Help with elevator

Have you considered a Ferris Wheel? http://mekoramaforum.com/media/mekorama.2829/ has a one that worked well. You can make the speed faster or slower based on the length of the arms. If you are ok with the player having control over the elevator, you can use a pushable that does not start touching the elevator (metal fuses together). This way they can hold the elevator at various points.

 

Here's a simple mechanism.



It's best, and smoother, to have the lengths of the interfacing parts be sufficient that the are always tangential to each other in the first stage.

You can add another, slightly more eccentric cam to interfere with the last, non-elevator slider.

This kind of motion interruption idea also makes it easier to design levels where B has to get to halfway across a spinning rod, but no further, to prevent being flung off when it does another partial rotation. Giving B enough time to get almost to the other side encourages the player to aim for speed ("I almost made it that time!") instead of exploring a more prudent course of waiting.

Sorry for the necrobump, but I thought it would be good to have this idea demonstrated.