Thames & Kosmos DLX, Experiment Manual, Page: 59 / 132

Drawing a circle of
sand with the crane
YOU WILL NEED
› The assembled crane
› IR remote control
› 5 AA batteries or 5 AA rechargeable batteries
› Small paper cup
› 2 paper clips, pin
› Fine sand
› Trowel and hand broom
HERE’S HOW
1. Use the pin to poke two small holes on opposite sides
near the cup’s rim. Thread a paper clip through each
hole. Now you have made a cargo basket that you can
carry around with the crane.
2. Familiarize yourself with the controls of the crane and
set the basket within the reach of its arm.
3. Drive the crane up to the cargo basket so that all you
have to do next is hang the paper clips through the
holes of the crane’s hook.
4. Then lift the basket up. Swing the arm around in a
circle and set the basket down in another spot.
5. You can also use the crane to draw a circle. It’s best to
do this outside.
6. To do that, take your cargo basket and poke a hole in
its bottom. Make it just big enough to let the sand
trickle out slowly.
7. Set the paper cup on the ground and fill it with sand.
Depending on how much sand you use, you might have
to mount a counterweight on the driver’s cab behind
the receiver.
8. Hang the cup on the hook. Now you can slowly lift the
cup and swing it around in a circle. As the sand trickles
out, it will create a circle of sand all around the crane.
How cleanly can you draw it?
9. Don’t forget to sweep up the sand afterwards.
WHAT’S HAPPENING
Since the motors are mounted on the crane in a way
that makes them easy to see, let’s take this
opportunity to look into the motor box. You can see
how the transmission system is assembled in the
motor and how the different gears mesh with one
another. There’s an important concept at work
here: the transmission ratio. This refers to the
ratio among the numbers of gear wheel teeth.
Your motor’s transmission system consists of
three transmissions: Set A has a ratio of 20 to
8, Set B a ratio of 28 to 8, and Set C a ratio of
30 to 8. So the overall ratio is 20/8 x 28/8 x
30/8, or 32.8125 to 1.
In other words: If the motor turns 32.8125
times, the shaft will turn once. If the motor
is turning at 3,200 rotations per minute, the
shaft will turn about 100 times.
This kind of transmission ratio lets the
motor exert a lot of force to the shaft
through the gears. That way, you can use
the crane to lift heavier weights.
Shaft Motor Set A Set B Set C
EXPERIMENT 8
57
Robots for Transport