Jump to content
 

Servos used as point motors


Dan6470

Recommended Posts

Guest baldrick25

Most people these days probably won't be using a circuit like this at all, but instead will be using a microcontroller based solution such as the MERG Servo4. Such devices can be programmed to give any desired pulse width range and rate of change of pulse width, i.e. the speed at which the servo moves from one position to the other can be controlled too.

With a simple 'two different pulse width' switching circuit the servo always moves at its maximum rate every time the switch is thrown.

The ability to set and vary individual servo end stop positions is also useful, as is the option to use a PC program for setting-up and recording the stored settings.

I would take great issue with that all sweeping statement . Most railway modellers WILL be using circuits like that - a small minority will go to the trouble of using microprocessor based solutions. If your statement was true then there would internet webpages everywhere with the deatils, and that just is NOT true- they are all timer based.

You will be telling me next that scratchbuilding is dead, buy something R-T-R . Sorry but most of the enjoyment comes from seeing something you built and designed , working.

A 555 or 556 based solution is a lot less cash outlay than the MERG offering , and a potentiometer a lot less cash than a PC. Add-in that a pot is adjustable by anyone and the results immediately obvious and the best all round solution is a 555 cicruit.

As for this myth that the servo will only ever run at maximum speed between postions, when the solution is a simple resistor / capacitor combination added is all that is needed. Make that a pot and the speed is user friendly speed adjusted whenever you want.

Well done DAN6470 and long may you continue with your development of a satisfactory circuit, don't be misled by the promise of gold at the end of the microprocessor rainbow.

Link to post
Share on other sites

I would take great issue with that all sweeping statement . Most railway modellers WILL be using circuits like that - a small minority will go to the trouble of using microprocessor based solutions. If your statement was true then there would internet webpages everywhere with the deatils, and that just is NOT true- they are all timer based.

You will be telling me next that scratchbuilding is dead, buy something R-T-R . Sorry but most of the enjoyment comes from seeing something you built and designed , working.

A 555 or 556 based solution is a lot less cash outlay than the MERG offering , and a potentiometer a lot less cash than a PC. Add-in that a pot is adjustable by anyone and the results immediately obvious and the best all round solution is a 555 cicruit.

As for this myth that the servo will only ever run at maximum speed between postions, when the solution is a simple resistor / capacitor combination added is all that is needed. Make that a pot and the speed is user friendly speed adjusted whenever you want.

Well done DAN6470 and long may you continue with your development of a satisfactory circuit, don't be misled by the promise of gold at the end of the microprocessor rainbow.

I would take even greater issue with your unsubstantiated assumptions of my views on topics such as scratchbuilding and self-assembly :angry:

I am certainly all for people making things themselves, myself included.

You clearly overlooked my use of the word 'probably' in the first sentence, because certainly I have no proof but then neither do you with your assertion based on the simplistic notion of webpage count.

You also ignored my use of the word 'option' when I mentioned using a PC. No-one is saying you MUST do it that way - but at least it is an option.

With a 555 or similar 'analogue' solution you have no choice but to set everything up by hand, each with its own controls which must remain connected to the circuit for the rest of its life.

With a microcontroller solution you only need to attach pots OR a PC once, while you set the thing up. Thereafter the numbers are all held inside the device. So, only one set of pots is required for your entire system.

A single 14 pin chip can drive 4 or more servos simultaneously, and costs about a pound. Four off 556's would be about the same, so cost is not the differentiator you claim it to be either, especially when you take all the peripheral things into account such as power supplies which all solutions need regardless.

How would you propose to include things such as 'bounce' for signals with a 555 based solution? Or control a sequence of movements to anywhere within the throw of the servo - not just switching between two end positions?

Hardly the best all round solution I would suggest, when you compare it with the flexibility that a digital solution brings.

Link to post
Share on other sites

Guest baldrick25

 

A single 14 pin chip can drive 4 or more servos simultaneously, and costs about a pound.

Add on the joining fee of MERG of £18 per year, every year or more, and the equation looks a bit different now.

