Session 6 – Lunar Levers

Just as gears change speed and strength (torque), Levers are an important simple machine that can be used to make work easier.

Review from Last Session

Let’s review what we learned at our last session of Lego Engineering.

What are three type of gears that we explored last session?

Spur, Double Bevel and single bevel. What are two different ways to figure out how many teeth the gear has?

Count or on the Spur gear, it’s printed on the gear.

What was the feature that makes bevel gears different spur gears?

They can mesh at 90 degrees or what we call a right angle. While spur gears can only mesh in line or parallel.

What does Gear Ratio mean? and how does it change the work that is performed?

The different sized gears can make the system turn faster, or stronger depending on the size difference. Remember that torque is the word for strength while rotating or spinning.

If the Larger Gear is the gear, is the smaller gear going to turn faster or slower compared to the larger gear?

The smaller gear is going to rotate faster.

Since we know how many teeth are on each, we can actually calculate how much faster the 8 tooth smaller gear will rotate.

the Gear ratio 40:8, which reduces to 5:1 so the smaller gear will rotate 5 times faster

Or you can think of it as rotating 5 times for every one rotation of the 40 tooth gear.

Now think about the opposite, if the 8 tooth gear is the drive gear, it will only spin 1/5 th of the big 40 tooth gear. But the energy in the system stays relatively the same, so the big gear is going to have 5 times the strength (torque)

So if you wanted a super strong motor output, you could connect many small to large gears. Look at this gear box and follow the input from the motor to the output axles. Would the output be faster or slower than the input from the motor?

Switching Gears to remembering your Mnemonic for the Planets…

Coach A’s was: My Very Energetic Mother Just Sang Ugly Notes

What was yours???? MVEMJSUN

Now to Lunar Levers!

Let’s start with word the word Lever comes from. If you take the word apart, the ROOT of it is LEV

LEV comes from Latin and means to make weigh less. (Can you think another word that uses the root LEV that means to float in the air, maybe a Harry Potter Spell???

Look at the work tree below and see all the words that have LEV in them

Now onto the LEV-ERs

The classic lever is the see saw. For any Lever you have three parts:

The fulcrum (the pivot or support point), effort (the black heavy brick) and load (Lego Dude). Point to the fulcrum, effort and load in this picture. One way to remember the parts of a lever are by the Mnemonic ELF : effort, load and fulcrum

Here are other Levers, that are not quite as obvious for the ELF parts as the seesaw. Point at the ELF parts in each of these Lev-ers. Which one do you think is the Class of Lever that is a Catapult?

Here is a simple large “L” beam. Where is the ELF on this machine?

Intro to Video of the Day!

One famous Scientist, Archimedes, once said, “Give me a place to stand, and I shall move the Earth.”

We are going to start our first video to look at how Lev-ers make work easier for us.

So you only need a lever that is a quadrillion light years long to lift earth!!!! One light year is only about 6 trillion miles….

BUILD

So today, our first build is the see saw. I call it the balancing Lever, We are going to build a base that we will use for the see-saw, and then move the arm of the see-saw and create a catapult.

Start with building a strong base. This can be built with regular Legos, technic bricks or beams. Make the base so that it’s about 5 to 10 bricks high. Here are a few ideas below.

Then place technic bricks ( or anything with a hole for an axle) for the fulcrum area.

Here are three other examples of Lever bases.
More involved Lever base

Now make a long arm that is the actual Lever part. You can use a 15 long technic beam. Also, you can make it longer if you use two friction pegs and more technic beams. n

Now that you have a lever arm built. Attach it to your base so it is balanced/equal on both sides with an axle and bushings on the outside to keep it in place

Now for the experiment!!!!!!

Place two Lego People (or bricks) on one side of the beam. (All bricks and people should be the same) Make sure your arm is balanced and freely moves before starting.

Now, where would you place one Lego Person (or bricks) to balance the other other two on the other side? What is the distance from the fulcrum for the two bricks, and what is the distance from the fulcrum for the one brick?

Can you think of three different ways to solve this problem? Take Pictures.

Part 2 of Levers – 

Skip Video if running short on time and go directly to the catapult build

Now, one thing that Levers help us overcome is Gravity. Let’s look at the Gravity on Earth and on the other Planets.

One thing that we will need to understand on Earth and on Mars is Gravity. (Play up to about 4 minutes in, just after it talks about Mars)

So the gravity on Mars is 0.38 Gs, or very similar to the Moon. So even on Mars, we will likely need simple machines to help get work done.

Our next challenge is to build a catapult using the engineering principles that we just learned to launch a Martian Rock ( a 2×2 brick). We will see which team of engineers can develop a catapult that will launch him the farthest.

A catapult is a type of lever that uses rubber bands or rope to store potential energy till it is needed to launch. Identify the ELF( where is the effort placed, where is the load, where is the fulcrum?

Start by modifying your previously built base. Remember the engineering method of design, test and re-design. Here a few examples.

In this model, the axle is a fulcrum and also a “stop” for the lever arm. This launches the load forward.


In this Catapult there is no “stop” for the lever arm. So it depends more on the length of the arm and the tension of the rubber bands to “aim” the load

This next one is a little more involved and uses a ratchet and pawl to wind up the rubber band. Then when ready, you pull the pin.

This model uses a brick on the base to act as a “stop” for the lever arm.

Have a contest to test which Catapult can Launch a Lego astronaut the farthest. Take Pictures!

Likely that will take all the time up for Session 6!!!!

If time you can move onto Linkages

From levers to linkages

An interesting thing happens when you connect ends of two
identical levers located one above the other: The elements
connecting their ends will maintain the same position as
the levers move. This happens at every point in the levers’
range of movement, regardless of their length. We can use
this system of parallel levers, also known as a 4-bar linkage,
to our advantage.


BUILD

Now we are going to create a lever/linkage system to launch the Space Travel Model. The cars start on the orange pad at the top of the ramp. Your mission is to create a lever/linkage system that will lift the cart to send it down the ramp. Only Legos can be used as the support for your lever. You can use a finger, rubber band or power function pack to be the potential to kinetic energy to the lever.

Once complete. Share your ideas with the group. Take a picture!

Today, we learned that lev- means to lighten and it the root of the words Lever and to Levitate. We built a special type of lever a Catapult. We then linked the levers, to make a lift to launch the Space Travel cars.

Here is extra information on Linkages!

Chebyshev linkage


The Chebyshev linkage, also known as Tchebycheff’s linkage,
consists of three links and is driven by the rocking motion
of the lower links (light grey). This motion makes the central
link (yellow) move so that its center (marked by the red pin)
follows a straight line. The motion continues to the point
at which the central link becomes vertical. The central link
needs to be the shortest of the three to prevent it from
colliding with the supporting structure (dark grey).

Sarrus linkage


The Sarrus linkage consists of four links in two identical
groups that are perpendicular to each other. All links are
of equal length, and the linkage is driven by the rocking
motion of both lower or both upper links. The advantage of
the Sarrus linkage is that it can be used to lift the structure
connecting the upper links, providing an impressive range
of movement as seen in Figure 8-19). Note that the perpendicular
links work in different directions and thus exert
stress on each other, which is why they need to be very rigid
and preferably several studs wide for the linkage to work
properly.
The disadvantage of the Sarrus linkage is that it
requires one link from one group to be moved simultaneously
with a second link from a second group. In other