FISCHER Profi Cartech Manual Del Usuario página 15

In the fischertechnik electric engine, you can reverse the rotational direction
easily by reversing the poles of the power supply. This is not possible with
a combustion engine; it always runs in the same direction. The rotational di-
rection is reversed there via a gearbox with a reverse gear. This model
demonstrates how this functions using the example of a simple, stationary
gearbox.
Task:
1. How can you achieve the different rotational directions in a gear-
box with forward and reverse gears?
2. Calculate the transmission relation in the forward and reverse
gears.
Solution:
We already saw in our first experiment with gear shifting that the
driven gear rotates in the opposite direction to the drive gear. We re-
verse the rotational direction once again for the reverse gear and re-
quire a third gear to do this. Consequently, gear shifting with forward
and reverse gears involves two gears working together one time and
three gears working together another time.
The transmission relation is the same in the forward and reverse
fears, i.e., 10:10 = 20:20 = 1
Model: Vehicle with Reverse Gear
(see the assembly
instructions on
page 20)
A gearbox with reverse gear is built into the vehicle in this model.
Task:
What are the transmission relations in the forward and reverse
gears?
Z20
Solution:
The transmission relation is 1:1 each time between the gears, which
are responsible for the change of direction (2 toothed gears Z20 in
the forward gear and 3 toothed gears Z10 in the reverse gear). This
means that we do not need to consider them in the calculation. Con-
sequently, we restrict our calculation to the transmission between the
geared engine shaft (toothed gear Z15) and the first toothed gear
Z20 as well as to the last two toothed gears Z10 and Z20 on the
rear axle of the vehicle.
We again calculate the total transmission by multiplying the individ-
20
ual transmissions:
*
15 10
The transmission relation is the same in the forward and reverse
gears.
Model: Vehicle with Reverse Gear and Chain
Drive
(see the assembly instructions
on page 22))
Because a real vehicle goes faster in forward gear than in reverse gear, this
model has different transmissions in both gears.
Z10
20 4 2 8
= * =
3 1 3
GB+USA
13