Rack and pinion gears are accustomed to convert rotation into linear movement. A perfect example of this is the steering program on many vehicles. The steering wheel Bearing rotates a gear which engages the rack. As the gear turns, it slides the rack either to the proper or left, based on which way you switch the wheel.
Rack and pinion gears are also found in some scales to carefully turn the dial that displays your weight.
Planetary Gearsets & Gear Ratios
Any planetary gearset has 3 main components:
The sun gear
The earth gears and the planet gears’ carrier
The ring gear
Each one of these three parts can be the insight, the output or could be held stationary. Choosing which piece has which part determines the gear ratio for the gearset. Let’s check out a single planetary gearset.
One of the planetary gearsets from our transmitting includes a ring gear with 72 tooth and a sun gear with 30 tooth. We can get several different equipment ratios out of this gearset.
Input
Output
Stationary
Calculation
Gear Ratio
A
Sun (S)
Planet Carrier (C)
Ring (R)
1 + R/S
3.4:1
B
Planet Carrier (C)
Ring (R)
Sun (S)
1 / (1 + S/R)
0.71:1
C
Sun (S)
Ring (R)
Planet Carrier (C)
-R/S
-2.4:1
Also, locking any kind of two of the three elements together will secure the complete device at a 1:1 gear reduction. Notice that the first gear ratio listed above is a decrease — the output rate is slower compared to the input rate. The second reason is an overdrive — the output speed is faster compared to the input swiftness. The last can be a reduction again, however the output path is definitely reversed. There are several other ratios that can be gotten out of this planetary gear set, but they are the types that are highly relevant to our automatic transmission.
So this one set of gears can produce all of these different equipment ratios without needing to engage or disengage any other gears. With two of these gearsets in a row, we can get the four forward gears and one invert equipment our transmission needs. We’ll put the two sets of gears together in the next section.
On an involute profile equipment tooth, the contact point starts nearer 
to one equipment, and as the apparatus spins, the contact point moves from that equipment and toward the other. If you were to follow the contact point, it could describe a straight collection that begins near one equipment and ends up near the other. This means that the radius of 
the get in touch with point gets larger as the teeth engage.
The pitch diameter may be the effective contact diameter. Since the contact diameter is not constant, the pitch diameter is really the common contact distance. As one’s teeth first start to engage, the very best gear tooth contacts underneath gear tooth inside the pitch size. But notice that the area of the top equipment tooth that contacts the bottom gear tooth is very skinny at this point. As the gears convert, the contact point slides up onto the thicker part of the top equipment tooth. This pushes the top gear ahead, so that it compensates for the somewhat smaller contact size. As the teeth continue steadily to rotate, the get in touch with point moves even further away, going beyond your pitch diameter — however the profile of underneath tooth compensates because of this movement. The get in touch with point starts to slide onto the skinny area of the bottom tooth, subtracting a little bit of velocity from the very best gear to pay for the increased size of contact. The end result is that even though the contact point diameter changes continually, the velocity remains the same. So an involute profile gear tooth produces a continuous ratio of rotational speed.