You seem to trot out the MERG solution as though its something superior at every mention of a timer based solution, which in my experience, is far better, and more understandable by the modeller than a digital solution will ever be.

How would you adjust a servo at the far end of an 18 foot layout, whilst its working?. I just use a small screwdriver and can see immediately what the result is.

If the MERG solution was so great, why did not a single exhibition layout at the Leamington model railway Ex last weekend not use it.

You would be very hard pushed to find one at Warley either. I only found one last November and that wasn't the MERG design, but a commercial item called 'bouncer', just operating a signal or two.

For DIY the timer based solution is far far superior anyday.

Link to post
Share on other sites

  • RMweb Premium

Add on the joining fee of MERG of £18 per year, every year or more, and the equation looks a bit different now.

You seem to trot out the MERG solution as though its something superior at every mention of a timer based solution, which in my experience, is far better, and more understandable by the modeller than a digital solution will ever be.

How would you adjust a servo at the far end of an 18 foot layout, whilst its working?. I just use a small screwdriver and can see immediately what the result is.

If the MERG solution was so great, why did not a single exhibition layout at the Leamington model railway Ex last weekend not use it.

You would be very hard pushed to find one at Warley either. I only found one last November and that wasn't the MERG design, but a commercial item called 'bouncer'.

For DIY the timer based solution is far far superior anyday.

 

 

Hi

 

Sorry but I have to disagree. MERG is not £18 per year it is £13. The first year is £18 due to the joining fee.

 

Re your 18 foot layout - you would adjust the servo by connecting the PC to the Servo4 board near the point that needs adjusting. The Servo4 pcb is sited near to the servos that it operates. Also how using your prefered method would you connect this up to a DCC system?

 

Do not ridicule something that you obviously don't know much about.

 

I have used the MERG servo4 on my new layout and found it to be perfect for my needs.

 

Cheers

 

Paul

Link to post
Share on other sites

Hi Guys.

 

What I'm trying to do in this thread is to discuss the use of servos as point motors. I'm not too bother whether I use a microprocessor/pic or a 555 timer solution. My only requirement is that it has got to be cheap and reliable. Currently the MERG solution, although I am sure is a good tried and tested solution, is a greater cost then what I want. Of course when I first started thinking about point motors, Tortoise and the likes of, at £13 to £18 a pop then the MERG solution is remarkably cheap. I calculate £1.125 + cost of the servo per point, not including membership fees. However, my train set which seems to keeps growing in my minds eye, is now at 78 points. I intend to hand build all of them, although having never built a point in my life, perhaps I'm living in cloud cuckoo land, nevertheless, due to budgetary concerns and also the fact that I'm from Yorkshire ;), I have to try and keep costs down. In this regard, providing I can get the 555 timer to do what I want, and there lies the problem, it will prove to be the cheapest option - Four 555 timers and a dozen or so resistors/capacitors, a couple of driver transistors and at the moment 78 SPDT switches. It may be a crap idea, I don't know and this is why I need your input, if the 555 can't do this tell me why but please lets keep it focused.

 

Dan

Link to post
Share on other sites

The trigger pulse is still an item I am unsure of. Almost all the information I have attained point at using a trigger pulse at 50hz with a pulse width of various durations. One site that I looked at stated that I would need to keep the pulse width at less than 5% duty cycle because, Quote "The monostable 555 (the right hand 555 circuit) will not reset if the trigger is held high" but as I mentioned earlier, I am have great difficulty in achieving a duty cycle of this duration. However, is it feasible to run the trigger pulse at a much higher frequency, say 1khz which with a 50% duty cycle, much higher than a 5% duty cycle and perhaps easier to attain, would result in a pulse width of 0.5msec. I hope my maths are correct here ~ can somebody please confirm?

 

Also Gordon A and Bertiedog both mentioned servo chatter. Will increasing the trigger pulse overcome this problem?

 

Dan

Link to post
Share on other sites

  • RMweb Premium

Hi Guys.

