Wednesday, July 17, 2013

Placing and Fitting Gears

LEGO Mindstorms NXT hobbyist, how are you? I hope you is still motivated for following my posting. Lets We learning about gears again.It is continue topic before, about Limiting Strength with Clutch Gear. The LEGO gear set includes many different types of gear wheels. Up to now, we played
with the straight 8t, 24t, and 40t, but the time has come to explore other kinds of gears, and to discuss their use according to size and shape. In studless buildings, unlike traditional studded building, the holes in TECHNIC beams stacked atop one another are the same distance apart as holes in a single beam. This means gears connected together will be the same number of holes apart, whether connected horizontally along the same beam or vertically across multiple beams (see Figure
2.7 and Figure 2.8).

Figure 2.7 Vertical Matching of Gears

Figure 2.8 Matching gears horizontally and vertically

Figure 2.9 The 16t Gear

Its radius is 1, and it combines well with a copy of itself at a distance of two. Getting it to cooperate with other straight gears, however, is very difficult.

When you are using a pair of 16t gears, the resulting ratio is 1:1.You don't get any effect on the angular velocity or torque (except in converting a fraction of them into fiiction), but indeed there are reasons to use them as a pair~for instance, when you want to transfer motion from one axle to another with no other effects. This is, in fact, another task that gears are commonly useful for. There's even a class of gears specifically designed to transfer motion from one axle to another axle perpendicular to it, called bevel gears.

The most common member of this class is the 12t bevel gear, which can be used only for this task (Figure 2.10), meaning it does not combine at all with any other LEGO gear we have examined so far. Nevertheless, it performs a very useful function, allowing you to transmit the motion toward a new direction, while using a minimum of space.There's also a 20t bevel conical gear with the same design of the common 12t (Figure 2.11). Both of thesebevel gears are half a beam in thickness, whereas the other gears are one beam in thick.

Figure 2.10 Bevel Gears on Perpendicular Axles

Figure 2.11 The 20t Bevel Gear

The 24t gear also exists in the form of a crown 2ear, a special gear with front teeth that can be used like an ordinary 24t, but can also combine with another straight gear to transmit motion in an orthogonal direction (that is, composed of right angles), possibly achieving at the same time a ratio different from 1:1 (Figure 2.12).

You may have noticed another group of gears in your collection. They are wider and the edges of their teeth look like the bevel gear on both sides. These are double bevel gears. Count the number of teeth on them.You will find they are 12t, 20t, and 36t gears (see Figure 2.13).

Figure 2.12 The Crown Gear on Perpendicular Axles

Figure 2.13 12t, 20t, and 36t Double Bevel Gears

You will notice when you place these gears on a single beam that two gears of the same size will not mesh with one another. For this reason, double bevel gears are generally used in pairs of different sizes, either a 12t and a 20t, or a 12t and a 36t. These gears are designed to work well in both perpendicular and horizontal setups (Figure 2.14).

Figure 2.14 Meshing Double Bevel Gears

Mismatched pairs of double bevel gears use the same hole spacing as straight gears, so pairs of them can be used in place of a pair of straight gears, offering some new gear ratios~for example, a 12t and a 20t double bevel gear pair mesh at a distance of 2, the same as an 8t and 24t straight gear pair. Be careful when mixing and matching double bevel gears and straight gears; although they use some of the same hole spacing, double bevel gears and straight gears don't work with each other. To use them together you will have to use them in pairs (Figure 2.15).

Figure 2.15 Double Bevel Gears and Straight Gears in a Geartrain

The last gear that we'll describe doesn't look like a gear at all. In fact, it isn't known as a gear, but as a knob wheel (Figure 2.16)

Figure 2.16 TECHNIC Knob Wheel

Examine the knob wheel and you will find that it is basically a 4t gear (see Figure 2.17). Connect it with another copy of itself and you will see that it works very well as a gear. Like double bevel gears, it can also work in perpendicular setups.

Figure 2.17 TECHNIC Knob Wheel on Perpendicular Axles

In perpendicular setups, knob wheels have one major advantage over double bevel gears. Connect two knob wheels. Examine how much area on each tooth of the knob wheel contacts a tooth on the other. Compare that to a pair of double bevel gears. The knob wheels have much more contact area. This means they can transmit much more torque from one axle to the other.

The final class of gears is actually a combination of gears and bricks. They are clear LEGO bricks with gears encased inside them and axle holes on the faces. These bricks are commonly referred to as TECHNIC gearboxes (see Figure 2.18).They come in three different types. The first is a worm gearbox that functions exactly like the worm gear block with the 24t gear discussed earlier. In fact, it even has the same gear ratio, as the gear inside is a 24t gear.The second type is a 90-degree angle gearbox. Encased within it are two bevel gears at a right angle to each other. This can be used exactly like the bevel gears previously discussed. The final gearbox type also uses bevel gears at right angles. However, instead of having just two axle holes, it has three, so it can be used as a T-connection. It can be used to split the output of a single driven axle into two outputs.

Figure 2.18 TECHNIC Gearboxes

These gearboxes are functionally no different from the bevel gears previously discussed. The same gear trains could be built with the bevel gears and worm gears already discussed. However, the gearboxes do have two major advantages. They take up very little space and are able to transmit quite a bit of torque. The gears are firmly encased in the LEGO bricks, so there is very little opportunity for the gears to slip. These gearboxes do have two drawbacks.

The first is their availability. The gearboxes have been included in only a few sets and are not widely available. Second, the bricks are studded, which means they are primarily designed to be used with traditional studded TECHNIC bricks, not the studless beams included in the NXT kit and most new TECHNIC sets. This doesn't mean they cannot be used in studless constructions; as you will see in Chapter 6, using both studded and studless building techniques in a single creation is possible. Lego Mindstorms NXT hobbyist, see you next topic about Pulleys and Belts.

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