Shake Tables in the Park

Thanks to Pepsi Refresh, I was able to build my shake table and bring it and the building supplies to the park.  I decided to up the building material limit to 100 toothpicks to see if 12" could be obtained and it was!  I decided not to

We had a lot of new faces join us this week.  We had tons of fun.  Here are just a few pics of our fun times.

Our friends learned about strong shapes and started building strong and tall!

Some friends tested their designs at each new level.

He's doing a happy dance that his tower was over 12 inches and it stayed longer than 20 seconds on the shake table.

Showing off his masterpiece.

J decided to go more jungle gym than tall tall tower.

Good building by a good friend.  It too survived 20 seconds on the shake table.  Good job, buddy!

The Leaning Tower of Pisa.  It didn't start this way.  On a fun note, a random kid stopped by the table after this tower's designer had left and asked to keep this tower.  I guess it had personality.

This Saturday will be our last official Pepsi Refresh sponsored project in the park.  We're building Lego race cars and sending them down ramps of different heights and different landing surfaces, learning about coefficients of friction.  It'll be Saturday, June 30, 9:30a-noon.  Please RSVP using the email address over on the sidebar <=== - and I'll give you the location.

Shake Table Structures - Preschool

I took my homemade shake table to J's preschool for the 4-5 yr olds to do science.  I wanted to try out the tables and building materials before bringing it to the public with science park day.

Here's how my preschool visit went:

Some kids experimented with different shapes before deciding what to build:

This would be a good point to demonstrate the strength of the shapes.  Triangles stand tall and don't collapse when you push down and them.  Squares collapse under the weight of you pushing down on them.  Ask which shape they'd rather have for their houses.  You can also ask why roofs are triangular shaped.

They had some good building going on.

They learned a little about measuring during this lesson.

I gave them 50 toothpicks and hoped they could make 12 inches tall (no limit to the marshmallows since the more they are handled, the more squishy and less reliable they get).  The tallest structure we got was 7".  This was our winner who was the tallest and lasted 20 seconds on the shake table.

**Don't worry if you don't have the time or resources to make a fancy shake table.  You can make an easy shake table with two pieces of cardboard, 4 same size bouncy balls, and 2 rubber bands.  See Raft's Shake Table on how to construct the simple shake table.  Marshmallow structures work for those shake tables too.

I'll post my lesson that preceded the shake table structures in a few days on the layers of the earth and a brief discussion about plate tectonics.  They were surprisingly interested in the brief lesson and game I had.

Tada! Homemade Shake Table

Isn't it so pretty?  I am so excited about completing this shake table lesson plan, as it was a favorite of mine as a kid.  It actually took some engineering thinking to completely enclose it and give me all the features I wanted.  I also got some much needed practice soldering.

Here's what I did:

1. Based my design around the Exploratorium's homemade shake table - mainly a 1.5-3V motor spinning an offcenter weight (wingnuts and washers), with a potentiometer to vary resistance and shaking speed, which runs off of 1-2 D sized batteries.  I kept the same base and shake table sizes, along with the square edge lining.  The top is still attached to the bottom via rubber bands.

The innards of the raised shake table

2. Completely redesigned it to stand on 4 pillars (~3 inches tall), so I could mount the motor on the underside. I super glued milk caps (instead of film canister lids - who has those nowadays anyways?) to the pillars to house the marbles the shake table sits on.
3. Adapted the circuit so it can run off of batteries or AC (plug into a household socket).  For this I got a power adapter that goes down to 3V.  I found a plug for that adapter and bought an extra plug of the same size, which I soldered to a plastic 2 D battery holder.  Since I want to do this in places without running electricity (like the park tomorrow) and I didn't want to waste batteries if I go into schools or do this at community centers, it was an important feature for me to have both options.

4. Added an on/off switch to the circuit.  Who doesn't like turning on a switch and being in control?

On/Off switch + variable resistor (potientiometer)

5. Since I wanted it enclosed, having rubber bands sticking out in the bottom wasn't going to work, so I took small eye screws that came in a wall mounting kit we bought moons ago.  I opened each hook up slightly (enough to insert a rubber band without breaking it).  I mounted four screws on the underside of the shake table ==> one at the halfway mark of each side.  I made sure they were mounted directly under the piece of wood on the end of the shake table.  Four more screws were placed on the plywood base, 3 inches back from each side on the mid-line.
6. The motor was mounted on an extra block of wood I had leftover from raising the table up 3". My husband made a custom mount piece using his 3D printer.
7. For the enclosure, I created a drawing of what I wanted and cut 0.25" thick alder board with the laser cutter in a puzzle-like interlocking pattern.
8. To keep the top from falling down, I super glued small metal L brackets/corners on the side piece which allowed the top to be flat but not glued to it (I want to be able to remove the top pieces).
9. The two sides with electronics on it were fixed to the plywood base and each other via wood glue.
10. The two remaining sides were attached to the fixed sides and each other via cabinet magnets.  I wanted to be able to remove the top and access the underside of the shake table if anything (like the rubber bands or motors) decided to poop out on me.

Then of course Big J and I tried out the marshmallow structures before the kids and successfully made ~12 inch structures out of 40-50 toothpicks.  Mine was taller and was stable on the shake table, buuuut, it collapsed on itself overnight which is fine - it did what it needed to do.  I called it the giraffe (on the shake table below).