 

What I'm trying to do in this thread is to discuss the use of servos as point motors. I'm not too bother whether I use a microprocessor/pic or a 555 timer solution. My only requirement is that it has got to be cheap and reliable. Currently the MERG solution, although I am sure is a good tried and tested solution, is a greater cost then what I want. Of course when I first started thinking about point motors, Tortoise and the likes of, at £13 to £18 a pop then the MERG solution is remarkably cheap. I calculate £1.125 + cost of the servo per point, not including membership fees. However, my train set which seems to keeps growing in my minds eye, is now at 78 points. I intend to hand build all of them, although having never built a point in my life, perhaps I'm living in cloud cuckoo land, nevertheless, due to budgetary concerns and also the fact that I'm from Yorkshire ;), I have to try and keep costs down. In this regard, providing I can get the 555 timer to do what I want, and there lies the problem, it will prove to be the cheapest option - Four 555 timers and a dozen or so resistors/capacitors, a couple of driver transistors and at the moment 78 SPDT switches. It may be a crap idea, I don't know and this is why I need your input, if the 555 can't do this tell me why but please lets keep it focused.

 

Dan

 

Hi

 

Fair enough.

 

I would just like to say that if the 555 doesn't provide what you want the Servo4 circuit is freely available to anyone on the MERG website

http://www.merg.org.uk/resources/index.htm#Turnout

 

Cheers

 

Paul

Link to post
Share on other sites

Guest baldrick25

The servo jitter you mention is inherrent in the way that the design of any individual servo works.

There are typically 256 'steps' inside a servo from one end of the rotation to the opposite end. The motor in the servo is usually a coreless DC motor driving quite a high reduction gear train . The motor is driven from an op amp type of circuit with two inputs. One input connects to an internal pot on the output shaft (usually) and the other input is connected to a pulse-width-to-voltage converter- driven by the input pulse width you are talking about. With the servo stationary then the ouput of the converter matches the voltage by the feedback pot. There is an inherrent designed in dead-band whereby the input pulse width may very slightly vary before the servo motor kicks off to move a 'step' either way. ( they are not physical stops , or notches, just electronic notches caused by the 256steps end to end ( 8bit converter)).

There will always be inherrent noise , and the point where the input pulse is half way between 'steps' , and thats jitter as it 'hunts' to try and find the matching position. Normally a 1/256 of a rotation will make no difference , and the servo itself is designed ignore a one step movement , but there will always be jitter from the stability of the pulse input ( doesn't matter if its generated analogue or digital), its just the limits of the rsolution of the electronics.

If you are using just a very small angle of rotation ( ie just a few 'steps) of the servo output shaft, then jitter will be more noticeable.

There is no cure , except to select a more and more expensive servo, where the electronics may or may not be better.

The backlash in the reduction gearing is another source where it may 'hunt'.

Link to post
Share on other sites

I would just like to say that if the 555 doesn't provide what you want the Servo4 circuit is freely available to anyone on the MERG website

http://www.merg.org....dex.htm#Turnout

 

Cheers

 

Paul

 

Hi Paul,

 

Just checking on the MERG web site and it would seem that the Servo4 is still out of stock but it would seem that a revision/Updated design is underway.

 

Since, as you say, you use the Servo4 on your layout have you noticed the problem of Servo chatter as mentioned by Gordon A and Bertiedog? I'm just curious to know if the problem is reduced or even overcome by use of the Pic solution.

Thanks

 

The servo jitter you mention is inherrent in the way that the design of any individual servo works.

There are typically 256 'steps' inside a servo from one end of the rotation to the opposite end. The motor in the servo is usually a coreless DC motor driving quite a high reduction gear train . The motor is driven from an op amp type of circuit with two inputs. One input connects to an internal pot on the output shaft (usually) and the other input is connected to a pulse-width-to-voltage converter- driven by the input pulse width you are talking about. With the servo stationary then the ouput of the converter matches the voltage by the feedback pot. There is an inherrent designed in dead-band whereby the input pulse width may very slightly vary before the servo motor kicks off to move a 'step' either way. ( they are not physical stops , or notches, just electronic notches caused by the 256steps end to end ( 8bit converter)).

