Sorry, I coudln't think of an intelligent way of snap-shotting my question. Here's the deal, I have this lab test tube rocker, which oscillates the platform back and forth like a see-saw. It works just like a piston engine, with an electric motor that has something like a crank, and something like a connecting rod, such that it converts angular motion to linear. You probably know what I'm talking about, but I've attached a photo. Because it oscillates on a sine wave the platform spends an equal amount of time at every phase of the wave. But I want it to spend more time at each end of the oscillation, the peak and the trough, more like a sigmoidal curve. What do you think would be the best (easiest) way to do this? Mechanical or electrical? Mechanical seems cumbersome. Have the pin on the crank "float" (so that it has a variable radius) and then have it follow an elliptical (or sigmoid) track? Or have the crank be toothed gear that turns a track that could be shaped over an elliptical or sigmoidal shape, and have the pin come off the track? That seems unnecessarily complex. The easier option (I think), would be to create a timer/switch so that every 180 degrees of rotation, at the ends of the oscillation, the timer turns the motor off for a second. But I have no idea how to do that.