Peco Turntable (4mm)

[Ceptic]

In view of the comments by Beeman above I thought I would post the following video even though the installation is not complete. I don't think despair is quite required as you can see from the video that the standard Peco turntable with no added bearings and driven by the Expo motor mounted via its gearbox directly onto the spindle gives a quiet, slow turn which easily allows the exit tracks to be lined up. Also the wheels do turn as the turntable actually runs on them. As for backlash I don't think I can detect any or if its there its not a problem.

If it works why make it complicated.

Note that sound was recorded - if you listen carefully about halfway through you can here the click as the electrical contacts under the deck switch over.

 

http://www.youtube.com/watch?v=T967RCaO_Ng

 

Ceptic - I think the depth of your well is the same as mine. Look at the wheel height in relation to the top of the well. There are 3 drains on mine.

 

Cheers

 

Keith

 

 

That is one smooth operator, Keith .

Re: The depth. I see what you mean. It must be a trick of the light, or my eyes, more likely.

My t/t is 23 mm..deep by the way.

 

Thanks again, Frank.

[beeman]

I apologise if some words I used were not appreciated by some members. However some seem to think that a kit is easily 'built' to produce an operating turntable. I was not familiar with the Peco until having a look a short while ago. I viewed the article on Motorising the Peco T/T on the Heywood Model Railway Group site. This is an informative article and the writer addressed some of my concerns about shortcomings I highlighted, and well worth a read. The Peco unit does appear to have a lot going for it, but imagine if the worm gear could be a similar diameter to the well, how that would reduce the backlash at the table track ends as highlighted in the HMRG item', any play being multiplied by the distance from the central spindle, I still maintain that some play at the track ends is inevitable with this drive, especially if reversing it.I would agree if the T/T end wheels are used then vertical track alignment could be addressed. If you want reliable automatic operation, as I did, being Retd Elec/Mech eng., latterly with high speed automatic packaging machinery, then virtually zero backlash was the aim. Many years back, like 'melmerby' idea,I played around with mechanical positioning, today its much easier to use an opto switch, locating notches cut into an under table disc have to be very accurate, particularly having a few of them, its simpler to bend a target wire for the opto switch. There are also those who perhaps do not have the engineering abilities to be able to produce this kind of item albeit their desires are there, same reasons most clubs have a Sparky for the electrics. My posts on T/T's, using experience/mistakes from past years were to help steam era modellers to succeed with theirs. Beeman

[kipford]

Beeman

You are correct using the expo style drives you inevitably end up with backlash and some movement at the outer radius, you cannot beat physics, a couple of thou movement at the pivot becomes quite large at the outer edge of the table, especially on a large table like this. You can drive around it and with experience learn how to position the table accurately, but occasionally you will find the table moves (at the wrong time normally) losing its alignment. I used 2 or 2 of these drives on a Peco turntable for about 5 years before getting fed up with them failing, with extensive exhibition use they just break up! I eventually put in an industrial 24 v portescap with a machined gearbox in (driving on the 12v supply), That solved the relaibilty issues and virtually all the backlash, but it still had some. When I do another one I will use your method. Clubmember Richard Butlers Westcliffe uses the same system and it is the dogs B$£$$%^ no backlash!

 

One point to note, make sure you can remove the table from the well, because the springs that load the track feed plungers sometimes slacken off losing the plunger contact with the rail, so they have to be adjusted!

 

Regards

 

Dave

[ozthedog]

Beeman

 

 

Your words were not unappreciated. All valid comments are worth considering. Indeed I fully accept the limitations of the Peco turntable. It is self evident that a primitive bearing made of plastic could be improved. I just thought your negativity could discourage others from using this kit as it produces a reasonable looking functional turntable for the average modeller who will not give it heavy use. For me it is an interim stopgap that is likely to be replaced at some time in the future.

 

Having got that out of the way I would appreciate it if you could use your experience to answer a question re turntable automation for those of us not qualified in electronics. Would a stepper motor provide a satisfactory turntable drive? It appears that they rotate in 180 steps per full turn so one could calculate the degree of turn rquired in 2 degree increments to locate the turntable exits. From research on the internet it looks as though this could be possible. The difficulty for someone like myself with no electronics training the problem appears to be with the controller for the motor which would require a sotware driven solution. How could one deal with this?

