Gear Shifting - FISCHER Profi Cartech Manual Del Usuario

The transmission ratio is often written using a colon instead of a fraction:
Transmission ratio in:
Experiment 1 = 20:10 = 2:1 Experiment 3 = 20:20 = 1:1
Experiment 2 = 10:20 = 1:2 Experiment 4 = 10:10 = 1:1
If the number before the colon (toothed gear number of the driven gear) is
greater than the number after the colon (toothed gear number of the drive
gear), it is a transmission into slower rotation, called "speed reduction". If
the number after the colon is greater than the number before, transmission
is to faster rotation.
The way you write this down is up to you. We will use both ways in the ex-
periments below.
Using this knowledge, you can build cars that move either fast or slowly.
Take a look at the assembly instructions. You can find three vehicles there
(a tractor, a racing car and an off-road vehicle), which use a chain as a
drive.
Models: Tractor, Racing Car and Off-Road Ve-
hicle Drives
(see the assembly instructions on page 8)
The three models only differ in their combination and arrangement of
toothed gears.
Task:
Write down the number of toothed gears of the drive and driven toothed
gears for each model in the table and calculate the transmission.
Model Drive gear
Tractor
Racing car
Off-road vehicle
(4-wheel drive)
Solution:
Modell Drive gear
Tractor Z10
Racing car Z20
Off-road vehicle
Z20 and Z10
(4-wheel drive)
Assembly the models one after another and make the following experiments
with each model:
Experiment 1:
How fast is the model?
Set a distance, e.g., one meter long, and measure the time that the
model requires for it using a stopwatch.
Driven gear Transmission
Driven gaer Transmission
Z20 2:1
Z10 1:2
Z20 and Z10 1:1
Experiment 2:
What incline can it ride up?
You can use a board for the incline, for example, which you lean on
a pile of books or a chair.
What can you observe?
Observations:
The tractor is the slowest model, but is able to go up the highest in-
cline. The racing car goes the fastest, but is only able to go up a
slight incline. The off-road vehicle is between the other two.
Results:
You can see that the faster the car, the less power the wheels have.
This power is called "torque" in engineering. The torque is in an in-
verse relation to the transmission, i.e., if the rotational speed is dou-
bled between the drive and driven gears, the torque is halved (racing
car). If the rotational speed is halved, the torque doubles.
Now you can imagine why although your bicycle is slower in 1st gear, you
can ride up almost every mountain (slow speed, high torque).

3. Gear Shifting

You can change the rotational speed and torque not only with a chain, but
also with gears in which the teeth grip one another directly. Of course, this
saves space. Contrary to chain drive, the driven gear rotates in the opposite
direction of the drive gear.
Why do we use gears? We could also regulate speed simply by using the
gas pedal.
Most engines have too high a rotational speed and too little power without
gears, so that the wheels cannot be driven directly. That is why we reduce
the rotational speed with a gear and increase the available power at the
same time. Additionally, many engines do not provide the same power in
each rotational speed range. By shifting gears, an engine can always run in
a favorable rotational speed range, regardless of how fast you want to go.
Similar to in a car, we are now going to assemble a gearbox with which we
can switch gears using a shift stick. So that it does not get too complicated,
we will assemble a gearbox with only two gears.
Model: Gear Shifting
(see the assembly instructions
on page 14)
GB+USA
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