[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.41,0:00:04.38,Default,,0000,0000,0000,,The planetary gear set, also known as, \Nthe epicyclic gear train
Dialogue: 0,0:00:04.38,0:00:07.94,Default,,0000,0000,0000,,is one of the most important and\Ninteresting inventions in engineering.
Dialogue: 0,0:00:08.64,0:00:13.02,Default,,0000,0000,0000,,They are great speed variation mechanism \Nand are often used in automobiles
Dialogue: 0,0:00:13.02,0:00:15.76,Default,,0000,0000,0000,,as a vital part of automatic transmissions.
Dialogue: 0,0:00:18.90,0:00:22.14,Default,,0000,0000,0000,,Let's explore the secrets of \Nthe planetary gear set in this video
Dialogue: 0,0:00:25.14,0:00:27.65,Default,,0000,0000,0000,,A planetary gear set has four main parts:
Dialogue: 0,0:00:29.04,0:00:29.87,Default,,0000,0000,0000,,the sun,
Dialogue: 0,0:00:30.93,0:00:32.09,Default,,0000,0000,0000,,planet gears,
Dialogue: 0,0:00:33.24,0:00:34.37,Default,,0000,0000,0000,,ring gear,
Dialogue: 0,0:00:35.90,0:00:36.94,Default,,0000,0000,0000,,and carrier.
Dialogue: 0,0:00:37.82,0:00:40.44,Default,,0000,0000,0000,,You can see that it sometimes rotates quickly,
Dialogue: 0,0:00:42.07,0:00:43.26,Default,,0000,0000,0000,,sometimes slowly,
Dialogue: 0,0:00:46.50,0:00:49.01,Default,,0000,0000,0000,,and sometimes even in reverse.
Dialogue: 0,0:00:50.48,0:00:52.39,Default,,0000,0000,0000,,But how does this happen?
Dialogue: 0,0:00:52.92,0:00:55.75,Default,,0000,0000,0000,,You will be able to predict the motion\Nof this gear set completely
Dialogue: 0,0:00:55.75,0:00:58.12,Default,,0000,0000,0000,,if you understand one simple fact.
Dialogue: 0,0:00:59.52,0:01:01.73,Default,,0000,0000,0000,,When two gears are moving as shown
Dialogue: 0,0:01:01.73,0:01:04.76,Default,,0000,0000,0000,,they should have the same\Nspeed at the interface.
Dialogue: 0,0:01:05.22,0:01:07.58,Default,,0000,0000,0000,,This means that the speed of gear A
Dialogue: 0,0:01:07.58,0:01:10.60,Default,,0000,0000,0000,,should be the same as gear B\Nat their mating point.
Dialogue: 0,0:01:17.59,0:01:19.61,Default,,0000,0000,0000,,The speed has to be the same
Dialogue: 0,0:01:19.61,0:01:23.27,Default,,0000,0000,0000,,otherwise the gear teeth\Nwill penetrate each other as shown
Dialogue: 0,0:01:23.27,0:01:25.81,Default,,0000,0000,0000,,that is an impossible condition.
Dialogue: 0,0:01:27.12,0:01:29.63,Default,,0000,0000,0000,,Just apply this fact to \Nplanetary gear sets,
Dialogue: 0,0:01:29.63,0:01:33.57,Default,,0000,0000,0000,,and you will be able to predict how\Nspeed variation is achieved.
Dialogue: 0,0:01:36.17,0:01:40.17,Default,,0000,0000,0000,,Assume that the ring gear is held\Nstationary and we rotate the sun gear.
Dialogue: 0,0:01:44.13,0:01:46.74,Default,,0000,0000,0000,,Think of what happens to the planet gears:
Dialogue: 0,0:01:48.44,0:01:51.75,Default,,0000,0000,0000,,At point A the planet gear should\Nhave a certain speed
Dialogue: 0,0:01:51.75,0:01:56.56,Default,,0000,0000,0000,,and at point B the speed should be \Nzero as the ring gear is stationary.
Dialogue: 0,0:01:57.16,0:02:01.16,Default,,0000,0000,0000,,However, how are both of these conditions\Npossible at the same time?
