What you need:

plastic utility pulleys (for dog lines)

Smooth wheels are hard to make unless you have a machine called a lathe. So this design uses 2 "off the shelf" pulleys. They are sold in building centers (cheapest) and pet stores to tether dogs to an overhead line, giving them lots of room to run without entanglement. Try to find something pretty close in shape to the illustration, or you will have to modify the bicycle design.

I got the cheapest, smallest one I could find. If the part that sticks out from the wheel is much wider than 1", you can photocopy and enlarge the pattern until it fits.

Nails for weight

It is the weights --positioned below the string-- that make the bicycle balance. I use big nails because they are readily available and cheap. The size of nails is denoted by the somewhat archaic "penny." For one project I get 16 twenty-penny common nails (about 2/3 of a pound).

2 half-gallon milk cartons or poster board or cereal boxes.

Milk carton material is quite stiff, but you have to scuff up the surface where glue will stick to it. You should also scuff it before painting. You can use poster board or cereal boxes instead, though you might have to add layers to the acrobats for greater rigidity.

duct tape or electrical tape

The tape will attach the nails to the bar (coat hanger). It will also cover the nails. Both duct tape and electrical tape come in a variety of colors.

Pliers, scissors, string, metal coat hanger, glue gun and glue sticks, sandpaper (if using milk cartons)

Step 1

Start making the bicycle frame.

Click here and print out the pattern. Check the printed paper to make sure it did not re-scale the size of the pattern. If it says something like, "Scaled-60%" try another browser. Netscape seems to be the worst at re-scaling. Remember, though, the pattern might have to be re-scaled depending what size pulley you have. Use rolled tape "donuts" to stick the pattern in several places to the milk carton or other cardboard. Cut out on the solid lines. Take care not to cut on the dashed lines.

Fold on the dashed lines instead. Remove the paper pattern and fold into the three dimensional shape shown. Carefully glue it with the hot glue gun so it stays together. Be careful. Hot glue comes out hotter than boiling water. As you press the tab to the body to adhere it, the hot glue might squeeze out and drip .

If using milk carton, scuff up the areas that will be glued, with sandpaper.

Step 2

Glue in the wheels and strengthen the frame.

Glue the pulleys in with plenty of hot glue, as shown. Make sure the wheel does not rub against the body. Continue to coat the entire inside of the frame with it, too. The glue becomes a structural component as well as adhesive. You need this extra strength because the frame takes a huge amount of stress. Be patient when applying the glue. If you apply too much at once it drips all over. Apply a little, then do something else for awhile while it cools, before putting more on.

Step 3

Attach the bar.

With the pliers, untwist the neck of the coat hanger and straighten it out as best you can. You can find the middle of it by measuring or just balance it on your finger. At that middle point, put some kind of bend in the wire. I know it can be hard to bend such thick wire, but it needs to be done to keep the wire from rotating (even inside the glue), which will keep it from doing its job when the the weights go on. Trust me on this.

It is important that the bends be within an area the size of the the top of the bicycle body (shown as orange in the illustration).

Glue the middle of the wire onto the top of the bicycle frame, with the bend flat against the cardboard.

Step 4

Attach the weights

Bundle 8 of the big nails together. Hold them together with some electrical or duct tape. Push one end of the coat hanger wire into the middle of the bundle of nails. Then wrap more tape around the nails and also around the coat hanger so they stay together.

Step 5

Cut out and attach the acrobats.

Click here and print the page of four acrobat patterns. Unfortunately, people using the Netscape browser are finding it is re-scaling the size of the patterns. Explorer and Mozilla seem to be OK, but check to make sure the print out doesn't say anything like "Scaled-84%." Rough (bubble) cut the figures out. Stick these patterns to the cardboard (milk carton or other) with tape donuts and cut them out. Remove the patterns.

I make the bottom acrobat double layer so it's a stronger base for the two top acrobats. I just stick them together with hot glue. Next lay out the three acrobats. If you are using milk carton, scuff with sandpaper the parts that overlap so the glue will stick.

Glue the bottom acrobat onto the cycle at the head and the two hands. Using permanent colored markers is the easiest way to decorate the acrobats. You could glue some white paper to the print side of milk carton first before decorating. If you paint the milk carton, the paint will stick better if you scuff it first.

Because making the adjustments to make the acrobats to balance is inexorably tied up with why it works, all of that information is on the MORE ABOUT BALANCE page.


For explanations, activities and cool links related to whistles click here or on the picture.

Back to the tightrope acrobats page.

Back to the science toymaker home page.

I'd like to know how this project goes for you. I'm happy to answer questions about it. Feedback from you is an important way for me to know what works and what needs clarification.
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