Bath Queen Square

[Compound2632]

Stepper motor? I don't know how reproducible the positioning would be - probably proportional to price. 

[Dunsignalling]

39 minutes ago, Compound2632 said:

Stepper motor? I don't know how reproducible the positioning would be - probably proportional to price. 

A group I was then active with purchased a stepper system from the USA about 20 years ago.

 

Horribly expensive, almost scarily powerful and consistently accurate until it lost its programming due to receiving no power for an extended period, requiring a fresh set-up routine. Seemed like a good idea at the time!

 

It eventually died and was replaced with a home-brewed set-up (at a fraction of the cost) that multiple members understand and can "deal with" if it malfunctions.

 

John

[Izzy]

Getting the micro switches to reliably work in precisely the same spot each time will most probably be the key, the lag/wind-up pressure sometimes present in large multiple gear stage drives. The problem I’ve encountered being the pressure relaxes when power is removed and the drive unwinds a bit so indexing moves. Do I take it the wheels don’t actually revolve/run on the rail but just the skids? 
 

Bob

[queensquare]

33 minutes ago, Izzy said:

Getting the micro switches to reliably work in precisely the same spot each time will most probably be the key, the lag/wind-up pressure sometimes present in large multiple gear stage drives. The problem I’ve encountered being the pressure relaxes when power is removed and the drive unwinds a bit so indexing moves. Do I take it the wheels don’t actually revolve/run on the rail but just the skids? 
 

Bob

 

You are absolutely right Bob. Getting the table to stop in the same place each time I dont think will be a big problem, there doesnt seem to be any slack or over-run at all with the motor/gearbox. The tricky bit will be to get the notches for the microswitch rollers to drop into perfectly opposite each other. Ive cut out two pcb discs in anticipation of not getting it right first time!

 

No, the wheels are simply discs soldered solidly to the brackets that sit a few thou above the rail - they dont even go round but should look the part in the shadow under the table. The table is supported on the skids which keep it square and level as well as acting as pickups.

 

jerry

[queensquare]

1 hour ago, Compound2632 said:

Stepper motor? I don't know how reproducible the positioning would be - probably proportional to price. 

 

Hi Stephen, I think some of the top end commercial tables available use this technology but its way above this bear of little brain I'm afraid. I'm much more at home with home-brewed electro-mechanical - I can fiddle with it until it works and usualy fix it when it doesnt! 

 

Jerry

[DavidLong]

Excellent work, as usual, Jerry. All in all though an excellent argument for modelling diesels! Although I believe in the early days of EE Type 1s use was sometimes made of still-extant turntables to get the cabs to face front.

 

I thought that John Greenwood may get a mention. 'Bodmine' had one at the station but the real 'tour de force' was the train table in the fiddle yard which could be operated, several feet away, from the station. The noise that it generated confirmed that it was working!

 

David

[Izzy]

1 hour ago, queensquare said:

. The tricky bit will be to get the notches for the microswitch rollers to drop into perfectly opposite each other. Ive cut out two pcb discs in anticipation of not getting it right first time!

I hope you will forgive me Jerry, I like challenges like this, but would the answer be twofold. Mount the switches on sub-bases for adjustment. And just use one notch. Designate a ‘lead’ end of the turntable and then you could adjust each microswitch to drop-in separately at the correct position. I just can’t work out, being my usual dim self, how you’d wire the two anyway, so one didn’t override the other.

 

Bob

[queensquare]

8 minutes ago, Izzy said:

I hope you will forgive me Jerry, I like challenges like this, but would the answer be twofold. Mount the switches on sub-bases for adjustment. And just use one notch. Designate a ‘lead’ end of the turntable and then you could adjust each microswitch to drop-in separately at the correct position. I just can’t work out, being my usual dim self, how you’d wire the two anyway, so one didn’t override the other.

 

Bob

 

Great minds and all that.... Ive been thinking about one notch, two switches but, like you havent come up with how to overide one switch.

 

A notched, indexing disc can definately be made to work in 2mm.....

 

Jerry

 

[queensquare]

1 hour ago, DavidLong said:

Excellent work, as usual, Jerry. All in all though an excellent argument for modelling diesels! Although I believe in the early days of EE Type 1s use was sometimes made of still-extant turntables to get the cabs to face front.

 

I thought that John Greenwood may get a mention. 'Bodmine' had one at the station but the real 'tour de force' was the train table in the fiddle yard which could be operated, several feet away, from the station. The noise that it generated confirmed that it was working!

 

David

 

Denys Brownlee's Burnham also had an automatic train table when I first took it on. It had a mains powered moter which I quicly removed!

