At-Home Engineering Challenge #1

For all you students and engineers bored at home, I present my At-Home Engineering Challenge 1: Bridge Building.

2 small drinking cups (3oz bath cups or functionally equivalent)
No more than 20 cotton swabs (Q-Tip brand or similar)
Dental Floss

Using 2 small drinking cups as a foundation, 20 or less cotton swabs, and dental floss,
Construct the longest bridge you can.

-Length is the span between the 2 drinking cups.
-Drinking cups must be resting on a flat surface. No anchoring!
-Bridge must span/rest on the drinking cups, and may only touch the drinking cups (If the bridge sags below the drinking cups / touches any other surface, it doesn’t count)

-Competition runs through 5pm Eastern on Sunday (March 29th).
-Please link pictures of your build (with measuring tape verifying measurement).
-Kids are encouraged to participate.

Prize. I will run a series of these challenges weekly, as well as post my solution. Most points wins. You will earn:
1 point for every competition you participate in
1 point for making it easy to verify you followed the rules
3 points for besting my solution
2 points for the “most ingenious” solution. This will be awarded at my discretion.
5 points for the “best” solution. In this challenge, the longest bridge wins.
All rulings final. Don’t like my rules? run your own competition.

When either:
I can’t think of any more engineering challenges
The quarantine in the US lifts
There isn’t any more interest in the engineering challenges

I will declare a grand winner, and award that person a $50 Amazon gift card.


An example bridge and example materials for Challenge 1.

Rules Question:
In the event of only have 5 ounce drinking cups, may we measure out 3 oz of water and cut them down to size

Functionally equivalent.
My drinking cups are approximately 2 1/8 inch tall, and weigh approximately 1.667 grams each.
5 oz probably doesn’t give you too much of an advantage?

My co-worker did the challenge with bathroom tissue tubes, and his design didn’t take advantage of the additional height, so it was ruled legal.

Also there will be more challenges. If you don’t have the exact materials please try the challenge anyway, and post your substitutions. Also please don’t buy anything extra! :slight_smile:

Here is my design not sure if it is allowed because the Q-tips sag below the cups but don’t touch the ground. It spans 19.5 inches between the cups.


Well done! It doesn’t look like it sags below the cups to me (table surface is below the cups, and your bridge doesn’t break that plane)

I would like to introduce my bridge design, Convergence.
It measures 70.25 inches. I used 14 cotton swaps (and way too much dental floss).

Apologizes for the blurry pictures, I tried to include enough to prove it wasn’t touching the ground.


Does this mean you can’t attach the cotton swabs to the cups?

It means you can’t tape or otherwise affix the cups to a surface.

1 Like

Great thank you! Also, this bridge can simply be anything, like the floss or the cotton swabs?

Or components of the floss, or cotton swabs. If somehow you could spin cotton thread out of the ends of 20 cotton swabs, you could use that I suppose.

I’m not the GDC, The rules are simple for a reason :wink:


@UnofficialForth Same concept, different execution. :grinning:

Measured in at 84.25". Used all 20 cotton swabs, and whatever floss I could find.


I applaud you, my good person, wonderfully executed


Well done. Did you have much trouble balancing everything? That was the hardest part of my solution – standing it up without another pair of hands.

Took a little bit of tweaking, but nothing problematic - the groove I put in the cup did a nice job keeping the floss centered.

similar concept, slightly different execution :slightly_smiling_face:
it’s just slightly longer with 88.75" between the cups, using 17 Q-tips


Interested to know if people have seen tipping of the cup or sliding of the cup to be the bigger issues. Those seem to be the two separate failure points when I was testing.

That’s going to depend on how you secure the bridge to the cup, and the CoF between the cup and the floor/carpet. The farther back (away from the center of the span), the lower the anchor point, and the lower the CoF, the less likely tipping will be an issue and more likely sliding will be the issue.

I love this! Mind if I steal your challenges for my at home middle schoolers?

Go for it!