Ch11 - Frogs
About 400 known frog species exist. They vary in size, shape, color and lifestyle. All frog species, including true toads, midwife toads, spadefoot toads and tree frogs, are classified as tailless amphibians.
Frogs move in an easily recognizable fashion. Their long, strong rear limbs adapted to performing long leaps. The best frog jumpers can hop as far as 4 meters at once. Such long leaps are perfect for running away from danger, but not all frog species move like this; some prefer running or marching. Others, like the species that live in aquatic environment, are great swimmers.
Flying frogs are also intriguing. They perform characteristic gliding leaps that allow them to cover great distances. Those "flights" are possible thanks to the special build of these frogs. They have widely webbed feet and some even developed lateral skin flaps that enlarge their body surface.
Leaps are one of possible ways to avoid danger. Coloration is another. There are two types of frog coloration – bright colors, which warn enemies of a frog’s toxicity, and camouflage browns and greens, which help the animal hide from predators.
Toads have an interesting defensive mechanism. Whenever they sense danger, they inflate and pretend to be too big to swallow.
Many frog species produce poisonous toxins. They are found on the surface of frogs’ skin and can induce swelling, muscle paralysis, or even death. Frog toxins contain substances from poisonous ants, termites, millipedes or small beetles – all of which compose a part of frogs' diet. Toxins are absorbed from the food and transported to poison glands.
Toxic frogs are usually brightly colored. Thanks to these colors, poisonous frogs are true gems of rainforests. Poison dart frogs and phyllobates are counted among the most toxicant species; their secretions were once used to prepare poisonous arrows. However, the most poisonous species in the world is the golden poison frog. This small animal produces toxin capable of killing several adult humans.
Not all frogs are poisonous. Some species’ secretions have healing properties, like the waxy substance produced by an Amazonian frog species, potentially useful in treating patients with AIDS. Another species produces substances used in creating a powerful painkiller that does not cause any side effects.
The goliath frog is the largest species of frogs on Earth. It inhabits a small area in Africa. The frog is an endangered species protected internationally. The goliath's meat is very tasty, which contributed to the threat of extinction. These frogs can grow up to 30 cm long and weigh over 3 kg.
The Brazilian gold frog, in turn, is the smallest frog in the world. Adult specimens are less than 1 cm long.
Everyone knows frog's croaking. This sound helps male frogs to intimidate other males and attract females at the same time. Interestingly, every species has its own distinctive croak. In Borneo, a frog species was discovered, which communicates not only via the old-fashioned croaking but also relies on ultrasounds.
Baby frogs do not resemble their parents at all. They have a different lifestyle, their build and diet also differ from their parents’. In the larval stage, they hatch from eggs as tadpoles. They have tails with fins and breathe through gills. The changes they undergo to become adult frogs are called metamorphosis. During this process, tadpoles lose their tails, form limbs and lungs, and gain the coloration of adult frogs.
Build
To build this model, you will need LEGO Education WeDo 2.0
Explore
The main part of this model is composed of two frogs, out of which only one can jump at a given time.
The user can choose which one should jump via a lever with a tilt sensor installed.
The drive from the motor is relaid through a smart transmission.
The construction relies on three electronic elements.
1. The hub powers and controls the elements connected to it, in accordance with the program created.
2. The motor propels the two frogs. By changing its rotation direction, you can move either the first or the second frog.
3. The tilt sensor allows to control which frog should move.
1. You can choose which frog should jump by using the lever in front of the construction. The tilt sensor installed underneath sends a signal relevant to the position it is currently at.
According to the program, you choose the frog by tilting the lever in its direction.
Let's take a closer look at the mechanism separating the motor drive on two sides: right and left.
1. The motor propels one axle equipped with: a small cogwheel, a loosely installed beam, and small bushings operating a yellow rubber band.
2. The beam creates a movable arm, which tilts to the right or to the left side. The last small cog on the arm meshes with a large cogwheel on either side and thus, transfers the power.
3. To sum up, the construction has two transmissions, but only one of them operates at a given time. In each, the first cogwheel has 8 teeth, the last one 24. It means that the gear ratio is 3:1 and the speed decreases.
Tilting the arm, which transfers the drive onto either of sides, happens after switching the rotation direction of the motor.
1. The axle receives drive from the motor and rotates the bushing, which turns yet another bushing on top of the arm, via a rubber band.
2. The short axle with two bushings rubs the arm while rotating, which makes the rubber band tighter on one side. As a result, the arm tilts to this side.
1. The motor steadily propels the brick with two blades.
2. The black pin is lifted by the blue blades and drops afterwards.
3. The tan pin limits the wheel movement on the other side.
4. The brick at the end of the axle creates a moving spot, where the frog figurine stands.
5. The mechanism on the other side is a mirror image of the one described above.
1. Two frogs sit across from one another. Only one can jump at a time.
They are green, as all true frogs should be.
Program
Let's begin the jumping frogs program with the starting block.
