Installing the turntable - part two

Work to re-ballast all the sidings that were previously ripped up has now been completed.

Some more foliage has been added around the turntable and from this angle, the LED housing can't be seen (obscured by the tree!)

The signal box, now relocated, has its own pathway and a few flowers

And while we were at it, some repairs to the upper loop tracks were done to improve the connection between the boards, which should improve reliability. 

We're ready for exhibitions again!

Clan Line repaired

When Clan Line failed during our last exhibition, there was concern that the armature had been cooked. Lots of smoke from the cab and no sign of life whatsoever.

Having stripped it down, the armature shows equal resistance across all three poles and no earth faults. Upon reassembly the issue was found to be that there wasn't enough free-play in the armature. Fine when cold but with heat comes expansion, and that expansion was enough to jam the armature. It had been running for some considerable time before it failed and was pretty hot.

A quick tweak of the end bearing screw and some light lubrication and Clan Line is back in service, ready for the next exhibition.

You wouldn't get that kind of luck with a modern plastic loco!

Installing the turntable - part one

The last time I had a genuine Dublo turntable, it was on the old layout...

So with this one in need of replacement, and with the motorised HD version completed (as per the last post) it's time for this one to come out...

Should be a nice, simple task shouldn't it?

Nope.

To demonstrate the problem more clearly, here's the Märklin being installed in 2014. Note the track positions on both sides...

And compare that to how the genuine version looks (this is the same turntable being re-used!)

One of the many lessons learnt with the first layout was to keep all trackwork as straight as possible - lots of kinks and bends on the turntable siding created lots of issues. To do that here, we'll need to do some serious re-modelling.

So out with the old and onto the first problem...

A big hole! - The only way to overcome the difference in track height between the two systems.

Then all the sidings have to come up as these will no longer line up...

To get the straight track that we need, we needed to scale back the hillside in the centre board (known as Miller Mound!) so drastic measures required...

Not bad for shed insulation. We could have left it as a chalk face, but we prefer grass!

Still on deconstruction at this point...

The old turntable made a very good template to cut a new piece of board. The hole is required for the motor & gearbox...

And of course all the ballast has to come up...

Miller Mound being remodelled with leftover polystyrene...

Filling the gaps...

A better look at the mound, with its new, narrower profile...

Which then had modrock applied...

 Then painted ready for new grass...

Then the grass is applied in layers. It's very hard to see the join!

With the board suitably prepared, time to fit the new (old) turntable and start laying the tracks...

The new trackwork to the turntable is now straight. There's another reason for making this straight (watch this space...) the signal box has had to be relocated from the end board to the centre and is placed in between the tracks...

Still more track to be laid..

Checking alignment, the turntable bridge isn't quite centred here so looks slightly out of line...

More grass applied, loading gauge put back...

More alignment checking as the rest of the siding tracks are put back. Much narrower than with the previous turntable...

Some paint and ballast starting to appear. The track along the back isn't fixed because I have another plan...

I reckon, with a bit of modification, we could sneak in a 6th road at the back...

Ballasting the tracks leading to the turntable...

The points had to be moved further back to accommodate the new alignment, so all the trackwork and ballast had to be dug out from the main lines to the tunnel...

 See - I said we could get another road in there!

A modified pair of points needed to create road six...

 Some more greenery starting to appear...

 Had to remove the LED strip from the outer board and rewire it into the centre board, so here it's being glued back into the signal box...

So we'll now have room to park two more locos and all six roads should be full usable, unlike with the old version!

We're happy!

But still loads to do...

Turning the turntable - Dublo version

This is a little project that's been ongoing for some time, way before the Arduino shuttle was created, in fact the Arduino shuttle came about while I was researching ways to automate a standard Hornby Dublo turntable. It was while doing my research that I first saw examples of turntables being motorised using the Arduino and stepper motor system and started devising ways to make it work for a Dublo version. 

The following is the result of over eight months work, including lots of research, mock-ups, lots of testing of Arduino sketches, blagging the services of a skilled metal lathe operator (although I did get go have a go) and many, many hours. Up until now I've kept details about this to a minimum and deliberately kept it away from this blog, just in case the whole thing failed. So here's what's been going on...

It seems a very long time ago that I did this to a Märklin turntable...

