Rubber-band Racers

This lesson plan is a derivative of the Rubber-Band Powered Car
created by Thingiverse member mrigsby

Energy is the ability to do work. All forms of energy fall into two basic categories:

potential energy
kinetic energy

Potential energy is mechanical energy which is due to a body's position. It is also known as stored energy.

The vehicle you will be making is powered by a rubber-band. When you wind up the rubber band, you build up potential energy. The more you wind the rubber-band, the more potential energy you'll have. The moment you release the rubber-band, that potential energy is converted into kinetic energy. Kinetic energy is the work needed to accelerate a body of mass from rest to its current speed. The kinetic energy stays the same until the speed of the mass is altered. This new form of energy makes your car accelerate forward and race across the floor!

Can you answer this question?
Does the size of the body or the wheels affect the speed

Instructions

Download the Stls files from Thingiverse
Print one base, two sides and four wheels.
Snap the sides onto the base.
Insert a round pencil into the wheels and through the base.
Add a rubber band.

For more details on construction, go to: Rubber-Band-Car-Printed-in-3D

Extensions

How does the width or diameter of the wheels affect speed?
What other variables can you change that might affect how fast the vehicle travels?

Modify the design and test.

Questions to consider

Where does the energy to move the vehicle come from?
What affects the distance the vehicle travels?
If you were going to make improvements to your vehicle, what would they be? Why would you make them?

Have students build, weigh, and test their vehicles. Students can make as many changes to their vehicles as time allows.

Use the masking tape to mark the starting line and one-meter intervals down the course. As a class, decide on a consistent method for launching vehicles so that students do not add energy with a forward hand motion when the vehicles are launched.

Conduct the competition. Have each team carry out three or more trials of each of the last two performance expectations (farthest distance traveled and farthest distance traveled with load), and average the scores for each expectation. Someone must be the scorekeeper.

Following the competition, have each team present its design approach. Have students consider the following questions:

After each of your tests did your vehicle perform as expected? Explain.
What final modifications did you make to your vehicle? Why?
As a class, summarize the most successful characteristics of the overall winning designs and the most successful characteristics of those designs that were top in their performance expectation categories. What did the winning vehicles have in common? If students had another chance at design, what would they do for their next-generation vehicle?
As an extension, have students race their vehicles on a completely different terrain, such as grass or dirt. How did the vehicles perform? What changes would students make to the vehicles based on test results? Why?

Wind Turbines

Converting kinetic energy into electrical energy. Kinetic energy of wind turns the blades which drives a generator that converts the kinetic energy to electromagnetic energy.

The current is used to do work, while voltage (the resulting force after overcoming resistance) is the energy required to drive the flow of the current.

A Turbine

The basic concept is simple. A framework or support column holds up a large wheel or turbine blades that looks like a fan or airplane propeller. The angled blades catch passing winds and deflect some of the wind's energy, which pushes the blades around, turning a central shaft. The shaft can be connected via gears or belts to machinery on the ground or in a nearby structure. Alternatively, the shaft can be connected directly to a generator that produces electricity, which is then transmitted.

Blades

Blades of a windmill spin because of two principles:

Newton's Third Law—For every action there is an equal and opposite reaction. So when the wind hits the blade, the blade is pushed. If the blade is at a certain angle, the wind is deflected at an opposite angle, which pushes the blades away from the deflected wind. You can see this in action with the flat blade. If you push the blade it will will move in the direction away from your finger.
The Bernoulli Effect—Faster moving air has lower pressure. Wind turbines are cambered so that the air molecules moving around the blade travel faster on the downwind side than on the upwind side. This shape is like a teardrop. The downwind side is curved, while the upwind side is almost flat. Air moves faster on the curved, downwind side of the blade so there is less pressure on this side of the blade. The difference in pressure on the other side of the blade causes the blade to be lifted toward the curve of the airfoil.

