Can you fix this?

Caroline E. Condon '13
 

  When I was in Chile, the third step in at least 90% of conversations I held (at least with new people) concerned my major: Where are you from? -> Why are you here? -> Oh, what do you study? I had a strong incentive to derail this conversation train because I knew I was going to mangle the word for engineering irreparably, but I usually wasn't successful. After we finally got through my stumbling through "ingenería", the rest of the conversation proceeded apace (in Spanish):

"What kind?"
"Mechanical"
"Oh, can you fix my car?"

Halfway through the semester, someone explained to me that the word I was using for mechanical (engineer) was really (shop) mechanic. What I really was, is a "civil engineer" - the opposite being a "commercial engineer" in management/business.

But really, even in a language I'm certain about, I get asked to fix a lot of things once I'm identified as an engineer. I love it. Engineering is technical problem-solving; we fix things - processes, machines, tools, paradigms, your great-aunt's computer, whatever you've got.

But especially your great-aunt's computer. Why? Well, because you're an engineer and it's your family, and I just can't resist that combination. So when I go home, I love it when my family suggests things to fix - and this time they had a more out-of-the-ordinary problem: how can a person with minimal muscle strength play with their 70-lb dog?

Keep reading for the answer...

Ans. Pulleys! Congratulations!

(I will also accept "levers!" because that's a pretty safe answer to any mechE question, and really, pulleys are pretty much just a way of doubling over a flexible lever).

Here's a 1st prototype I rigged up after a quick visit to a hardware store.

AstonWithRopes.PNG

 
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Systems of pulleys are awesome. They let you trade distance (how far you pull your end of the rope) for force (how hard you have to pull to exert a desired force on the other end). In the pictures above, the pulley in the right-hand corner is attached to a large post as an anchor (by the black strap). The dog is pulling on a toy attached to the second pulley, and a person is pulling on the line pointing to the left.

Here's a simplified diagram. Basically, the force of the dog pulling is now split between the rope going to the person, and the rope going to the anchor - so to win this game of tug-of-war, the person needs to be pulling just more than 1/2 as hard as the dog.

CapturePulleys.PNG

I think before I came to Olin I would have been much less likely to actually build something like this. Not that it really required any particularly difficult technical skills, but I hadn't quite realized I could just go get stuff and make a rough draft of an idea. But after 3 (and counting) years filled with projects and a "bias to action" (better to do something and fail than not do it at all - within limits!), it just seemed natural to me to pull together a prototype and see if I could actually make it work, instead of just thinking about it. And I think Aston (the dog) agrees:

Aston.PNG

 
Posted in: Class of 2013