There will always be inherrent noise , and the point where the input pulse is half way between 'steps' , and thats jitter as it 'hunts' to try and find the matching position. Normally a 1/256 of a rotation will make no difference , and the servo itself is designed ignore a one step movement , but there will always be jitter from the stability of the pulse input ( doesn't matter if its generated analogue or digital), its just the limits of the rsolution of the electronics.

If you are using just a very small angle of rotation ( ie just a few 'steps) of the servo output shaft, then jitter will be more noticeable.

There is no cure , except to select a more and more expensive servo, where the electronics may or may not be better.

The backlash in the reduction gearing is another source where it may 'hunt'.

 

Thank you for the explanation baldrick, its really good info. I gather that an increase in trigger frequency will have no effect on the chatter, bertiedog did mention "damping the output with capacitance" but I guess that a pulse width of half-a-step is half-a-step and consequently hunting or jitter/chatter will occur within the servo.

 

May I ask how you are driving your servos, I presume its based on the 555 timer circuits?

 

Dan

Link to post
Share on other sites

Guest baldrick25

I use a 555 as a master 70HZ** oscillator, which triggers a pair or more of 556's in monostable mode which drive individual servos. 2x 556 will drive 4x servo, if you see what I mean. I use good quality 10 turn trimpots for adjustment from here TRIMPOT link and 20K horizontal 20 turn pots from the same source, except they don't have any on offer at the moment. I know they cycle their adverts over a 2 week period, so they will be probably be on their site next week. Give them a ring , they will always help. I'm often in Runcorn, so I collect, so they are cheap. The 555's are from the same source LINK. The 556's are from here LINK as are the 78M05's , veroboard, and other small components ( to combine the postage).

 

In the fiddle yard another 555 drives 7x 556 to give me the 14 points I need there. On the main boards ( layout is 18 foot long so its split into 'boards') I use them for GWR semaphores and other things as well on the same basis -1x555 + anynumber of 556's per board. I use a 9Volt supply to the servo/electronic boards, with a 78M05 regulator on board each one , so the servos only have 5 Volts. It doesn't affect the speed of rotation or anything but 6Volts is max for them. There are currently over 40 servo's in use , from 555/556 circuitry without any problems. There are spare 556's on the PCBs, all wired up, but not connected so if I think of anything else to automate, or an extra signal or something , its all there. The controls are effected via an 8bit decoder, partially decoded so the wiring is there for up to 256 per board if I want it.

 

** Why 70 HZ , well frequency of pulses doesn't matter ( within limits) but I figured that with lots of 50HZ around from the mains everywhere, and 6 foot long unshielded wiring under the baseboards, that I might just get a 'beat frequency' set up which could cause unexpected operations. I have never seen it, or shown it to effect, but its easier to take into account before you build and pick a frequency that doesn't clash ( particularly with high level DCC 50HZ pulses.. The 555's are free-running with components picked to give the nominal 70HZ and nothing to adjust.

 

The servo operator I designed, along with the kit of 0.060 inch plasticard bits all cut from a small square sheet, 10cms x 9cms. Takes me about 20 minutes to mark them out, cut and assemble to the stage you can see here. The spare bits of plasticard are cut up into small right angle triangles for a bit of extra support between the pieces. There are a coupe of fixing holes to be drilled , which I do in bulk after I've made a few. The electrical switches ( 2x changeover contacts) are just visible. Sometimes they are the low current ones here , but I prefer to use V4 types if I can get them through surplus outfits at the right price. The servo , although looking black in this shot is actually dark blue and I use the cheap SG90's.

 

PICT0733.jpg

Link to post
Share on other sites

  • RMweb Premium

Hi Paul,

 

Just checking on the MERG web site and it would seem that the Servo4 is still out of stock but it would seem that a revision/Updated design is underway.

 

Since, as you say, you use the Servo4 on your layout have you noticed the problem of Servo chatter as mentioned by Gordon A and Bertiedog? I'm just curious to know if the problem is reduced or even overcome by use of the Pic solution.

