Rack and pinion gears are accustomed to convert rotation into linear motion. A perfect example of this is actually the steering program on many cars. The steering wheel rotates a gear which engages the rack. As the apparatus turns, it slides the rack either to the right or left, based on which way you switch the wheel.
Rack and pinion gears are also used in some scales to turn the dial that presents your weight.
Planetary Gearsets & Gear Ratios
Any planetary gearset has three main components:
The sun gear
The planet gears and the earth gears’ carrier
The ring gear
Each of these three parts can be the input, the output or can be held stationary. Choosing which piece has which function determines the gear ratio for the gearset. Let’s check out an individual planetary gearset.
One of the planetary gearsets from our transmitting has a ring gear with 72 tooth and a sun gear with 30 teeth. We can get lots of different gear 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 components together will lock up the complete device at a 1:1 gear reduction. Notice that the first equipment ratio in the above list is a decrease — the output swiftness is slower than the input velocity. The second reason is an overdrive — the result speed is faster compared to the input velocity. The last is normally a gear box for greenhouse reduction again, but the output path is definitely reversed. There are many other ratios which can be gotten out of this planetary equipment set, but these are the ones that are relevant to our automatic transmission.
So this one set of gears can produce all of these different equipment ratios without having to engage or disengage any kind of other gears. With two of these gearsets in a row, we are able to get the four forward gears and one reverse gear our transmission needs. We’ll put both sets of gears together within the next section.
On an involute profile equipment tooth, the contact point starts closer to one equipment, and as the gear spins, the contact point moves from that equipment and toward the other. In the event that you were to follow the contact point, it could describe a straight collection that begins near one gear and ends up near the other. This means that the radius of the contact 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 size is really the common contact distance. As one’s teeth first start to engage, the very best gear tooth contacts underneath gear tooth in 
the pitch diameter. But notice that the part of the top equipment tooth that contacts underneath gear tooth is very skinny at this point. As the gears turn, the contact stage slides up onto the thicker part of the top gear tooth. This pushes the very best gear ahead, so it compensates for the slightly smaller contact size. As the teeth continue to rotate, the get in touch with point moves even more away, going beyond your pitch diameter — however the profile of the bottom tooth compensates for this movement. The contact point starts to slide onto the skinny section of the bottom tooth, subtracting a small amount 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 quickness remains the same. Therefore an involute profile equipment tooth produces a continuous ratio of rotational acceleration.