Mechanical Wind Turbines for Lifting Weights — Two-Session Format

This post details the two-session version of the mechanical weight-lifting variant of the Wind Turbine module (see the Overview Post for the electrical versions). The one-session version can be found here.

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Supplies

Disclaimer: We have no financial ties and receive no financial support or free/discounted supplies from any company mentioned in this activity. All recommendation comes from our personal experience.

Wind Turbine(s)

For 24 students:
Minimum = two turbines (teams of four students, three teams per turbine)
Better = three turbines (teams of four students, two teams per turbine)
Best = four turbines (teams of three students, two teams per turbine or pairs of students with three pairs per turbine)

Plans for a mechanical wind turbine are included. You can built it out of nominal 1×2 or 2×2 furring lumber — “economy” grade is fine — or any scrap lumber will do. You will also need two screw eyes, a piece of coat hanger or similar-weight wire, glue, and two clamps to attach the turbine to a stable or counter.

Hubs

One hub per team or pair of students.

Hubs from Tinkertoy or MakeIt Toy sets can be used.

Fans

One per turbine. The fans should be identical if you plan to compare results of blades tested on different turbines. If they aren’t, and your students are competing to make the best performing blades, you’ll need to retest your top candidates on the same turbine. Both floor fans and box fans work, but you’ll need to put the box fans on a table or counter level with the turbine hub.

Blades for Parameter Testing

• Assorted blade material — Examples are 1/8-inch-thick foam core board, thin corrugated cardboard, 1/8-inch-thick balsa wood, chipboard, poster board, etc.
• Tools to cut the blade material safely — Sharp scissors, hobby/precision knives (e.g., X-Acto brand), etc.
• Wooden dowels for blades — Dowel diameter depends on the size of hole in the hubs use:
  • 5/16-inch diameter for MakeIt Toy. You will have to put a little masking or painter’s (preferred) tape over the dowel end for them to fit snugly into the hubs.
  • ??? for Tinkertoy
• Glue — Use yellow carpenter’s glue for the two-day format and making the initial sets of blades. Use hot glue for student-designed blade assembly in the workshop setting.

Other Supplies

• Tape measure, yard stick, or meter stick — One per turbine
• Pencils — One per team plus extras
• Safety glasses or goggles — One per student and volunteer or several pairs peer turbine. If you don’t have enough for each person, only those wearing eye protection can be anywhere near the spinning turbine. All others must be out of the “line of fire” should a blade come out of the hub or come apart during testing.
• 0° to 180° protractors — One per team, commercial or homemade (template included)
• Timer — One per turbine, count-up capable
• Assorted MakeIt Toy or Tinkertoy rods — If using MakeIt Toy or Tinkertoy hubs
• Extra dowels ~6 inches (15 cm) long — To augment the commercial rods if using MakeIt Toy or Tinkertoy hubs. 5/16″ for MakeIt Toy (you’ll need masking or painter’s tape, as well).
• Assorted paper and plastic cups — Preferably in multiples of at least four per type
• Sturdy disposable plastic or paper cup — One per turbine
• 1/4 Inch handheld hole punch — As many as possible, up to one per team/pair
• Chipboard (cereal box)
• Scissors — One per team/pair
• ~2 yards of string — One per turbine
• Small weights — 1 to 5 grams each, about 100 grams total per turbine. Pennies work well.
• Clamps to secure the base to a table or countertop — Two per turbine
• Paper or whiteboard and marker(s)
• Record sheets
• Printed pictures or slide show of wind turbines and windmills, historical and modern (Optional)

Printables

Printable versions of all necessary record sheets, blade design sheets, protractor templates, and turbine plans can be downloaded via the button below.

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Preparation

At Home (Day 1)

Construct the wind turbine bases for toy hubs (full plans included in downloads).

Choose one cup to hold the weights for each turbine. Attach string to each. You can add a wire handle to make a “pail” if desired.

Glue the protractor sheet(s) onto heavy cardstock or thin cardboard. Cut out when dry.

Prepare the Blades:

(This is time-consuming the first time you do wind turbines. Thereafter you will simply inspect blades for damage and make repairs!) The estimates below are for six teams of four students.

Item	#
5/16″ diameter dowels, cut 5 inches long	40
5/16″ diameter dowels, cut 7 inches long	4
2″ x 4″ rectangles	12
Triangles, 1.5 inch base, 5 inches high	8
1″ x 4″ rectangles	4
Three-inch diameter circles	4
Two-inch diameter circles	4
2″ x 8″ rectangles*	4
4″ x 4″ squares	4

Glue the 7-inch long dowels onto four 2” x 4” blades, leaving four inches exposed for the shaft that will go into the hub. Glue the 5-inch long dowels onto the remaining blades leaving two inches exposed for the shaft. For the triangle blades, glue four with the exposed shaft on the base end, glue the other four with the exposed shaft on the vertex. Clamp the dowels in place while the glue dries, or carefully lay books on top of groups of blades. (Laying a book on just one blade will often dislodge the dowel.)

Apply masking or painter’s tape to the free end of each dowel. One way is to cut ¼ inch wide strips of tape about 1 ½ inches long. Apply them one at a time over, not around, the end of the dowel. Test between each piece of tape until your dowels fit snugly enough not to fall out when the blades spin, but not so tight that the tape is torn when inserted. Then wrap one piece around the dowel to cover and secure the exposed ends of the tape.

Print record sheets, one per team/pair. Assign a wind turbine base to each team.