Dialogue: 0,0:02:01.96,0:02:07.16,Default,,0000,0000,0000,,There is only one way the planet gear should spin as well as turn
Dialogue: 0,0:02:07.77,0:02:13.60,Default,,0000,0000,0000,,The spinning will produce velocities in opposite [directions] at the top and bottom points as shown
Dialogue: 0,0:02:13.94,0:02:17.70,Default,,0000,0000,0000,,Whereas the turning Produces unidirectional velocities
Dialogue: 0,0:02:19.07,0:02:26.14,Default,,0000,0000,0000,,at the top the spinning and turning velocities are in opposite directions, so the velocity [of] point B is zero.
Dialogue: 0,0:02:26.82,0:02:29.23,Default,,0000,0000,0000,,at The bottom they get added up
Dialogue: 0,0:02:30.08,0:02:36.38,Default,,0000,0000,0000,,in short the Planet gears are forced to turn in order to satisfy the condition of velocity.
Dialogue: 0,0:02:36.54,0:02:41.81,Default,,0000,0000,0000,,as The carrier is attached to the planet gear it will turn along with the planet Gears
Dialogue: 0,0:02:42.82,0:02:48.37,Default,,0000,0000,0000,,Now let's see what happens when the sun gear is held stationary and the ring gear is rotated
Dialogue: 0,0:02:50.40,0:02:55.64,Default,,0000,0000,0000,,This is the exact opposite to the previous case at the inner point of the planet gear
Dialogue: 0,0:02:55.64,0:03:01.04,Default,,0000,0000,0000,,the Velocity should be zero and the outer points should have the speed of the ring gear.
Dialogue: 0,0:03:01.04,0:03:06.70,Default,,0000,0000,0000,,in This case the planetary Spin will reverse in order to satisfy the speed conditions
Dialogue: 0,0:03:08.100,0:03:11.74,Default,,0000,0000,0000,,However this case has one more difference
Dialogue: 0,0:03:12.29,0:03:17.55,Default,,0000,0000,0000,,The speed of point B. Will be higher than [the] speed of point A in the previous case
Dialogue: 0,0:03:18.21,0:03:21.77,Default,,0000,0000,0000,,This is obvious as the ring gear radius is higher
Dialogue: 0,0:03:26.16,0:03:33.76,Default,,0000,0000,0000,,This will make the planet gear spin and turn at a higher speed thus the carrier will turn at a higher speed
Dialogue: 0,0:03:36.57,0:03:40.37,Default,,0000,0000,0000,,Let's now explore this reverse mechanism of Planet Gears
Dialogue: 0,0:03:42.58,0:03:46.69,Default,,0000,0000,0000,,For this what you have to do is just arrest the motion of the carrier
Dialogue: 0,0:03:47.100,0:03:53.15,Default,,0000,0000,0000,,This means the Planet gears are not allowed to turn and can only spin
Dialogue: 0,0:03:55.02,0:03:58.44,Default,,0000,0000,0000,,This Spin will be opposite to the rotation of the sun gear
Dialogue: 0,0:03:59.63,0:04:04.28,Default,,0000,0000,0000,,This spinning Planet Gear will make the ring gear rotate in the same Direction
Dialogue: 0,0:04:04.62,0:04:12.02,Default,,0000,0000,0000,,In short the direction of rotation of the ring Gear will be the opposite to the sun gear thus we will get the reverse gear
Dialogue: 0,0:04:15.37,0:04:22.63,Default,,0000,0000,0000,,Here you can note that in order to achieve different speeds the input must be given to different parts of the planetary gearset
Dialogue: 0,0:04:22.63,0:04:25.70,Default,,0000,0000,0000,,This is practically difficult in an actual mechanism
Dialogue: 0,0:04:26.53,0:04:29.08,Default,,0000,0000,0000,,in an automatic transmission [to] achieve this
Dialogue: 0,0:04:29.08,0:04:35.21,Default,,0000,0000,0000,,Three planetary gear sets are connected in series as shown with coaxial Shafts
Dialogue: 0,0:04:35.70,0:04:41.82,Default,,0000,0000,0000,,To understand how this arrangement effectively transfers the input rotation to different parts of the planetary gearset
Dialogue: 0,0:04:41.82,0:04:44.66,Default,,0000,0000,0000,,Watch our video on automatic transmission
Dialogue: 0,0:04:45.61,0:04:49.61,Default,,0000,0000,0000,,Your support on patreon.com is greatly appreciated to make our educational service sustainable. Thank you