2.1 CRITERIA

2.1.1 SOFT CRITERIA

Make use of existing foundation; In front of the train station of Delft are twenty-one anti-terror bollards situated, designed to look like seats to wait for the coming buses. Aim of this project is to use these bollards as the foundation of the shading.

Manually useable; the shading will be manually closeable so that people can choose when to close down the system.

Lightweight fabric; the fabric used for shading should have an almost negligible weight in order to make the construction of the urban shading as slim as possible.

Convertible; during the night the system will be able to close down in order to allow fresh air to cool the area beneath the sunshading.

Provide shade during the day for people standing around the bollard; Aim of this project is to provide shade for people waiting for their bus. Standing next to these bollards will offer unique shading throughout the day for passangers standing in the public square of Delft. Convertible; during the night the system will be able to close down to allow fresh air to cool the area beneath the sun shading.

Easy to operate; the system will close in such a way that it is easy to comprehend and straight forward to use.

Construction as light as possible; the construction of the urban shading should be as light as possible while still maintaining enough strength to function.

Variation of fins; the rotating system contains a variety of fins casting a unique shading pattern.

Durable; the shading is able to exist for a long time without significant deterioration in quality or value.

2.1.2 HARD CRITERIA

Attached to the center of the concrete bollards; the fins of the shading should be attached to a center pole which is then connected to the center of the concrete bollards in such a way that sitting on the bollard is still possible.

Opened in less than a minute; the shading should open in such a way that it takes less than 1 minute from closed to open state.

At least 2.2 meter of free height at the lowest point; the shading should feel safe to use without concern of bumping your head.

Rotational opening; the multiple fins of the urban shading should open through a rotational motion.

Lightweight material (to be calculated); the material of the fabric used for the shading should have a maximum of 250 grams per square meter.

At least 3.0 m wide diameter; the diameter of the fins of the biggest fins should be at least 3.0 meter to provide enough shading to feel comfortable. Shades touch each other

The biggest side orientated to the South; the biggest of the fins should be orientated to the South in order to maximize the shading capacity of the urban shading.

2.2 MATERIAL RESEARCH

The structure of the Ostra sun shade should be light enough to have a large span, enabling an efficient amount of length for the shadow. However, it should also have enough stiffness to avoid bending. The materials shown below comprise of these characteristics where recycled materials, plastic or used wood, natural or artificial fibers might be a solution. In addition to the structure, the rotating elements will be filled with a material that will ultimately provide shade.

2.2.1 RANGE OF OPTIONS

1. Graphene: With a density of just 5%, can have strength 10 times that of steel. Might be expensive to get.

temperatures and low thermal expansion. Is relatively expensive but not as graphene.

5. Recycled Wood:

Material made from recycled wood is five times stronger than naturalwood and can be made from any timber product, including shavings and sawdust.

2. Carbon fibre:

Lately being used in sciences and sport fields due to its many advantageous properties, such as high stiffness, strength, and chemical resistance, as well as its ability to tolerate high

3. Steel: Very common to use in urban equipment of minor scale and urban furniture. Its major advantage is durability.

4. Aluminium: Highly useful in producing light structures for outdoor settings. Lightweight, strength, and is easy to work with. Resistant to corrosion and requires minimal maintenance.

4. Plastic Fibres:

Made by recycled polyester, mostly used in hightech greenhouse agriculture, planting, etc. Have a good look and works fine for sunshade & rainproof. Its life time is long and easy to find and install.

6. Hemp Fibre:

Hemp plant-derived natural fibres are strong, biodegradable and lightweight, making them ideal reinforcements for composite materials. They also have inherent mechanical, thermal and acoustic properties.

2.2.2 FINAL SELECTION

As a result of comparising different materials, steel was the ideal material for the principal vertical structure of OSTRA, which will support the fins and the rotational system. For the fins structure, the carbon fibre was the optimal choice due its stiffness and lightness, for the element which will connect the fin and the column, called joint, aluminium was the perfect selection for its versatility and easy way to mold. Lastly, for the final cover, the hemp fibre was selected as a material but opting for a textile made out of it. The lightness of this element is crucial in order to not add unnecessary weight to the entire structure which will made the rotation harder.