Experiment:
1. Take two pieces of paper
2. Fold them in half
3. Unfold them and them together so that the folds you made line up but the creases should be on the outside
4. Blow between the papers
5. Did it match your expectations
The speed of the air is higher between the two pieces of paper than outside the papers. Higher velocity leads to a lower pressure between the sheets.

How blades capture wind power

Wind turbine blades work by generating lift with their shape. The more curved side generates low air pressures while high pressure air pushes on the other side of the airfoil. The net result is a lift force perpendicular to the direction of flow of the air.

Lift and Drag Vectors from WE Handbook- 2- Aerodynamics and Loads

The lift force increases as the blade is turned to present itself at a greater angle to the wind. This is called the angle of attack. At large angles of attack the blade stalls and the lift decreases again. When it comes to generating the maximum lift, there is an optimum angle of attack.

Another force also exists. This is called drag. This force is parallel to the wind flow, and also increases with angle of attack. If the airfoil shape is good, the lift force is much bigger than the drag. But at very high angles of attack, the drag will increase dramatically. When the angle is slightly less than the maximum lift angle, the blade will reach its maximum lift/drag ratio. The best operating point will be between these two angles.

The blade's own movement through the air means that the wind is blowing from a different angle. This is called apparent wind. The apparent wind is stronger than the true wind but its angle is less favorable: it rotates the angles of the lift and drag to reduce the effect of lift force pulling the blade round and increases the effect of drag slowing it down. So, to maintain a good angle of attack, your blade must be turned further from the true wind angle.

The closer to the tip of the blade you get, the faster the blade is moving through the air and the greater the apparent wind angle is. Therefore the blade needs to be turned further at the tips than at the root. Your blade must be built with a twist along its length. Typically the twist is around 10-20° from root to tip.

In general the best lift/drag characteristics are obtained by a blade that is fairly thin.

Length: The blade length determines how much wind power can be captured.

Aerodynamic Section: The blades have an aerodynamic profile in their cross section to create lift and rotate the turbine.

Planform Shape: The planform shape gets narrower towards the tip of the blade to maintain a constant slowing effect across the swept area. This ensures that none of the air leaves the turbine too slowly (causing turbulence), yet none is allowed to pass through too fast (which would represent wasted energy).

Airfoil Thickness: The thickness increases towards the root to take the structural loads, in particular the bending moments. If loads weren't important then the section thickness/chord ratio would be about 10-15% along the whole length.

Blade Twist: To maintain optimum angle of attack of the blade section to the wind, it must be twisted along its length.

Blade Number and Rotational Speed: Typically three blades.

Pitch Control: Because the wind power varies so greatly (with the cube of wind speed), the turbine must be able to generate power in light winds and withstand the loads in much stronger winds. Therefore, above the optimum wind speed, the blades are typically pitched either into the wind (feathering) or away from the wind (active stall) to reduce the generated power and regulate the loads.

Assignment

Create a mechanism that will spin in the wind. Attach the mechanism to a low RPM motor. Attach the leads of the motor to an LED. As the blades spin, the LED should light up.

Vocabulary

Axle – The central shaft for a rotating wheel or gear.

Friction - The resistance of an object to the medium through which it is traveling, such as air or water, or that it is in contact with, such as a solid floor. Inertia–The tendency of a body at rest to stay at rest and a body in motion to remain in motion unless acted upon by an outside force.

Kinetic energy– The energy due to the motion of an object.

Potential energy– The energy an object has due to its position or internal condition rather than its motion.

Forces - Forces are the pushes and pulls in different directions. The direction and the strength of the force will be dependent on the strength and direction of all of the forces created by the forces added together. Scientists and engineers refer to this as the "sum of all the forces."

Project 3

This project was inspired by wings.avkids.com

Working in groups, build a toy helicopter just like the Wright Brothers did!