Thanks

Dan

 

Hi

 

No problem at all with the SWD (http://www.southwestdigital.co.uk/)(look under point control) servo kits I used.

 

I have also tried servos by TowerPro SG90 and Hitec HS322. Neither of these showed any twitching either.

 

Yes the Servo4 is being redesigned but there is nothing to stop you building your own PCB from the link I posted which also includes the firmware for the PIC.

 

Cheers

 

Paul

Link to post
Share on other sites

The trigger pulse is still an item I am unsure of. Almost all the information I have attained point at using a trigger pulse at 50hz with a pulse width of various durations.

That is correct.

 

One site that I looked at stated that I would need to keep the pulse width at less than 5% duty cycle because, Quote "The monostable 555 (the right hand 555 circuit) will not reset if the trigger is held high"

That's sounds like a limitation of that particular circuit, or a typo.

 

The maximum pulse width for a servo is around 2ms which is a 10% duty cycle.

 

When there are so many sources giving the correct information, compared to one dubious source, I know which I would trust:-)

 

Rob Paisley's site is good for MR electronics ideas. See http://home.cogeco.ca/~rpaisley4/xServoTest555.html for a (three position) servo controller generating 1-2ms pulses at 49Hz, but no control over servo speed.

 

Andrew Crosland

Link to post
Share on other sites

Thanks for all the info guys.

 

Baldrick - The method that you use for control is a little different to how I envisage my method. Putting aside the master 70hz oscillator, it would seem that you are using one 555 timer circuit, albeit within a 556 package, to drive each individual servo and that various resistor networks are switched into circuit for the required servo movement which have been preadjusted by the use of trimpots. Clearly you are using a much greater number of timer circuits then my idea of just using two 555 circuits to output either, say, a 0.6mses pulse or a 2.4 msec pulse and for these two output pulses to then be switched to each servo through SPDT switches. Is there a reason why you don't do it this way? Currently this method makes sense to me but is only theoretical at this stage, it may not work for reasons that I haven't thought of, or come across yet.

 

 

Paul - Thank you for the link to SWD, the assembly for fixing the servo and associated micoswitches is very interesting, once built it resembles the tortoise in the operation of the actual point switching but perhaps its construction is not as deep. Am I right in thinking that this type of assembly has to be mounted directly below the tiebar? As I said, the assembly is very interesting just a shame about the price, although it should be possible to construct something similar.

 

I have downloaded the info from MERG and think I am able to follow the info but the problem that I would have in realizing this method would be with flashing (is that what they call it?) the Pic and I'm not too sure I want to go down that track at this moment but thanks for the info.

 

 

Andrew - Thank you for the link to Rob Paisley "Model Railroad &Misc. Electronics" Web page. There's a lot of interesting circuits there, its surprising where the time goes when you start to read about the different circuits. Excellent stuff though, thanks.

 

Best regards

Dan

Link to post
Share on other sites

  • RMweb Premium

 

Paul - Thank you for the link to SWD, the assembly for fixing the servo and associated micoswitches is very interesting, once built it resembles the tortoise in the operation of the actual point switching but perhaps its construction is not as deep. Am I right in thinking that this type of assembly has to be mounted directly below the tiebar? As I said, the assembly is very interesting just a shame about the price, although it should be possible to construct something similar.

 

I have downloaded the info from MERG and think I am able to follow the info but the problem that I would have in realizing this method would be with flashing (is that what they call it?) the Pic and I'm not too sure I want to go down that track at this moment but thanks for the info.

 

 

Best regards

Dan

 

Hi

 

The swd point motor is about 60mm deep and I have mounted mine directly under the tie bar but I guess like the tortoise you could mount it remotely.

 

Yes you would need to be able to program pics to use the MERG design but if you decide to go down that route I have the necessary equipment so could do that for you.

 

Cheers

 

Paul

Link to post
Share on other sites

Yes you would need to be able to program pics to use the MERG design but if you decide to go down that route I have the necessary equipment so could do that for you.

