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R-clip ( 15368 views )
R-clip 
An R-clip, also known as an R-pin, R-key, hairpin cotter pin, hairpin cotter, bridge pin, hitch pin or spring cotter pin, is a fastener made of a springy material, commonly hardened metal wire, resembling the shape of the letter "R".
R-clips are commonly used to secure the ends of round shafts such as axles and clevis pins. The straight leg of the R-clip is pushed into a hole near one end of the shaft until the semicircular "belly" in the middle of the other, bent leg of the R-clip grips one side of the shaft resisting any force removing the R-clip from its hole. To assist insertion the end of the bent leg is angled away from the straight leg. This angled end rides the side of the shaft and opens the "belly" mouth enough to pass the widest part of the shaft as the R-clip is inserted.
There is also a double loop variety when a wider range of suitable shafts is required. It also spreads out the stresses more evenly for a longer life.
This type of pin is usually made of round wire of a harder metal than is appropriate for traditional cotter pins.
R-clips are similar in function to split pins and linchpins. Compared to split pins, they are easier to remove and are re-usable.
R2-D2 ( 11880 views )
R2-D2
R2-D2 is a fictional robot character in the Star Wars franchise created by George Lucas, who appears in the original trilogy, the prequel trilogy, the sequel trilogy, and Rogue One. A small astromech droid, R2-D2 is a major character and appears in all Star Wars films to date. Throughout the course of the films, he joins or supports Padmé Amidala, Anakin Skywalker, Leia Organa, Luke Skywalker, and Obi-Wan Kenobi in various points in the saga.
English actor Kenny Baker played R2-D2 in all three original Star Wars films, and received billing credit for the character in the prequel trilogy, where Baker's role was reduced, as R2-D2 was portrayed mainly by radio controlled props and CGI models. In the sequel trilogy, Baker was credited as consultant for The Force Awakens, however Jimmy Vee also co-performed the character in some scenes. Vee later took over the role beginning in The Last Jedi. R2-D2's sounds and vocal effects were created by Ben Burtt. R2-D2 was designed in artwork by Ralph McQuarrie, co-developed by John Stears and built by Tony Dyson.
Rabbit ( 25499 views )
Rabbit 
Licensed under Creative Commons Attribution-Share Alike 3.0 (Larry D. Moore).
Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are eight different genera in the family classified as rabbits, including the European rabbit (Oryctolagus cuniculus), cottontail rabbits (genus Sylvilagus; 13 species), and the Amami rabbit (Pentalagus furnessi, an endangered species on Amami Ōshima, Japan). There are many other species of rabbit, and these, along with pikas and hares, make up the order Lagomorpha. The male is called a buck and the female is a doe; a young rabbit is a kitten or kit.
Race track ( 19917 views )
Race track 
Licensed under Creative Commons Attribution-Share Alike 3.0 (Ronny Astrada).
A race track (or 'racetrack', 'racing track' or 'racing circuit') is a facility built for racing of vehicles, athletes, or animals (e.g. horse racing or greyhound racing). A race track also may feature grandstands or concourses. Racetracks are also used in the study of animal locomotion. Some motorsport tracks are called speedways.
A racetrack is a permanent facility or building. Racecourse is an alternate term for a horse racing track, found in countries such as the United Kingdom, India, Australia, Hong Kong, and the United Arab Emirates. Race tracks built for bicycles are known as velodromes. Circuit is a common alternate term for racetrack, given the circuit configuration of most race tracks, allowing races to occur over several laps.
A race course, as opposed to a racecourse, is a non-permanent track for sports, particularly road running, water sports, road racing, or rallying. Many sports usually held on racetracks also can occur on temporary tracks, such as the Monaco Grand Prix in Formula One.
Rack and pinion ( 56583 views )
Rack and pinion 
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move relative to the pinion, thereby translating the rotational motion of the pinion into linear motion.
For example, in a rack railway, the rotation of a pinion mounted on a locomotive or a railcar engages a rack between the rails and forces a train up a steep slope.
For every pair of conjugate involute profile, there is a basic rack. This basic rack is the profile of the conjugate gear of infinite pitch radius (i.e. a toothed straight edge).
A generating rack is a rack outline used to indicate tooth details and dimensions for the design of a generating tool, such as a hob or a gear shaper cutter.
Rack railway ( 17832 views )
Rack railway 
Licensed under Creative Commons Attribution-Share Alike 3.0 (Kabelleger / David Gubler (http://www.bahnbilder.ch)).
A rack railway (also rack-and-pinion railway, cog railway, or cogwheel railway) is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with this rack rail. This allows the trains to operate on steep grades above around 7 to 10%, which is the maximum for friction-based rail. Most rack railways are mountain railways, although a few are transit railways or tramways built to overcome a steep gradient in an urban environment.
The first cog railway was the Middleton Railway between Middleton and Leeds in West Yorkshire, England, United Kingdom, where the first commercially successful steam locomotive, Salamanca, ran in 1812. This used a rack and pinion system designed and patented in 1811 by John Blenkinsop.The first mountain cog railway was the Mount Washington Cog Railway in the U.S. state of New Hampshire, which carried its first fare-paying passengers in 1868. The track was completed to reach the summit of Mount Washington in 1869. The first mountain rack railway in continental Europe was the Vitznau-Rigi-Bahn on Mount Rigi in Switzerland, which opened in 1871. Both lines are still running.
Rack unit ( 15338 views )
Rack unit 
A rack unit (abbreviated U or RU) is a unit of measure defined as 44.50 millimetres (1.752 in). It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby the height of the frame or equipment is expressed as multiples of rack units. For example, a typical full-size rack cage is 42U high, while equipment is typically 1U, 2U, 3U, or 4U high.
Racket (sports equipment) ( 13741 views )
Racket (sports equipment) 
A racket or racquet is a sports implement consisting of a handled frame with an open hoop across which a network of strings or catgut is stretched tightly. It is used for striking a ball or shuttlecock in games such as squash, tennis, racquetball, and badminton. Collectively, these games are known as racket sports. This predecessor to the modern game of squash, rackets, is played with 30 1⁄2-inch-long (77 cm) wooden rackets. While squash equipment has evolved in the intervening century, rackets equipment has changed little.
The frame of rackets for all sports was traditionally made of laminated wood and the strings of animal intestine known as catgut. The traditional racket size was limited by the strength and weight of the wooden frame which had to be strong enough to hold the strings and stiff enough to hit the ball or shuttle. Manufacturers started adding non-wood laminates to wood rackets to improve stiffness. Non-wood rackets were made first of steel, then of aluminium, and then carbon fiber composites. Wood is still used for real tennis, rackets, and xare. Most rackets are now made of composite materials including carbon fibre or fiberglass, metals such as titanium alloys, or ceramics.
Catgut has partially been replaced by synthetic materials including nylon, polyamide, and other polymers. Rackets are restrung when necessary, which may be after every match for a professional.
Radial engine ( 54742 views )
Radial engine 
Licensed under Creative Commons Attribution-Share Alike 1.0 (Stoianovici).
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is called a "star engine" in some languages (German Sternmotor, French moteur en étoile, Japanese hoshigata enjin, Italian motore stellare). The radial configuration was commonly used for aircraft engines before gas turbine engines became predominant.
