Sunday, 6 February 2011

Armature construction task

My armature task required me to design and create a wire armature suitable for use in stop-motion animation. Now, the armature of a model is rarely seen, since for the most part they are covered with plasticine or clay. It goes without saying that armatures therefore are designed purely with function in mind. Before creating an armature, it is necessary to plan what character you are making it for (since armatures are usually character specific, unique due to proportion and size), and also what movements are required of that character, since this will affect how the armature must be jointed or hinged.

Akin to the sculpting task, there was no real animating for this task, instead focusing on the development of skills which will soon be put to use in later projects. For this reason, I decided to create a basic ‘human’ armature, focusing on obtaining realistic and accurate proportions, and adding secure joints where needed.

Of course, I planned my armature extensively before making it, taking note of tips and points to avoid. The upper body should be lighter than the lower body, to lower the centre of mass for better balance. Most stop motion characters have exaggerated hands and feet providing greater support. Models have weak points too, particularly the head, and so care should be taken to ensure stability. I learnt that I should avoid using a single arched wire to create both arms/legs, since this inhibits their ability to move independently. Furthermore, to prevent the plasticine from losing its shape as the model is moved by hand, the bulk of the model should be ‘padded out’ with a strong material (possibly epoxy putty), with the plasticine applied as a thin coating to the outside. Lastly, there were smaller details to note such as twisting two wires together to increase the strength, using component parts so that when a wire eventually breaks, it is relatively easy to replace, and incorporating a nut into the feet of the armature enabling the model to be firmly secured by screwing it to the base of the set. 

The tricky part really is to ensure that movement capability of the joints is not the price to pay for stability. Taking into account the considerations above, I bought a range of materials to meet all requirements. 

Milliput epoxy putty is strong and hard wearing, and once set can be sanded, drilled etc. This was used to add a strong base for the plasticine on my armature’s hands and feet. The second image shows a terminal connector strip, intended for electronics and wiring, however due to the ability to screw wires in place, this proved very useful with regards to making my armature as separate components.

Square brass tubing was used to provide support for the sections of the armature representing bones, such as the forearms and shins- areas where the body does not bend. For the joints, such as elbows and knees which do need to flex, I added some heat-shrinking tube to coat the wire, adding further strength and support.

The Process

First things first- twisting wire increases its strength. By folding a length of animation wire in half, and placing the ends in the chuck of a power drill, I was able to quickly and effectively twist the wires together, looping at the end, achieving a solid and uniform twisted wire.

After cutting my terminal strip to a row of five connectors (to ensure even spacing between the arms on either end and the body/neck in the middle), I was able to cut a length of my wire for each of the arms and secure them into the connectors with screws on the back.

As you can see with the image on the left, I was careful to use enough wire for accurate proportions- it is better to need to clip the wires to size than realise they are too short. The loop at the end of the twisted wire made a good ‘head’, whilst I left enough space for the model’s neck. The same wire continues down to form what is effectively the armature’s spine.

Cutting a slightly shorter strip of four connectors to represent the hips of my armature, I cut two longer pieces of wire for the legs, screwing these in place. Though it had not been my original intention to do so I might add, I quickly realised these wires could continue straight up and also be connected to the spaces between the shoulders and neck. Of course, with a row of four connectors, there is no distinct middle position, and so when looking to secure the ‘spine’ to the hip section, I untwisted the end of the wire and screwed each smaller wire into its own connector. These decisions made my armature far stronger, and provided accurate spacing between the wires. Having three double wires through the torso certainly made this critical part of the armature far more durable. 

(Above: close-up views of the screws on the reverse of the connectors, holding the wires in place, as well as the untwisted spine secured into separate connectors at the hip).

Short lengths of brass tubing were cut and slid over the wires to form rigid sections for bones, then glued in place. Heat shrinking tube was cut to length and applied in the joints. I had hoped to apply the heat shrinking tube first, then slide the brass over the top, however a test proved that with the extra thickness from the heat shrink, the wire could no longer fit through the brass tubing. Heat shrinking tube shrinks to half its original diameter when heated.

As you can see, the heated shrink tubing moulds to the form of the wires beneath, providing a tight protective sleeve that adds to the strength of the wire. I continued to apply both brass and heat shrink to the remaining limbs of my armature. 

Akin to the spine/hip connector, to create basic feet and the palms of the hands, I untwisted the ends of the wires and bent them into loops. Note that this was only temporary for the hands.

I admit that for some time I was puzzled as to how I could create fingers that were secured to the palm in some way. The fingers themselves are a thinner wire, twisted in the same way as before. I found quite a good solution however- by cutting the plastic coating off some spare terminal connectors, revealing the metal insert (into which the screw goes), I could use this as a bracket. Removing the screws entirely provided me with a solid metal ‘palm’ with four holes- one either end, two at the top.

By bending short wires in half to create two fingers (see image above left), I was able to use the four holes in the bracket to hold the fingers (above right).

Now the fiddly part! Using the untwisted wire of the temporary palms, I could grip the finger bracket in place by inserting it into the ends of the bracket. This actually worked very well, and I am pleased with the result.

The thumbs were created in a similar way to the fingers, this time instead using the metal inserts from a smaller set of terminal connectors. The thumb was basically a length of thin twisted wire, glued into the bracket. I filled in the palm with Milliput epoxy putty, providing a strong base for plasticine to be applied over the top. When first mixed, Milliput is very tacky and awkward to sculpt, so I used a little water (following the product guidelines), and smoothed the surface with modelling tools. Milliput has strong adhesive properties, and so I was able to press the thumb brackets into place on the inside of the palms.

I am very satisfied with my armature’s hands, which I feel have a strong sense of proportion with the rest of the body. The following images show the completed hands:

The same technique used to fill in the palms was used to pad out the feet of the model:

After being sculpted to form a sturdy base for my model, I pushed two nuts into the bottoms of the feet, which will enable me to screw the armature to a set if need be. Once the Milliput was hardened, I finished off the surface with a fine file.
My final armature is as follows:

As you can see, the armature is free-standing, able to support it’s own weight and balance well. Thanks to the myriad of flexible joints, the design is fully articulated and features very realistic proportions and posture.

Overall, I found the process of creating this armature rewarding. It is something that I have not done before, and I must say I found it interesting to approach this task akin to product design; to draw up a specification of it’s requirements, and then attempt to meet these requirements with unique solutions. I am most proud of the hands, since this is an area which I found difficult. My solution, I feel, was appropriate and (a little surprisingly) works very well.

The completed armature is fit for its purpose, capable and durable, and best of all relatively low cost to produce. 

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