Intro: How to Make a Cardboard Frog Robot
I'm glad I have finally taken the time to create this guide for making a frog robot! There are quite a few video guides on YouTube right now that show how to make a model similar to the one I have created here. So this is my variation on the frog-robot theme. I am hoping this guide will provide the details necessary for anyone to easily make one of these. I made four of these robots before I got one to actually work, and this guide is a documentation of my working model.
This instructable is mostly organized by task (measuring, cutting, painting, drilling, gluing, assembling, etc.), but feel free to jump around and create the parts in any order you wish. I also created a YouTube video guide for this project at https://youtu.be/2izbRRDDycI. I link to various segments of the video guide throughout this instructable.
I created a PDF version of this instructable (download below) and I've also provided the SVG file (download below) template to quickly plot the holes on triangles.
About a year ago, after I made this robot, my friend Justin, now in 4th grade, showed me how this frog robot works just as well, and moves even faster, when placed on its head. This now has me imagining a penguin model with the sides and base painted black; and a white cardboard pulley for a belly. I'll need to figure out the wings and beak. (Inspiration for another project!)
Step 1: Supplies List
Cardboard (I used an Elmer’s tri-fold display board measuring 22” W x 14” H)
Mini craft sticks
Cooking skewers or dowel sticks (1/8” diameter)
Mini duct tape (I used Duck Brand Ducklings Mini Duct Tape, Pink)
Masking tape (optional)
Googly eyes (23mm)
Pony beads (optional)
Rubber bands (1.75” or 1.5” diameter w/ 7mm Motor Pulley. 1” rubber band w/ 16mm motor pulley)
Low-speed, high-torque DC motor I used the following motor from Home Science Tools:
Small Motor Pulley I used the pulley with a 6-7mm outer diameter from
Mini rocker switch I used the following C&K On-Off switch:
9v battery connector w/ leads I used Pangda I Type Long Cable Connection Hard Shell Black Red 9v Battery Clip Connector
Acrylic paint (Green)
Small cup or bowl to hold paint
Glue sticks for glue gun
Solder (optional). Connect wires w/ electrical tape as alternative.
Rubber gloves (optional) (Use nail polish remover if you super glue your fingers together)
Step 2: Tool List
Ruler (with centimeters and inches, clear plastic)
American quarter (25¢ coin)
Drill with the following bit sizes: 1/16, 5/64, 3/32, 7/64, 1/8, 9/64, and 5/32.
Gimlets (3mm, 4mm, and 5mm) (I used Robert Larson Gimlets)
Nail (for initial hole pokes in cardboard and glue-stick stoppers)
Rubber Mallet or Hammer (Optional) (Used for creating initial hole in glue-stick stoppers)
Block of Wood (Optional) (I used a scrap piece of wood measuring 10” L x 1.75” H x 3.5” D)
Soldering iron (optional). Connect wires w/ electrical tape as alternative.
Utility scissors (for cutting cardboard)
Box cutter or utility knife (for cutting or slicing cardboard)
Handi-cut Utility Cutter (Craftsman). Any type of gardening/pruning shears for clipping sticks will work.