 

Jerry

[ShadowinLinby]

Jerry - it might be worth having a chat with Laurie as he's sorted the same problem on his train table

 

ChrisB

[Chuffer Davies]

1 hour ago, queensquare said:

 

Great minds and all that.... Ive been thinking about one notch, two switches but, like you havent come up with how to overide one switch.

 

A notched, indexing disc can definately be made to work in 2mm.....

 

Jerry

 

Hi Jerry,  I’ve not posted here before so may I start by saying how much I enjoy your topic on RM Web and how much I appreciate your 2mm finescale modelling.  
Now then I think a simple latching relay circuit and two micro switches will meet your needs.  If you are interested I’d be more than happy to draw up a circuit for you. 
Frank

[queensquare]

1 hour ago, ShadowinLinby said:

Jerry - it might be worth having a chat with Laurie as he's sorted the same problem on his train table

 

ChrisB

 

Thanks Chris, I dont have any problems with my train table - its fully digital - either left or right! 😀

 

Jerry

 

 

[queensquare]

1 minute ago, Chuffer Davies said:

Hi Jerry,  I’ve not posted here before so may I start by saying how much I enjoy your topic on RM Web and how much I appreciate your 2mm finescale modelling.  
Now then I think a simple latching relay circuit and two micro switches will meet your needs.  If you are interested I’d be more than happy to draw up a circuit for you. 
Frank

 

I'd be very grateful of any input though you do understand that you would have to talk very slowly and do it in crayon as my understanding of things electrical is minimal.

Seriously, if its simple enough for me to follow I'd be interested. I'm going to have a go at one switch, two notches but if that fails then one notch two switches is another option - more complex wiring but should be easier to set up mechanically. What I like about the former is its simple, just a push button to momentarily over ride the microswitch. Im afraid I dont know what a latching relay is.

 

Jerry

[Chuffer Davies]

15 minutes ago, queensquare said:

 

I'd be very grateful of any input though you do understand that you would have to talk very slowly and do it in crayon as my understanding of things electrical is minimal.

Seriously, if its simple enough for me to follow I'd be interested. I'm going to have a go at one switch, two notches but if that fails then one notch two switches is another option - more complex wiring but should be easier to set up mechanically. What I like about the former is its simple, just a push button to momentarily over ride the microswitch. Im afraid I dont know what a latching relay is.

 

Jerry

Hi again,

happy to draw up a circuit.  Not sure about using crayons on the computer screen but I can try.  Also not  sure how talking works on RM Web slow or otherwise.  
I’ll wind up the lap top and draw a picture for you.  Back later.

Frank

[ShadowinLinby]

I was referring to how he gets his tracks to line up and whether that solution would work for your turn table

 

ChrisB

[Argos]

Hi Jerry,

 

I'm watching with interest as I've a set of Jim's turntable etches soldered up and ready for building into the board.

Embarrassingly from your photos I've noticed I've bent some of the tabs the wrong way , so you've already been a great help!

Also I missed the blindingly obvious of using brass blocks as skids rather then trying to create accurate working wheels.

 

By chance I've bought the same motor to power the table.

 

I'm not entirely convinced that indexing is worth the effort, particularly if the motor speed is slow enough. 

But then I've been wrong many times before!

[queensquare]

4 minutes ago, ShadowinLinby said:

I was referring to how he gets his tracks to line up and whether that solution would work for your turn table

 

ChrisB

 

Ah, sorry, with you now Chris.

 

Jerry

[queensquare]

3 minutes ago, Argos said:

Hi Jerry,

 

I'm watching with interest as I've a set of Jim's turntable etches soldered up and ready for building into the board.

Embarrassingly from your photos I've noticed I've bent some of the tabs the wrong way , so you've already been a great help!

Also I missed the blindingly obvious of using brass blocks as skids rather then trying to create accurate working wheels.

 

By chance I've bought the same motor to power the table.

 

I'm not entirely convinced that indexing is worth the effort, particularly if the motor speed is slow enough. 

But then I've been wrong many times before!

 

Ive only used the girders from Jim's etch as mine is an unprototypical hybrid - essentially a 50' table trying to look like a 42'one.

 

If my table was at the front of the board I might not have bothered with indexing either although I do like the idea of just pressing a button and the loco turns and stops.

 

As for being wrong many times - you and me both! 😀

 

Jerry

[Chuffer Davies]

Now that I have studied the problem in more detail I realise that the circuit is far simpler than I first thought and there is no need to use a latching relay to control the operation of the turntable.  It would seem easier to use two micro switches and a single notch in the PCB rather than trying to get two notches exactly positioned so that a single micro switch can be used.  Either way the the following circuit works for both options.  

