In the last Hacking and Kids post, I talked about an activity you can do with kids when you don’t have a lot of time or resources. The key idea was to have fun and learn a little bit about open and closed loop control. One of the things I usually briefly mention when I do that is the idea of a design trade: Why, for example, a robot might use wheels instead of legs, or treads instead of wheels.
Engineers and makers perform trades like this all the time. Suppose you are building a data logging system. You want precise samples, large storage capacity, and many channels. But you also want a low cost and low power drain. You might also want high reliability. All of these requirements will lead to different trades. A hard drive would provide a lot of space, but is more expensive, less reliable, larger, and more power hungry than, say, an SD card. So there isn’t a right choice. It depends on which of the factors are most important for this particular design. A data logger in a well-powered rack might be well served to have a terrabyte hard drive, while a battery powered logger in a matchbox that will be up on the side of a mountain might be better off with an SD card.
We can all relate to that example, but it is pretty boring to a kid. You probably can’t get them to design a data logger, anyway. But if I have about an hour and a little prep time, I have a different way to get the same point across. It is a modified version of the classic “egg drop”, but it is simple enough to do in an hour with very little preparation time.
Here’s how it works: I have a step stool or something that will safely hold my weight in front of the class. I climb up on it with an egg in a baggie and I drop the egg. So far, that always results in a messy broken egg (inside the baggie, hopefully). Now I have their attention.
I tell them that the egg is an astronaut and when the space ship she’s in lands, we don’t want her cracked up like Humpty Dumpty. I split up the kids into a few teams (with reasonably even distributions of ages, if they are a mixed group) and I show them that I have lots of materials in yet more baggies. Exactly what I have will depend on what I had on hand. I might have marshmallows, flour, cereal, sand, cut up sponges, newspapers, or packing peanuts. I’ll also have some basic supplies like tape, scissors, and markers. There’s also a scale.
Each team picks a name and decides how they want to protect their egg. Here’s the catch: each bag of materials has a cost. I will tell the kids that we will have a prize for the lowest cost solution and the lightest solution (as long as they, of course, don’t break the egg). I assign costs based on my judgement of how lightweight the material is along with how well I think it will cushion. So marshmallows and cereal are expensive. Sand is less expensive. I try to make them struggle to get both light and cheap in the same design.
Most of the kids will pack things around the egg inside the baggie. Younger team members can have the job of decorating the egg. I’ve seen kids make parachutes out of newspaper and secure them with duct tape. You never know just how creative the kids will get.
This is, of course, not an original idea — egg drops have been going on in one form or another for a long time. However, by using the premade baggies it is quick to set up and quick to do. Using the baggie for structure prevents a mess and also saves time from having to build a box or get a suitable box for each team. But the key point is the use of minimal weight and cost and how it feeds the design trades they must make. You can show them how they make trades like this all the time in everyday life, from which route to take home to how to spend their allowance.
But it is also undeniable fun. When they shout out 3…2…1… before you drop their egg, you can feel the excitement. The suspense when you open the baggie to see if the egg survived is palpable. The fun keeps them interested and it will help them remember the lessons you teach them. For a quick run of it, you can set a maximum weight and continue dropping things from the step stool. If you have time, you can try dropping them out of a window and get a little more impact. Some eggs will break. I always remind the kids that you often learn more from a failure than from a success.
As engineers or makers or designers or whatever label you apply to yourself, it is tempting to go overboard on something like this. We could build test fixtures with instruments. A shock absorber design immediately comes to mind. Resist that. Keep it simple and save those ideas for long term science projects. A simple activity like this will let you share your love of creation with a large group and maybe start a kid on the road to being a hacker like you.
By the way, if you need some help on figuring out what might work well, [Mark Rober] has a pretty entertaining analysis of what makes egg drop capsules successful in the video below (and he should know since he worked on the Curiosity rover).