EEF Mousetrap Challenge Instructions
Welcome to my mousetrap (read golfball trap) construction instructions! Special features include; a stiff cylinder based design and an automatic locking mechanism. Originally designed for my Engineering for an Equitable Future class the mousetrap had to meet the following criteria:
- Trap the golfball (pretend mouse)
- Have an active trigger
- Hold the ball during three strong shakes
- Be built of only paper, tape, paperclips and rubber bands
- Be an original design
- Be easy to use
- Bonus points were awarded for design elegance
This mousetrap design met the above criteria, passed all the tests and received the maximum number of points. The tools and materials required for this build are listed below:
- A 30cm x 50cm piece of heavy paper
- 50cm of wide masking tape
- 4 paperclips
- 2 skinny rubber bands
- Box cutter or x-acto knife
- A round object 8mm in diameter and more than 15cm long (I used a pencil)
- A second round object 4mm in diameter and at least 20cm long (I used a length of threaded rod I found)
- Needle nose pliers
- Wire cutters
Throughout this instructable the pictures will be a valuable resource in helping you construct the trap, so make sure to check them out.
Head to the next step to start building.
Download the pdf named paper_pattern.pdf attached to the bottom of this page and print it out, then grab your heavy paper. We need to transfer the development style design in the pattern to the paper, so get out your pencil and ruler and duplicate the pattern on your paper. Dimensions are given and unless otherwise noted, all the angles are 90 degrees. Make sure to copy everything including the dotted lines and the piece numbers. Some of the pieces will have to be drawn out multiple times in this case there will be an "x(the number you need to make)" next to the part number, for example, if there was "x9" next to the piece number you would need to copy and cut that pattern 9 times.
Once you are done transferring the pattern it is time to cut out the pieces. Using your box cutter, or Exacto knife cut along the solid lines. Do not cut the dotted lines, these will be used as fold lines and to guide assembly later.
Next, download the pdf named paperclip_pattern.pdf and unfold all of your paper clips. Using your needle nose pliers create the paper clip shapes labeled Stakes, Brace, Catch, and Latch_one according to the dimensions in the file. Note, do not make latch_one and latch_two on two on two separate paperclips. They are two steps in the creation of the overall latch paperclip.
Finally, take your 50cm of masking tape and cut it in half straight down the middle so you end up with two 50cm lengths that are half as wide as the original tape. This effectively doubles our tape supply, and since we are using the wider type of masking tape our new tape strips are still just as wide as the normal skinnier masking tape.
Tube Rolling and Base Construction
The reason this trap is so rigid and durable is the fact that it is constructed mostly out of rolled paper tubes. Rolling the paper gives it strength in more than one dimension keeping it from buckling under the tension applied by the rubber bands.
To start, take one of the paper pieces labeled with a 1. Place the larger of your cylindrical objects (we'll call this a "roll form" from now on) on the paper and tightly roll the paper around the roll form "hotdog style" (the roll form should be parallel to the long edge of the paper). Before sliding it off of the roll form, secure your roll using the smallest amount of tape you can. I found three squares of tape, one in the middle and one at each end worked well for me. Once your roll is good and secure, slide it off of the roll form and repeat these steps until all the pieces labeled with a 1 are gone. Each of the tubes should be around 1cm in diameter. If yours are off then either adjust the size of your roll form or modify the dimensions of the rest of the trap.
Once the rolling is finished gather all the tubes and lay them side by side so they resemble a tiny log raft. Once again using as little tape as possible but still making it strong, tape the tubes together at both ends (see the picture for a visual example). When doing this make sure to keep the tubes flat and aligned with each other.
That's it, the mouse trap base is done! Move on to the next step to create the moving element of the trap.
More Tube Rolling and Trapping Element Construction
This mousetrap operates much like a conventional mousetrap with a base and a spring-loaded trapping element. In this step, we will make the trapping element.
Take one of the pieces labeled 2 and use your skinnier roll form to roll up the paper "hotdog style" (the roll form should be parallel to the long edge of the paper). Tape the roll and then repeat the process with the second piece labeled with a 2. This rolling job may be a little trickier as the tube being created is much longer and skinnier than before.
Once you have both tubes rolled, it is time to connect them to create one long tube. Slide the end one of the tubes into the other, crushing and folding the end of one of the tubes into a pointed shape can make the process a bit smoother. Tape this joint.
These tubes make up the frame of the trapping element and will provide structure for the paper box added on top, but we still need to create a pivot to allow for movement. To make the pivot, roll the piece of paper labeled 3 around the long tube you've just created. You want it tight enough that there isn't much play but not so tight that you can't easily spin the skinnier tube inside the pivot tube. Tape the pivot tube and leave it on the long tube.
To finish the frame of the trapping element, fold the long tube to create a 6.5cm by 7cm rectangle with the pivot tube on one of the shorter sides. Connect the two ends of the long tube by pushing one into the other like before and tape the joint.
