

They may have been taken down for a reason or it may just be Photobucket blocking images again.

 

I am well aware that the images have gone, and the response by kipford , is indicative of the reason why.

PM's received, and the fact that many posts were made that MERG could do better , left me feeling that there was a violent outburst because someone else, me, wanted to take a different route to developing a simple , easy to build alternative to that which was available , along with an understanding of what they were building and more.

Accordingly I stopped taking photographs, and notes of any further constructions, circuits etc, but now it stands as being fully built and developed . It comes as up to 8 servos outputs per PCB ( 8 because its being driven by a computer of 8 bits output, serial or parallel inputs) has individual speed operation for each servo that allows the speed of the points adjusted to suit the eye of the operator, electriconally adjustable motion ranges , such that above board point rodding can be used to simulate operation, time out of operation in the case of 'jammed' or 'failed' point blades,and add to that sequential operation of each of the outputs. This is necessary because should 8 outputs be toggled together then a very large surge current would be needed to be provided by a power supply - by operating sequentially , and only operating the next servo when the first has finished allows a very much smaller power supply and wiring can be used. It is also much much more realistic as signalmen rarely operated 8 points at the same time.

All this adjustable by the constructor, ( MERGs offering needs software adjustment to change- hands up anyone on this forum who has the skills and knowledge to write and program the software- not many then ) for less than MERG costing less than £4 ( not including the switches required to operate, which could be simple 'stud' operation, up to levers that look like the real thing, or a computer control system) Each servo comes with up to two changeover microswitches, to operate signalling or other accessories , or blade and frog switching.

The idea was to develop and post information at a speed that other forum members could keep up with, answering problems and questions as it went along.

Such is life that in a railway constructors forum, the majority still want to 'buy' something ready made , without a clue how to make it work how they want.

[Kenton]

left me feeling that there was a violent outburst because someone else, me, wanted to take a different route to developing a simple , easy to build alternative to that which was available , along with an understanding of what they were building and more.

I hope that impression was not from any of my posts in this thread. If it was I apologise - I was finding it interesting, albeit a bit confusing.

I still believe servos have a great deal of potential ... if only I could get them to work (and you will see from the other thread that I have tried and sort of given up).

 

I'm one of those who am not a great fan of MERG no axe to grind just don't particularly like the way things are though we probably all will plump for an off the shelf product if it works. The controllers I purchased (NOT MERG) didn't.

 

Don't be put off by the few, the silent majority who view the forum and don't post could well be interested and remember if you are the recipient of any particularly nasty PM just refer it to Andy. He considers such a thing a gross abuse of the privilege of being a member of this forum.

 

I hope you come to reconsider your continued contribution to this thread.

[melmerby]

Why not PM baldrick25 and ask ? He may not know.

They may have been taken down for a reason or it may just be Photobucket blocking images again.

 

Of course the old motto is if you find a thread interesting on RMWeb - make a copy - as simple as pressing Ctrl+S

 

Spotted the post and by then the photos were not accessible/available.

I searched on Photobucket for the photo numbers in the links and it says they are not there.

As far as I can tell they are not just blocked.

 

Keith

[Guest baldrick25]

Spotted the post and by then the photos were not accessible/available.

I searched on Photobucket for the photo numbers in the links and it says they are not there.

As far as I can tell they are not just blocked.

 

Keith

Re your PM , see post 47 in this thread, its already been answered.