To do a trammel lets first talk about just one hand. If are spinning forwards, your arm is going to come up above your head, which will force your poi to do an anti-spin. As soon as it get to the top of its spin at the top of the extension of your arm, bring your arm straight down and this will cause the poi to extend down.

So anti-spin up for 1 beat then extend down. The other hand is doing the exact opposite in both the direction and placement of the arm.

This is a split time, opposite direction, extension vs. anti-spin, CAP.

Have fun!