112.187 Tutorial Gear Technique Program Basic gear techniques through practical and theorical Jobs from the topics : Pulley drive : - chain drive - bande drive Wheel drive : - worm gear drive - tooth rack drive - crowne geat drive - friction drive - universal drive Geat box : - two speed gear - two speed gear with reverse Please Note The OPITEC range of projects are not primarily intended as toys for young children. They are for teaching Designing and Making to ensure that pupils experience a range of tools and processes. 1
CONTENTS : 3 holed metal sheets 0,7 x 50 x 100, Ø 3 holes 3 holed metal sheets with 5 holes, Ø 3 holes for winch (shorten from strips 10 x 160 mm) 2 holed brackets 100 mm, Ø 4,5 hole 3 threaded rods M3 x 100 mm 1 brass chain 200 mm 1 rubber band Ø 50 mm 3 crown wheels, Ø 16,5 mm, Ø 3 hole 30 nuts M3 5 gears 15 mm, Ø 3 hole 1 gear 20 mm, Ø 3 hole 4 gears 40 mm, Ø 3 holes 2 pulleys/plastic Ø 21,5 mm, Ø 3 holes 1 pvc rack 1 expansion spring 20 mm 8 machine screws M3 x 20 mm 8 machine screws M3 x 6 mm 1 pulley Ø 15 mm, Ø 4 holes 1 pulley Ø 30 mm, Ø 4 holes 2 brass caps 4/3 x 8 mm 1 pvc worm GENERAL REMARKS ABOUT THE MONTING OF THE GEARS The separate models should be mounted on a fixture which can be used for all models. Screw the holed metal sheets together with the holed brqckets (see diagramm). The holes in the brqckets are spaced differently than the holes in the sheets. You will still find two holes on top of each other and put the screws through them. A total of eight screws and nuts will be needed. hold metal sheet holed brqcket A winch will be used to operate the model. The winch is made out of a holed metal strip with 5 holes, two screens and three nuts (see diagram). Push the winch through a hole and mount the suitable wheel with two nuts (see diagram). winch wheel mount The wheels, which are mounted to the holed metal shets without the winch have to turn easily. For that, a screw and nut are put in the holed metal sheet and then the wheel does not fall off (see diagramm). 2
GENERAL INFORMATION A lot of gears are mounted in machines. What is a gear really necessary for? It is the job of the gear to transmit and increase power. The direction of the power is also passed on and/or reversed by the gear. To transmit a power and the direction of power, the geat has to be propelled from a power source on the driving side. Since it supplies the power and the direction of the power resp. the side of the supplied power is called the output side. The gear consists of three main groups : 1. DRIVING SIDE takes the power 2. GEAR takes care of the flow of the power 3. OUTPUT SIDE supplies power Dr. Ge. Ou. Je nach Aufgabe gibt es unterschiedliche Bauformen von Getrieben, die wichtigsten werden mit diesem Lernprogramm vorgestellt und kennengelernt. Eine Reihenfolge muß nicht eingehalten werden, empfiehlt sich aber, weil die Getriebe-Modelle aufeinander aufbauen. Tips for mounting : PULLEY DRIVE THE CHAIN DRIVE The position of the gears can be chosen as desired, use the diagram as a guide. The mounting of the winch and geat is described on the page with GENERAL REMARKS. For this chain drive model, the chain has to be shortened according to the distance of the gears. The chain can be closed through the opening and closing of a link put around the gears. gear 3
Use in technique : The most common use of the chain drive is on a bicycle. A lot of cars also have a chain drive. There, a chain connects the crankshaft with the camshaft. Generally you can say : Where a distance between has to be bridged, a chain will be used. Otherwise a lot of gears would have to be put beside each other. Imagine such a bicycle. In some cases a band drive is used instead of a chain drive. When playing with the chain, you will notice that the chain is loose and sometimes skips over. It will have to be tightened. You know from you bicycle the possibilities of the moving of the gear to tighten or loosen the chain. On our model (and lot of uses in techniques) the gears can not be moved. Here a tension roller has to tighten the chain. Make a second winch, mount the small gear on it and put the winch over the chain in a hole of the holed metal sheet (see diagramm). Tighten a spring between the big and the small gear. This spring wil put the tension roller onto the chain. The tension roller adjusts itself over the lever of the winch to the notion of the chain and keeps it under tension. tension roller Use in technique Even when a chain is under tension, it could loosen up while in use. Because of the warming up of the links, the material expands and the chain will get longer. For this reason,a re-tightening unit (as with the bicycle) or the tension roller is necessary. Chain gerars with tension rollers are used for the same purpose as chain gears without tension rollers. The only advantage is that user does not have to keep on re-tightening the chain. Some theory about the Pulley Drive When you turn the handle with the big gear (driving side), you will notice that the small gear (power output side) will rotate faster. The rotation is transmitted but is faster. We describe this as a Tansmission to the Faster. 4
