And when you pedal backward, the wheels will follow the backward direction. If you pedal forward, you will move forward. Your pedals will move along with the wheels. The gear of this kind of bike is ‘fixed’ and does not permit coasting. In other words, the pedals need to work together with the rear wheel to create movement. What is a Freewheel on a Bike and How Does It Work?Ī fixed gear bike is a type of bicycle that comes with a drivetrain but without freewheel mechanism.What is Fixed Gear and How Does It Work?.An automatic transmission uses planetary gearsets to create the different gear ratios, using clutches and brake bands to hold different parts of the gearset stationary and change the inputs and outputs. This would give you a 1.17:1 gear reduction. You could rearrange things again, and this time hold the sun gear stationary, take the output from the planet carrier and hook the input up to the ring gear. This is because the planet carrier circled the sun gear once in the same direction as it was spinning, subtracting one revolution from the sun gear. In this case, the planet carrier and planets orbit the sun gear, so instead of the sun gear having to spin six times for the planet carrier to make it around once, it has to spin seven times. For instance, if the input is the sun gear, and we hold the ring gear stationary and attach the output shaft to the planet carrier, we get a different gear ratio. You also find planetary gear systems inside automatic transmissions.Īnother interesting thing about planetary gearsets is that they can produce different gear ratios depending on which gear you use as the input, which gear you use as the output, and which one you hold still. You can see a picture of a two-stage planetary gear system on the electric screwdriver page, and a three-stage planetary gear system of the sprinkler page. The output shaft is attached to the blue ring gear, and the planet carrier is held stationary - this gives the same 6:1 gear ratio. Because there are three red gears instead of one, this gear train is extremely rugged. All three are attached to a plate (the planet carrier), and they engage the inside of the blue gear (the ring) instead of the outside. In this gear system, the yellow gear (the sun) engages all three red gears (the planets) simultaneously. In that case, you can use a planetary gear system, as shown here: A common place where this same-axis capability is needed is in an electric screwdriver. However, imagine that you want the axis of the output gear to be the same as that of the input gear. The size of the red gear is not important because it is just there to reverse the direction of rotation so that the blue and yellow gears turn the same way. In this train, the blue gear has six times the diameter of the yellow gear (giving a 6:1 ratio). One way to create that ratio is with the following three-gear train: Let's say you want a gear ratio of 6:1 with the input turning in the same direction as the output. Planetary gears solve the following problem. One specialized gear train is called a planetary gear train. Because the dials are directly connected to one another, they spin in opposite directions (you will see that the numbers are reversed on dials next to one another). If you can see inside your power meter and it's of the older style with five mechanical dials, you will see that the five dials are connected to one another through a gear train like this, with the gears having a ratio of 10:1. In the same way, you could attach a 2,500-rpm motor to the red gear to get 100 rpm on the purple gear. That means that if you connect the purple gear to a motor spinning at 100 revolutions per minute (rpm), the green gear will turn at a rate of 500 rpm and the red gear will turn at a rate of 2,500 rpm. In this train, the smaller gears are one-fifth the size of the larger gears. The gear train shown below has a higher gear ratio: The red gear turns at twice the rate as the green gear. The green gear turns at twice the rate of the purple gear. In the case above, the purple gear turns at a rate twice that of the blue gear.
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