Monday, June 24, 2013

Riding That Train: The Geartrain

LEGO Mindstorms NXT hobbyist, Before... we have learn about Gearing up and down. All right.. we continue to learning about gears. The largest LEGO gear is the 40t, and the smallest is the 8t (used in the previous discussion). Thus, the highest ratio we can obtain is 8:40, or 1:5 (Figure 2.2).

Figure 2.2 A 1"5 Gear Ratio

LEGO Mindstorms NXT hobbyist, What if you need an even higher ratio? In such cases, you should use a multistage reduction (or multiplication) system, usually called a geartrain. Look at Figure 2.3. In this system, the result of a first 1:3 reduction stage is transferred to a second 1:3 reduction stage. So, the resulting velocity is one-third of one-third, which is one-ninth, and the resulting torque is three times three, or nine. Therefore, the ratio is 1:9.

Figure 2.3 Geartrain with a Resulting Ratio of 1:9

Geartrains give you incredible power, because you can trade as much velocity as you want for the same amount of torque. Two 1:5 stages result in a ratio of 1:25, whereas three of them result in a 1:125 system! All this strength must be used with care, however, because your LEGO parts may get damaged if for any reason your robot is unable to convert it into some kind of work. In other words, if something gets jammed, the strength of a LEGO motor multiplied by 125 is enough to deform your beams, wring your axles, or break the teeth of your gears. We'll return to this topic later.
Remember that in adding multiple reduction stages, each additional stage introduces further friction, the bad guy that makes your world less than ideal. For this reason, if you're aiming for maximum efficiency, you should try to reach your final ratio with as few stages as possible. 

Lego Mindstorms NXT hobbyist, we will return with the worm gear topic.

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