Materials

2 Makerbotted Propeller blades
2 Makerbotted fins and strut
Makerbotted base and cork replacement
17" Long Rubber Band
1-Inch Diameter Domed Washer
2 Heavy Duty Paper Clips
Super glue
Needle Nose Pliers
Wire Cutters

Here is a template for the propeller:
Recreate this:

Open this stl in OpenSCAD and make a hole through the top for the wire.

Make a cone with a small hole in the center. and two other holes for the struts

Make the struts attached to fins.

Make a base with hole.
Bend the bottom of one of the paper clips into a hook shape as shown. Insert it through the bottom cork of the helicopter assembly. Bend the upper portion also into a hook shape.

Make a base with hole.
Bend the other paper clip in a tight hook so that it slides through the propeller hub (hole). Pass the paper clip through the domed washer with the dome (convex) side against the propeller. Now pass it through the upper cork end and bend the end of the wire into a hook.

Make a base with hole.
Attach the rubber band stretching between the upper and lower clips.

Make a base with hole.
You are ready to launch your helicopter! Holding the bottom base, wind the rubber band into a spiral. Hold the helicopter in one hand by the base, away from you but pointing up. Release the propeller and allow it to build up speed for a second, then let go of the base. The helicopter should rise 10 to 15 feet before the rubber band unwinds.

Make a base with hole.

Blender

Using Blender

The Loft tool is turned off as the default in Blender 2.62 and may not exist in your Blender 2.63 version.

To use it in version 2.62 or before open User Preferences>Add-Ons>Mesh>LoopTools
If you don't have the LoopTools option go to this page, download the python script (put it in a convenient place). Click on install AddOn
Install the Add-On
Enable it
Click as Save As Default

To use it in version 2.63 you may need to download and install the bsurfaces addon from here. If you don't find it in User Preferences>Addons>Mesh then download it.

Open User Preferences>Addons>Mesh
Click Install Addon... and navigate to your download
Enable it
Disable Smooth Stroke in preferences in Editing preferences
Click as Save As Default

Using LoopTools

To use the Loft tool you must be in Edit mode. Select the vertices and press W, then Loop Tools and Loft.

You need to make sure that your shape in Manifold (water-tight).

Select SHIFT+CTRL+ALT M if anything is selected go to Object mode and apply a Solidify Modifier

Return to Edit mode and reselect SHIFT+CTRL+ALT M. Still a problem? Try recalculating normals and try again.

Using BSurfaces

bsurfaces is an AddOn that allows you to create meshes from curves and the grease pencil.

Add in a mesh in Object mode
Go to Edit mode
Delete the vertices (X)
Press N to open the right panel. Add in a grease pencil layer (but don't hold D and drag because this will be perpendicular to the view).
Set Drawing Setting to Surface
Now hold down D and LMB drag/ D and RMB erases
Strokes (or curves splines) must be drawn in the order you want the surface to be built. The direction of the stroke determines how the surface is built. The first point of each stroke will be connected to the first point of the next, and each last point to the last point of the next.
Drag a few lines to describe start middle and end
Add surfaces from the BSurfaces Panel in the tool shelf
After the surface is built, the number of face-loops crossing the strokes and face-loops following the strokes can be edited. Other Bsurfaces options can also be tweaked in real-time in this panel.
OPTION/ALT RMB click on the last loop to select it and add more lines. Connect them by adding surfaces

How to use Loft in Blender

Add a bezier curve and adjust the curve in Edit mode
Back in Object mode, make a duplicate (SHIFT+D) or add another curve. Edit the curve in Edit mode
Dupe or Add and edit a few times
In Object mode convert each curve to a mesh
Select the separate meshes and join them (CTRL+J)
In Edit mode select all the vertices (A), press W and select Loop tools and Loft
In Object Mode add a Solidify modifier
In Edit mode check for Non-manifold SHIFT+CTRL+ALT M.
If something is selected try Recalculating Normals
Retry SHIFT+CTRL+ALT M