Rack and pinion gears are used to convert rotation into linear motion. A perfect example of this is the steering program on many vehicles. The tyre rotates a equipment which engages the rack. As the gear turns, it slides the rack either to the 
right or left, depending on which way you convert the wheel.
Rack and pinion gears are also found in some scales to carefully turn the dial that presents your weight.
Planetary Gearsets & Gear Ratios
Any planetary gearset has 3 main components:
The sun gear
The earth gears and the earth gears’ carrier
The ring gear
Each one of these three parts can be the insight, the output or can be held stationary. Choosing which piece plays which function determines the apparatus ratio for the gearset. Let’s take a look at an individual planetary gearset.
One of the planetary gearsets from our transmitting has a ring gear with 72 teeth and a sun gear with 30 tooth. We can get lots of different equipment ratios out of the 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 parts together will lock up the complete device at a 1:1 gear reduction. Observe that the first gear ratio in the above list is a reduction — the output acceleration is slower compared to the input quickness. The second is an overdrive — the output speed is faster compared to the input acceleration. The last is a reduction again, but the output path is normally reversed. There are several other ratios that can be gotten out of this planetary equipment set, but they are the types that are highly relevant to our automatic transmission.
So this one group of gears can make most of these different equipment ratios without having to engage or disengage any kind of other gears. With two of the gearsets in a row, we are able to get the four forwards gears and one invert equipment our transmission needs. We’ll put both sets of gears together in the next section.
On an involute profile equipment tooth, the contact stage gear motor for greenhouse starts closer to one equipment, and as the apparatus spins, the contact stage moves away from that equipment and toward the other. If you were to check out the contact stage, it would describe a straight line that starts near one gear and ends up near the other. This implies that the radius of the contact point gets bigger as the teeth engage.
The pitch diameter may be the effective contact size. Because the contact diameter isn’t constant, the pitch size is really the average contact distance. As the teeth first start to engage, the top gear tooth contacts the bottom gear tooth within the pitch size. But observe that the part of the top gear tooth that contacts underneath gear tooth is quite skinny at this time. As the gears turn, the contact point slides up onto the thicker part of the top gear tooth. This pushes the very best gear ahead, so that it compensates for the somewhat smaller contact diameter. As the teeth continue to rotate, the contact point moves even further away, going outside the pitch diameter — however the profile of underneath tooth compensates because of this movement. The contact point begins to slide onto the skinny area of the bottom level tooth, subtracting a little bit of velocity from the top gear to pay for the increased diameter of contact. The outcome is that despite the fact that the contact point diameter changes continually, the velocity remains the same. Therefore an involute profile gear tooth produces a constant ratio of rotational quickness.