Rack and pinion gears are used to convert rotation into linear motion. A perfect example of this is actually the steering system on many vehicles. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way you turn the wheel.
Rack and pinion gears are also found in some scales to turn the dial that displays your weight.
Planetary Gearsets & Gear Ratios
Any planetary gearset has three main components:
The sun gear
The earth gears and the earth gears’ carrier
The ring gear
Each of these three parts can be the insight, the output or can be held stationary. Choosing which piece has which role determines the gear ratio for the gearset. Let’s check out an individual planetary gearset.
Among the planetary gearsets from our transmission has a ring gear with 72 teeth and a sun gear with 30 tooth. We can get lots of different gear 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 two of the three components together will secure the whole device at a 1:1 gear reduction. Observe that the first equipment ratio in the above list is a decrease — the output rate is slower than the input rate. The second is an overdrive — the output speed is faster than the input acceleration. The last can be a reduction again, however the output path is reversed. There are several other ratios that can be gotten out of the planetary equipment set, but they are the types that are highly relevant to our automatic transmission.
So this one group of gears can make all of these different gear ratios without needing to engage or disengage any other gears. With two of these gearsets in a row, we are able to get the four forward gears and one reverse equipment our transmission needs. We’ll put both sets of gears collectively 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 stage moves away from that equipment and toward the other. In the event that you were to follow the contact stage, it would describe a straight range that begins near one gear and ends up close to the other. This means that the radius of the get in touch with point gets bigger as the teeth engage.
The pitch diameter is the effective contact size. Since the contact diameter is not constant, the pitch diameter is really the average contact distance. As one’s teeth first begin to engage, the very best gear tooth contacts China Pulley underneath gear tooth inside the pitch size. But observe that the area of the top gear tooth that contacts underneath gear tooth is quite skinny at this stage. As the gears convert, the contact point slides up onto the thicker portion 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 steadily to rotate, the contact point moves even more away, going beyond your pitch diameter — but the profile of the bottom tooth compensates because of this movement. The contact point begins to slide onto the skinny area of the bottom tooth, subtracting a little bit of velocity from the top gear to compensate for the increased diameter of contact. The outcome is that even though the contact point size changes continually, the velocity remains the same. Therefore an involute profile gear tooth produces a continuous ratio of rotational velocity.