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Automated Motorised Traverser

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John Holden's "Lime Street" has a stepper motor controlled traverser amongst other wondrous items.

 

See "Lime Street Station" although I think there'snot too much detail about the traverser

 

Cheers,

Mick

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If you're anywhere in the Thames Valley, the MERG Thames Valley Area Group are running a series on PICs starting this Tuesday evening at Grazeley Village Hall.

 

I thought about building a motorised traverser at my last address, but hadn't figured it all out before I moved house. After moving, I had enough room to add a fan of pointwork before the traverser so am connecting the points up to a laptop using CBUS (integrated to the operating sequence), which will mean the only thing I need to do to the traverser itself is pick it up and turn it round when all the trains are facing the wrong way!

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Interesting. I'm looking at a very small one - about 18" x 8", with two O gauge roads on it that I can have in a hidden area at one end of the layout that will only hold a single car DMU or a loco - to take place of some run round loop points (which otherwise would take up nearly 4ft) so I can move an off scene loco from one track to another - so there will only be two possible positions and one track.

 

Obviously none of this fancy computer controlled stuff is necessary but what would be the easiest, cheapest way of achieving this automatically? I'm thinking of a simple sort of drive (I have some drawer runners already) and perhaps microswitches to cut it off when it reaches the right position, with an on/off/on switch for me to manually power the motor.

 

I've already discounted putting some N gauge track underneath it and mounting the traverser on a Farish 37 chassis, and dismantling an old printer... but some Lego 'steering rack' blocks and a slow motor might just do the job?

Edited by cromptonnut
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I've had a look at this too, and after several hours of 'Google'ing, it looks as though the best way would be to use a dedicated microprocessor and a stepper motor. This can be programmed to move the same amount forth and back every time. The simplest type of drive seems to be a length of M8 rod with a bolt that is connected via a coupling to the motor. The bolt is glued welded to the traverser bed and moves when the rod is rotated. This also has the advantage of locking the bed in place such that it can't move and would give good alignment (better than Lego anyway). Something like this:

 

 

If you're using microswitches to set the limits and only have two positions, then a simple geared DC motor could be used (e.g. http://www.active-robots.com/motors-wheels/dc-motors). Obviously the motor's polarity is reversed to move between positions.

 

Sounds like a nice interesting project - good luck!

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Interesting equipment that would definitely do the job but I don't see any prices quoted on their website - which is usually a bad thing, as if you need to know the price there's often a good chance you can't afford it.

 

Going down the "M8 threaded rod" route, I'm finding them on ebay for just a couple of pounds each so that will probably end up being the option - just need to find a motor.

Edited by cromptonnut

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Going down the "M8 threaded rod" route, I'm finding them on ebay for just a couple of pounds each so that will probably end up being the option - just need to find a motor.

 

Somewhere, sadly can't remember where - possibly on the web but may have been at a MRS, I saw this achieved using one of those reversing power screwdrivers. No additional gearing was used just tightened the chuck on the end of the long threaded rod and powered by a simple on-off-on reversed switch. The turn of the rod was slow enough to control the traverser (the weight may have helped here) and the road alignment stop was simply done visually = though I guess some sophistication of proximity or IR sensor could be arranged.

 

As always the hardest part is getting the traverser in perfect alignment and sliding as if on air.

Edited by Kenton

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Now that is a neat idea... will look for a cheap one on Ebay and dismantle it. Depending on the power load I can put a cheap chip on the motor and run it that way.

 

I bet there aren't many DCC powered screwdrivers out there.

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A DCC screwdriver would be handy, but a decoder would be expensive. Even a tame 12v motor would pull 2A! How about using a point decoder to drive 2 x relays to switch power?

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Somewhere, sadly can't remember where - possibly on the web but may have been at a MRS, I saw this achieved using one of those reversing power screwdrivers. No additional gearing was used just tightened the chuck on the end of the long threaded rod and powered by a simple on-off-on reversed switch. The turn of the rod was slow enough to control the traverser (the weight may have helped here) and the road alignment stop was simply done visually = though I guess some sophistication of proximity or IR sensor could be arranged.