On Site (Day 1)

Determine the placement of fans and turbines. The importance of this step cannot be over emphasized. The centers of the hubs and the fans must be aligned, and one foot apart.  This distance and alignment must be maintained for every test so students can compare results. Attaining this may require liberal use of stacks of books, fans on tables, turbines on the floor, turbines on chairs etc.

Make sure that fans can be plugged in safely. If you must use an extension cord, take steps to prevent people tripping over it.

If you are pre-selecting team members (advisable, especially for mixed ages) put team identification slips in the name tag lanyards.

Before the activity begins show your volunteers how to attach toy hubs or insert shaft/hub units, and how to attach the cup and string. The string from the cup should be wound on the shaft so there’s no slack when the cup is resting on the ground before timing begins. Remind them to make sure the hub and fan center are aligned and one foot apart before each trial. Finally, remind them to always wear eye protection, and to make sure children do as well, or are kept out of harm’s way.

At Home (Day 2)

Prepare the student-designed blades.

Prepare a large piece of paper or whiteboard for teams to post results. Punch holes in cups, two per cup across from each other just inside the rims. Enlarge one side of each hole by nipping out ~ 1/16 inch on one side of each hole with the punch.

On Site (Day 2)

Set up turbines and fans as before.

Running the Module

Day 1

Introduction (5 minutes)

The first practical wind power plants were built in Persia (now Iran), around 600 AD. These windmills were used to grind grain or draw up water.  (Show pictures if you have them.)

Torque is rotational force. While linear force is a push or a pull, torque can be thought of as a twist to an object. A weightlifting wind turbine needs to develop torque to lift loads.

• There are many parameters or variables that determine how fast a hub with blades spins. Drag, pitch, number of blades, and shape of blades are some of them.
• Have children rub their hands together until they feel heat, i.e. the effect of friction. The friction of air against the blades is called drag. Put dots on one blade, one close to the tip, one close to the blade shaft. Which dot moves fastest when the hub spins? Which dot feels the most drag?
• The angle the blade makes with the direction of the wind is called pitch. The pitch can be anything between 0 and 90 degrees. Show the students how to estimate pitch using the protractor (see below).

• Demonstrate adjusting pitch by grasping the shaft, not the flat portion of the blade. Twisting the blade alone, especially if the hub has been tightened, inevitably leads to broken blades (balsa) or blades being ripped off of the shafts (foam core board, chipboard, corrugated cardboard.)
• Explain that they must share blades today, so it’s important to take only the blades needed for each test, and return them right away when finished with that test.
• Explain that there are five tests to explore these parameters or variables. Each test changes only one variable at a time. Do the one marked on the record sheet first, then the other three in any order until time is called.

Tests (35 minutes)

Allow the teams to work on the five tests. Call time after 35 minutes, or when all teams have finished all five tests, whichever comes first. Teams that finish ahead of the others can do additional Test 5 trials using different blade designs.

The tests investigate the impact of (1) number of blades, (2) distance of the blade from the hub on drag, (3) distance of blade surface area from the hub on drag, (4) blade pitch, and (5) blade shape. The procedures are detailed on the provided record sheet.

Design (20 minutes)

Gather the students, seated together by team and turbine. If any teams did not complete Tests 1-4 they should now get that data from another team that used the same turbine.

Hand out the blade design sheets. Explain that the blade will be cut out and the shaft glued on exactly the way it is drawn on the grid. Display blade materials if more than one will be offered.  Before students leave make sure names are on the record and design sheets, and that they’ve chosen a company name.

Day 2

Introduction (5 minutes)

The challenge for today is to pretend each team is a wind turbine company. Their customers want to know what blades to use in order to generate the torque to lift the most weight as quickly as possible.

Return the record sheets to each team. Ask teams about the trends they saw at the last meeting with the blade experiments. How did number of blades and pitch effect lifting speed? What about shape, surface area, and distance from the hub effects on lifting speed?

Challenge Activity

Teams will maximize the torque produced by the blades they designed last week. Remind students to change only one variable at a time for best results. Teams test their original design and configuration, then continue to adjust and test until time is called. Teams should use the same turbine for each trial.

Testing for speed alone provides for the fastest turn around, keeping students actively engaged.

To keep enthusiasm high let teams post their results by “company” name on posted paper or whiteboard whenever they beat the current best time. Substitute seconds for volts in the sample below.

Stop when you have about thirty minutes left or when enthusiasm starts to wane. Ask each team to prepare its fastest blade configuration, and retest these to determine the maximum weight they can lift. Students add weights to the cup as it’s rising, starting over as many times as needed until the limit is reached. For example, if the cup contains 10 grams when it reaches the top return the cup to the floor, restart the fan and add more weight. If the cup holds 25 grams when it reaches the top return the cup to the floor, restart the fan and add more weight. Repeat these steps until the cup and weights no longer rise. When all teams have finished testing, gather the students.

Close

Which company made the fastest blade configuration? Which company’s blade configuration lifted the most weight? Were they the same? What characteristics did successful blades have in common?

If Time Allows…

You are likely to have some time left over, especially if you stopped speed testing before thirty minutes. Show the students how to slide the cups onto Makeit Toy or Tinkertoy rods, and how to punch holes in chipboard blades, then slide them onto shafts. Show them how to make blades by sliding a piece of chipboard into the slot in the rod, and hold it place with another bit of chipboard. (Sometimes you have to peel the chipboard wedge to make it a bit thinner.) Allow teams to freely experiment with these materials until time is up. Again, test only for speed to allow as many trials as possible.

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How did your young engineers do? Did you make any tweaks to the activity that worked well for you? What blade designs and setups worked best? Any surprises? We’d love to hear from you! Drop us a note or leave a comment!