Kobalt 8-in Home Repair Linesman Pliers (optional)
Wire stripper & cutter
Small paint brush
Tweezers (Helps to remove rubber band if it gets stuck in cardboard pulley while removing/inserting)
Step 3: Prepare Robot Parts
Measure, Draw, Cut, & Paint
a. Draw and cut out 4 triangles from cardboard measuring 14 cm wide by 7 cm high. (Sides & Feet) I cut out one triangle and used it as a template to trace/draw 4 triangles of equal size and shape. Also, mark an “L” for “left” on the backs of two triangles, and an “R” for “right” on the backs of the other two triangles. This will be useful in keeping things aligned when forming holes later on. Video guide at https://youtu.be/2izbRRDDycI?t=7s
b. Draw and cut out 1 rectangle from cardboard measuring 14 cm long by 7 cm wide. (Base)
c. Using a compass, draw and cut out 2 circles from cardboard with a diameter of 6 cm each. (Outer sides for big pulley) Video guide at https://youtu.be/2izbRRDDycI?t=41s
d. Using the compass, draw and cut out 1 circle from cardboard with a diameter of 5.5 cm. (Inside middle of big pulley) **Cover the outer perimeter of this inner pulley piece with a strip of mini duct tape. See video guide at https://youtu.be/2izbRRDDycI?t=1m10s
e. Using the compass, draw and cut out 2 circles from cardboard with a diameter of 2.5 cm each. Or trace an American quarter: 25¢ coin. (Eye supports)
f. [Optional] Draw and cut out 6 little circles from cardboard with a diameter of 1.5 cm. (Inner & outer washers/spacers) **Form holes in circles before cutting them out** Video guide at https://youtu.be/2izbRRDDycI?t=1m33s
g. Cut 3 sticks (axles) from 1/8” cooking skewers/dowel sticks measuring 11.5 cm each. Then, with a pencil, draw 2 marks on each stick at 2.1 cm in from both ends. These marks will act as guides to help keep things aligned when assembling the robot. Video guide at https://youtu.be/2izbRRDDycI?t=1m49s
h. Cut 6 short sticks from 1/8” cooking skewers/dowel sticks measuring 2.5 cm each.
i. Beginning at 2 cm from one end, mark 2 holes with a pencil in the middle of 6 mini craft/popsicle sticks. Video guide at https://youtu.be/2izbRRDDycI?t=2m5s
j. Paint any pieces where you wish to see color. I painted the top of the base, the outsides of each triangle, and the outsides of the eye supports. Video guide: https://youtu.be/2izbRRDDycI?t=2m44s
Step 4: Make the Holes
Fashion Holes in Triangles, Pulley, and Mini Craft Sticks
Begin by plotting holes on just one of the cardboard triangles. Once the holes are marked and formed, use the cardboard triangle as a template to mark the remaining three triangles. The quickest way to plot the initial three holes on a cardboard triangle is to print the provided SVG file containing a triangle with marked holes. Cut out the triangle from the printed SVG file to use as a template. Once it is aligned over the top of a cardboard triangle, poke the initial holes using a nail through the three plotted points on the template. See video guide at https://youtu.be/2izbRRDDycI?t=3m4s
The goal is to get the size of each hole to be slightly bigger than the diameter of the skewer/dowel stick. This allows the top-middle stick/axle to rotate freely within the holes; and permits the bottom two holes of the feet-triangles to rotate freely around the front and back mini joint-axles. I like to start small and work my way up in size when forming holes so that I don’t tear any of the cardboard. I started with a nail, then 3mm gimlet, and finally used the 5mm gimlet. The 5mm gimlet will provide the perfect size for each hole in the triangles.
To plot the holes yourself, without using the SVG file, measure 2.1 cm horizontally from the bottom-left of the triangle, and then go 1.2 cm vertically to plot the first point. Next, measure 2.1 cm horizontally from the bottom-right of the triangle, and then go 1.2 cm vertically to plot the second point. Finally, measure 7 cm horizontally from either the bottom-left or bottom-right of the triangle (center), and then go 5.25 cm vertically from bottom-center to plot the third point. See video guide at https://youtu.be/2izbRRDDycI?t=3m17s
Tip: I first plotted and formed my holes on one of the triangles marked “L.” I used that triangle as a template for plotting holes on the other three triangles. Both triangles marked “L” were face-up when I traced with the “L” template triangle. Both triangles marked “R” were face-down when I traced holes using the “L” template triangle face-up. This helps keep the holes closely aligned on both sides so that the sticks/axles running through them are as straight as possible. See video guide at https://youtu.be/2izbRRDDycI?t=3m33s
Form initial hole with nail and work your way up in size using the 3mm gimlet followed by the skewer, or dowel stick. Watch the video guide for more info: https://youtu.be/2izbRRDDycI?t=4m3s
Mini Craft Stick Holes