When you mount another winch to the small gear and turn it, you will notice that the big geat will slow down. We describe this as a Transmission to the Slower. If both gears were the same size, the rotations would be the same. This is an Equal Transmission. The transmission of the rotation to the slower or to the faster is described with the term : transmission ratio. We can calculate the transmission ratio. For this, the rotations (n 1 ) and the rotations (n 2 ) have to be known. The formula sign for the transmission ratio is : i n 1 The formula is : i = ----- n 2 When, for example, the small gear needs to rotate twice for the bog gear to rotate once, we will have a ratio of i = 2:1 Final clause : The rotation of the driving side is always n 1 and the output side is always n 2! Besides the rotations, we can also use the number ot teeth (z 1 /z 2 ) or the diameter of the gears (d 1 /d 2 ) to calculate. n 1 z 2 d 2 Here are three possible formulas : i = ----- or i = ----- or i = ----- n 2 z 1 d 1 During the experiments, you will have noticed that there is more strength necessary to turn the big wheel than the small wheel. Why is there a difference? Every gear has a handle. The small gear has a short handle and the big gear a long one (see diagram). a = 5 mm b = 10 mm 5
You know from your physics course (handle law = golden rule of mechanics) that a long handle saves more strength than a short handle. When you turn the small geat, at the same time you turn the handle of the big gear. You have to turn the small gear a few times to turn the big gear once. You have saved strength but you had to go a longer way (more rotations). The big gear has fewer rotations but because of the long handle it can release more power. The big geat wins the imaginary power increase because the small gear has to go a longer way (more rotations, with modest power). Changes in rotation change the power. To get to the point: When a high number of rotations are put in with little power on the driving side, we will get a smaller number of rotations and more power on the output side and the other way around. You can test this on a two speed hand drill. Turn the winch at a certain speed and remember the numbers of rotations of the drill and the necessary force. Now use the other speed. You will notice that with more power the drill turn faster and with less power the drill turns slower. Of course, you also have to observe the number of rotations of the winch. Less rotations with less power = few rotations with a lot of power. The power acts in reverse to the rotations. When cutting the rotations down to one half, you will get twice the power. Through Changing The Rotations The Power Changes. THE BAND DRIVE The position of the band pulley can be chosen as desired, use the diagram as a guide. The mounting of the winch and gear is described on the page with GENERAL REMARKS. After mounting the band pulleys, a rubber band is pulled over the two pulleys. The band drive is finished. Use in technique: Basically, a band drive can be used instead of a chain drive. But the band drive has a few disavantages compared to the chain drives: - it slips - it is not as tight - it is not as long-lasting 6
Nevertheless, the band drive is still used in a lot of machines. A band is consireably lighter than a chain and it is maintenance-free (oiling of chain). At a car engine, the water pump and the generator are operated by a band drive. In agriculture, the tractor and disc saw, for example, are operated by a hand drive. THE CROSSED BAND DRIVE What does the carpenter do when the disc saw the wrong way. This shows us another difference of the band drive compared to the chain drive. Through the simple crossing of the band, the direction can be changed. Then we have a CROSSED BAND DRIVE. If you look in your history book, you may find a picture from the industrial revolution with a mill from around the time. The machines were operated with a band over a transmission (transmission shaft). Today all machines have their own electric motors, by the column-type drilling machine. Fill in the blanks: When you turn pulley A, you get a transmission to... The ratio is...:... When you turn pulley B, you get a transmission to... The ratio is...:... Notes: 7
