How does a transmission work? | gear stage | calculation transmission ratio | speed | torque | power

0:00in everyday life there are many

0:02Technical Systems that are powered

0:04either by muscle power or by tools such

0:06as motors for example the rear wheel of

0:08a bicycle is powered by the rider's legs

0:11in ebikes the rear wheels are powered by

0:14electric motors another example of a

0:16system powered by muscle is a handheld

0:18drill as used in the early days of

0:20woodworking today powerful electric

0:23motors are used in drills in all of

0:25these cases the muscles or Motors

0:27provide the energy required for the

0:29component such as the Chuck of a drill

0:31or the rear wheel of a bicycle however

0:34all these different examples have one

0:35thing in common the mechanical Power of

0:38Motors or muscles is generally not used

0:40directly in a bicycle for example the

0:43pedals are not attached directly to the

0:44rear wheel but the rear wheel is driven

0:47by Chain rings and a chain similarly in

0:49a hand drill the rotation of the crank

0:51does not directly turn the drill but is

0:54transmitted to the drill by a ring gear

0:55and bevel gear even with the electric

0:58hand drill the motor does not drive D

1:00the drilling spindle directly a look

1:02inside the drill shows that the electric

1:04motor is connected to a small gear this

1:06so-called pinion then drives a larger

1:08gear wheel and only then is the drill

1:10chuck set in rotation the picture is

1:12similar for larger drill presses again

1:15the electric motor is not used directly

1:18to drive the drilling spindle in pillar

1:20drills power is usually transmitted

1:22between the motor shaft and the drilling

1:24spindle by pulleys and

1:26belts these examples show that in most

1:28cases a technical system system is not

1:30driven directly by the motor but as we

1:32have seen by gears belts or chains the

1:35reason for this is that depending on the

1:38application the motor power must be

1:40provided in different ways either for a

1:42high force or for a high speed it is not

1:45possible to have both at the same time

1:47as the everyday example of a bicycle

1:49makes very clear for example when

1:51starting off the force resulting from

1:53the drive power of our legs or the motor

1:55must be as great as possible in order to

1:57set the bike in motion that's why we

1:59usually shift into a low gear when

2:01starting off the large forces on the

2:04rear wheel then help us to be able to

2:06start up a steep hill however we cannot

2:08reach high speeds in such a low gear to

2:11do this we have to shift into a higher

2:13gear then it's no longer so much about

2:15generating as much force as possible but

2:18about reaching the highest possible

2:19speed in order to get to our destination

2:21quickly the power of our legs or a motor

2:24can therefore be designed for maximum

2:25force on the one hand or high speed on

2:28the other it is precisely this control

2:30between force and speed or between

2:31torque and rotational speed that is

2:33achieved by differen sized sprockets in

2:36the case of a hand drill the necessary

2:38adjustment of the torque and speed is

2:39achieved by the differently sized gears

2:42in the drill press this is achieved by

2:44the differen sized pulleys these

2:46Technical Systems for controlling force

2:48and speed or Torque and rotational speed

2:50are generally referred to as

2:51Transmissions or somewhat imprecisely

2:54gearboxes Transmissions are also used to

2:57control the direction of rotation take

2:59the reverse RSE gear of a car for

3:01example gearboxes therefore basically

3:03fulfill the following tasks transmission

3:06of power control of the direction of

3:08rotation and the aforementioned control

3:10of speed and

3:12torque depending on the components used

3:14to create a transmission it is referred

3:16to as a chain drive a belt drive or a

3:18gearrain Transmissions can also be

3:21divided into shiftable and non-

3:23shiftable transmissions in the hand

3:25drill shown here the speed and torque

3:27conversion of the motor cannot be

3:28changed due to the dimensions of the

3:30Gear wheels this is a non- shiftable

3:33gearbox in contrast the conversion of

3:35speed and torque on a bicycle can be

3:37varied over a wide range by the derailer

3:40this chain drive is therefore a

3:42shiftable

3:43transmission why a gearbox can only ever

3:46increase either speed or Force but never

3:48both at the same time is a direct

3:50consequence of the conservation of

3:51energy in order to understand this we

3:54will take a closer look at mechanical

3:56Power in the case of translational and