 

As always the hardest part is getting the traverser in perfect alignment and sliding as if on air.

 

There was an article in Model Rail recently on such a scheme. OK a look at the index suggests it could have been issue 160 September 2011.

 

http://www.ukmodelshops.co.uk/ModelRail

 

Kevin Martin

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There was an article in Model Rail recently on such a scheme. OK a look at the index suggests it could have been issue 160 September 2011.

 

http://www.ukmodelsh...co.uk/ModelRail

 

Kevin Martin

 

Don't take Model Rail, and it does go back much earlier than that. But interesting to hear that it has been revisited recently. Some of the early battery driven screwdrivers didn't seem to last long before the battery gave up completely - they were then just thrown away still having a perfectly working motor.

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I reckon the key is to come up with a DCC-controlled stepper motor or using JMRI / RocRail to control a stepper motor via USB. I've not seen this done, does anyone have any pointers?

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I believe MERG could provide something (to members of course!) - they can supply parts to build a turntable stepper circuit (which could probabaly be adapted to work a traverser) as well as the CBUS and RPC systems to connect to a PC.

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This topic is of interest to me as a comparison to my V.S.U. and turntable/s. The problem with a single screw would be attempted twisting of the traverser frame,If 2 screws were used , one each end would eliminate as long as they were coupled, rotating together. Another option would be timing/toothed belts available in lengths of over a metre.{ RS Comp. dunno whether they will supply non trade.] Again possible to use an old power drill or similar for the drive . Forget the complicated electronics for operation see http://www.rmweb.co....h__1#entry88907

My circuit here would be ideal for operation, I also used a slight mod on this a year or so back for the V.S.U. The great advantage of this is the 'slow down' when approaching the stop position. This would of course need the appropriate resistor values relative to the chosen drive motor. A circuit could not be made any simpler than this, and the accuracy of stopping is determined by the 1mm wire interrupting the opto switch. The pics on the link are now obsolete since making a 'proper' large pulley and generally tidying. The belt now having a spring tensioned motor gearbox drive making smoother.

Link to similar for ideas http://www.rosewarne...alTraverser.htm

I wonder if the previous link item was successful using the one screw and linking system to each end ?. My VSU used two car screw jack screws, 2 worm gearboxes with a coupling shaft connecting. similar to what I would do for a horizontal traverser. http://www.rmweb.co....orage-unit-and-

backscene/page__p__311277__hl__alangdance__fromsearch__1#entry311277k/commu Hope this provdes some ideas, good Luck Beeman.

Edited by beeman

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The problem with a single screw would be attempted twisting of the traverser frame,

 

Not so convinced that this is a problem. You start with the conventional traverser on rails/sliders at each end that prevents the twisting imparted by the screw mechanism in the centre. I also think that the computer/PIC solution is taking matters beyond the basic fuctionality. I still see the main issue being the feedback to the controller to secure reliable track alignment stops.

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Further to position stopping , I recently built another turntable to see if I could better engineer, which resulted in re-hashing my existing T/T. In each case I blu tacked a laser on to the deck, projecting from the deck center point onto the wall 3.2M away. The repetition of the stopping position, both clock and anti clock was within + - 5mm of a pencil line on the wall.Attempting to work this out as to the difference at the end of the T/T rails I reckoned around 8 to 10 thou. Available for anyone to visit/see who may wish, p.m please. next Sunday its Brittannia or the Duke on the turntable, Churston not mine.Steam on Torbay Express.

The recently built unit, not fitted,made to replace my existing if needed, was operated by a similar geared motor/belt but the stopping device was a small metal tag soldered to a relay armature, into a 'road' register slot.Whilst stepper motors may be accurate there is always the question of any play/slack/backlash in the drive mechanism that needs to be factored in. Sorry to disagree 'Kenton' if a traverser is on rails and trains need to be run on/off both ends, both need to align accurately, there will always be some twist created by friction/drag.The precision needed to achieve being well outside the capabilities of the best modelers. . .A sector plate only needs accuracy one end. I would also suggest with experience of my VSU, irrespective as to how accurate a traverser and stopping is made, some track adjustment is available at the ends. IF timber is used temperature and humidity changes will affect slightly, adjustment being required occasionally,. Beeman.

