Aerodynamic testing at the Purbeck School Science Fair

tl:dr – Make LEGO models and test them in our Scale Wind Tunnel, test and improve!

At the recent Purbeck School Community Science Fair, I was fortunate enough to be running a Scale Wind Tunnel manufactured by Clive Evans at Scale Engineering.

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Quote in wired magazine about making your own wind tunnel. 

These are truly magnificent pieces of engineering, and we were very lucky to be able to use one for the day.

Our version had been outfitted with a Lego studded test bed, which allows for the rapid testing and prototyping of Lego models.   As you can see from the picture above, the tunnel is a finely-engineered beast.

 

On the left of the tunnel is a laminar air intake, which forces the air through a honeycombed aluminium structure to reduce the turbulence.  Once through this, the diameter of the tunnel reduces sharply, increasing the airspeed through the test bed.

The LEGO bed is attached to two load sensors as can be seen below.  One senses movement in the vertical direction, which indicates a Lift force in Newtons, and the other senses the Drag generated by the model in Newtons.  The machine outputs the readings to two digital 7-segment LED displays, and are accurate to 0.01 of a Newton.   The air exits via the exhaust side, and is driven by a mains-powered air conditioning fan.  This is adjustable up to 18m/s at top speed, so the tunnel can really push the limits of most lego models.

It is very hard to directly visualise the airflows without some seriously dense smoke (which would set off alarms, asthma), but we have cotton thread on a wand that can be used to directly visualise the airflow over a model by tracing it around the outside of the model.

After the initial setup in the school library, I opened up my Big Box o Lego (TM), featuring many classic LEGO pieces from the golden era of 1980s space lego, and infused with Dexter’s more contemporary LEGO star wars pieces.  We even took my younger son’s duplo airplane as seen above.

The basic procedure was outlined:

(1) Build a model, get it tested in the wind tunnel

(2) Record the Drag and Lift Values from the tunnel

(3) Refine your design, retest.

(4) Repeat.

We had an incredible variety of models made, from the austere and efficient to the beautifully sculpted and adjustable masterpieces.  Over 45 different models were made and refined over the course of the day, involving multiple rounds of testing.

The best models of the day tended to have the best Lift to Drag ratio, the best being 1.09N Lift,  0.38N Drag. We discussed how you could make them more efficient, including using flat pieces to reduce drag around the studs, removing unnecessary fandangles and gizmos.

The crowd that gathered was equal parts boys and girls, as well as equal part child and adult.  LEGO is a great leveller, and many families had to pull away their participants in order to see the amazing things on offer elsewhere in the Science Fair.

This close-up shows the control unit, with readouts as well as the test bed.  Models to be tested are also lined up on the bottom.  That's me twiddling knobs.
This close-up shows the control unit, with readouts as well as the test bed. Models to be tested are also lined up on the bottom. That’s me twiddling knobs.
This was a particularly sassy model, with adjustable angle of attack for the wings.  The builder decided that inverting the wings would reduce drag.  He was right!
This was a particularly sassy model, with adjustable angle of attack for the wings. The builder decided that inverting the wings would reduce drag. He was right!
I was constantly surprised at the amazing variety of designs that people were able to make out of my limited pool of LEGO.
I was constantly surprised at the amazing variety of designs that people were able to make out of my limited pool of LEGO.
Two different solutions to aerospace design: reduce the surface friction, or go for maximum lift
Two different solutions to aerospace design: reduce the surface friction, or go for maximum lift
The fan running at 70% power.  This was, of course, off limits to members of the public in the rare case of a 'testing to destruction' event.
The fan running at 70% power. This was, of course, off limits to members of the public in the rare case of a ‘testing to destruction’ event.
This gives an idea of the beautiful engineering that went into the creating of this incredible wind tunnel.
This gives an idea of the beautiful engineering that went into the creating of this incredible wind tunnel. Thanks to Clive Evans for the loan of the wind tunnel.
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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.

IMG_1814
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

IMG_1760-0

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.