Rack and pinion gears are used to convert rotation into linear movement. A perfect example of this is actually the steering program on many cars. The tyre 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 used in some scales to turn the dial that presents your weight.
Planetary Gearsets & Gear Ratios
Any planetary gearset has 3 main components:
The sun gear
The planet gears and the earth gears’ carrier
The ring gear
Each one of these three elements can be the insight, the output or can be held stationary. Choosing which piece takes on which part determines the gear ratio for the gearset. Let’s check out a Taper Lock Pulley single planetary gearset.
One of the planetary gearsets from our transmission includes a ring gear with 72 teeth and a sun gear with 30 teeth. 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 elements together will lock up the whole device at a 1:1 gear reduction. Observe that the first gear ratio listed above is a decrease — the output rate is slower than the input swiftness. The second reason is an overdrive — the output speed is faster compared to the input speed. The last is a reduction again, however the output 
path is normally reversed. There are many other ratios which can be gotten out of the planetary equipment set, but these are the types that are relevant to our automatic transmission.
So this one group of gears can produce most of these different gear ratios without needing 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 reverse gear our transmission requirements. We’ll put both sets of gears jointly in the next section.
On an involute profile gear tooth, the contact point starts nearer to one equipment, and as the apparatus spins, the contact stage moves away from that gear and toward the other. If you were to check out the contact stage, it could describe a straight range that begins near one gear and ends up near the other. This implies that the radius of the get in touch with point gets larger as the teeth engage.
The pitch diameter may be the effective contact size. Because the contact diameter is not constant, the pitch size is really the average contact distance. As the teeth first start to engage, the very best gear tooth contacts the bottom gear tooth in the pitch size. But notice that the area of the top equipment tooth that contacts underneath gear tooth is quite skinny at this time. As the gears change, 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 somewhat smaller contact diameter. As the teeth continue steadily to rotate, the get in touch with point moves even more away, going beyond your pitch diameter — but the profile of underneath tooth compensates because of this movement. The contact point begins to slide onto the skinny part of the bottom tooth, subtracting a little bit of velocity from the top gear to pay for the increased size of contact. The end result is that even though the contact point diameter changes continually, the swiftness remains the same. So an involute profile equipment tooth produces a constant ratio of rotational quickness.