 

Any thoughts?

 

Thanks

 

Keith

[beeman]

Further to some of the replies can I suggest that interested members have a look at my post 'table a la carte' http://www.rmweb.co.uk/community/index.php/topic/10116-table-a-la-carte/page__view__findpost__p__88907__fromsearch__1 . There are on the net posts,mainly USA., showing stepper driven circuits which are somewhat involved, must admit I am not that electronically orientated. However as you can see if perusing my post, it is a relatively simple circuit, an advantage of it 'slowing' via the motor series resistor when one of the two opposing main targets contacts the position micro switch. The accuracy is created by the opto switch, this is operated by a paper clip wire, one for each position. Tweaking these can be a little finicky to get correct, better if you have an assistant, someone above the baseboard and an 'adjuster' below. saves getting up and down. I have recently altered the 16 Relay circuit on my vertically operating fiddle yard/ storage unit to a slight variation of this circuit with satisfactory results, this again needs to stop accurately vertically, for the tracks to line up. Another advantage for the T/T is it runs off a mobile phone 'wall wart' charger at about 4.5 volts, ok for motor, relay and opto switch. One idea I toyed with was an old record player turntable on the underside . Some of the better 'transcription deck' units I recollect were advertised as having belt drives which sound like they could be the better bet. Visit sale rooms or S/H/charity shops possibly required. If I were doing it again this is the route I would take. As I suggested previously the T/T itself should only be the 'Cloak ' for the actual mechanism, again choosing which model may depend on the 'look' accuracy one wants.The Dapol certainly the cheapest. Another point I suggested was to make the unit so it could be fitted from the underside of your baseboard, easy removal if probs occur. I have just had to replace the slipring due to occasional shorting ,this is made from a piece of laminate board then the copper cut in the appropriate places by 4 cuts to give a dead spot allowing the polarity change without shorting. I hope I have not 'put off' any enthusiast from building a T/T by highlighting limitations, such that their efforts do not end in disappointment. If you are contemplating a T/T look at the Heywood Model Railway Group site, I found this a very useful place for info about the hobby we share.and well worth a look for useful ideas. Beeman

quick addendum here for ozthedog, if you particularly wanted to follow the stepper motor route, Poundstretcher sell a kitchen grinder which has a toothed belt drive with the larger pulley about 60 mm or so for £9.99, could be of use.One suggestion would be to invert the belt, and glue it on to the O/D of a wooden disc to make a large'Gear',The stepper motor would need a gearbox between it and the 'gear' to reduce the speed,with the appropriate output shaft pinion to mesh with this to create a drive. Mounted on a 'spring hinge' unit so it is kept in mesh as any tooth jump/slip would make the step settings useless.

[beeman]

Further to using stepper motors for a T/T drive, I foresee this would need involved electronics. The reason for this depending on the number of tracks to/from the T/T. , also infinitely changing positions as to start/finish,. In my case I have 6 actual tracks to the T/T. this means a total of 12 for the dead ends. The table can be either way around at any of the positions,so which direction should it rotate. If you were the loco driver/fireman the nearest/easiest way to get your loco where you wanted to go. Stepper motors/electronics would be too involved for my liking. You would still need a selector switch to choose your path, Far simpler to use a circuit like I concocted, you operate it as it would be in actuality, with the two switches, choosing the position,, and selecting rotation, and simpler if probs occur. Another issue with stepper motors would be that you control the rotation from the motor, so a toothed belt drive , like a PC. printer, would be a 'must', so no slip between motor and T/T. I used the belt from a broken up Pc printer and the stepper motor drive toothed gear fitted to the VCR cassette loading drive. I decided on this for accuracy in positional stopping, but on reflection, this could have been a flat belt as the actual 'command' to stop, the paperclip wire in the opto switch, one for each position, is on the pulley/disc, so 'fixed' to the T/T deck, so any slip would not matter. For a belt, the large elastic bands from model shops for keeping aircraft wings in place may be OK. Stepper motor end plates have super plain bearings fitted and could make good central shaft T/T bearings, usually having 4 holes if the square type motor, easily screwed to either face of the T/T base. This has to be dead square with the shaft, also necessary to obtain a longer shaft of the correct size,i.e. ground silver steel, to give an accurate fit. Motor shafts/ vcr/pc printer components have excellent surface finish these days. A few suggestions/ideas for thought, hope they may help, Beeman.

