How I used Tinkercad to build a locomotive - PART 3 - Printing and construction

 In the first two parts of this series, I described how I used a drawing of the loco to scale and design the parts and then how I drew them in Tinkercad.

• Part 1 - Scaling down and deconstruction
• Part 2 - How I drew the various parts
•  Part 3 - How I printed and constructed the loco

 In this part I will describe how I printed and prepared the parts and then how these were assembled into the loco.

 Printing the parts

 I have a filament printer and a resin printer so one of the first decisions I had to make was which I would use for what. Resin printers are great for finer detailed parts, and so I decided to use it for:

• the nameplates
• the maker's plates
• the springs
• the backhead
• the smokebox door 
• and the tank filler

 When preparing the parts for printing I try to use as few supports as possible and so, with this in mind, I divided the parts with overhangs into two. For example, the saddle tank was split in half, ....

 

 ..... as was the smokebox.

 

The boiler was split into two sections, near one end, ....

 .... the cylinder was drawn in two parts .....

.... and various other parts were similarly divided to ensure that printing could be done without the need for additional supports; the tank filler ..... 

..... the smokebox door .......

.... and the sandbox.

The parts were then sliced using Cura and printed out, ready for construction.

 

 Painting

 In the past, I have usually left painting until the model was fully constructed. However, on this occasion, because there were a few areas which would be difficult to access once the model was finished, I decided to paint the various parts first.

My usual go-to source for paint is Halford's car spray aerosol rattle cans but, for some reason, they have stopped making Rover Brooklands Green which is my default livery for locos, so on this occasion, I used Hycote grey primer and Hycote Rover Brooklands Green.

The cab sides, rear and front, the saddle tank, the boiler, the cylinders and the sand boxes were given a couple of coats of primer .......

.......followed by two coats of Brooklands Green.

 The insides of the cab were given a couple of coats of primer, followed by three or four coats of brush-painted cream acrylic paint.

The running plate, firebox, smokebox, springs and brakes were given a couple of coats of black primer, followed by a couple of coats of Halfords Satin Black.

 The buffer beams on the running plate and footplate were marked out at 5mm intervals and half-round nail-art gems glued on to represent rivet heads. I had no idea as to their exact number and positioning, having no photos of the front or rear of the loco, but assumed they would be in line with the chassis frames.

They were given a couple of coats of red oxide primer (hand-painted).....

.... before being given a couple of coats of Signal Red acrylic (also hand-brushed).

 [Awaiting photo]

  

The roof took a little more preparation. When I tried marrying the two halves together, it was clear some distortion had occurred during the printing process. I repeated the printing, but the warping was still very much apparent. 

So, I placed the two sections on a flat surface and glued them together as best I could. The I applied copious amounts of Humbrol filler into the gaps.

 As you can see, the limitations of the Tinkercad cylinder shape meant that the surface of the roof was somewhat undulated (Note to self - I should have used Tinkercad's multi-sided cylinder!). The surface was smeared with filler and rubbed down.

After a couple of coats of black primer, the roof was brush-painted with a couple of coats of silver-grey acrylic paint.

 Once all the painted parts had been allowed to dry and the paint harden, construction could begin.

 

Construction 

 As always, I started with the running plate. 

Firstly, the footplate section was glued to the main running plate.

 I started on the cab. The rear and one side were glued together first, using my favoured

The second side was then added, followed by the cab front.

The assembled cab was then glued to the running plate.

The backhead was then glued to the firebox ......

.... before the firebox was glued into place in the cab, ........

..... projecting out through the cab front.

 The bunker sides........

 .... were then glued into place........ 

 .... and then boiler was glued on.

The chimney and smokebox door were glued to the smokebox .......

 ..... before being glued on to the front of the boiler.

The tank was slotted into place. This will remain removable to provide access to the electrics inside the boiler and tank.

Before fixing the running plate to the Bachmann Porter chassis, I had to find a way of securing the motor in place. I used a technique, I've used previously with one on my own powered chassis - a cable tie. However, I needed to make a channel for the cable tie, so I filed a groove in the side of the motor housing on the chassis .....

.... and a similar groove in the underside of the running plate.

 This allowed a thin cable-tie to be slotted in and tightened around the motor.

 I then had to find a way of getting power to the motor from the inside of the boiler where the electrics will be located. The wires from a 2-pin JST socket were soldered to the motor .....

 

 

 ...... and the wires tucked under the cable-tie

To fix the chassis to the running plate, one self-tapping screw was used at the front .....

 

.... and two at the rear, using the holes provided in the Bachmann chassis, ......

