I believe you are wanting to create a mixture design that will allow the estimation of a special cubic model as there is not a design called a special cubic design (to my knowledge).
There are a couple of ways to create this type of a mixture design. The "old" traditional way would be to go to DOE > Classical > Mixture Design.
Enter the mixture component information and click Continue.
Choose a Simplex Centroid design with the appropriate K to get a design that will estimate the special cubic model.
The drawback to the traditional method is that it requires you to have an unconstrained mixture design space, which is not very realistic for most problems.
The approach that I would recommend:
Go to DOE > Custom Design.
Enter the number of factors and click Add Factor > Mixture. Notice that you can specify the limits for each of your mixture components.
Click Continue.
Now specify your special cubic model. This can probably be done just by using the Interactions button. Alternatively, you could click on the Scheffe Cubic button and remove the unwanted cubic terms.
Specify the number of runs you wish to perform (the default is usually a good starting point).
Click Make Design.
This recommended approach provides more flexibility while still allowing you to estimate your desired model.
Dan Obermiller
