M314 Motion Tracker

Building a 3D printed replica of the classic prop

Building the M314 Motion Tracker

The Aliens Motion Tracker project was brilliant fun. It had all the things I love best (In a really geeky way), and it made me feel closer to some of my all-time prop-building heroes.


An actual MT from the film, you can see the paint chipping off around the handle showing the red-plastic drill underneath.

For me Aliens is one of the most iconic and influential film from my youth. I can’t remember how old I was when I first saw it, something around maybe ten or twelve (yes, far too young in many ways!). I was really blown away by the pulse-pounding ride and far from being scared I felt exhilarated by the experience, it’s one of the films that made me want to work in special effects and prop building in the first place.

My friend asked me to make a Motion Tracker for his Colonial Marine costume, scratch-building a fairly complex prop reproduction is never particularly easy and I knew it was going to take quite a long time, but once I started the research I really enjoyed diving back into such a great film universe.

I knew I wanted the MT to end up pretty cheap, I know you can spend weeks/months researching and collecting the actual prop-parts and sourcing them from ebay and various places. I know you can get this amazing resin casting set from Nickatron to build your own too. I wanted mine to fall into a price range that was going to make it available to people who don’t have the money and/or time to make one from scratch or to find someone selling one of the Master Replica versions and persuade them to sell! Even if you get something like the Nickatron kit you still need to invest a chunk of time in putting it together – though you end up with something amazing if you can put the time in, I know not everyone can do that.

Also I knew mine was going to be 3D printed, because I love 3D printing and I wanted to do something ‘big’ with it to test both my own abilities and to see what the printer can do, so it was going to have limitations on the surface quality that comes with that.

The Beginning:

I started by scouring the internet for images, reading forums and generally standing on the shoulders of others who had gone before in terms of getting good pics, finding out what’s what and working out how it was going to end up looking.


The 3D model

The best thing about so many reference images is that I could pick the best ones to see all the angles I needed. I decided at this stage I was going to try to replicate the actual prop as closely as possible, including all the seam lines and screw holes. I always feel that the little details really make the thing come together in the end and I was hoping this would hold true!

After that I fired up CorelDraw and created a flat reference sheet of all the parts I’d need. This was tricky since I didn’t have many actual reference points and due to the non-flat nature of the MT shape and the distortion that comes from taking photos of it I had to flatten out and in some cases guess at the exact dimensions of many of the parts.

From here I imported that reference sheet into Sketchup and started modelling.

The Prototype:

After about a week of fiddling and refining, comparing to the reference images and even more refining, I was ready to start printing the prototype. This thing took something like 80 hours to print entirely (at this point it was mostly solid shapes!) and because of the sheer amount of plastic going down it suffered from some warping.


Prototype! The victim of paint tests.

However, the prototype did the job and I was able to finally hold it in my hand and get a feel for it and test some paint on it. It felt pretty awesome to be honest. This is the first big thing I’ve made completely from scratch and 3D printed so it was really something to actually be holding it (and yes, wandering around making a ‘ping ping’ noise a little bit too).

A few things were apparent from proto’:

  • It was pretty heavy
  • Where the viewer joined the body, that pin wasn’t quite right and wobbled a lot.
  • The joints where the wires go into the body and viewer mere messy
  • Some major warping
  • Insane print time
  • Several screw holes were far too tight and needed drilling
  • The trigger (which at this point was part of the handle) had a seam line running down the middle from where the two halves of the handle met, this just didn’t feel good.
  • The plastic sling loops were definitely not strong enough to hold anything (as suspected).

30+ parts to make a MT

Version One – First complete print.

After making modifications from the prototype I was pretty confident that I’d got something that was ready to print. Version one took about 60 hours total, though this one was done in 16 small sets rather than 4-5 full plates. I did it this way because if one plate goes wrong towards the end of a 20 hour build, it really hurts, whereas this new way meant I was going to need to set the next plate going every 1-3 hours (except the two large body sections that took about 12 hours each), but if something went wrong it was much easier to recover from.


My earlier research revealed that the paint used on the film (Humbrol 170) is no longer available unless you can find tins of it in some back-room somewhere, but fortunately some brilliant people found that Revell #46 is exactly the same colour. I did some pre-assembly of big sections and started painting. I like airbrushing 3D prints because you don’t get brush marks and it seems to ‘bleed’ into the plastic a little better. Probably just an illusion, but I like it!


Painting, airbrushed on acrylics to avoid brush marks.

It was a fairly quick process to paint the major parts (Acrylic dries fast!) and after a bunch of coats the green bits were done. I masked off the green and airbrushed the black bits – except the mesh bit on top, I brush painted that because of the funny shape, it was just easier and the mesh wouldn’t show brush-marks anyway.

Next was some more assembly, a little bit of glueing (not much since almost all of it is held together by screws) which actually took the longest since it takes a few hours to set properly. Relatively soon it was ready for stickers – though they aren’t really stickers – I created the custom graphics from photos and shots of the actual prop (and things the prop is made from), printed them on photo paper and cut them to size. They were stuck on with simple PVA since the varnish would seal them in. Then the varnish coat, spray varnish was great and in 20 mins it was touch dry which let me get through most of the spraying nice and quick.

The wires are just power cables that I have spare (I have an entire box of old cables for situations just like this!) I stripped out the wiring and just left the black rubber jacket to make it more flexible. These are just pushed into the new sockets which are nice and tight and create a good seal, no glue needed.



Blips or no blips on the screen? Our survey said: No blips.

I debated this a lot. If you look at the screen prop it’s really beaten up. It’s got paint chipped off in places, there’s what looks like black electrical tape on the back of the viewer and general grime and wear and tear all over. To me, this makes sense, it’s a Colonial Marine tool, it’s worn on a strap banging against combat armour, being dragged through whatever the Marine is crawling through at the time and generally used and abused. Although I imagine they’d be maintained, I figure a certain amount of wear and tear and (more importantly) dirt and grime would work its way onto the device during its lifetime.

So I took a plunge and started mixing up some ‘dirt’. I used black acrylic to over-brush some areas of the black, I’d noticed on the prop pics they looked a sort of matt-ish black in places, presumably rubbing-wear so I replicated that a little bit. Then I started adding thin black and dark brown washes to the device. I focussed on areas around the handle and top-outside housing, figuring they would take the most handling. I kept adding layers until it looked fairly grimy in the creases and joins, then I did a light dry brushing of some parts with black/brown to try to get a look that might be similar to grease or oil being transferred from armour/weapons etc. It’s quite hard to see it on the pics I took of it, I’m really bad at taking photos but trust me, it’s there!

I feel I probably could have done a bit more on the ‘dirtying up’, but there’s a fine line between arty used-looking and just looking crappy and I didn’t want to cross it on this one as it’s going to my friend who is himself very good at painting anyway.