I got my 2000 ml Erlenmeyer flask today and got it to spin once but then I turned it off and when I turned it back on it kept throwing the bar. I got irritated and gave up but I'm guessing it has to do with that big stir bar (which is the hexagon type). The new one I have on order is smaller and round so I'm thinking it will do better in the flask.
As for speed... that picture is the lowest setting. Unfortunately I didn't heed the advice of others here who said 12 v might be too much. The fan is 12 v and I let the guy at radio shack talk me into the 12 v DC power pack, he said the fan wouldn't run on anything lower. I'm a dummy... next time I'll know better
Is there a problem if the vortex is too strong?