..... making sure the socket for the motor was tucked inside the boiler.

  

 The cover for the end of the motor inside the cab was now glued into place.

 Next came the cylinders. The two parts of the cylinder ......

..... were glued together, after a 3mm drill bit was slotted into the piston rod hole on the main part of the cylinder ........

..... to ensure the parts were perfectly aligned.

 The cylinders then went to the paint shop (see above).

The crosshead from the Bachmann motor was firstly slotted on to the upper slidebar ........... 

..... before the slidebars were glued into the slots on the face of the cylinder and the cylinder glued into the alignment hole on the side of the running plate.

The support for the slidebars was then glued beneath the running plate.

The steps were then glued beneath the running plate below the cab entrance.

The loco was now in its raw finished form.

 It was time to install the electrics.

 

Electrics

 The electrics in all my locos follow the same format.

Having built well over twenty locos, I tend to follow the same process for installing the electrics - no point in changing what works......

Firstly, I check what size li-ion cells need to be ordered by test fitting cells into the available space. With some builds where I know space will be tight, I design the loco to ensure there will be sufficient space to accommodate the cells (eg the De Winton loco). I discovered that three 18650 li-ion cells would fit easily inside the saddle tank even when a large lead weight (rescued from an LGB Otto loco) was also sharing the space, .......

 

......... so I placed an order with my tried and tested supplier (Ecolux), as he will also add solder tags to cells for a modest charge.

Whilst awaiting delivery of the cells, I decided where to position the SPDT (centre off (ON-OFF-ON) switch and the 2.5mm DC charge socket.

 

 Again, on most of my more recent locos, these are placed inside the front of the cab alongside the firebox. There was sufficient space and so 5mm and 8mm diameter holes were drilled to take them. (Note: I have included these holes in the .STL file which can be downloaded from the gardenrails.org forum).

Before putting them in place, I soldered wires to the connectors on the switch (note red wire to the centre terminal and orange wires to the outer terminals) .....

.... and the 2.5mm DC socket (note orange wire (from one of the switch terminals) to LH connector, black wire to the middle connector and a grey wire to the RH (switched) connector).

 

Heat shrink sleeves were then applied to prevent accidental short circuits. 

 

Next came the fiddle bit of threading the socket and the switch through the holes in the base of the cab. Firstly, the loose wires were threaded through a hole in the side of the firebox. I had to drill a hole awkwardly from inside the firebox but on the .STL file downloadable from the gardenrails.org forum, I have included a hole.

The DC socket was threaded into its hole first, because it was the most awkward.

Then the switch was threaded into place, making sure the connector for the charge socket was facing forward.

The slack in the wires was taken up by pulling the wires through from inside the firebox.

 Once the engine driver and the roof are in place, the wiring is almost impossible to see from the outside.

 

Wiring up the cells 

Once the li-ion cells had arrived (usually the next working day after the order was placed), I could begin the slightly hazardous process of wiring them up.

I always start with the BMS battery protection board ......

 .... and the balance charge plug.

NOTE: BMS boards can be bought on eBay. I have a stock of them of various sizes for my loco builds. In this case I needed a 3S board (ie 3 cells in Series) as I was using three lithium cells. 

I use JST sockets for balance charging as that is what my iMax B6 charger uses (see A quick introduction to the iMax B6 charger)

It's important to check the connections on the BMS board as the wiring-up can be counter-intuitive. For example, on the board I used ......

..... B1 is adjacent to B+ and so it is natural to assume that this will connect to the positve end of the second cell connected to B+. In fact, as you can see, it connects to the positive end of the third cell.

 This does seem to be the convention, numbering the cells from the negative end of the series .....

 .... but it would be wise to double check this before attaching any wires. Some BMS boards are more helpfully labelled ......

..... so it might be worthwhile checking the labelling on any boards or downloading the circuit diagram when you purchase them.

 

Although it might seem obvious at first glance, here are the steps I went through in wiring-up the BMS board, based on experience from having done this several times before and learning from mistakes. I always attach all the wires needed to the board and the JST balance charge socket, before connecting anything to the lithium-ion cells. It is so easy to accidentally short-circuit one or more of the cells if you solder to them first.

 

 I think these steps are self explanatory:

 

 

 

 

 

Before soldering the leads on to the individual lithium-ion cells, I placed heat-shrink tubes over the bare wire ends, again to ensure that none accidentally shorted-out the circuitry.

I then soldered the wires to the cells, covering the soldered ends of the cells with insulation tape as soon as the solder had hardened.

 Finally, the output wires from the BMS board were soldered to the P+ and P- terminals .......