 

With reference to the diagram the circuit could work as follows:

The micro switch/es are wired so that they remain closed when the turntable is revolving but will open when a switch drops into the notch in the PCB disc.  The diagram represents the situation when micro switch 1 (MS1) has dropped into the notch and MS2 is still resting on the circumference of the PCB.  If only one micro switch is used then MS2 is omitted.

Pressing push button 1 (PB1) temporarily provides power to the motor allowing the turntable to commence turning.  This will release MS1 from the notch closing the switch at which point power is supplied to the motor via MS1 and MS2 and the push button can be released.  When the notch aligns with MS2 this switch will open interrupting power to the motor. 

Pressing PB1 will again start the table turning, MS2 will close and power is once more provided to the motor via MS1 and MS2.  This time MS1 will drop into the notch interrupting the feed to the motor.

 

Sorry about the lack of crayon, I typed this with one finger so hopefully I didn’t go too fast for you.  I look forward to seeing further pictures as the turntable progresses.

Hope this helps.

Frank       

[queensquare]

2 hours ago, Chuffer Davies said:

Now that I have studied the problem in more detail I realise that the circuit is far simpler than I first thought and there is no need to use a latching relay to control the operation of the turntable.  It would seem easier to use two micro switches and a single notch in the PCB rather than trying to get two notches exactly positioned so that a single micro switch can be used.  Either way the the following circuit works for both options.  

 

With reference to the diagram the circuit could work as follows:

The micro switch/es are wired so that they remain closed when the turntable is revolving but will open when a switch drops into the notch in the PCB disc.  The diagram represents the situation when micro switch 1 (MS1) has dropped into the notch and MS2 is still resting on the circumference of the PCB.  If only one micro switch is used then MS2 is omitted.

Pressing push button 1 (PB1) temporarily provides power to the motor allowing the turntable to commence turning.  This will release MS1 from the notch closing the switch at which point power is supplied to the motor via MS1 and MS2 and the push button can be released.  When the notch aligns with MS2 this switch will open interrupting power to the motor. 

Pressing PB1 will again start the table turning, MS2 will close and power is once more provided to the motor via MS1 and MS2.  This time MS1 will drop into the notch interrupting the feed to the motor.

 

Sorry about the lack of crayon, I typed this with one finger so hopefully I didn’t go too fast for you.  I look forward to seeing further pictures as the turntable progresses.

Hope this helps.

Frank       

This is fantastic Frank, very many thanks. It is simple, elegant and easily understood by an electrical duffer like me. It is definitely the inter web version of talking slowly and using crayons😊
 

Jerry

[queensquare]

Last night I connected the motor to the table using a collar kindly turned for me by a friend - I have a big enough lathe but didnt have a suitable lump of brass!

The idea is that the pcb indexing disc will be bolted to the flange on the collar then trued up so that it is perfectly concentric with the shaft which should give me a fighting chance.

I was a little concerned when I connected the motor up to my 5v wall wart (ex phone charger I think) and found that there was an enormous over run when the power was switched off - bad news for accurate, consistent allignment but when I connected it to an old Gaugemaster controller all was fine - I presume its something to do with the fact I was using an old charger. The table turns nicely and lines up both ways such that I can roll a light wagon across the table by gravity without incidend.

 

Next job is to mount the indexing disc, microswitches and fettle - easy to type! 😀

 

Jerry

 

 

 

[CF MRC]

And there was me thinking you had finally used my old ML10…

 

Tim

[queensquare]

2 hours ago, CF MRC said:

And there was me thinking you had finally used my old ML10…

 

Tim

Just back up from the shed having used the Myford to true up the indexing disc now it’s mounted on the collar - still as sweet as ever Tim!

 

Pictures to follow, but probably not tonight.

 

Jerry

[queensquare]

Well I got a lot further than I expected this evening and the turntable is now working really rather nicely. The short lengths of track either side are temporary and also took a bit of stick whilst I had the deck upside down to fit the mechanism and do the wiring but the table lined up with them well, turning 180 at the push of a button.

Power is provided by 3 x AA batteries in the black box taped to the bridge. Whether this is permanent or not I don’t know but it’s certainly convenient whilst testing. Chuffer’s circuit proved simple to install and works perfectly - thanks again.

Next job is to replace the temporary bits of track with some short, permanent stubs then it’s fine tuning and the rest of the cosmetic stuff on the deck.

Feeling rather chuffed, hence a beer.

 

Jerry

 

[queensquare]

…. and here it is. Probably not the most gripping film you’ll watch this weekend but I’m rather pleased!

 

Jerry