3:58rotational motion let's look at the

4:00example of a motorized rope winch that

4:02pulls a load upwards at a constant speed

4:05the winch drum is connected directly to

4:06the motor so that the motor shaft drives

4:09the winch drum directly let us first

4:11consider the question of what motor

4:12power is required to lift a load of 200

4:15kg at a lifting speed of 20

4:17cm/s to do this we first determine the

4:20power with which the load is lifted the

4:23mechanical Power of a moving body is

4:25defined by the work done and the time

4:26taken the more work done in a given time

4:29the greater the mechanical Power by

4:32definition work is the product of the

4:34force and the distance over which the

4:35force acts if the winch pulls the load

4:38by the distance Delta s with the force F

4:40within the time delta T the power is

4:42calculated according to the formula

4:44given the fact that the quotient of the

4:46distance traveled and the time required

4:48is equal to the speed at which the load

4:49is lifted can be used here so note the

4:53mechanical powerp required to move a

4:54body at a constant speed V with a

4:56constant force f is the product of the

4:58two quantities

5:00with a force of 2,000 Newtons and a

5:02lifting speed of 0.2 m/s we get a power

5:05of 400 watts to be transferred to the

5:07load if the friction of the rotating

5:09winch is neglected this corresponds to

5:11the required motor power as the motor

5:13must ultimately deliver this calculated

5:15power to the lifting

5:17load if a greater load is to be lifted

5:20at the same lifting speed more motor

5:22power is required however Motors cannot

5:25provide an unlimited power if only a

5:27certain motor power is available it is

5:29clear from the formula just derived that

5:31a higher force can only be achieved at

5:33the expense of speed a heavier load can

5:36therefore only be lifted with greater

5:37force if the speed is reduced

5:39accordingly for example if a higher

5:41force of 2,500 Newtons is to be applied

5:44a lifting speed of only 16 cm/s can be

5:48achieved with a maximum motor power of

5:49400 watts conversely a lighter load can

5:53be lifted at a higher speed for a given

5:55motor power for example with a lifting

5:57force of just 1,600 Newtons the lifting

6:00speed can be increased to 25 cm/s with a

6:04maximum motor power of 400 wats this is

6:07where gearboxes come in gearboxes are

6:09used to control the power in favor of a

6:11higher force or a higher speed it is

6:14therefore not possible to increase both

6:15at the same time as this would require

6:18an increase in power however the power

6:20is predetermined by the motor and cannot

6:22be changed by a gearbox so note

6:26gearboxes do not change the mechanical

6:28Power but only the ratio between force

6:30and speed for a given power this means

6:33either greater force at lower speed or

6:35more speed at lower force in a perfect

6:37case all the drive power delivered by

6:39the motor is transmitted to the output

6:41shaft of the gearbox in reality however

6:44power losses occur in the gearbox due to

6:46friction these are taken into account by

6:49an efficiency factor which will be

6:51discussed in more detail

6:53later the knowledge of the relationship

6:55between force and speed for

6:56translational motion can now also be

6:59applied to rotational motion to do this

7:01the winch is again considered this time

7:04however the rotational motion of the

7:06winch is examined in more detail let's

7:09take a closer look at the movement of

7:10the Rope as it is pulled up the linear

7:13upward movement of the Rope is converted

7:15into a rotational Movement by the drum

7:18however the speed of the Rope does not

7:19change for example if the Rope were to

7:22wind around the drum faster than the

7:24upward movement the Rope would be

7:25stretched and eventually break

7:28conversely if the Rope was was pulled up

7:30faster than it was wrapped around the

7:31drum it would be compressed the lifting

7:34speed of the translatory motion

7:35therefore also corresponds to the

7:37circumferential speed of the rotatory

7:39motion this circumferential speed is in

7:41turn directly related to the angular

7:43speed of the rotational motion the

7:45circumferential speed is the product of

7:47the angular velocity Omega and the

7:49radius are of the circular path since

7:52the force always acts parallel to the

7:54circumferential speed the power

7:56converted during the circular motion can

7:57also be determined from the product of

7:59force and speed however we express the

8:02circumferential speed as the product of

8:04the angular speed and the radius in this

8:06formula the product of force and radius