 

Cheers

 

Paul

 

Hi Paul,

 

I was dumbstruck when I first read your post, that's a very generous offer, thank you. If I decide to go down the MERG/PIC route I may well take you up on your offer.

 

Once again thank you very much.

 

Dan

Link to post
Share on other sites

Add on the joining fee of MERG of £18 per year, every year or more, and the equation looks a bit different now.

You seem to trot out the MERG solution as though its something superior at every mention of a timer based solution, which in my experience, is far better, and more understandable by the modeller than a digital solution will ever be.

How would you adjust a servo at the far end of an 18 foot layout, whilst its working?. I just use a small screwdriver and can see immediately what the result is.

If the MERG solution was so great, why did not a single exhibition layout at the Leamington model railway Ex last weekend not use it.

You would be very hard pushed to find one at Warley either. I only found one last November and that wasn't the MERG design, but a commercial item called 'bouncer', just operating a signal or two.

For DIY the timer based solution is far far superior anyday.

I merely used the MERG solution as an example of a microcontroller based servo driver that I am aware of which could do the job.

I would adjust a servo 18 feet away by taking my manual 'Setting Box' or PC to it and set it up as required. And be able to see what effect I was having immediately whilst doing so because I don't have to be under the baseboard to make the adjustment at the same time as trying to look at it.

Glad you mentioned the 'Bouncer'. I was asked by one of the crew running that layout at Warley if he could use the MERG setting up box or PC to adjust his because he was having trouble with the one that came with it. At the time the answer was 'No'. However, as a result of that episode, we now have some replacement code for the Bouncer that allows it to be set up using these MERG facilities.

Flexibility is the name of the game with this kind of solution. Stick with 555s and their like and you will soon find you are limited to very simple operation only.

I would still be interested to know how a bounce effect could be achieved simply using a 555...

Link to post
Share on other sites

I merely used the MERG solution as an example of a microcontroller based servo driver that I am aware of which could do the job.

I would adjust a servo 18 feet away by taking my manual 'Setting Box' or PC to it and set it up as required. And be able to see what effect I was having immediately whilst doing so because I don't have to be under the baseboard to make the adjustment at the same time as trying to look at it.

Glad you mentioned the 'Bouncer'. I was asked by one of the crew running that layout at Warley if he could use the MERG setting up box or PC to adjust his because he was having trouble with the one that came with it. At the time the answer was 'No'. However, as a result of that episode, we now have some replacement code for the Bouncer that allows it to be set up using these MERG facilities.

Flexibility is the name of the game with this kind of solution. Stick with 555s and their like and you will soon find you are limited to very simple operation only.

I would still be interested to know how a bounce effect could be achieved simply using a 555...

 

Have a look here tam valley depot No bounce (except on the 3 position ones) but no computer or setting box either from the look of them. Not tried them myself yet but for those interested you appear to be able choose whether to use DCC or non-DCC to operate.

Link to post
Share on other sites

  • 2 weeks later...
Guest baldrick25

Gordon H said

I merely used the MERG solution as an example of a microcontroller based servo driver that I am aware of which could do the job.

 

Perhaps Gordon H could state publicly his vested interest in the "MERG solution", which so far he has discreetly sidestepped. Perhaps others reading this thread and considering his written appraisal of the product, will then be able to assess why he constatntly plugs MERG and its products, in particular the servo driver.

Link to post
Share on other sites

  • RMweb Premium

Gordon H said

 

 

Perhaps Gordon H could state publicly his vested interest in the "MERG solution", which so far he has discreetly sidestepped. Perhaps others reading this thread and considering his written appraisal of the product, will then be able to assess why he constatntly plugs MERG and its products, in particular the servo driver.

 

Hi

 

As I have already pointed out in this thread the details of this are freely available on the MERG website and so anyone can build it without being a MERG member. I don't see the problem.

 

Cheers

 

Paul

Link to post
Share on other sites

Gordon H said

 

 

Perhaps Gordon H could state publicly his vested interest in the "MERG solution", which so far he has discreetly sidestepped. Perhaps others reading this thread and considering his written appraisal of the product, will then be able to assess why he constatntly plugs MERG and its products, in particular the servo driver.

