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Tema: MaKING OF: The Process of Modelling and Rigging a Mechanical Model

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    MAKING OF: The Process of Modelling and Rigging a Mechanical Model

    MAKING OF: The Process of Modelling and Rigging a Mechanical Model
    By Robert Burke

    Introduction I have been working on this model for some time now and rather than repeating the usual step by step tutorials, I have decided instead to write a brief article. The article will detail the process and a few of the techniques used to get from the first idea to construction of a complex mechanical model that could be animated, to the finished excavator.

    As with any project the first stage is planning, and as this was a learning exercise to get to grips with Blenders animation tools, I had to choose a machine that had a lot of moving parts. The excavator fit the bill perfectly.

    Now knowing what I was going to model, it was time to go off and find reference materials. A set of plans would be useful, but unfortunately none were available on the usual plan repositories. However, the manufacturer did have some reasonable side, front and rear views in their pdf literature. They didn't exactly scale through from one view to the next, but a little adjustment in Gimp got them near enough to be used.

    Besides the plans, Google was useful for finding photographs, and whilst passing a near by construction site, an excavator was parked alongside the fence allowing me to have a close up look at the machinery. Setting up plans in blender is quite a simple process, I usually work from three 3D views and toggle the active view to full screen with Ctrl-down arrow. As I only had a front, bak and side view of the excavator, these were set up.

    To set up the views, in the 3D view header clik View>Background Image and from the background Image window load the front view. To help align the other views drag a plane so the edges touch the extremities of the excavator front view. In the next 3D window load the bak image and then use the X Offset, Y Offset and the Size controls in the Background Image window to scale and align the image to the edges of the plane. For the front view you will need to rotate the plane 90 degrees on the Z Axis and align the image only to the top and bottom edges.

    Before I set about modelling the excavator, I thought it would be useful to make sure I could get it to animate. To do this, I simply traced the arms and buckets using Bezier Curves and used these as simple 2D cut-outs to help position the armatures. The pistons and cylinders used simple Trak To constraints with their ends parented to the respective component, in this case the cylinder to the arm and the piston to the fulcrum. The process is described really well in the Blender 2.3 Guide and is still relevant to the current versións of blender.

    It should be stressed that pivot and rotation points must be accurately set and aligned using Blenders Snap tools. The bucket movement was a little more complicated than a straight armature chain, requiring both ends of 3 bones to be set to fixed locations. This was achieved by adding an Armature Object at the pivot point of the fulcrum and parenting it to the arm and snapping the other end of the bone to the pivot point of the connecting rod. Another bone was extruded from this point and snapped to the interconnection between the Connecting Rod and Bucket. Then a third bone was extruded and snapped to the pivot point of the bucket. An empty was alos added to the pivot point of the bucket and parented to the arm, so the empty would move in relation to the arm's movement.

    The Fulcrum was parented to Bone 1, the Connecting Rod parented to Bone 2 and the Bucket to Bone 3. The trik to getting this type of mechanism to work was adding an IK Constraint to Bone 3 with the target set to the empty I had placed on the Bucket pivot point, with Use Tail selected in the IK Constraint.

    The two unused axes of the bones were disabled in the Armature Bones panel, allowing the bones to only rotate on the one axis. To animate the bucket movement now only required Bone 1 to be rotated in Pose mode and all the other components would follow.

    The front mechanism used a similar setup on both the front bucket rotation and the top cylinder fulcrum. Satisfied that the process of animating this machine could be accomplished, it wastime to start modelling.

    Precision Modelling tutorials, you should be familiar with all the tools and techniques needed to create any mechanical models. In fact its even simpler to create a model for animation, as it only needs to be a representation of the real thing and not a CAD perfect 3D reproduction.

    The process is therefore simply a matter of tracing áreas of the model from the background image in one view and then pulling the vértices to align with the corresponding point in the perpendicular view. The job is made even easier because the Tractor unit and front mechanism is symmetric between the left and right sides, so only one side needs to be modelled with the other being created using a Mirror Modifier.

    On complex models, working component by component can be a lot less daunting than trying to build the whole model as one mesh.

    Once comfortable with the process described in the Precision Modeling tutorials, it should become quite straightforward to build large complex models from numerous components. However being able to animate those models means you need to be fairly strict in the way you name each component and in the structure of how they are parented to each other. The Mirror Modifier was a useful short cut for modeling, but can cause some problems further down the line on this project, so I applied the modifier once the modeling was finished.

    With the basic model completed and all the parts parented to either the armature systems or the main body, it was time to start adding details.

    Moving hydraulic components need hydraulic fluid to be pumped through them, so this necessitated pipes and hoses. Pipes aren't a problem because they are static items in relation to the components they are attached to, but hoses need to flex and move with the animation.

    I experimented with a number of methods to achieve this, but found you could obtain a very realistic movement using just curves, hooks and empties. What's more, you can set the end tangency of the hose so it doesn't rotate at the end point. I will write the method up as a mini tutorial sometime in the future.

    With a few more details added, it was time to see how this model looked in a render. Basic materials were added for the paintworque and a highly reflective material added to the hydraulic piston to simulate the ground chrome material. The model was then positioned on a plane which was curved at the bak to simulate a studio bak drop. Two área lights were added together with a light behind and above the model relative to the camera.

    In order for a reflective material to look good it must have something to reflect.

    A basic reflection map was created by placing a UV sphere inside a box together with a few props to simulate a studio flash brolly. The UV sphere was set to the maximum reflection and an image renderer of the sphere. This was then used as an angle map in Blender's world settings.

    The end result was a fairly convincing image of an excavator, though, given time, the image could be improved considerably. This isn't the end of the excavator project; I now need to UV unwrap the model and add some realistic textures, then set the model in a construction scene. All that, however, is for a future date and I will post further information here when it is completed. I hope you have found this run-through of the project useful.

    By Robert Burke
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