8:09corresponds to the torque acting on the

8:11drum let's compare the two formulas

8:15whereas the power of translational

8:16motion is determined by the product of

8:18force and speed the power of rotational

8:20motion is given by the product of torque

8:22and angular speed here we can clearly

8:24see the respective quantities used to

8:27describe the different types of motion

8:29while the kinematics of translational

8:30motion is characterized by speed the

8:33kinematics of rotational motion is

8:34expressed by angular speed the strength

8:37of this motion is described so to speak

8:39by the force in the case of translation

8:41and by the torque in the case of

8:43rotation the product of both quantities

8:45gives the power of the translational or

8:47rotational motion note that the angular

8:50velocity is directly related to the

8:52rotational frequency f as shown in

8:55engineering the rotational frequency is

8:57also known as the rotational speed and

8:59is is often denoted by the letter N

9:01instead of f if we replace the angular

9:03speed Omega in the formula for the

9:05rotational power by the expression 2 pi

9:07* n we can see the relationship between

9:09power torque and rotational speed of a

9:11rotary movement in the case of the winch

9:14this power is again supplied by the

9:16motor and is initially transferred to

9:17the drum in the form of a rotational

9:19movement the winch then converts the

9:21rotational power into translational

9:23power this formula shows once again that

9:26for a given motor power the only choice

9:28is between height torque at low speed or

9:30low torque at high speed at some point

9:33the motor will reach its power limit and

9:35any further increase in torque can only

9:36be achieved by using a gearbox which

9:39will then result in the aforementioned

9:40reduction in speed so note again

9:43gearboxes do not change mechanical Power

9:46they only change the ratio of speed to

9:47torque for a given power this means

9:50either high torque at low speed or high

9:52speed at low

9:53torque from an energetic point of view

9:56it is therefore clear that an increase

9:58in torque results in a reduction in

10:00speed and vice versa in the following we

10:02will examine the technical way in which

10:04speed and torque are converted in a

10:06transmission as an example we will look

10:08at the gearbox of the hand drill which

10:10consists of two gears the small gear

10:13wheel is directly connected to the motor

10:15shaft and drives the large gear wheel

10:17which is connected to the drilling

10:18spindle the first thing you notice is

10:20that the large gear wheel rotates much

10:22more slowly than the small one the

10:24reduction in rotational speed can easily

10:27be explained by the different number of

10:28teeth the gear wheel on the drive shaft

10:31has a total of 15 teeth when the pinion

10:33makes one revolution these 15 teeth also

10:36push the driven gear on the output shaft

10:3815 teeth further however the driven gear

10:41has more teeth due to its larger

10:43diameter it is therefore not moved a

10:45full Revolution for each revolution of

10:48the pinion in this case the driven gear

10:50has a total of 90 teeth the pinion must

10:53therefore rotate six times to move the

10:55driven gear by 90 teeth which is one

10:57revolution the speed spe is therefore

11:00reduced to 1 16th by the two

11:02gears the change in rotational speed

11:05from a driving wheel to a driven wheel

11:06is described by the transmission ratio I

11:09also known as the gear ratio it is

11:11defined as the ratio of the rotational

11:13speed of the driving wheel to the

11:15rotational speed of the driven wheel in

11:17the case just described the transmission

11:19ratio is six because the driving gear

11:21rotates six times faster than the driven

11:23gear for Gears the transmission ratio

11:27can be determined relatively easily from

11:28the r ratio of the number of teeth gears

11:31are characterized not only by the number

11:33of teeth but also by their size to

11:36characterize the size of a gear the

11:38so-called pitch diameter is used in

11:40simple terms the pitch Circle diameter

11:43is the diameter of imaginary cylinders

11:45that roll on top of each other without

11:46sliding the circumferential speeds on

11:49the pitch circle of the two gears are

11:51therefore identical the pitch Circle

11:53diameter is referred to as such because

11:55the pitch of the teeth is based on the

11:57circumference as the number of teeth

11:59teeth is directly proportional to the

12:00pitch Circle diameter the transmission

12:02ratio can also be determined from the

