Introduction: Mechanical Frog Motion Simulator

This project shows how to build a machine that simulates basic frog movement.
The machine starts out flat on the floor. A motor pulls in the legs and bends spring steel strips. The spring steel strips cause the frog body to tilt upward off the floor and onto the foot. When the machine reaches a fully crouched position, the legs are released and the spring strips unbend, launching the body into the air. It lands flat on the floor and the cycle repeats. The PDF drawings below give a more detailed description.

The only power tools needed are a dremel, and a drill, the rest can be done with hand tools. The cost is low, about $30 including the motor. A second one can be built for about $15 more(the cost of a second motor).

I designed it myself,  using mostly left over parts from home improvement projects.
The machine is 32” long and weighs 2-3 pounds. It jumps 12 to 15 inches, but with more powerful springs, who knows?

I’m trying to start a mechanical frog jumping contest with my kids.
So far, they just want to make a big one we can ride.

Thank you for viewing my instructable. 
Hope you like it enough to build one, or two.

Step 1: Materials and Supplies Needed


 2-  21" lengths of metal electricians fish tape (A)
 1-   Hobby Motor (B) [ TAMIYA   6-Speed Gearbox H.E. ]
 1-   Wooden Axle Peg (C) [ Darice  Axle Pegs sold at  craft stores]
 1-  1" PVC Coupling (D)
 1-   3/4"x 5-1/2"x 12" Pine board (E)
 1-  15-5/8" length of 3/4" schedule 40 PVC pipe (F)
 1-  16" length of 1" schedule 20 PVC pipe (G)
 1-  16" section of a Saddle Threshold 3" wide x 1/2" deep (H) [ Frost King AT 43/36 ]
 1-  14-1/2" length of 3/4" hardwood dowel (I)
 1-  2-5/8" length of 3/4" hardwood dowel
 1-   Battery Holder for 2 AA Batteries w/ On/Off switch

 2-  #4 x 1/2" flat head wood screws
 4-  #6 x 3/4" round head wood screws
 5-  #6-32 x 3/4" flat head machine screws
 2-  #6-32 x 1/2" round head machine screws
16- #6-32 nuts
15 to 40-  #6 flat washers 

Miscellaneous Supplies:
    - PVC Primer
    - PVC Cement (Glue)
    - Epoxy Glue
    - Sandpaper ( 120 and 600 grit )
    - Duct Tape
    - Permanent Marker
    - Household tape
    - paper
    - 22 awg wire for motor to battery connection
    - solder or wire nuts
 2 - AA batteries

     - Basic hand tools ( scissors, screwdrivers,  hammer, pliers, vice grips, box cutter, etc )
     - Files ( 1/4" round,  medium flat, and fine flat  types needed )
     - Dremel  tool with cutting disks
     - Jigsaw with wood and metal cutting blades
     - Drill with an assortment of drill bits
            ( 1/16" , 1/8", 1/4", 3/8",  a countersink, and a 1-1/4" hole saw )
     - Tape measure, Ruler
     - Straight edge
     - Soldering Iron (Optional)

Outer Shell:

- 1" thick styrofoam sheet for forming the body
   - cardboard or foamboard for legs
   - fabric or paint to decorate

Miscellaneous Supplies:
  - rubber cement

  - scissors
     - knife
     - paint brushes etc.

Step 2: Markup the Worm Gear

Take a sheet of paper and cut it into 3/4" strips.  Tape enough strips together to create one strip about 3 feet in length.

Next, you will need a  hardwood dowel 3/4" in diameter and 14-1/2" in length.
Choose one end of the dowel to call the top. 

Tape the paper strip to the dowel about one inch from the top. ( see image below).  Wrap the strip around the dowel leaving a slight gap in the paper between the windings.  Stop winding about 1/2" from the bottom of the dowel.  Tape the botom end of the strip to the dowel to hold it in place.

Draw a line around the dowel 1"  from the top, and anouther 1/2" from the bottom.  These lines will mark the start and end points of the Worm Gear.

Find the top point where the gap in the windings crosses the line drawn around the dowel.   From this point, use a marker to fill in the gap that winds around the dowel. Stop when you reach the line near the bottom.

Remove the paper. 

You should now have a nice uniform spiral drawn around the dowel.

Step 3: Create the Worm Gear

Don't panic,  worm gears only look hard to make.  
The key is to take your time and try not to get too agressive.  Let the file do the work. 
I press the dowel against a scrap piece of wood mounted near the edge of my workbench.  This provides a good flat surface to support the dowel as it is transformed into a spiral masterpiece.  It also helps make the groove more uniform, since the dowel will tend to slowly rotate as you file. 

