Analyzing A Deceptively Simple Centering Spring for the Morph

This post will go over the centering spring design we'll be using on the Morph. This design has been used on the New England Handcycle for over 30 years with great success, and it was carried over to the Travel Bike (shown below) that was built for me by One-Off Titanium (Mike Augspurger). The Travel bike and the Morph share many design elements, including the 16" front wheel, the coupler to allow breaking the main frame into

Here is the centering spring as installed on my Travel Bike. Note the silver coupler in the main tube. Because the bike comes apart here, there two carabeners below allow the centering spring to be dismantled when the bike is taken apart.

Closeup of the centering spring. I can't say it's pretty, but it works perfectly, as the explanations below will outline. This same mechanism will be incorporated on the Morph, but on the front end, rather than under the main tube. And, we'll make it look much nicer.

This series of three photos shows how one chain becomes slack and the other stays tight when the rider starts turning the wheel.

This is a bottom view (well, the bike is flipped vertically) showing the size of the wings.

When the wheel is turned, the wings pull on one chain, thereby stretching the elastic.

As the wheel is turned, the moment starts decreasing, while the stretch on the elastic, (I call it the "gap"), increases. The lines in red on the left side show the relative sizes of the moment and the gap.

As you start to turn more sharply, moment starts to fall quickly, even though the elastic is still being stretched more. This creates exactly the characteristic you want: Good centering near center, and up to about 45 degrees, and then a reduction in centering as you turn even more. Because the handcycle can make extremely tight turns, even more than 90 degrees, its important the the centering spring not fight you when you're doing these tight maneuvers.

At 100 degrees, we see that that gap is big, but the moment has dropped to almost zero. Just perfect. You can steer as extremely as you want, but lets say you need to grab the rear wheels and push like a wheelchair -- the centering spring will make sure the wheel stays straight.

Below are the five slides in a picture viewer, so you can click through them without the explanations above.

Here is the Powerpoint in case you'd like to play with it.

The Morph will implement the same mechanism, but the wings will be fixed to the main tube, and the elastic will be on the front end.

Morphing Handcycle Reference Design V1 Released


Morphing Handcycle Reference Design - Low Rider, Side View


Morphing Handcycle Reference Design - High Rider, Side View

Move With Freedom has been working on the design of a practical Morphing Handcycle for a few years. We are now at an important juncture where we switch from the design process to that of helping the product get into production.
Move With Freedom makes open source designs. The design process can be traced right to its beginnings by looking at the posts in this blog:  You can see a movie of the Morph in action here.
Our designs are free and open to anyone who wants to use them. At the same time, we want to encourage manufacturers to add value to our designs and put them into production.
So, today we are announcing two important developments:
1. Availability of the Morphing Handcycle Reference Design V1 (PDF)
2. Move With Freedom, Inc. has placed an order with Intrepid Cycles for four production Morphing Handcycles, 
If you would like to design your own production versions of the Morph, we are ready to help. Just ask for what you need.
What follows are some illustrations from the document:


Morphing Handcycle Reference Design - Schematic of Key Components


Key dimensions are provided for all schematic parts.


Automatic Seat Tilt Linkage is explained.


Calculations for the Adjustable Lift System are provided.


A detailed design for the morphing pivots is proposed.


Dimensioned drawings are provided for all key parts. (This is a partial view)

Here is the Morphing Handcycle Reference Design V1 (PDF)
Note that you can download this document by clicking the link at the end of the post.


Powerpoint and Spreadsheet: Shock location and variable weight riders

[From Graham Butler February 26, 2010]

I think I have a handle on shock position. I have extended the slide show to include most of the process that I went through. There are some things that we can just talk about at 2.

Updated Powerpoint with more information on forces

Spreadsheet showing force calculations for lift system.

PDF: Morph 4 Dimensions Compared to Morph 2

[From Alan Ball: January 12, 2010]

A while ago you requested some orthographic views with key dimensions called out for the M4. Check out the drawing I have attached here. Is this what you had in mind?

For comparison , I have included a drawing of the M2 geometry, which I documented in CAD and was measured and confirmed against M2. As you can see, the basic dimensions are almost the same, with differences occurring due to M4 greater range of morphing motion.