12:04ratio of the pitch Circle diameters of

12:06the two

12:07gears the different number of teeth and

12:10the associated different pitch diameters

12:12not only result in the obvious change in

12:14speed but also inevitably result in a

12:16change in torque to understand this

12:19let's take a closer look at the forces

12:20acting on the tooth flanks suppose the

12:23motor has a torque M1 that drives the

12:25pinion the force F that this torque M1

12:28generates on the flanks of the opinion

12:29can be determined from the pitch Circle

12:31diameter D1 note that the torque is

12:33defined as the product of force and

12:35lever arm where the lever arm is equal

12:37to the pitch Circle radius which is half

12:39the pitch Circle diameter solving this

12:42equation for the force F gives the

12:43following formula which can be used to

12:45determine the force acting on the flank

12:47of the pinion for example assuming a

12:49motor torque of M1 equal 5 new M and a

12:52pinion diameter of D1 equal 10 mm the

12:55force acting on the flank of the pinion

12:57is 1,000 Newtons this force of 1,000

13:00Newtons now pushes the flanks of the

13:02driven gear downwards however as this

13:05gear wheel is considerably larger the

13:07force also acts on a larger lever arm

13:09and therefore also produces a greater

13:11torque with six times as many teeth the

13:14driven gear wheel is also six times as

13:16large and therefore has a pitch diameter

13:18of 60 mm it should be noted that the

13:20pitch diameter of Gears is directly

13:22proportional to the number of teeth this

13:25is because with double the diameter the

13:27circumference of the gear on the pitch

13:28circle is is also twice as large and

13:30therefore provides space for twice the

13:32number of teeth let us now calculate the

13:34torque M2 on the driven gear from the

13:36product of the force and the lever arm

13:38where the lever arm in this case is half

13:40the pitch diameter D2 the flank force of

13:42f equals 1,000 Newtons resulting from

13:45the previous torque of M1 = 5 new M now

13:48produces a torque of M2 = 30 n m on the

13:51driven gear so while the speed is

13:53reduced to a sixth by the two gears the

13:55torque increases by a factor of six so

13:58the torque increases to the same extent

14:00as the speed is reduced by the

14:02transmission ratio we can also show this

14:04in general terms to do this we use the

14:07force formula derived earlier in the

14:09formula for calculating torque it can

14:12now be seen that the increase in torque

14:14is equal to the ratio of the pitch

14:16Circle diameters this in turn

14:18corresponds directly to the transmission

14:20ratio

14:22I for a given transmission ratio the

14:25change in speed and torque can be

14:27determined as indicated the power at the

14:29output of the transmission is equal to

14:31the power at the input however this is

14:34only true in an ideal case in practice

14:37friction causes a loss of power these

14:40power losses are taken into account by

14:42means of a transmission efficiency

14:44factor four Spur Gears the efficiency is

14:47about

14:4895% the power losses also affect the

14:51torque at the output shaft of the gear

14:52unit since power and torque are directly

14:55proportional a reduction in power means

14:57a reduction in torque to the the same

14:59extent therefore the transmission

15:01efficiency Factor must also be taken

15:04into account when calculating the torque

15:06however the efficiency of the gearbox

15:08does not play a role in the calculation

15:10of the change in speed because the

15:12change in speed is determined by the

15:13ratio of the number of teeth this is

15:16because the teeth cannot penetrate each

15:17other and thus produce a lower speed

15:19than the teeth ratio

15:21dictates in principle a gear unit can

15:24consist not only of a single pair of

15:25Gears but also of several pairs of Gears

15:28connected Series this is called a

15:30multi-stage transmission each gear pair

15:33that meshes and changes speed represents

15:35a so-called gear stage each gear stage

15:38is characterized by a specific gear

15:40ratio resulting from the ratio of the

15:42number of teeth in this case the speed

15:45changes at a total of three pairs of

15:46Gears making it a three-stage gearbox

15:50the green and blue gear form the first

15:52gear stage the green gear wheel on the

15:54first gear shaft the so-called input

15:56shaft has 16 teeth while the blue gear

15:59wheel on the second gear shaft has 32

16:01teeth the gear ratio of this gear stage

16:03is therefore two the rotational speed is

16:06thus haveed within this gear stage in

16:09addition to the large gear there is