And this has served my layout reasonably well until recently when it died completely towards the end of an exhibition. There's also been the slightly annoying issue that by installing HD girders, I've made the bridge too narrow. This has meant that the outer tracks of the turntable were almost unusable and a better solution was needed. Once it died completely then the need to get my project work on the layout suddenly became more important.

Now the standard HD turntable is a pretty simple piece of kit. It's designed for manual operation and there are no gears, bearings or anything like that - just a couple of metal wipers in the bridge to ensure that contact is made to the right tracks and a centre boss that keeps it all centred, it's not even fixed to the bridge at all, so that was the first problem to overcome.

So we need a centre boss that can be driven by a motor shaft and that means that it needs to be firmly secured to the bridge of the turntable. That effectively rules out the original fixing. So after removing the single set of tracks on one side of the turntable, it was a reasonably simple task to strip it down.

After a fair degree of debating, the centre boss arrangement was designed (I can't take the credit for its design) that would effectively consist of a two-part fixing that would screw together. This would clamp the boss to the turntable to prevent slippage...

The top section of the centre boss is machined to sit snugly in the original hole...

With the bottom part designed to sit snug in the base...

By machining two flat edges, it was also possible to get pliers on this to tighten it up...

The centre rail has to be removed to gain access...

And then the motor was test fitted so that a suitable fixing bracket could be fabricated...

Like this...

 

 

Next thing required is the Arduino sketch to make it turn.

The plan was to use a rotary switch and program the Arduino to drive the motor by using pre-determined steps. This way it would avoid the need for any sensors or switches to index the turntable in the right positions. The switch was sourced and the code written, again after many hours of head-scratching I had a program that worked... in theory.

Sadly though, the little 5 volt stepper just couldn't turn the bridge. While a small child can easily turn an old Dublo turntable, a small stepper motor, driven from the centre shaft just couldn't do it.

So back to the drawing board. I decided that to get the torque required, a geared stepper was probably going to be the only way to make this thing move. Sadly that also meant that a new bracket was needed but a roughly mocked up system was used to test the power of the new, larger motor...

And this worked... sort of. It could turn the table but indexed in a different position each time, mainly because there was so much play in the bracket. The centre shaft also needed beefing up, so this time I was let loose on the lathe to machine a larger one...

Original vs beefed up version...

Now to mount the motor. Again more head-scratching and eventually the simplest way was to use two Nema mounting brackets. This worked perfectly...

After more testing, the turntable moved gently and quietly...

But it still refused to index correctly. Because we've introduced gears to the system, we also now have some free-play in the gearbox. Not much but enough to throw things out and stop the tracks lining up. Another solution was needed...

Within my original Arduino developer's kit was a couple of LDRs. So one of these was soldered to a piece of bread board and this was positioned through the hole of the original latch mechanism. The idea being that as the slits of the turntable come into view, the change in light level could be used as the trigger. I didn't want to use the old latch as it could create more drag on the turntable and put excessive strain on the motor. The LDR breadboard can just be seen below...

And if this was being used in a room with a constant light level, this would probably have been enough. BUT, we exhibit at various locations with varying light. A constant level of light was needed and the only logical thing to do was to drop in a LED through the top of the turntable and solder it to the bread board. This then needed some kind of housing... 

An old signal, filed down, filled and painted. Makes a very good LED cover...

A little bit of light escaping as the cover has yet to be fixed into position.

This then meant that the original idea of using a selector switch would need to be revised. In the end, a much simpler sketch was created that uses the original toggle switch from the old Märklin turntable. This also means that the turntable behaves exactly like the old one did. 

The sketch is in two parts. By holding the switch in position, the turntable will rotate continuously. Once the switch is released, the second part of the loop is programmed to look at the light sensor reading and if the turntable has been moved by the first step. The turntable will then continue to move until light is detected, it will then stop and the cycle is reset. Quite simple really!

Here the turntable is being tested for the first time...

And that's basically it, apart from some tweaking of the sensor levels, which can be done once installed to the layout.

So to make your own motorised turntable, you will need:

Arduino (I use a nano)
Easy stepper motor controller
Nema 17 motor with planetary gearbox
Motor mounting brackets
Toggle switch (on-off-on)
LED + resistor
LDR + resistor
A replacement centre boss
Wiring diagram:

All we need to do now is install it to the layout, that'll be dead easy... won't it..?