WHEEL DRIVE Tips for mounting: The position for the rubber pulleys can be chosen as desired, use the diagram as a guide. The mounting of the winch and gear is described on the page with GENERAL REMARKS. When mounting the rubber wheels, make sure they rub frmly against each other. rubber wheels Use in technique: These friction drives are used when the drive with the output side should be separated from the machine or instrument, ie. on a sewing machine, the thread can be wound onto the spools with a friction drive. For this a mount with the spool is affixed to the hand wheel of the sewing machine and the spool rotates. The connection can be separated just as easily. Maybe this example is familiar to you: A merry-go-round is operated.with a drive in the motor. A car tyre (that s right a car tyre ) is in the drive, it turns and rubs against the metal tyre of the merry-go-round. In your tape recorder a friction drive transports the tape. Beside the soudfilm head you can see the puley, it pushes the soudfilm head against the driving shaft and with that friction the tape is transported. The two fixtures in the tape only wind the spools up. Friction drives have a simple detachable connection and need a high friction to be able to pass over the power and rotation. Tips for mounting: THE WORM DRIVE The position of the bog gear and the worn can be chosen as desired, use the diagram as a guide. The mounting of the winch and wheel is described on page GENERAL REMARKS. So that the worms can be pushed on the threaded rods, they have to be cut in half. Do not throw away the half with the hole, it will be neede later. 8
Use in technique: Worm drives have a big transmission ratio. Find this out : i =... :... Norm gears are used to transmit to the slower. The fixture on the speedometer on a bike has a worm gear. The worm drive can only be rotated on the driving side of the worm. This automatically gives a brake. Imagine a gear is mounted to the rope winch of a crane. If you pull up the weight the motor is turned off and the weight stays up there because the gear is stopped through the worm drive. If you use a drive made only out of gears, the weight would go back down, unless a brake was installed. Tips for mounting: THE TOOTH RACK DRIVE The position of the gear and the tooth rack can be chosen as desired, use the diagram as a guide. The mounting of the winch and gear es described on the page with GENERAL REMARKS. For the mount and rest of the tooth rack, two screws with nuts are screwed in the holed metal sheet. The tooth rack lies on the thread of the screws. The winch turns the gear. rotating movement Iinear movement Use in technique: Tooth rack drives are used to change rotating movements into linear movements or linear movements into rotating movements. The most known example is the rack railway. There are also a lot of machines with tooth rack drives, for example the conveyor belt. The rotating movement of the motor is used to transport the conveyor belt, at the same time the rotating movement, over a tooth rack, produces a linear movement with which the belt moves the items. 9
THE CROWN GEAR DRIVE The position of the two gears can be chosen as desired, use diagram as a guide. The mounting of the winch and gear is described on the page with GENERAL REMARKS. The crown gear is mounted on the threaded rod with two nuts. The lower crown gear is pushed on a screw loosely. Use in technique: Actually the use of the crown gear drive is clear when looking at the diagram. It transmits a power or rotating movement by 90. With reference to our example, the transmission ratio is the same because both gears have the same size. When the gears have different sizes, of course, the transmission ratio changes. The crown gear drive is easily recognizable at a handle drilling machine. Tips for mounting: THE REVERSING DRIVE The crown gear drive shall be expanded to the reversing drive. For this a second crown gear has to be mounted on the threated rod (see diagram). Only one of the two outer crown gears may be in contact with the middle crown gear. When the rod is moved to the right, the left gear will be in contact. When the rod is moved to the left, the right gear will be in contact. 10
Use in technique: The name reversing drive is self-explanatory, the drive is for reversing of a rotating movement. When the winch is turned one way and the rod with the two outer crown gear is moved, you will notice that the middle gear will turn right and then turn left. The rotation movement is reversed trough moving the road. If a motor is only supposed to turn one way (or it is only capable of turning one way, i.e. a internal combustion motor) the reversing drive makes it possible to change the way of rotation without changing the rotation of the motor. With the reversing drive, a ship can move backwards. On a car this achieved differently (see gear box). Tips for mounting: THE UNIVERSAL DRIVE The position of two gears can be chosen as desired, use a diagram as a guide. The mounting of the winch and gear is described on the page with GENERAL REMARKS. Use in technique: The universal drive can have a transmission to the slower or to the faster according to which gear the driving side is (A or B). Find out the transmission ratio: i =... :... or i =... :... Universal drives are for the transmission of powers and rotating movements just like the others, i.e. pulley drive. With respect to the hand drilling machine, it reduces the rotations of the motor, but increases the power. On the next page, you are supposed to build a universal drive on which the transmission to the slower is even larger. But how? UNIVERSAL DRIVE WITH MORE GEARS Following this, you are supposed to expand your universal drive. For this expansion, a smaller and a larger are put in a row on the universal drive. When you are done, please determine the transmission ratio i = : How do you explain the result? 11
