We built this enormous retractable pen as part of our Kinematics class at BYU.

The goal was to build a mechanism big enough to teach and be handled by fourth-graders.

Collaborators: Ryan Anderson, Scott Taysom, Steve White, Brettany Rupert, Clifton Dudley, Wyatt Felt

Here's a look at the materials we used:
Giant Spring (taken from a broken fan base)
clear tube: 30"
plexiglass: .25" or .375" thick, 5" long .5" (2 of them) wide
plexiglass: whatever thick and abt 2.75" dia

1" PVC pipe  abt 3'
upper pusher - 2.25" diameter plastic 8" long
lower pusher - 2.25" diameter plastic: 7.5" long
tip   -  2.75"+dia  4.5"long
spacer  - 2 1/4" by   1.5" long

set screws - various sizes
Big ol' Marker
Small spring and guide rod for cams

~$60, weighs in at 4 lbs

Step 1: How It Works

The mechanism for a clicking pen is a bi-stable cam system. It is actuated by a guide pin and a compression spring  In the retracted position the spring is pre-loaded in order to keep the upper and lower cam pressed together.

When the pen is pressed to the change point, the lower cam clears the guide pin (Fig. 1b). The force of the compressed spring is larger than the friction on the inclined surfaces of the cams, and the lower cam rotates as it retracts into the extended position (Fig. 1c).

By compressing the spring past the change point again, the lower cam rotates and the upper cam is guided back into the retracted position (Fig. 1d). The stroke length from the retracted to extended position is 1”.
<p>Sweet project, very cool way to demo the concept. I found this project while looking to understand the mechanism in a conventional retractable pen and it is worth pointing out that this is not that mechanism.</p><p>In Fig.1, the system is locked in step C by pressure from the spring and the upper cam must be retracted by a different force. Pulling on the clicker (as in the video) or adding a second spring to the upper cam would accomplish this, but that is not how click pens work.</p><p>I am not detracting from the project or its aim of introducing mechanical thinking to young students, but maybe I can save the next person some time modeling and 3D printing this design, as I did, only to find that it does not work like a click pen.</p><p>Still a cool giant pen.</p>
That is a boss pen but I don't think it's going to fit in my pencil case.
Congratulations on winning the Big and Small contest!!
This is amazing! I'd love to have this in my room with a huge piece of paper and have kids draw with it! Well done!
Are you old enough to remember the teaching slide rules hanging above the blackboards in math class? This pen would go perfectly with one of those!
Oh dear now I am going to date myself! yes I am old enough to remember that!! Also all the giant compass, protractors and other gizmos on the chalk board, now we don't even use chalk boards because of asthma (and smartboards are way cooler anyway lol)
Where can I buy one? Hehe) <br> <br><a href="http://novenkaya.org/" rel="nofollow">Novenkaya</a>
Pocket protector, instructable, next? <br>Great work.
As a former industrial modelmaker and prototyper I have to say &quot;Great job&quot;.
This is fab! And the information on the mechanisms is really useful too - brilliant :)
I'm from Utah too! But I like the U of U
Very Cool! I really like this one. Well documented and also great to have the challenges/refinements section. That section helps us to learn from your experiences. It's good to see what bumps in the road you came upon - and how you handled them. <br> <br>To me this project is a piece of functional art. <br>Keep up the good work.
Go BYU!!! <br>
Oooo. I wish it would click louder so I can build one of these and annoy the hell out of the clicker-nuts at the office. :-) <br> <br>Very cool pen.

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