Some time ago there was a forum request for information about motorising a Dapol turntable and the good advice given to the member was don't bother. Much better if he bought a proper turntable like Peco, Hornby or Helijan, etc.

The thing is I already had a Dapol kit and plenty of spare time to bash it and the turntable was already planned into my layout, so it had to be done.

I had already made up the Dapol kit so it had to be butchered to provide parts to dress up the mechanism.

What you must remember here is that this thing was not going to end up prototypical, it would just be a functional item to go on my non-protoypical layout.

So how do we go about it...

At the turntable location on my baseboard I scribed 2 concentric circles, one the same as the outside diameter as the Dapol track ring and the other to match a length of a trimmed Hornby standard R601 track. The centre point gets a 1/4" (6mm) pilot hole drilled through it.

Now onto the bridge...

The track mounts onto a piece of aluminium extrusion that I had lying around, rather than the flimsy Dapol track bed. The extrusion was previously an office door nameplate and the Dapol bridge parts are glued around this to dress it up. Not very pretty but OK for my purposes.

Before you can do that though there is a bit of work to do to make an accurate pivot. I had seen a web article ages ago that used a 1/4" (6mm) jack plug and socket, so I looked into the wiring that would be needed for my application. I used a Maplins right angled stereo jack plug and socket.

To run power to the bridge track only, you will need a mono jack, but if you want to power LEDs on the bridge you will need a stereo jack. The wiring details are shown here.

Dismantle the jack plug to access the solder tags and discard the cover plate. Drill a hole at the exact centre point of the aluminium bridge large enough to clear the jack plug tags. Attach the jack plug to the aluminium using tiny self-tappers. They should stick through enough to contact one of the rails as you need to solder these together later.

Mount a length of stock rail (I used Hornby R601 - you will have to trim the centre sleepers to clear the tags) to the aluminium bridge using track pins into 1mm diameter holes with glue as back-up, then solder one rail to the 2 self tappers, which is effectively the outer tag of the jack plug.

Solder the other rail to the other tag. For a mono plug there is only one other tag, for a stereo plug there are 2 other tags so use the middle one of the three for the rail.

The inner tag is used as a common return for the LEDs. I soldered a short length of rail to the centre tag then glued the rail to the sleepers to stop the inner tag rotating. This also makes soldering the LEDs into circuit easier. I wanted LEDs to indicate if the DCC 'polarity' was correct for the bridge position. Green if OK, red if not. A DPDT switch can be used to reverse the polarity manually - see wiring diagram, or you can wire in an auto-reversing module.

The jack socket is eventually wired per the diagram back to the various connection points via the DPDT switch once the fixed centre circle is finally mounted in place.

Now plug the jack into the pilot hole in the baseboard and swing the bridge around to check track layout, etc before committing your baseboard to the saw.

Make up a couple of softwood bearers and screw them to the underside of your baseboard where they will support the turntable inner circle. Now remove the bearers, marking the wood so you can refit them in exactly the same place. This is important as the next step cuts out the circle and effectively loses your centre point.

Using a jigsaw with a fine blade carefully cut around each marked circle until you have a circle and a do-nut shaped ring. Sandpaper them smooth and round.

Mount the jack socket to the centre of the inner circle. I used a 3" (75mm) square of aluminium to attach the socket to and opened up the plywood centre point to match the Dapol track ring boss, which is necessary to allow the jack plug to rotate cleanly. The aluminium plate was screwed to the plywood with small screws. from underneath. The centre circle was then refitted to the bearers.

Rebate the plywood circle to accept the Dapol track ring and glue the ring in place making sure it is truly circular. The bridge can now be trial fitted to check it swings OK.

Remove the bridge and drop the do-nut piece of plywood into the slot and remount the bridge. Make sure everything is aligned and screw the bridge to the do-nut. Repeat swing checks to ensure adequate clearances and nothing is binding up.

Mount the gearbox in a suitable location that won't interfere with the bridge swing and screw it to the baseboard. Wire from an DC AUX supply on your controller (I use a spare analogue controller to power my accesories such as motors, lighting, etc) via a centre off DPDT switch. Get a sprung to centre one if you can.

I tried removing a pair of cogs from the gearbox to up the ratio a bit as the full cog set gives an output shaft speed of 2 RPM, which coupled to the wheel/tyre drive system meant I may never ever get to see the table move. The adjusted ratio proved to be too fast so I went back to the full gear set.

The wheel/tyre diameter is not critical but if you can't find one the right size to mate the gearbox height to the turntable ring height then it will mean rebating the baseboard to suit. To get the right height I eventually had to cut through the baseboard completely and screw a plate underneath to support the gearbox.

To get adequate friction bewtween the drive wheel/tyre and the do-nut ring I stuck on some of that rough emery paper used as anti-slip on metal steps. A fairly soft tyre help with grip. A Lego wheel/tyre drilled as a tight fit for the gearbox 3mm output shaft looks promising. Mine came from a 50- € cents toy jeep.

At present I have the gearbox mounted on top of the baseboard and this limits the arc of travel of the bridge, which is not a problem on my layout, except I obviously can't swing a loco 180 degrees. I will remount it under the baseboard later to solve this problem. Unfortunately an underslung mount could lift the turntable out of the jack socket and cause a DCC 'Error' to kick in, so more work is likely to be needed there. Maybe topside hold-down wheels for the do-nut ring?

I had originally planned to fit a pair of red/green LEDs to the bridge ends to indicate if the DCC 'polarity' was correct for the bridge position but with the limited arc of travel this isn't necessary at the moment.

To avoid the bridge over-running and crashing into the motor/gearbox unit I will have to wire a couple of micro-switches in series with each direction of the motor that will cut power should I fall asleep at the controls or be otherwise engaged with say a pint of local brew.

Well thats it - a fairly rough and ready but functional motorised turntable.The basic drive-ring principle and underslung motor could be used on a more prototypical turntable and by holding tighter tolerances for the ring cuts the do-nut ring could be disguised much better than I have done on a scenic layout.

I hope this helps others who fancy having a go at motorising a turntable without the expense of buying an RTR version.

Robbie