Using a 1/4" round file, carefully file along the line.  Start from the top end and work your way down to the bottom, cutting into the wood about 1/8" on each pass.  Remember to support the dowel as you file.  Take your time.  The wood can snap, if you get to aggressive, especially when it is close to being completed.  Also be sure to
taper the groove at  each end. 

The ultimate goal of your completed worm gear is to drag an Axle Peg along a slot  by
forcing the head of theAxle pin to stay in the grove of the worm gear while it rotates.  The groove should be smooth and large enough to fit the head of the axle pin with a little room to spare.

When the worm groove is the correct size, use sandpaper wrapped around the file to smooth out the surface.

Step 4: Finish the Worm Gear

Round the bottom edge of the worm gear with a flat file and  sandpaper.

Drill a 1/4" hole 1/2" deep in the center of the  top end of the worm gear.

Finally, Cut a 1/16" wide notch in the top end of the worm gear 5/8" deep.

This will be used later to attach the motor.

Your Worm Gear is complete.

Step 5: Motor

For this project I used a Tamiya 6-Speed Gearbox H.E. for the motor.
I choose this motor because it was inexpensive ( About $15 ),  and it  had
good selection of gear ratios ( 11:1,  30:1,  77:1,  197:1,  506:1, and  1301:1 ).
It also comes with a variety of  output plates ( I will call Transfer Plates), for
connecting the motor to whatever it is you want to spin. 

Assemble the motor, following the directions in the box for whichever gear ratio
you choose.  I started with 506:1 since I was not sure how much power would be required.  Later, I switched to 196:1.  77:1 would probably work fine as well. 
When in doubt, go for the higher ratio.

The circular Transfer Plate will need to be modified slightly .
Cut two 1/16" notches in the plate as shown below.

Step 6: Back Plate

See PDF document for detailed drawing.

Step 7: Motor - Worm Gear Adapter

Use a leftover scrap from the previous step as material
for the Adapter plate. The plate should fit into the notch on the
worm gear. Small tabs will protrude from the worm gear that 
should fit into the slots cut into the motor Transfer Plate.

Step 8: Worm Gear Carriage Part 1

For this step you will be using the 15-5/8" length of 3/4" schedule 40 PVC Pipe.

There are two ways to layout the pipe for cutting.  The easy way would be to print both pages of the the WormGearTemplate PDF document at full size and follow the
instructions included.

If you can't print the template document correctly,  View the WormGearCarriageDetail PDF document.  It contains all the details and measurements  needed to build the Carriage.

If you are using the template (recomended) ,  make sure to drill the holes before using the cutting disc.

If you are not using the template, drill the holes last.

Use a dremel tool with a cutting disc to cut the pipe.

After the holes are drilled and the pipe cut out,  Countersink the 3 1/8" holes from the
inside surface for #6 flat head screws.  Countersink the 2 1/16" holes from the outside surface for #4 flat head screws.

Step 9: Worm Gear Carriage Part 2

The carriage built in the last step needs to be modified to make it work correctly.

Here are a few new names I just made up for two of the important  sections of the Worm Gear Carriage. The letters refer to the picture below.

A) Axle Peg ejection zone.

B) Axle Peg capture zone.

Here are the required modifications:

Mod 1:

Carefully enlarge the slot using files and sandpaper so that the Axle Peg shaft slides freely along it's entire length.

Mod 2:
Flatten out the outer top surface of the slot by about 1/32 of an inch using a file and sandpaper. This will help the Axle Peg slide along the top of the carriage when it is ejected from the worm gear.

Mod 3:
Taper the underside of the slot at the ejection zone end of the carriage.  This will help prevent damage to the Axle Peg when being ejected from the worm gear.

Mod 4:
Taper the capture zone end of the slot to guide the Axle Peg into the slot when captured by the worm gear.  Because the Carriage Sleeve ( Built Later) needs to be a loose fit, the Axle Peg will rarely line up perfectly with the slot on it's own.  This taper is critical.

Mod 5:
Insert a 2-5/8" length of 3/4" hardwood dowel into the the carriage at the capture zone end.
Screw the dowel into place using 2 #4 flathead screws through the holes drilled during step 8.
When fully inserted, the worm gear should extend 3/4" to 1" beyond the Carriage Body.  Adjust the dowel if needed.