16:11another small gear on the second shaft

16:12of the gearbox this one also rotates at

16:15a much slower speed note that all gears

16:18on a gear shaft generally rotate at the

16:20same rotational speed this small blue

16:23gear and the yellow gear now form

16:24another gear stage in this case the

16:27small blue gear has 15 teeth and the

16:29large yellow gear has 45 teeth three

16:32times as many within this gear stage the

16:34speed is reduced to 1/3 the gear ratio

16:37in the second gear stage is therefore

16:40three with respect to the input shaft

16:42the third gear shaft now rotates at only

16:441 16th of the original rotational speed

16:47next to the large gear on the third gear

16:49shaft is another small gear wheel

16:52together with the Red Gear this small

16:53yellow gear now forms the third gear

16:55stage in this case the small yellow gear

16:58has 24 teeth and the large red gear has

17:0036 teeth which means 1 and 1/2 times as

17:03many the gear ratio in this third gear

17:06stage is therefore 1.5 with respect to

17:09the gearbox input shaft the output shaft

17:12turns at only a 9th of the original

17:13rotational speed the total transmission

17:16ratio of the gearbox is therefore nine

17:19the overall transmission ratio of a

17:21multi-stage gearbox is therefore the

17:23product of the gear ratios of the

17:24individual gear stages it should be

17:27noted that by multiplying the individual

17:28gear ratios each gear stage ultimately

17:31has a direct effect on the overall

17:33transmission ratio this means for

17:35example that doubling or tripling the

17:37gear ratio of a gear stage also means

17:39doubling or tripling the overall

17:40transmission

17:42ratio the overall transmission ratio of

17:4499 in this example could in principle be

17:47achieved with just one gear stage

17:50however the gear on the output shaft

17:51would have to be nine times larger than

17:53the gear on the input shaft the gearbox

17:56would be large and heavy multi-stage

17:58gearboxes therefore offer the advantage

18:00of dividing the required ratio between

18:02several smaller gears thus keeping the

18:04overall dimensions of the gearbox small

18:07however it should be noted that the

18:09influence of friction increases with

18:11each gear stage on the one hand this is

18:13due to the fact that more teeth mesh

18:15with each other which generally slide

18:17against each other and therefore

18:18generate more friction on the other hand

18:21because the shafts of the gear stages

18:23have to be mounted and therefore cause

18:25increased bearing

18:26friction in the case described so far

18:29the gearbox is designed to increase

18:31torque and therefore reduce speed in

18:33these cases the gear ratio is always

18:36greater than one this is also somewhat

18:38imprecisely referred to as a power ratio

18:41however many technical applications also

18:44require an increase in speed in these

18:47cases a large gear needs to drive a

18:49smaller gear this can be achieved by

18:51simply rotating the gearbox 180° and

18:54turning the original gearbox output

18:56shaft into the gearbox input shaft in

18:59this case there is an increase in speed

19:01between the gearbox input and output

19:03which inevitably leads to a reduction in

19:05torque in this case the gear ratio is

19:08less than one and this is known as a

19:09speed ratio shiftable Transmissions such

19:12as derailers on bicycles can change the

19:15gear ratio as needed an important

19:17characteristic of such shiftable

19:19Transmissions is the increase from the

19:21minimum to the maximum transmission

19:23ratio the greater the ratio between the

19:25maximum and minimum transmission ratio

19:27the greater the speed rate range that

19:29can be shifted this is also referred to

19:31as the transmission spread if for

19:33example the maximum transmission ratio

19:36is 1.2 in the highest gear and 0.2 in

19:39the lowest gear this results in a spread

19:41of six this means that the transmission

19:43ratio can be increased by a factor of

19:45six starting from the lowest

19:48value with chain drives the transmission

19:50ratio is determined in the same way as

19:52with gears by the ratio of the diameters

19:55of the chain Rings or by the ratio of

19:57the number of teeth the main difference

19:59in power transmission is that the chain

20:00rings do not directly touch and transmit

20:02the power but the power is transmitted

20:04through the chain depending on the

20:06diameter the driving chain ring pulls on

20:08the chain with a certain force due to

20:10the torque applied with this Force the

20:13chain now pulls on a larger or smaller