Start by drilling with the smallest drill bit (1/16) and work your way up in bit size. The goal is to get a hole the size of the 5/32 drill bit. Position the sticks on top of a wooden block when drilling. Try drilling through 3 sticks taped together with masking tape. It is difficult to drill the hole up to the desired size without splitting the stick. I often drill up to the 1/8 bit size and then gently form a bigger hole with the 4mm gimlet; followed by just the tip of the 5mm gimlet. Never force the gimlet when it meets resistance in the hole or the stick will split. Gently turn the gimlet back and forth, moving right and left as if taking great care to gently lock and unlock a door. Keep the clockwise motion sensitive to the resistance, working away at the wood a little bit at a time. Work at forming the hole from both sides of the craft stick. These craft sticks are fragile with drill bits, so definitely have extras available because some will break. See video guide at https://youtu.be/2izbRRDDycI?t=4m58s
Step 5: Glue Cardboard Pulley Circles Together
To align the cardboard circles when gluing together, place them on the skewer/dowel but do not glue them to the skewer/dowel stick yet. Start by gluing the inner pulley piece (5.5cm) to one of the outer pieces (6cm). I put the glue on the inner pulley piece when gluing it to the outer pieces. See video guide at https://youtu.be/2izbRRDDycI?t=4m18s
Step 6: Create the Joints
To create a joint, we need to connect a 2.5 cm stick with a mini craft stick. Using the glue gun, put a drop of glue on top of one hole in the craft stick. Then insert the 2.5 cm stick through the bottom of the hole and glue drop. Put the stick all the way through the hole, and then twist it back down with the glue into the hole so that it is almost flush with the upper rim of the hole. Try to keep the two parts in an “L” shape as they dry by placing on edge & side of wooden block; or at the edge & side of a tabletop. Once the initial glue dries, I recommend gluing the other side of where the stick meets the hole to make the connection extra secure. See video guide at https://youtu.be/2izbRRDDycI?t=5m40s
Next, draw a mark 8 mm away from the outer edge of each hole on the mini craft sticks. Then cut the craft sticks at the 8mm marks, and clip the corners to make them more rounded. See video guide at https://youtu.be/2izbRRDDycI?t=6m5s
Step 7: Solder (or Tape) Motor Leads to Battery Connector & Switch
Strip the ends of each wire.
Connect the positive (+ red) wire of the battery connector to the “O” (off) side of the mini on-off rocker switch.
Connect the positive (red) wire of the motor to the “I” (on) side of the rocker switch.
Finally, connect the negative (- black) wire of the battery connector to the negative (black) wire of the motor to complete the circuit.
Secure the connections by either soldering or taping with electrical tape.
Watch the video guide for more info: https://youtu.be/2izbRRDDycI?t=7m
Step 8: Glue Sides to Base
Using the glue gun, apply glue to the bottom of one triangle and place it on top of the base so that it sits flush on the edge of the base. Hold triangle in place while glue dries.
Next, apply another line of glue where the inside bottom of the triangle meets the base. See video guide at https://youtu.be/2izbRRDDycI?t=6m28s.
Step 9: Position Motor, Battery, and Switch
Insert the front and back axles before positioning the motor, battery, and switch. The motor is placed at the front-left with the switch on the back-left side. Make sure the motor does not touch the front axle before gluing in place. The battery will sit on the right side, between the back axle and the motor pulley. Add a healthy portion of glue where the motor will sit. Place motor in glue. Apply pressure and hold in place while glue dries. See video guide: https://youtu.be/2izbRRDDycI?t=8m15s
Tape the battery in position and add another healthy portion of glue to the bottom-right side of the motor (the side of motor facing the switch, or back of robot ). Video guide: https://youtu.be/2izbRRDDycI?t=8m27s
Put glue on the left side of switch. Position switch on back-left side of robot so that the switch is flush with the angle. Make sure the switch is placed high enough so that it is clear of the back-left washers. Apply pressure and hold in place while glue dries. See video guide at https://youtu.be/2izbRRDDycI?t=8m38s
Step 10: Align Cardboard Pulley With Motor Pulley
In preparation of gluing the cardboard pulley to the middle axle, wrap a rubber band around both the motor pulley and cardboard pulley. Position the cardboard pulley on the axle so that it is in direct alignment with the motor pulley. Be sure that the guides marked on the axle (Step 3, g.) are even on either side of the robot as the pulleys are aligned. Once pulleys are aligned, draw two marks on axle to plot the width and position of the cardboard pulley. See video guide: https://youtu.be/2izbRRDDycI?t=8m52s
Add rubber bands and the washer to the axle before gluing cardboard pulley to the axle. I added three 1”, five 1.5”, and five 1.75” rubber bands. It seems like a lot; however, the rubber bands will stretch and eventually break.