Test the Mods:
Insert the worm gear into the carriage. Place the Axle Peg into the worm gear at the slot in  the capture zone. Turn the worm gear. The Axle peg should travel smoothly along the length of the slot, falling out when it reaches the ejection zone.  Adjust as needed.

Step 10: Carriage Sleeve Body

This step uses the 16" length of 1" schedule 20 PVC Pipe.

Drill a 1/4" diameter hole through the center of the pipe 7" from the top end.
Starting from the top end, cut lengthwise through the pipe parallel to the drilled hole, 1/4" in from the edge,
stopping 1-3/4" from the bottom.  At the 1-3/4" endpoint, make a perpendicular
cut, removing the 1/4" strip from the pipe.  Use sandpaper to smooth out the edges.
 See the attached PDF for better detail.

Step 11: Carriage Sleeve Spring Mount

See PDF document for detailed drawing and instructions.

Step 12: Carriage Sleeve Axle Peg Mount

See PDF document for detailed drawing and instructions.

Step 13: Carriage Sleeve Assembly

See PDF document for detailed drawing and instructions.

Step 14: Foot Plate

See PDF document for detailed drawing and instructions.

Step 15: Spring Body Mount

See PDF document for detailed drawing and instructions.

Step 16: Springs

For this step you will need 2-  21" lengths of metal electricians fish tape.

Using a vice grips bend loops into the ends of the pieces.  Use a hammer to gently
tap the loops closed.  These loops should be slightly loose on a #6 screw, and
all the loops should be fairly uniform.

Step 17: Upper Body Assembly

See PDF document for detailed drawing and instructions.

Step 18: Install the Battery Pack

Find a location for your battery pack that will not interfere with any moving parts or decorations that you may want to add later.  One option is at the lower end of the Worm Gear Carriage.
If you choose this location, make sure to avoid  the end of the worm gear.  You may also
need to raise the battery pack up on a few washers,  to avoid the foot when the
machine is fully compressed.

Once the battery pack is mounted, extend the motor wires along the outside of the back plate to the battery pack.  Test the motor.  The worm gear should spin so that the Axle Peg will travel toward the motor if placed in the groove at the capture zone.  If it spins the wrong way reverse the wires on the battery pack.

Use Duct tape or Aluminum tape to hold the wires in place.

Step 19: Complete the Mechanism

See PDF document for detailed drawing and instructions.

Step 20: Time for Frog Legs

Create a frog leg template. 
On a sheet of paper draw two separate lines. One line 8 inches in length, the other 6-1/2. 
Draw a frog leg segment outilne around these lines.  The longer line will be the lower leg.
The short line is the upper leg.

Make the Legs.
Cut out the shapes and trace two of each onto cardboard or foamboard.
Punch small holes in the leg segments at the endpoints of the lines on the template.
Cut out the cardboard leg segments.  
Decorate the Leg segments as desired.

Use the hardware shown below to install the legs.

For the knee joints:

Place a washer onto a fastener. Then insert the fastener through the upper leg knee hole.  Next, place a second washer onto the fastener.  Push the fastener through the knee hole in the lower leg segment and add one more washer.  Finally, bent the fastener ends open.

For the Hip Joint:
Place a washer onto a fastener.  Then insert the fastener through the upper leg hip hole.
Next, place a second washer onto the fastener.  Insert the fastener through one of the 1/4"  holes at the bottom end of the Back Plate.  Add one more washer to the fastener, then bend the fastener ends open.

For the Ankle Joint:
 Use a washer and a #4 screw to attach the lower part of the leg to the foot.  Do not  fully tighten the screw. The leg segments need to move easily.

Step 21: Fabricate a Frog Form From Foam

This can get messy! 

Outline the Back Plate onto a  1" thick sheet of styrofoam. Draw and cut out a basic outline of a frog body from the foam around the Back Plate Outline.  Stack two more layers of foam around the outline to thicken up the sides and front of the future frog form.  Glue the layers using rubber cement.  When the glue dries, use a knife and sandpaper to carve the foam into a more acceptable frog shape. Next form some eye bumps and glue them down to the body.

Step 22: Finish the Frog Form

At this point, it's all about decorating.  I chose to cover the foam shell with green spandex.
I applied rubber cement over the entire outer surface and just stuck the fabric on. After the glue was fully set, I trimmed off the excess with a razor knife, and glued on some eyes.
You could add on some arms.   I probably should have. 

Attach the Frog form to the Back Plate using double sided tape or loops of duct tape.

Happy Hopping.

Kinetic Sculpture Design Contest

Participated in the
Kinetic Sculpture Design Contest