20:15chain ring therefore the force acts on a

20:17smaller or larger lever arm and causes a

20:20change in torque depending on the gear

20:21ratio in the case of chain drives the

20:24change in rotational speed can again be

20:26clearly explained by the different

20:27number of teeth mesh with the chain

20:29again friction only affects the change

20:32in torque not the change in speed note

20:35that the chain moves at a constant speed

20:36regardless of whether it is running over

20:38a large or small chain ring therefore

20:41the circumferential speeds on both chain

20:43rings are always the same only the

20:45rotational speeds are

20:47different belt drives use a belt instead

20:49of a chain power is transmitted by

20:52friction between the belt and pulley

20:54rather than by interlocking elements the

20:56transmission ratio is determined by the

20:58ratio of the differently sized pulleys

21:01again the change in torque can be

21:03explained by the different sizes of the

21:04lever arms on which the force acts

21:06resulting in an increase or decrease in

21:08torque depending on the transmission

21:10ratio for belt drives the change in

21:12speed as a function of transmission

21:14ratio can be clearly explained by the

21:16different pulley circumferences for

21:18example when the small Drive pulley

21:20completes one full Revolution it pulls

21:23the belt forward a distance equal to the

21:24circumference of the pulley the large

21:26pulley will also move the same distance

21:28on its circumference however because it

21:31is larger it will not complete a full

21:33Revolution for example if the large

21:36pulley is twice the size and has twice

21:38the circumference one revolution of the

21:40small pulley will move the large pulley

21:42only half a revolution the rotational

21:44speed is therefore haved the ratio of

21:47the pulley circumferences therefore

21:49corresponds to the change in speed since

21:51the pulley circumferences are directly

21:53proportional to the pulley diameters the

21:55ratio of the circumferences equals the

21:57ratio of the diameter

21:59and therefore the transmission

22:00ratio friction can also be taken into

22:03account in belt drives with an

22:05efficiency factor that results in a

22:06reduction in output torque however

22:09unlike chain or gear drives the

22:11elasticity of the belt affects the speed

22:13conversion while in chain drives the

22:15chain speed and therefore the

22:16circumferential speed of the chain Rings

22:18is the same this is no longer the case

22:20in belt drives due to the elasticity of

22:22the belt let us first look at the belt

22:24drive in an unloaded state for better

22:27orientation white lines are drawn on the

22:29belt at regular intervals underload the

22:32belt is now stretched considerably on

22:34the side on which it is pulled over the

22:36drive pulley the distances between the

22:38lines increase this belt section is also

22:41referred to as the tight side and is

22:43under high tension in the opposite belt

22:46section where the belt runs off the

22:47drive pulley the belt does not have to

22:49pull any load in principle this belt

22:52section is called the slack side and is

22:54only under low tension the distance

22:56between the lines is significantly

22:58smaller it should be noted that the

23:00elongation of the individual belt

23:02sections in the animation is greatly

23:04exaggerated due to the visualization

23:06however it illustrates the following

23:08phenomenon as the belt passes over the

23:11drive pulley the tension in the belt

23:13decreases therefore the belt contracts

23:16as it moves around the pulley the

23:18Contracting belt then slides over the

23:20drive pulley on the slack side the belt

23:23moves slower than the circumferential

23:25speed of the drive pulley this can also

23:27be seen by comparing the speed of the

23:29white lines on the tight side with the

23:30speed of the lines on the slack side

23:32this phenomenon where the belt slips

23:34over the pulley due to stretching is

23:36called slippage when the belt runs onto

23:39the driven pulley slippage also occurs

23:42the tension in the belt increases from

23:44the slack side to the tight side

23:46therefore the belt stretches as it moves

23:48around the pulley the stretching belt

23:50slips over the pulley as a result the

23:53tight side of the belt moves faster than

23:55the circumferential speed of the driven

23:57pulley

23:59therefore if the drive pulley is

24:00generally moving faster than the belt

24:02and the driven pulley is moving slower

24:04the circumferential speeds of the pulley

24:06will no longer be the same ultimately

24:08there is a loss of speed and therefore a