 

I have just found that many of my pics are available in My Media Library, Thought I had deleted some of these, pics of the mechanism I built are within. The slot shown in the 'road register' is a single hacksaw blade cut, a few thou wider so the tag can enter.the screw in the register providing a little adjustment.

 

 

 

 

 

 

 

Edited by beeman

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Thanks for your comments, all good stuff!

 

I spent my lunchtime researching microcontrollers and it seems like a viable solution would be to use an Arduino controller (http://www.arduino.cc/) with a twin stepper motor shield.

 

This way, the inputs to the microcontroller could be from an accessory decoder (ie. a spare Lenz LS150 that I have) and the outputs could be 2 x stepper motors. Doing it this way would ensure proper alignment at both ends of the traverser, no 'shimmying' to worry about with the table and plenty of 'oomph' to move the table with two motors.

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In my previous post the motor/gearbox unit was around £2.00, the belt and centre bearing from scrap VCR and PC Printer, micro switches and various other odds and sods ..Scrap microwaves can often yield a few microswitches.Can be bought from 50p- £1, number needed depending of roads.The relay was a PO 3000 type from the bit box. a bit more difficult to find these days. An Arduino controller alone will cost at least £25.00. I do not understand why some are prepared to throw money at a project, no better in performance, perhaps not as good.. One modeller recently produced a very elaborate made stepper motor/electronically controlled T/T, I asked how accurate was the stopping , this had the silly worm and relatively small diameter gear on the center shaft. Backlash unlimited.!!!. So far, no reply. It is not electrically possible to produce a simpler electrical circuit that works accurately and automatically as my effort. Sorry for my ego but the facts/ results are positive proof. I could guarantee that a 'straightened' out version of this would work perfect if applied to a traverser and as said previous, one is controlling the motor, when using 'steppers', so no play/backlash must exist in the mechanics, otherwise the accuracy will be lost. 'Dagworth' recently stated ' why do I bother' with advice, why do I ?., considering my VSU carries 24x 5 coach/goods sets and works. Case rested. Beeman.

Edited by beeman

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Running the vid of the huge traverser in the first post, watch closely the 'elevating bridge' section, there is some sort of mechanism for alignment to the traversing tracks. It can be seen to 'twist' slightly as it enters the locating dowel. Also when the loco exits it zig zags a little. This suggests the traversing is not perfectly accurate due to some backlash, which I would think unavoidable in such a large unit, I like the 'weights' on the 'bridge', bolts held on with masking tape. never the less 'Brilliant' if the room/stock available.

Beeman.

ps A further look shows that there is a dowel location plate, assumedly adjustable, at the end of each track, the male dowel being on the u/s of the ' bridge'.

Edited by beeman

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An alternative to the Arduino might be the Picaxe system, which uses a higher level programming language, easy to learn if you've used BASIC.

 

http://www.picaxe.com/

 

Dave

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Hi Beeman,

Thanks for the informative post - Having read your comments regarding backlash, I see this as being less of a problem on a traverser than a TT. If a worm drive is used at both ends, couldn't a light spring me used to keep the inevitable backlash to one side (like gravity does on a VSU?).

 

Your TT positioning system is novel, and well thought through. Fair play to anyone who can get a VSU to work at all, let alone correctly! One question those, I don't understand how that TT alignment 'key' system works, is the 'key' on a solenoid to line everything up perfectly?

 

I hadn't appreciated just how basic the control of your TT was until I reread the post properly, it really is impressive and something that I'd overlooked at first glance. How close can you get the opto-switch, to 0.5mm say, then take up the slack with the keying device?

 

The problem that I have in creating something similar is that I don't have a massive shed full of old VCRs and microwaves like you seem to have, where do you get all those scrapped yet still useful things from?!!!!???!!

 

Also, what sort of force would be needed to move a loaded 3000mm 9-road traverser on ball bearing runners and would a 5v motor (or two) from a VCR be man-enough to move it at a sensible speed?

