Straight vs. Cut/Welded Linkage Arm Design Using Ball Joints for Bearings

[January 29, 2010] From Graham Butler:

After our last meeting I thought long and hard about the design of the linkage arms.  You guys were right about the cut and welded design being a difficult thing to manufacture. So I started working on some simpler linkage arms, where we would have some stock billet aluminum parts that were welded to straight tubes.  I have attached some screen shots of how this would look.

I don't really like this  (please let me know your impressions and opinions).  I think that the upper linkage arm is one of the most visually dominant parts of this bike, and I think that if it looks great, then the entire bike will have a better aspect.  So I went back to tubes, but this time bent instead of cut and welded.  ( I should be able to make a bending die that will be able to take care of this).  This time however, I put in the tie rod ends as the pivot points.  This would legitimately save us from machining precision bearing seats.  As long as the linkages are stiff, it should work fine.  I have attached some screen shots of this.

Having been around the mulberry bush a few times now, I think that really we are now at a choice junction.  We need to decide on the direction of design for out pivots bearings or tie rods.

Bent welded linkage arms.

Example of straight linkage arms.
Machined plug inserted and welded into square aluminum tubing.
Straight tube linkage arm.

Cut/welded linkage arm. (From hard will it be to make this?)
Ball joints used for bearings.
Another view.
Top view of cut/welded design.

New Frame Design for the Morph: Back to a Single Tube. The Bike Look is Back, But We Kept all the Good Stuff.

Just received this concept model from Alan Ball. Rory, Bill and Alan will have an online design meeting tomorrow to discuss this new approach. We have moved back to a more "planar" and more bike-like frame with single tubes. One wheel is hidden to reveal the frame.

Here you can see the "fork" apprach to what we used to call "twin flanking members." These forks let the frame overlap, and allow the morphing to go lower, for good distance riding stability and cornering.

Low rider mode. Not sure about the curved sections. They could be hard to fabricate. But this is just a concept model.

Wheel and seat removed, and you can see how the fork allows the main tube to morph lower without interference.

Here's a look at the previous design, which spead the frame members out to the sides. Better for strength, but many more parts, more metal, and it loses the bike look. That's way we went to this design, that combines the single tube look with the forks that give us our flanking members.

Click here: to download the viewer for Mac or PC. You'll need it to see the files below: Note that this concept design doesn't show the handcranks or any of the front end.


A New Look at the Morphing Handcycle - Space Frame for Rigidity and No Gas Springs

Alan Ball sent along this concept that is based on our recent design meeting at John Baron's shop. This design separates two morphing arms to make the rear frame more 3D, instead of the earlier designs that essentially have the frame all in one vertical plane. The idea is to get better torsional rigidity and reduce weight. This design is based on using an NEMSHPEC gravity reduction system. (NEMSHPEC stands for Nylon Encased Multi-Strand High-Performance Elastic Cord ... or to most consumers "bungee" cord.) Instead of the gas springs of our earlier designs, this vehicle will actually use a multistrand shock cord to provide the morphing lift. We've tested it, and it works great. Its also much easier to adjust than a gas spring, and it will be lighter and less expensive. I also belive it will be more reliable. At New England Handcycles, we used shock cord for seat components, and for the centering spring. The cords are waterproof, tough, and seemed not to care about sun exposure, even over long periods of time. (years)

The cords are not shown in this early mock up.

Here is the e-Drawings file for the SolidWorks model:  You'll need the free e-Drawings Viewer (for Mac or PC)

A Self-Adjusting Seat Mechanism for the Morphing Handcycle - Refining the Design (including a 3D Model)

This is an improved design from Alan Ball that uses the morphing struts to correct for seat tilt as you morph up and down.

Close-up of the seat adjustment mechansim showing the base supports for a slung seat design. The link arm shown in red causes the seat to adjust as the morphing happens.

The next step is to build a test rig to see how all of these designs work in real life before committing them to a finished design.

Here is the e-Drawings file for the SolidWorks model:  You'll need the free e-Drawings Viewer (for Mac or PC)

A Self-Adjusting Seat: Alan Ball Presents Two Designs for the Next Morphing Handcycle

Rory, Alan and I had an online design review session today. The latest design from Alan Ball looks at two ways to make the seat self adjusting when you morph. This version puts a hinge below the seat, at the same joint as the front morphing joint. There is a knuckle attached to the seat back that forces the seat forward as you morph down.

Bobby Hall seat positions shown in blue. Note that the Morph in low rider is a longer vehicle than the Bobby Hall. And that the rider sits further forward. Our seat height is about the same.

Now in high rider mode. Notice that the knuckle behind the seat is shorter. This tilted the seat back in high rider.

This is a different approach. A subframe is hinged just below the front of the seat. A tab pushes up the rear of the seat as you morph down. The seat tilts up at 11.5 degrees, which is what you want.

Version 2 showing the seat inn high rider mode. The mechanism has lowered the rear of the seat, and reduced the tilt. The grey lines show what the tilt would be without the mechanism. That tilt would be uncomfortable at best.

We are 2.87 degrees tilted forward. This seems to work well in high rider mode.

Without a seat tilt correction, the tilt is almost 11 degrees forward, which is not acceptable.

Click on the two versions of the model below to see it in 3D. You'll need the free e-Drawings Viewer (for Mac or PC)

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!