Tip: Remove rubber band from pulleys when robot is not in use. This helps to prolong the life of the rubber band.
Step 11: Glue Washers & Cardboard Pulley to Axles
Two washers are positioned on each axle: one outside and one inside the robot. This helps to keep all three axles in alignment. Both the middle and back axles have washers on the left side. The front axle has washers on the right side.
Position the two washers on the axle so that they both slightly touch the outside and inside of the triangle. They should be able to rotate without rubbing too hard against the triangular side. Be sure the axle is even on both sides of the robot before gluing. Only glue the side of the washer that faces away from the triangle.
With the axle even on both sides of the robot, start by gluing the washers to the middle axle on the left side of the robot.
Double check the alignment of pulleys before gluing cardboard pulley to middle axle. Adjust position if needed. Glue the cardboard pulley on both sides where the pulley shaft meets the axle.
Glue washers on front and back axles.
See video guide at https://youtu.be/2izbRRDDycI?t=9m31s
Step 12: Glue Joints to Axles
Attach joint to robot axle with joint being perpendicular to the robot; and mini-joint axle positioned below the robot axle; facing away from robot. Leave a little space from the axle’s edge to apply a drop of glue. Once glue is applied to axle, rotate the joint; moving it towards the edge of the axle. Have the joint sit almost even with the edge of the robot axle. Be sure to have the glue dry with joint in original position, perpendicular to robot.
Once the initial glue dries, glue the other side of the joint where the axle meets the hole to make the connection extra secure.
Use a scrap piece of wood or small box as a lift so the joints cannot touch the surface when gluing. Having the joints hang off the edge of a table will work, too. Just be sure to glue all the joints in the same position on both sides of the robot.
See video guide at https://youtu.be/2izbRRDDycI?t=10m57s
Step 13: Glue Eyes
Add 3-5 drops of super glue to the bottom of the googly eye. Place googly eye with glue in the center of eye support. Hold and apply pressure while it dries.
Next, glue eyes to the robot. Apply super glue on the bottom of the eye support, a bit off-center, and place on the front perimeter of the triangle side. Hold in place while glue dries.
See video guide at https://youtu.be/2izbRRDDycI?t=11m37s
Step 14: Create 12 Washers/Stoppers From Glue Stick
Cut or slice 12 pieces from a glue stick, roughly 1/2 cm wide. Initiate a hole by forcing a nail through the center of the slice. Turn nail upside down with point facing up, and push the glue-stick slice down into the nail with your thumbs on outer edges of slice.
Next, run a wooden skewer or dowel stick through the glue stick slice several times. Then rotate or twist the slice on and across the stick to remove pieces of glue from center.
See video guide at https://youtu.be/2izbRRDDycI?t=12m15s
Step 15: Attach Feet to Joints
Add a glue-stick washer to each little axle on the joint. Then attach the triangle foot, putting the little joint axles through each hole in triangle. Add a second glue-stick washer to each little axle on the outside of triangle to keep the foot straight and in place. Leave just a tiny bit of space between the triangle and washers. See video guide at https://youtu.be/2izbRRDDycI?t=13m
Pony beads are an alternative to making the washers from glue sticks. Some pony beads fit the 1/8” dowel stick perfectly, while some are too loose. If they are a snug fit, I would highly recommend using the pony beads as an alternative.
Attach the rubber band to both pulleys, flip the switch, and watch the robot do its thing!