 

Dave

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Ho Dave, The opto switch on my installed T/T is capable of being operated by 1mm wire, the wire entering/moving into the slot until the o/p from the transmitter half is reduced sufficiently until switch off .this applies to either direction and chosen as it will switch a small relay direct. As Duchmaster says scrap equipment can be found, recycling depots, boot sales.S/H shops etc.very cheap. Most PC printers and scanners have a suitable belt along with the tooth gear on the drive motor. A lathe was needed to machine the video head drum into a useable flanged bearing. this only needed for a T/T of course. Rather than your suggested spring, I would fit a suitable counter weight. I include the later circuit with some notes that uses the relay rather than the opto switch. Each 'road' register operates the appropriate micro switch, disabling the relay power. The tag/nib which must run close to the register end soldered to the armature drops back to the register end.The retaining contact opening, motor supply now being via the speed reducing resistor. The motor contact opening when the tag reaches/enters the slot. Thus stopping and providing the accurate stop. The relay armature was tweaked to give a bit more movement.This relay type is very suitable for this application, and as said if the 'circular construction was 'straightened out' ideal for a traverser. The registers would be fitted to the traverser table itself so 'solidly' connected in relation to each road. and no backlash if counter weight fitted. The suggestion of an old battery drill motor/gearbox could be useful, the trigger speed control could be adapted to give a preset o/p speed, perhaps mounted with a screw adjuster pressing .Try an old resistance or transistor controller direct to the motor, should not take much to move being flat.The main critirion will be to make an accurate rigid traversing frame/unit. If you can fit 2 coupled screws at each end the track on which it moves can be less accurate. The length you aspire to will be a major prob due to sag. Cantilever brackets fixed to a solid wall with rollers on each may be reqd, So very good alignment will be needed, along with a metal supporting frame under the deck I suspect. My VSU needed 5 supports along each level Good Luck keep us informed of your progress. .Beeman

 

ps A traverser would only need one register for each road, A T/T needing 2 due to either end needing to stop at the chosen position.

Re. Dwg notes, once the relay is disabled, the spring pressure of the contacts on the armature presses the nib against the edge of the register until the slot is reached, as the nib enters the slot the motor contacts open. The nib position must be adjacent to the register before the micro operates. A further pic for clarification shows the need for only 2 cams to operate each road micro switch. the micro sw. mounting position being relative to each road. position.

 

 

Edited by beeman

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Further to the post re Traversers , although seeing no gain against a fiddle yard, pondered how I would proceed if wanting to do myself. A few ideas for thought. rather than screws, Bike chains and sprockets, the chains sliding on the edge of a metal angle, obviously all needing to be fitted to a substantial support frame. Chain sprockets fixed to a cross shaft with suitable bearings. The table itself , 22mm Particle flooring sheet, heavy but rigid in itself with additional supports needed to stop any sagging, Or maybe aluminium angle screwed to u/s. to stiffen, subject to the sizes decided. Suitable tension devices needed at one end for each chain. The chain fixed to the table u/s, screws not rubbing the angle edge, or perhaps using wider chain joiners in suitable positions. The outer support could be wheels fitted to the underside of the table running on a further angle ’rail’ . The drive on one cross shaft, preferably on end, especially if further belt reduction reqd..to reduce the speed further , using a suitable motor gearbox unit or discarded battery drill, timing gears/belts, readily available from robotics equipment suppliers. This demonstrates that this type of ‘accessory’ needs to be well engineered to be successful particularly if automatic. I imagine the original post pic. of the ‘monster’ was created for a large layout having very large space available for a reversing loop facility, Few ideas/suggestions for those wanting. Beeman.

Edited by beeman

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Not got round to trying this, but have spent time thinking about using an old daisy wheel or dot matrix printer, which comes complete with microprocessor and stepper motors for carriage and / or head. Hard wire a Tab key and other keys required to set the tab position and each time the Tab key is pressed, the carriage ( traverser ) moves to the next position. The Return key would send the head back to the start position and the original printer sensor could be used to set this position.

Regards Snitzl

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