A few weeks ago, Professor Ernst Ferg, Associate Professor – Physical Chemistry at South Africa’s Nelson Mandela University bounced (pun intended) some questions off me about deploying response surface methods (methods) on a catapult operated for education purposes by three of his students. I built up power and developed insights on relative performance of the artillerists by rebuilding his results into a fully replicated blocked design.

Now, aided by Stat-Ease software for DOE, you can see surprisingly close agreement on the central composite design’s center-point set-up (red dots) for the catapult (the reason for this soon to be revealed).

Pooling all the results into one model produced a very impressive 3D graph of distance as a function of the two biggest factors—release angle (A) and cup elevation (B).

Being impressed by Ernst’s initiative to teach his students RSM, I asked him to send me pictures of them operating the catapult. Ernst replied, “LoL, I am approaching this very much in the digital way of things: I made them use Virtual Catapult^© from SigmaZone.”

It turns out that Ernst learned about the Virtual Catapult (free!) from Tom Keenan—one of four DOE educators who shared their experiences Teaching Design of Experiments in Higher Education. Tom said that “I love the way that it shoots the ball but doesn’t give you the measurement. It comes to rest next to a tape measure that the students have to read.”

Tom also likes the way that the Sigma Zone simulation incorporates some variability, thus every student gets slightly differing results. He collects the results in blocks and does an analysis similar to what I did for Ernst—being watchful of students who deviate from the others.

Fun!

PS: After gaining possession of a South Dakota Mines trebuchet from Professor Dave Dixon (one of the four panelists), I enlisted my son Hank to run an RSM optimization on this more efficient counterweight-driven cousin of the catapult (powered by torsion). We ran a Box-Behnken design, which simplified the operation to only 3 levels of each factor (versus 5 levels required for a central composite design). Ultimately, we worked out a set up that would shoot a salt-weighted raquetball over our backyard bush into a bucket on the upper level of our play fort. Empowering! For all the details on our trebuchet experiment (and pictures), see Messing With Medieval Missile Machines (Part 2).