2.3 GEAR SYSTEM

The rotational opening of the urban shading asks for some sort of gear system that rotates the central joints to which the fins are attached. Different types of gears were researched in order to find the correct solution for this particular design.

2.3.1 SPUR GEAR

A spur gear is a type of cylindrical gear, with axes which are both coplanar and parallel, the teeth are straight and orientated parallel to the axes. It is possibly the most simple and common type of gear, it is easy to manufacture and suitable for a big variety of purposes.

Pros:

Transmission efficiency; spur gears have a high power transmission efficiency, making them ideal for preserving efficiency in some types of systems.

Gear train; multiple spur gears can be used in series (referred to as a gear train) to achieve large reduction ratios.

Straightforward design; a spur gear has a straightforward design which makes it easy and cheap to manufacture.

Cons:

Noise production; the method of tooth meshing causes high stress on the gear teeth and thus high noise production. Therefore they are most commonly used in lower speed applications.

Stress; spur gears take up a lot of stress, so they are not ideal for heavy loads. If they do take up heavy loads, they will experience a lot of wear and will not be very durable

Pros:

Same rotation; while when two simple spur gears are used it changes direction of rotation, with an internal gear the rotation remains the same when pairing it with a spur gear.

Short center distance; the centre distance of the two gears can be shortened by using this type of gear system. This makes a space-saving design possible.

Better protection; when designed properly, an internal gear offers better protection against dirt due to the internal teeth.

Lower wearage of gears; when an internal and external gear touch it has a large contact area, which results in a lower tooth load and therefore a reduction in the wear of the gears.

Cons:

2.3.2 INTERNAL GEAR

An internal gear is a gear with its teeth cut in the internal surface of a cylinder and meshes with a spur gear. An internal gear wheel is sometimes simply called a ring gear

Expensive; because this type of gear system is only used in some special cases the production is expensive.

A bevel gear system contains of two gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped. Most commonly the gears are mounted on shafts with an angle of 90 degrees between them. These gears are used to transfer horizontal energy to vertical energy.

Pros:

Same rotation; while when two simple spur gears are used it changes direction of rotation, with an internal gear the rotation remains the same when pairing it with a spur gear.

Short center distance; the centre distance of the two gears can be shortened by using this type of gear system. This makes a space-saving design possible.

Better protection; when designed properly, an internal gear offers better protection against dirt due to the internal teeth.

Lower wearage of gears; when an internal and external gear touch it has a large contact area, which results in a lower tooth load and therefore a reduction in the wear of the gears.

Cons:

Expensive; because this type of gear system is only used in some special cases the production is expensive.

Basically, a worm gear is an angled and curved teeth screw that is butted up against what looks like a standard spur gear. An electric or manual force applies rotational power via the worm gear, the worm gear then rotates against the spur gear. This way the plane of movement changes due to the position of the worm wheel, besides this, the rotational movement also rotates by 90 degrees.

Cons:

Lubrication; with a worm gear, sliding motion is the only transfer of power. As the worm gear slides across the teeth of the spur gear, it slowly rubs off the lubricant, until there is no lubricant left between the teeth, and as a result, the worm gear rubs at the metal of the wheel and slowly creates more resistance between the two gears.

Pros: High reduction ratio; A worm gear has a great reduction ratio, it either reduces the speed of the gear or create more torque in the rotation of the gears.

Inability to reverse the direction of power; for this project the main reason to use this gear is the inability to reverse the direction of power, meaning: the worm gear can only rotate the spur gear and not the other way around

Change direction; this gear makes it possible to change the operating angle.

Taking into account the pros and cons of both the worm and bevel gear, for this project the worm gear comes out on top. The amount of precision needed for mounting the bevel gear is too high, especially for making the prototype in the building weeks. Besides that the worm gear has the inability to change direction of power between the gears, which is needed for this project.