........ and the BMS board shorouded in clear heat shrink tubing.

 

 It may not look pretty, but I know it's safe (provided the vents at the end of the cells are only covered loosely with insulation tape).

 

 Finishing the wiring

 It was now just a case of completing the wiring. The output wires from the BMS board were connected to the black and red wires from the switch and the charge socket, and the grey and orange wires from the socket and switch were connected to the Micron MR603 receiver/controller and to the MyLocoSound (MLS) card. 

 The motor outputs from from  Micron MR603 were connected to the motor and the motor input on the MLS card. A wire triggering the whistle on the soundcard was connected from P6 on the MR603 to the whistle trigger input on the soundcard and a small speaker was connected to the speaker output on the soundcard. The speaker was attached to the underside of the cab roof using double sided sticky pads.

 All was now set for a test run.

 

 Test run and rethink

 I was disappointed with the first test run.When travelling forward, the loco was jerky and the mechanism noisy. 

I stripped the loco down and I fiddled with the motor mounts to see if I could improve the mesh between the worm and the worm wheel when the loco was running forward. I reached what I felt was a sweet-spot for the mechanism and reassembled to loco. There was some improvement, but after a couple of runs back and forward the loco stopped completely. I could hear the motor whirring but the gears had become unmeshed.

Another strip-down and I discovered, the worm had stripped the teeth on the worm-wheel. 

I rummaged in my mechanisms bits-box and unearthed a couple of Mod 1 spur gears which seemed to match the pitch of the worm-wheel. I had to carefully reem out the hole in the centre from 4mm to 6mm to be a tight fit on the Bachmann axle and tried again.

I could tell immediately, it wasn't going to work. As I cranked up the speed of the motor, I could see shards of plastic being shaved off the worm wheel and before long it too lost its teeth.

Time for another rethink. I rooted through my bits-box once more and unearthed a metal worm wheel and a brass worm which seemed to mesh, but from my previous experience, I wasn't sure it was worth trying to redesign the motor mounting to accommodate the larger worm-wheel. It would also mean having to hack the loco body around as the motor would be sitting much higher.

Having had some success with designing and making my own chassis which used bevel gears with a GA25-370 gearmotor, I did some test-fitting and worked-out the gearmotor would easily fit between the frames of the chassis and, furthermore, would set lower than the original motor and hence would mean the body could remain unmodified. However, it would require a completely new chassis.

Half a day's work with Tinkercad and I was ready.....

This was duly printed out and, after a few minor tweaks was ready for receiving the wheels, motor and gears.

However, I had to order a new set of bevel gears as my stock didn't include any with a 6mm bore for the Bachmann axle. The only place I could find any which were suitable was on AliExpress, and so they had to be ordered from China with a frustrating two-week delivery wait! Once it arrived, ........

 ..... I could continue with construction.

The loco was rubbed down and a couple of coats of Hicote Rover Brooklands Green were applied to the cab, boiler and tank.

 Clack valves and copper piping were added .......

.... as were the reverser drain cock linkages. 

The sandboxes and their linkages were added ......

.... as were the springs, together with the copper pipework leading to the smokebox from the cab. 

Whitemetal handrail knobs (from Garden Railway Specialists) were glued to the sides of the tank and handrails from brass rod threaded through them. 

 

 A loop of brass rod was added to the front of the tank with a couple of decorative brass washers.

Loco lamps were resin-printed ........

.... assembled .......

.... painted white and fitted with 5mm red/white bi-colour LEDs.

These were wired-up to the loco's electrics, ....... 

.... to provide forward and reverse lighting of appropriate colour.

Nameplates were resin printed, ......

 ..... painted .....

.... and glued to the sides of the tank.

 

 Resin printed builder's plates were added to the cab sides and a 3D printed driver added to the cab.

A cast brass whistle was added to the front of the cab (I think it was from Roundhouse bought years ago). 

Centre buffers and my own design of hook and loop couplings were added to the headstocks, then the wheels and cab interior were masked before the loco was given a couple of coats of Halford's Satin Lacquer.

The loco was then given a test run, to make sure it not only looked OK, but would actually run.

Conclusion

 This turned out to be a more complicated build than I had envisaged. Not only did I have to replace the motor and gear mechanism, I also had extreme difficulty in quartering the driving wheels when I had removed them to replaced the worm wheel with a bevel gear.

However, I feel it was worth the effort. I had to make a few compromises over the chassis in relation to the original photos of the loco, but overall I feel it is a sufficiently accurate representation of the loco and won't look at all out of place.