Notes the result of the experiment: You have found out that the transmissio ratio has not changed to the first universal drive. Why not? Through simply putting gears behind each other, the transmission ratio is not changed. When you turn the first small gear first once, then the second small gear only turns once. You can observe the same with big gears. The reason for this is the grouping of the gears, each is put on its own axle. You have to mount the gears differently. But how? Tips for mounting: Thr diagram is from a top view. For the mounting, you need the threaded rods. On it, the gears are mounted with nuts. Screw the winch on the threaded rod with the small gear. threaded rods Now determine the transmission ratio. For this, turn the winch until the last big gear has turned once. How did you get this transmission? The number of the gears stayed the same! i =... :... 12
When you turn the winch approx, three times, the big gear turns once, the threaded rot of the big gear only turns once and the small gear turns once. This small gear has to turn three times so that the gear turns once. Tat means have turn the winch approx, nine times. The drive has two transmission: 3:1 and again 3:1. Both transmissions multiply to a product of 9:1 Tip: In front of the rotations is the word approx, because the ratio of the gears is not a full number. The transmission ratio is i = 9:1 Now it should say: i G = 9:1 because it is the product of the single transmissions, this way the i G = total transmission. The diagramm shows how the two transmission ratios work together. i = 3:1 i = 3:1 i = 9:1 Formulas for the calculating of the transmission ratios i G : n A i G = ---- Hier the initial number of rotations (n A ) and the final number of rotations (n E ) zählt have to be counted, then i can be calculated. z 2 x z 4 x z 6 x... i G = ---------------------- Here the number of teeth of the gears have to be counted, then i can be calculated. z 1 x z 3 x z 5 x... i G = i 1 x i 2 x i 3 x... Here the single transmissions have tobe multiplied in order to calculate i.. GEAR BOX Tips for mouting: For the conclusion of your introduction to the gear techniques, you will get to know the gear box. Parts of the universal drive can be used for this. Mount the threaded rods with the gears as shown in the diagram. Make sure the driving rod can slide easily, the propulsion is done ove a winch. Mount a rubber wheel to the output rod, this symbolizes a car gear. Through the sliding of the driving rod, two different transmission can be chosen. Find out: i 1 =... :... i 2 =... :... 13
Use in technique: The most know use of the gear box is the box gear shift in the car. Other machines also have boxes, when a different number of rotations or power is needed, for example, the drill with two or more gears. Decreasong the number of rotations causes the power to increase. A car cal also drive backwards. How is this achieved? Work on the next page. Assembly with reverse gear The two speed gear shall be supplied with a reverse gear. For this, two small gears have to be mountes according to the big diagram. For the inserting of a reverse gear, the driving rod is moved so that the outer small gear is in contact with the outer big gear. The other gears of the driving rod may not be in contact with any other gear. The connection of the driving rod to output rod is done over the outer big gear, this creates the creates the reversing of the direction of te rotation. Conclusion: These gears can be operated with a motor. For this the left-over piece of the worm is pushed on the axle of a cheap motor of a toy. The worm with its high transmission to the slower is used to operate the gears. outer gears view of the outer gears 14
Jobs 1. What kind of transmission are the following four examples? 2. On a chain drive, what has to be done to keep the chaon under tension? Name two possibilities! 3. On a worm gear drive, why can the worm never be the output side? 4. Using a tooth gear drive, the rotation movement is changed into a movement... 5. A special form of the drive is the...becaus ehere, the movement is not transmitted with gears, a chain or a band but with a... 6. The wings of a wind mill turn four times a minute. The grinder only turns twice. Calsulate the transmission ratio. Which formula are you using? 7. The driving gear of a universal drive has 99 teeth. The output gear only has 33 teeth. Calculate the transmission ratio. Which formula are you using? 8. Calculate the transmission ratio of a friction drive of a record-player. The turntable has a dia. of 300mm. The driving wheel has a dia. of 4mm. Which formula are you using? 9. For a gear with several transmission stages, the i G has to be calculated. Stage 1 has a transmission ratio of i = 4:1. Stage 2 has a transmission ratio of i = 8:1. Stage 3 has a transmission ratio of i = 3:1. Which formula will you use to calculate i G? 15
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