To create the box that connects to the frame, take the piece labeled with a 4 and fold along the dotted lines. A ruler can be used to help make the creases nice and sharp. If done correctly this should result in a box which is open on one side. Tape the open edges.
Take the two brace paperclips you made earlier, place them on the corners that are not next to the pivot tube and tape them. Look at the picture for more details. These braces will keep the frame from collapsing on itself. Insert the box into the space in the middle of the trapping element frame and tape the box to the three edges of the frame that do not have the pivot on them.
The trapping element is finished. Next up, assembly.
Assembly time! Take the trapping assembly and place it on top of the mouse trap base so that the trapping assembly pivot is about 1cm from the end of the base. Verify that the trapping assembly is positioned squarely over the base, then line up the stake paperclips so that they go over the trapping assembly pivot and down in between the tubes that make up the base.
Using your needle nose pliers twist the ends of each paper clip together to cinch down the trapping assembly pivot tube to the base. Avoid twisting the paper clips too much as this will crush the pivot tube and prevent the trapping assembly from moving. Clip off the remaining ends of the paperclips when they are tight enough and you are done twisting. Using paperclips to anchor the pivot tube creates a strong connection to withstand the tension of the rubber bands.
The locking mechanism employed in this trap is designed to engage as the trap closes. Because everybody's trap is built slightly different this will most likely be the most finicky part of the build and will require some trial and error to get right. If the paperclips aren't exactly fighting with your design modify the angles and lengths to get it to work.
Grab your Latch_one paperclip you bent into shape earlier. Cut a tiny bit off of the straight end of the paperclip at as steep an angle as possible to create a sharp point. Mark a point along the side of the base 5cm back from the front edge of the base. Using pliers take the pointed end of the paper clip and at the point you marked push it straight through all the tubes in the base and out the other side. While doing this it is extremely important that the paperclip goes straight through and does not go off at an angle.
Once the paper clip is through the base, bend the pointed side of it so that it mirrors the design labeled Latch_2 in the paperclip pdf. See the pictures above for a visual aid. The paperclip should now be unable to come out of the base and should be able to rotate back and forth freely. We will call this paperclip the latch
Take your catch paper clip you created earlier and poke it through the trapping assembly from the inside so that when the trapping assembly is closed it emerges directly above the point where the latch paper clip hook is and sticks out far enough for the latch to catch it. See picture 7 above for an example. We will call this section of paperclip the catch.
Tuning the Locking Mechanism
Now comes the tricky part. We need to tune the shape of the bends in the latch paperclip so that when the trapping assembly closes the hook on the latch catches the catch on the trapping assembly. The hook on the latch paperclip will be called the hook and the part of the latch which is moved by the trapping assembly will be called the timing lever. Look at image 1 above for a diagram
tuning the locking mechanism is achieved by adjusting the angle between the hook and the timing lever. To begin, open the trap and rotate the hook back so it is around 45 degrees or so away from vertical. Close the trap and watch as the hook moves towards the catch. If the hook doesn't make it to the catch even when the trap is all the way closed try making the angle between the catch and the timing lever smaller. If the hook overshoots the catch try increasing the angle between the catch and the timing lever. See image 2 above for a diagram of the tuning process.
Repeat this process of opening the trap, setting the latch, closing the trap and adjusting the angle until the hook reliably catches the catch. This trial and error will get you fairly close although some additional tuning may be necessary after the rubber bands are added as the trap behaves slightly differently.
The rubber bands provide the tension needed to snap the trap shut. To install the rubber bands take one of them, squish it and insert one end through the very top corner of the trapping assembly, between the frame and the box. once the rubber band is through there will be two loops of rubber band hanging down from the frame. Take one of these loops, pass it through the other and tighten the rubber band down on the trapping assembly frame. Do the same with the other rubber band.
To connect the rubber bands to the base close the trap and slide each rubber band between the tubes in the base that are directly below it. Then wrap the rubber band around the outside of the base and slide it between the tubes again to lock the rubber band in place. This method of attaching the rubber bands allows the tension to be fine-tuned by adjusting how much rubber band is being stretched when the trap is open. Just release and reattach the rubber band in a different spot to adjust the tension.
The trigger for this trap is a simple one consisting of a paper clip which props open the trap and is knocked out of the way by the golf ball when it rolls in. I found a paper clip with a 30 or so degree bend in it worked best as a trigger for my trap but feel free to experiment. to set the trap, prop the trap open with one end of the paper clip resting a bit back from the edge of the base and the other just on the inside of the trapping apparatus frame.
This trap was tested with a standard set up of two ruler sticks at around a 35 degree angle which guided the golf ball into the trap. I found the trap usually worked the best when it was not held in place. To use the trap set the tension of the rubber bands then prop the trap open with the trigger, rotate the hook back and roll a ball into it. The trap should trigger, but if it doesn't try experimenting with a different trigger shape or placement. As the trap closes the latch should catch the catch, but in the event that it does not try retuning it or if that's already been tried, try adjusting the shape of the hook.