Why is a gearbox geared this way?

[Thenior]

Move to other forum if this isn't the best one.

Look at this image:



Though it's not to scale, hopefully it conveys the idea. Why does this gearbox have these series of motors, instead of just going straight from a small gear on the motor shaft to a big one on the axle?

[snoopy]

Each stage provides more reduction.

Let's say that the motor (and the small shafts) has a diameter of 1, the large gears have a diameter of 2, and the big one on the axle has a diameter of 3.

If the motor directly drove the large gear on the axle, you would get 3:1 reduction - or a torque multiplication of 3.
As shown you get a reduction of 2*2*2*3:1 = 24:1.

Generally speaking, motors usually have a higher speed and lower torque than what you really need, especially as you go down in scale.

[Grendel]

Trying to avoid gears that are very small or very large & creating places where gears can be shifted. I'm sure there are more reasons.

[Isaac]

Each stage provides more reduction.

Let's say that the motor (and the small shafts) has a diameter of 1, the large gears have a diameter of 2, and the big one on the axle has a diameter of 3.

If the motor directly drove the large gear on the axle, you would get 3:1 reduction - or a torque multiplication of 3.
As shown you get a reduction of 2*2*2*3:1 = 24:1.

Generally speaking, motors usually have a higher speed and lower torque than what you really need, especially as you go down in scale.

tl;dr: Torque

Though it's not to scale, hopefully it conveys the idea. Why does this gearbox have these series of motors, instead of just going straight from a small gear on the motor shaft to a big one on the axle?

Saves space. Small gears can be set to conform to limited space. One big conversion would require a big ass disk. Source: Legos and Erector Sets.