Slow motion chemistry: A real storm in a teacup

Following on from my slow motion combustion reactions, which were really popular for classroom teaching, I thought I’d try the same formula with another crowd pleasing reaction: Neutralisation with universal indicator on magnetic stirrer.

First reaction was a real beauty, but there was lots of turbulence due to air bubbles caused by the height of the liquid in the conical flask and the high speed of the stirrer.

I decided to film portrait orientation. Although this gives large black bars when viewed online, it gave a really good view of the conical flask and the beautiful swirling purple colours as I added the sodium hydroxide.  It’s a really good talking point for classroom discussions about neutralisation.  -What’s going on?  Why doesn’t it all change at the same time? -Why don’t the liquids mix instantly?  What will happen? Why did it go Blue?

This was the least successful in terms of colour changes, but the vortex is really beautiful and engulfs the stirring bar. I love the final colour.

Genie in a bottle. 

I looked up a recipe from the RSC demonstration handbook for ‘dancing flames‘, which is a reaction between aluminium foil and copper chloride. The acidified solution eats away at the oxide layer, exposing the aluminium for reaction and then generating sweet hydrogen gas for the exploding. Watch the video for the burn:

This is a great experiment that allows a really good and deep discussion of reactivity, and also flame tests.  It’s applicable to KS3-5, and is a great point of focus as a demonstration with the lights off.

Lego Mindstorms EV3 ping pong challenge

Bournemouth University’s STEM outreach program came to visit Purbeck School on Monday, and bought with them 15 Lego Mindstorms EV3 kits. The kits had been made into pre-assembled robots with a Large Servo motor for lateral movement, and a medium motor to lift the arm assembly.  They had ultrasound sensors for distance sensing, and an IR sensor for manual control via the IR Beacon.

The brief of the day was simple: Write code for a Robot to be able to play a game of Ping Pong against another robot.  The challenge turned out to require problem solving, mathematics,  iterating, collaboration, failure, resilience and sabotage.

Mean looking Ping-Pong robots.   Note the Ultrasound sensor at the front.  The whole paddle assembly flipped up when the motor was set to turn.
Mean looking Ping-Pong robots. Note the Ultrasound sensor at the front. The whole paddle assembly flipped up when the motor was set to turn.

The challenge was really well structured, with the students learning the basics of connecting, writing code blocks and downloading them to the brick, and within about 20 minutes of starting, most groups had control of the servo motors, and shortly afterwards, they were able to add another loop to their program to control the flipper.  They had to figure out the correct number of degrees to rotate the arm in order for an efficient flip! IMG_1784

The code challenges were well-thought out, and got the students to learn the rudiments of controlling the robot successfully by thinking about how far the robots had to move by setting rotation limits on the motors, and learning to use logic and loops to make the robots respond to the infrared remotes.  They had time to test the robots out in the test arena,  and make sure that the robots were responsive to input, and could also hit the ball with the paddle.  There was  a key trade-off between Power and Speed at which the paddle moved, that the students had to find to hit the sweet spot.

Customisation was also a large part of the day, with some groups recording audio samples, or drawing their own pictures, or playing short musical sequences at the press of a button.  3 groups had ‘entrance moves’ and intimidating aggressive moves.

Once the matches began, it became evident that there were issues with IR interference from other groups since the EV3 kits limit you to 4 channels, and even in a large room, there was significant crosstalk between the groups.  (There was also a good amount of comedy sabotage to be had).

Playing the great game.  Getting the ball off the end of the table gains you a point.  The IR beacon was used to control the robots.
Playing the great game. Getting the ball off the end of the table gains you a point. The IR beacon was used to control the robots.
A Match in progress.  The board shows the channel choices.  Teams had to reprogram their 'bots to change channels between games .
A Match in progress with teams that finished 2 and 3rd.

There were 20+ matches, the competetive element was very strong and the quality of the sport got much better as the day went on.  In particular, the single-member teams did particularly well, ranking in 3rd and 4th place even though they had no previous experience with the NXT-G programming environment.   There had to be an overall winner, and team Virginia Tech prevailed in the end.

The winning team. Their robot’s unique skill was to shout ‘BANTER!’ during matches. It also played a nice jazzy arpeggio. They managed to overcome significant issues with controlling their robot.

We hope to be involved with Naomi and the STEM outreach team again.  The feedback was really positive from the students, and this would work really well with a younger cohort of students.

Lego drawing machine


We’ve been working on an art collaboration, and have built a drawing machine based around a pantograph and a rotating turntable. It produces a Spirograph-style pattern, which can be tailored by changing the arm length, pivot point, rotor speeds and turntable speed. The build is a prototype, and can be replicated with power functions motors, rcx, Nxt kits, or even old school technics kits. A build video will follow, but check the time lapse for a quick overview.

We used the power functions speed controller remote so that we can control the rotor speeds and directions, as opposed to the digital remote which only allows full on/full off.    If you were to replicate this build using NXT, you would have to set the Servomotor speeds in software, and then execute the program.  You can see in the video above that Shorna changes the drawing pattern at 0.08 seconds in the video.

Doodlebots @ STEM club.

Inspired by an article at Makezine on scribblebots, we decided to roll our own using some bits at school.

This video shows the bots in action in slow motion, and clearly shows how the eccentric vibration motor allows the bot to move in a circle.   We just used rubber bungs stuck onto the motor to create the offset motor.  We experimented with a range of pens, pencils and markers.  Sharpie style markers worked well with the sugar paper, but if you are tiling smaller sheets of paper, make sure to tape on the underside and make the seams as flat as possible.  The activity was great fun, and produced some crazy generative art, which was my lab wallpaper for a couple of weeks.  Check out the videos:  Continue reading