He is not the designer if that is what you are hinting at. That would be Mike Bolton (I'm 99% sure of that) who has generously made all of his DCC and other stuff freely available on the *public* pages of the MERG website.

 

No one has "vested interests" in MERG, other than promoting a society for the good of all it's members. No one gains individually (other than the Kudos of being identified as the designer of a kit, or giving freely to help others, certainly not financially) if that is what you are trying to hint at.

 

Perhaps you, "baldrick25", can explain exactly what issue you have with MERG? You have already accused us of only being in it for the money, in a previous thread about servo control, which is so far from the truth as to be laughable. A number of people put in a lot of their own time and resources to design, develop and support the sales of MERG kits to members.

 

There are very good practical and legal reasons why MERG kits are only sold to members. Like many other society an annual fee is payable for membership. Like many other society's an extra one off joining fee is also payable. If all you want is access to the MERG kits at prices little above the component costs, without putting something back, then MERG is obviously not for you. MERG does not deserve the criticism it gets from you.

 

Stop hiding behind an avatar and allow people a chance to address your issues. Even if you are beyond satisfaction it may allow things to be done better in the future.

 

Andrew Crosland

Link to post
Share on other sites

Guest baldrick25

I don't need to hide behind avatars and don't have an issue with MERG, unless you want to invent one . I do have an issue with the constant grinding of the organ barrel by MERG 'members' that MERG is the best solution to anything electronic, particularly when in the case of servos , may be the best technically but is entirely impractical for almost all of the modellers of this forum.

Its time you came clean with just what is required , and the costs involved , and stop griping that a 20P timer, pot, and screwdriver is not the best solution for what is basically modellers who express difficulty in soldering.

If the MERG solution was so good why did no layout at Leamington Modellex a few weeks back, as did not a single layout to my knowledge at Stafford Modellex use it. The only one who had a similar set-up. the 'Bouncer' had problems which were unsolvable on the day at an exhibition.

Many on this forum know exactly who I am, so what if I choose to use an avatar , which is normal practice on an online forum. Maybe MERG has a better solution to that as well.

Knowing what I do know, again, I ask - "Perhaps Gordon H could state publicly his vested interest in the "MERG solution".

 

I will publicly state I have no interest in ANY timer based solution , or processor based solution , except as a lifelong electronics engineer with some standing and as a hobbyist model railway-er, helping to pass the knowledge onto others for their own benefit.

Link to post
Share on other sites

Oh dear, guys. Getting a bit heated here! Calm down, all that most of us want is a solution that works, preferably one that doesn't need to be built, tested and require a membership to buy. As I pointed out on the other topic regarding use for signals (much more required as we have a number of solutions for points) the best unit, so far IMHO was the Embedded Controls system, followed by the only one really available just now which is the Heathcote boards. But these are not a patch on the Emmbedded Controls units. This is not a gripe at MERGS methods and I have seen examples of their boards and very good they are, but the majority of us shy away from building the things! Give us them ready made and I might join!

Link to post
Share on other sites

Perhaps Gordon H could state publicly his vested interest in the "MERG solution", which so far he has discreetly sidestepped.

 

 

Taking an outside perspective I can appreciate the beneficial side of MERG but I can also advise that there should be clarity on promotion of particular products (a society recommending its own products is a vested interest even if not directly remunerative).

 

Stop hiding behind an avatar and allow people a chance to address your issues. Even if you are beyond satisfaction it may allow things to be done better in the future.

 

Being combative and hostile won't resolve the issue and I think ScRSG's pragmatic view is good that both side shouldn't escalate the issue.

 

 

 

 

 

 

Link to post
Share on other sites

I don't need to hide behind avatars and don't have an issue with MERG, unless you want to invent one . I do have an issue with the constant grinding of the organ barrel by MERG 'members' that MERG is the best solution to anything electronic, particularly when in the case of servos , may be the best technically but is entirely impractical for almost all of the modellers of this forum.

