By Steve Jarratt
A number of robots are happily engaged in a series of repetitive tasks, completing each cyclic movement with clockwork precision. But when the system begins to accelerate, the poor automations are pushed beyond their operational limits, with grisly consequences …
Vicious Cycle is a personal project by director Michael Marczewski, who works as a motion designer at ManvsMachine in London (the studio responsible for the stunning Versus, commissioned by Maxon for the release of Cinema 4D R18). The film, which was completed entirely by Michael himself over the course of a year in his spare time, was a Vimeo Staff Pick and has been entered into several short film festivals.
"I've always been intrigued by intricate mechanisms," he comments, "and I began to play around and make some in Cinema 4D. Then the idea of connecting them to helpless robots came, and it evolved from there. My initial idea was to make a fake instructional video with the robots acting out various tasks to demonstrate how to do them but then everything starts to go wrong. I think the malfunctioning allows for a lot of comedic moments in the film."
The amazing thing about Vicious Cycle is that it was all done with just a handful of keyframes and not a single IK rig. Instead, Marczewski relied almost entirely on Cinema 4D's rigid body dynamics. "I designed the [mechanisms] to be simple yet effective but also look visually interesting. I set the scenes up, added a small number of keyframes here and there, and then let the dynamics in the scene play out."
Around 80 percent of the motion is dynamic but Michael admits that some moments had to be 'faked' by manually animating part of the scene, or baking the simulation and tweaking the keyframes. He also used cuts in the edit to switch between dynamic motion and faked animation.
Marczewski knew what motion he wanted the robots to perform and started by sketching out how each mechanism worked. "The trick was to link those two things together – it was done through a lot of trial and error! Each scene had to be approached a little differently to make sure the motion looked smooth and natural."
A typical setup starts with a keyframed object, such as a spinning cylinder with a Collider Body tag acting as a motor. However, Michael often used an animated object instead of a motor, as many of the setups use repeating keyframes and it was easier to keep track of the animation. A variety of Connectors were then used to link everything together. "The simplest setup was the waving robot in the intro," he says, "and the most complex was probably the baseball scene."
The film begins with a few rudimentary activities, and then we see a robot with the Sisyphean task of carrying batteries up an endless conveyor belt. The arms are rigged with springs in the shoulders, elbows and wrists, enabling it to carry its cargo. However, while only the legs are being driven, the robot remains suspiciously vertical. "His torso is kept upright with a connector and spring linked to the floor," admits Marczewski. "Looking back, I should have had a visible supporting pole to the pelvis."
Next, a serving robot collects plates of sushi and drops them onto a rotating carousel – and it's all done with physics. "The only thing in this scene that is animated is the sushi bowls coming down the tube to land on the tray one at a time. It was just too tricky to get a mechanism to work that would release a sushi bowl when the tray came under the tube. It would have been possible, I think, if I had had more time."
However, the first real cheat comes in the segment where a robot uses a chainsaw to cut chunks off an endless log. As the blade passes through the log, a Boolean object is used to cut a slice out, and then a new piece was made dynamic so it falls off. Marczewski also uses some slight of hand in the scene with the robots hitting and catching baseballs. First of all, despite Cinema 4D's support for Aerodynamics and Wind objects, the balls aren't really being held aloft in the tube by the air pressure. "I had to animate this bit," he concedes, "purely because the ball has to travel accurately and directly into the catcher's hand."
The striking of each ball was also animated manually in order to precisely guide the ball into the catcher's hand. Once the ball is caught, a keyframe is used to drop the ball back onto the track at the right moment. "The motion of the catcher's body is keyframed," acknowledges Marczewski, "but everything else in the scene is dynamic: the balls on the runs, the mechanism for releasing a new ball, the little see-saw that allows an extra ball through each time, and the swinging motion of the batter. The scene was quite fiddly because of the ball run – it was a chain reaction, with each part relying on everything else working."
Dynamics was largely responsible for the robots' natural-looking movement – with subtle jiggles and rebounds. "I used springs with the connectors. I just had to fiddle with the rest angle, strength and damping." To get the dynamics to work properly, Marczewski also used the same real-world scale for each setup, as if each was a miniature, desktop-sized scene. Then, for his settings, he used a value of around 15 Steps Per Frame, with Maximum Solver Iterations slightly higher.
The automatons' recurring duties are interrupted when the driving mechanisms inexplicably grow faster and faster. Unable to cope, the cycles are broken, often with gruesome consequences: limbs are removed, torsos splintered, and heads separated from bodies. Marczewski explains that the little spurts of robot 'blood' were produced using an emitter to generate tiny dynamic cubes. "Sometimes I needed to use a Cloner as an emitter, simply by keyframing the number of the clones, and the Dynamic tag on the cubes had an Initial Velocity to create the spurt."
One of the trickiest sections was with the pickaxe-swinging robot, which dislodges a chunk of mineral that flies out and hits his colleague in the head. The dizzied robot spins around and ends up on the rock just before the next, fatal blow. "This was a bit of a nightmare to do entirely with dynamics," the artist admits. "I couldn't get the second robot to land on the rock how I wanted. So, in the end, I used a cut in the edit and created two versions, which gave me a lot more control of the situation. In the film, the edit is pretty seamless – hopefully!"
In terms of modelling and rendering, the bodies, arms and legs of each robot were UV-mapped (under duress: Marczewski hates doing UVs and texturing), and then a texture was created in Photoshop to add subtle details and provide worn edges. Each scene was then lit with a traditional three-light setup: key, fill and back lights. Although some setups – such as the baseball scene – proved trickier because they had many points of interest to focus on. In those instances, a few smaller light sources were used to add specular details. The scenes were then rendered using Solid Angle's Arnold renderer, with motion blur at render time rather than in post. "I find the results much more effective."
For Cinema 4D users inspired to have a go with dynamics themselves, Marczewski suggests they "just play around and keep going! If you enjoy it, you'll get a lot of satisfaction from problem-solving and figuring out how to get objects to act realistically."
"A lot of beginner dynamics videos I see always look too slippery to me," he continues, "so I would advise to pay attention to the 'Friction' option in the Dynamics Body tag – I normally have it set quite high, between 60-80%. Also, while I'm talking about the Dynamics tag, try to use 'Box' as the shape as much as possible, It's limiting with complex shapes but it gives the best results from my experience, and it keeps your playback pretty quick. I never use the 'Moving Mesh' shape unless I really need to!"
Steve Jarratt is a long-time CG enthusiast and technology journalist based in the UK.