When Does a Morph Not Want to Morph? - A Design Issue of "Over-the-Center" Mechanics

One of surprising behaviors we found in the Morph III design was that once it got all the way down, it just didn't want to come back up. It just seemed to "lock" in the low position. The question is why, and how do we avoid this situation in the new design?

Alan Ball and I had a little online design meeting today, and here's what Alan proposes is happening. Start by drawing a line from the front wheel center to the rear morphing joint. Then draw a line to the middle morphing joint. In the Morph III CAD above, notice that the joint is below the wheel to rear-joint line. Since the way you get the bike to start coming up is to lock the front wheel and then roll the rear wheel forward, you can imagine that in this configuration, the middle joint will want to go DOWN. This explains the "locked" feeling. By the way, you can get Morph III to go up, but you have to lift hard. Probably to force your way past the over-the-center condition to the range where the mechanics work in your favor rather than against you.

Here is the Morph Out (same geometry as Morph II) design. Note that the triangle is flipped. Rolling the rear wheel forward with the front wheel locked WILL raise the bike. And the gas springs will be helping at the same time. We find that Morph II "floats" really nicely, and we want to have that same behavior on the next design. We're actually using the IDENTICAL geometry of Morph II, but will be using a different frame configuration to achieve that geometry.

Next Morph - 3D Model showing 5'2" and 6'2" Riders

We're just starting to look at different size riders for the Morph Out design. The 3D model below shows two rider sizes, 5'2" and 6'2", in low and high rider positions. Notice, for example, the position of the feet relative to the front wheel, and of the hands relative to the pedals. The bike is set for the larger rider.

The Solidworks e-Drawings file lets you see this vehicle in 3D, and also choose the configuration you wish to view (lower left of display). Get the free e-Drawings viewer here, and try it out!