Perhaps some of us are willing to give users of this forum a bit more credit as to their potential?

Its time you came clean with just what is required , and the costs involved , and stop griping that a 20P timer, pot, and screwdriver is not the best solution for what is basically modellers who express difficulty in soldering.

No griping involved. Just a contrary view to yours, backed up by several others in this thread.

Incidentally, if you look back up the thread, you will find my first contribution was an explanation of servo operation in response to the OP's misconceptions. The next contributor was the first to mention MERG.

If the MERG solution was so good why did no layout at Leamington Modellex a few weeks back, as did not a single layout to my knowledge at Stafford Modellex use it. The only one who had a similar set-up. the 'Bouncer' had problems which were unsolvable on the day at an exhibition.

How many of these layouts had servo controlled signals at all? Do you really go round and ask at every show you attend?

Knowing what I do know, again, I ask - "Perhaps Gordon H could state publicly his vested interest in the "MERG solution".

"None whatsoever".

As Andrew correctly pointed out, the Servo4 is a Mike Bolton design, nothing to do with me other than as a fellow member of the group.

However, I am able to appreciate what benefits such a methodology brings, so would actively promote microcontroller based solutions over analogue ones, regardless of source. Not because it benefits MERG, but because as an engineering solution it is a more predictable, more repeatable, more definable, more flexible solution to servo pulse generation. Funnily enough, the last MERG kit I did have a hand in producing - nothing to do with servos - DID use 555 timers, because they were appropriate to the task on that occasion.

I will publicly state I have no interest in ANY timer based solution , or processor based solution , except as a lifelong electronics engineer with some standing and as a hobbyist model railway-er, helping to pass the knowledge onto others for their own benefit.

Ditto.

 

Having looked back at the history of this thread, I was further intrigued to find this quote in Reply #35: "particularly with high level DCC 50HZ pulses".

What do 50Hz pulses have to do with DCC? Only when speaking of the UK version of Zero-1 as far as I'm aware.

Still, that's a separate subject.

 

With regard to Andy Y's comment about the interpretation of vested interests, does this mean that membership of any society, specialist or otherwise in this field, automatically prevents a person from making mention of their membership for fear of promoting something simply because they try to help a 'non-member' out with some information gained due to that specialist knowledge? I would guess (again) that a sizeable proportion of RMWebbers are a member of some society or other, so I really can't see how that approach would help anyone. Blatant plugging of a product for financial gain is obviously undesirable, but there must be scope for discussion, if only to raise peoples general awareness of what options are out there.

Link to post
Share on other sites

Dan

 

I think that since cost is clearly an issue for you a microcontroller based solution is the best idea. A 20-pin PIC like a 16F690 or similar will be able to smoothly operate eight or more servos from one chip and will only cost a couple of pounds. If you cannot afford the MERG solution (I am not promoting MERG here, it is just a freely downloadable project from a website and as far as I am aware the only freely published microcontroller based one to do this task) you will really have to homebrew your own solution. Any analogue 555 based solution is going to be far more complex and much more expensive.

 

What you are trying to do is an excellent starter project and should not be beyond the capabilities of any beginner to microcontroller projects. Here is a basic circuit diagram of all that you need:-

 

post-7495-0-32850400-1297295687_thumb.gif

 

I have only shown one servo but the other seven are connected to the PIC just the same. I have always favoured simply moving the servo from one end to the other and adjusting the linkage mechanicaly to get the throw right, and that method will keep the software simple.

 

The only tool that you will need that you will not already have is a PIC programmer, and they are not expensive.

 

The switches are all SPST, but you can just use one pole from a DPDT switch if you are using that to switch your frog polarity.

 

There is no need to be frightened of microcontrollers. It is a lot easier and cheaper to build a project based on a microcontroller than it is to use analogue electronics. It should be reasonably simple to get 250 steps between one end and the other for smooth movement, but 2000 steps is achievable - far better than any servo can track.

Link to post
Share on other sites

Archived

This topic is now archived and is closed to further replies.


×
×
  • Create New...