[beeman]

I have attempted to put a video of my T/T in demo action to show its stopping accuracy. I commented previously it was a bit fiddly to set up, so I've just altered the stopping target wires to be more practical , making adjustment easier. I found also the paper clip wire was a little undersized for the opto switch, not giving the same accuracy depending on travel direction. This was perhaps only by 0.5 mm or so but sufficient to derail in some positions, and dependant on the track end champher. I found a wire of 1.5mm seems to be better suited to the switching differential of the opto switch than the thinner paper clip I used previously. Shows always room for improvement..... . Included is an attachment to show the simple mod. This allows the target wire, soldered to the arm, to be radially adjusted without having to slacken the holding screw. I needed 12 of these 'arms', one to each track position. The loco is a Bachman K3,chipped and has DIY tender pickups fitted for reliable running. The vid was a continuous shot with no break in recording or editing.

The 'clicking' heard is the operation of the position selector switch and direction switch. a comparison with the sound from the T/T drive can be audibly made. The footprint for the Sandhouse can be seen at about 7 o clock, removed for video. Other info on this was posted previously here. My link Here is a most usefull link I found some time back about T/T construction.My link It suggests, if building a T/T,and comparing to mine, to obtain a good working unit similar ideas should be used. Also that the Teeton one was first posted in 98. Hope this post is of benefit. Beeman.

[Butler Henderson]

Occurred to me that rather than cutting a circular hole in the baseboard, a section of the baseboard could be set lower on which the turntable could sit overcoming the need for any bracing which many seem to recommend. It would allow for the outer ring wall to be modelled in part where it shows up due to the undularing surroundings. Or am I missing something?

[JeffP]

Many years ago I attempted to emulate, in 4mm scale, the turntable I saw in Railway Modeller, built for 7mm scale.

 

A friend at work turned me a base out of two bits of 12mm play glued together.

 

I spent quite a while accurately marking the centre, before drilling it to take a 1" bsp tank connector, as used in plumbing. The top of this was set so that it didn't protrude above the slimline brass nut that held it in place, the other end being held by the second nut.

 

I then bought a pair of bearings from a local place, their OUTSIDE diameter was just the right size for a good force fit into the tank connector, one near the top, one near the bottom. I used two, since they would keep the turntable shaft vertically in line.

 

The shaft was a piece of silver steel which, after much work with wet-or-dry, JUST slid tightly into each bearing. It's top end had a piece of brass attached by a grubscrew, the brass being slotted to take a similar crosspiece attached to the turntable.

This meant the turntable itself was supported on the outer wheels, and could be lifted off at any time. Wheels were Gibson LNER disc tender wheels.

 

The gearbox: a labour of love. I took the guts out of about half a dozen redundant clockwork timers, and, using only a Black and decker drill in a vertical stand, made a gearbox with a reduction ratio of over 1000:1, using clock gears, some 10mm x 1mm brass flats, and a few pieces of 6BA brass studding.

It was then slowed even further by springing the motor shaft against a wheel whose outer edge had a neoprene O-ring on it, and which was attached to the input gear, This took the drive from the motor to the turntable.

 

I was able to achieve one full turn in about 30 seconds, from a 3V motor which ran at heaven knows what speed.

 

I had just started work on indexing when I made the decision to change to 7mm.

I still have the gearbox somewhere..........

 

I do remember that in the original article, backlash wasn't as much of a problem as "run -on" : when the turntable SHOULD have stopped, it's momentum kept it going JUST long enough for the microswitch to close again, so it never stopped, but the author had solved that problem with some clever, but simple, electronics.

He had even modelled a couple of scale men, one of whom he called "Bert Locke" and who "pulled the lock off", and the other was called Fred Turner, and he apparently wound the turning mechanism.

Fasinating.