Session 5- Gearing for Mars!

Supplies: Paper and Pencils on each table, Dry Erase Marker, White Board, LEGOs!

Today we are launching to our nearest planetary neighbor, Mars!  Listen carefully about the characteristics of the planet to understand the challenges about sending astronauts there.

Team Challenge

Eight Planets-

One way to remember the order of the planets is something called a mnemonic. 

Write on White Board:  MNEMONIC     /nəˈmänik/

The weird spelling is because the word comes from Greek, mnēmōn , which means to be mindful or remember.

In Greek two consonants were voiced at the beginning, but in modern English, we only make the “n” sound.  Everyone practice saying “mnemonic”

A mnemonic is a saying, where you take the first letter of the saying to remember something else.

It helps are brain to remember the words more like a picture in our brains.

Let’s learn some mnemonics that are out there to help us remember the order of the planets:

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

My Violent Evil Monster Just Scared Us Nuts”

Or

My Very Educated Mother Just Served Us Nachos”

Also, there is the hand method to remember the Terrestrial planets versus the Gas Giants –

Put both hand in front of your face, flip your right hand so your palm is facing you.

Team Challenge

Your Challenge as a team is come up with a mnemonic for the planets that works for your team.  It can be funny, but it should not be violent or have inappropriate words…

Write the first letters out for the planets and come up with words that fit. 

For Coach A, this one helps her to remember,

My Very Energetic Mother Just Sang Ugly Notes”. 

It helps me to remember, because I love singing silly things to kids.

Now it’s your team’s job to come up with one. Get some paper and pencils.  Take 5 minutes to brainstorm together.  Then present your mnemonic to the group.

M V E M J S U N

Take a video of the kids performing their mnemonic.

Exploring Mars with Rovers

Now that we have the planets down, let’s look closer at what scientist are sending to Mars to study the planet.

What features are on the Curiosity Rover?

  • Radiation Protection
  • Cameras
  • Telescope
  • Sample Analysis of Mars – Takes Rocks to look for Gas and Water

As you can see, there are many parts!

To build a rover, we are going to learn a lot of building techniques, we are going to start with the wheels and powering the wheels. 

On the Curiosity Rover, there was a motor to each wheel, for our system, we will only have one motor to power the wheels.  To transfer the power to at least two wheels we will need to use axels and gears.

Gears are just circles with teeth that then “mesh” or interlock with each other to transfer power.

Why do we need them? 

Well we use them to transfer power from a mechanism and in our case the power function motor to the axel to turn a wheel. 

In Lego terms, these are called the spur gears, which only mesh in-line or parallel.  Mesh, means that the gears interlock so that one turns the other.

We define the gear by the number of teeth on it, but if you don’t want to count the teeth, you can look closely at the gear and it will have a faint imprint of the number of teeth on it.  See if you can find the number of teeth on the gears.

Part 2 start here!

ACTIVITY-

There are 5 sizes of spur gears.  In your teams, try to find one of each.  The 32 tooth spur gear may be difficult to find.

Place all of the gears on one 15 long beam. Use the tan-axel pegs (remember the tan pegs are not as tight as regular black friction pegs), or use short axels with bushings.

Space the gears so that they mesh. Place a longer axel in one of the gears on the end and make a gear handle to turn the gears.

One thing to notice is that the neighbor gear turns in the opposite direction of the driving gear. Does it take an even or odd number of gears to go the same direction as the drive gear?

Take a picture of the gear stick!

Spur Gears – Gear Ratio

Now let’s look at how using multiple gears can be to our advantage to help with work!

Activity:  In your teams build a Gear Box like the one below.

Place the crank handle on the axel with the 40 tooth spur gear and an indicator on the 8 tooth gear axel. Watch the indicator on the axel of the 8 tooth gear. What happens?

The axel with the crank/ motor is called the drive gear and the other gear is called the follower gear.

If you use a 40 tooth gear to drive a 8 tooth gear, the 8 tooth gear will spin 5 times for every one rotation of the 40 tooth gear. This is called Gearing Up (Speeding up)

We make a ratio of two number by placing the follower to the drive gear: 8 to 40 and reduce it by the biggest common number, in this case, 8 goes into 40 = 5 times.

Therefore the input gear drives the output gear 5 times faster.

Here is a chart of all the different combinations you could have with Lego gears. Find the 40 tooth driver gear on top, then down the left hand side find the 8 tooth gear.

So, what happens when we switch the crank handle and the indicator?

When we use a small gear to drive a large gear, this is called gearing down. The Larger gear is going to go slower, but what we gain is strength. Strength in a circular motion is called TORQUE.

We can use the same way to make a ratio as we did earlier. The follower gear is a 40 tooth gear that is driven by a 8 tooth gear.

Therefore, the ratio is 40:8. If we reduce or divide it out, we get 5:1. It takes 5 rotation for the follower to go around once. That means that the out put will be 5 times stronger, but 5 times slower depending on how you want to look at it.

Go back to the chart and find the 8 tooth driver to the 40 tooth follower.

Bevel gears!!

The other major type of Lego gear is the Bevel gear. As you recall the Spur gear usually mesh in line or parallel to each other.

The Bevel Gears can mesh at 90 degree angles

This is a double bevel gears

These are single bevel gears

This is a knob or bubble gear. It only has 4 teeth and is easier to use because it meshes easily, but the trade off is accuracy or the ability to control how precise the gears turn. It’s a “sloppy” gear.

BUILD!

Now, make a gear box or gear stick in which you change the angle of rotation by 90 degrees, pick one of the below to make!

If you used bevel gears of different sizes, calculate the ratio. Are you Gearing up (Speeding up) or Gearing down (Increasing Torque while decreasing speed)

WORM GEARS

There is one other type of important gear. The worm gear.

Worm gears are unique in that for 1 rotation of the worm gear, the gear that it meshes with only turns one tooth. This is true for any gear that it is paired with.

We use this property when we build machines that need to be super strong. If you drive a 40 tooth gear with a worm gear. You gear down 40:1 That means 40 times stronger, but also 40 times slower…..

The gear that meshes with a worm is always rotated 90 degrees to the worm gear.

The other unique property of worm gears is that it can only be driven in one direction. It can only be driven by the worm input, not the other way around.

WORM BUILD!!!

Pick a worm gear casing to build

Try to drive the gears by the worm and then by the other axel. Look at the gear chart for the gear ratio….Notice that worms are always the driver

SPECIAL BUILD:

Now, lets use all the gear knowledge!!

In teams decide if you would like to build a Rover for Speed of for Strength?

Step 1: Locate 4 tires that are similar (or at least two). The tires will help determine the size and shape of your rover.

Step 2: Find at least 2 long axels that will be used to keep your wheels connected.

Step 3: Build a chassis.

The word chassis comes from Latin and french and means outside box

Here are some ideas for a chassis: You could use long technic beams. Or build something entirely different

Then select the gears that you would like to use… or can find….

We decrease speed, but what increases?? torque, we will talk more about that next week!

Take Pictures/Videos of the experiment

Rover 1 Build!!!!

For your first Rover, we are going to keep it simple. Remember that frequently you will need to improvise for parts! Also, finding 4 tires that are the same will be tricky, do your best! Work together in teams to build your first rover. Below are a few ideas on builds, but feel free to design your own too!

Also, notice how the black friction pegs are used to stabilize the motor to the technic beam.

Take Pictures of your FIRST ROVER! Give it a name and present to the group it’s features.

Closing, so today we learned about mnemonics, the planet order, and gears!

https://www.youtube.com/watch?v=XrWvOWK-8S0