24:10loss of rotational speed the loss of

24:12speed is in the order of one to 2% it

24:15should be noted that slippage only

24:17affects the speed conversion But

24:19ultimately has no effect on the Belt

24:20force and therefore on the torque

24:22conversion however slippage has a direct

24:25effect on power transmission because of

24:27the reduced speed the efficiency Factor

24:29also influences the power output due to

24:31the lower torque since slippage is due

24:34to the elasticity of the belt it cannot

24:36be avoided in certain applications such

24:39as driving a print head in 3D printers

24:42this must be taken into account in these

24:44cases toothed belts also called timing

24:47belts can be used which prevents

24:49slippage over the pulleys due to their

24:50Positive Locking

24:52design finally the characteristics

24:55advantages and disadvantages of gear

24:57belt and chain drives are summarized in

25:00gear trains power is transmitted

25:03positively by meshing teeth this is also

25:05the case in chain drives in belt drives

25:09power is transmitted by friction between

25:11the belt and the pulley note that with

25:13chain or belt drives the direction of

25:15rotation is generally maintained unless

25:17for example a cross belt drive is used

25:20with gear drives however the direction

25:22of rotation is reversed from gear to

25:24gear with gear drives the backlash can

25:27be kept very small so gear drives are

25:29very accurate in terms of speed

25:30conversion for this reason gears are

25:33also used for very precise control of

25:35rotary motion such as in Clockworks with

25:38chain drives the backlash is much

25:40greater due to the many individual chain

25:42links in addition as the chain rotates

25:45around the chain Rings the rigid links

25:47cause the transmission ratio to

25:49fluctuate for belt drives with the

25:51exception of toothed belts slippage must

25:54be taken into account the disadvantage

25:56of precise and therefore Rigid power

25:58transmission in gear drives is their

26:00sensitivity to shock loads the rigid

26:02gears are not able to absorb shock loads

26:05and there is a risk of tooth flanks

26:06being damaged or even entire teeth

26:08breaking out in the event of overload in

26:10most cases the gear shafts and bearings

26:13are also damaged often causing the

26:15entire gearbox to fail under overload in

26:18contrast belt drives have excellent

26:20damping characteristics due to the

26:21elasticity of the belt and are

26:23relatively insensitive to shock loads in

26:25addition belt drives have a natural

26:27overload protection because in the event

26:29of an overload the belt simply slides

26:31over the pulleys protecting the entire

26:33transmission from major damage this is

26:35not the case with gear or chain drives

26:38gearboxes have disadvantages if large

26:41distances have to be covered between the

26:42input and output a large number of Gears

26:45must then be used which leads to a high

26:47gearbox mass and low efficiency due to

26:50the increased flank friction in contrast

26:52belt and chain drives can be used with

26:54almost any shaft distance with gear

26:57drives however the shaft distance is

26:59always equal to the sum of the radi of

27:01the meshing gears unlike belt drives

27:04where the belt needs to be pre-tensioned

27:05to generate the necessary pressure on

27:07the pulleys chain drives require no

27:09pre-tensioning of the chain this reduces

27:12bearing forces accordingly unlike chain

27:15or gear drives belt drives are very

27:17quiet however the belt is relatively

27:20sensitive to external influences such as

27:22temperature and humidity which affect

27:24its properties such as elasticity on the

27:27other hand belt drives do not require

27:29lubrication and are therefore relatively

27:31low maintenance chain and gear drives

27:34generally require lubrication chain

27:36drives can only be used with parallel

27:38shafts as the chains cannot be twisted

27:41with gear drives the output shaft can be

27:43arranged at different angles using other

27:45gear geometries such as bevel gears

27:47screw gears or worms with belt drives

27:50the gear shafts can be at almost any

27:52angle to each other depending on the

27:54Belt used in extreme cases the shafts

27:57can even be arranged at an angle of 180°

28:00to each other the result is a so-called

28:02crossed belt drive this makes it

28:04possible to change the direction of

28:06rotation please note that this summary

28:09only provides a rough overview in

28:11principle it always depends on the

28:13individual case as to which type of

28:15transmission is most suitable