Variable force using elastomers and inert gases

[January 29 From Graham Butler]

I talked to Bill earlier in the week about the possibility of using elastomers to create a variable force adjuster for the gas shock. I have been thinking about this idea, but I have been having trouble figuring out the geometry.

The reason: For it to work well you need 2 converging points on the frame where the maximum lift happens in the low rider position. There are lots of points where you get some lift in low rider position, and then progressively more lift as you morph up. Lets discuss these tomorrow.

I also did a bit of research into gas shocks. It turns out that the compressed Argon that I use for welding has almost the a similar individual gas constant as nitrogen (29kg/kg mole for Argon as opposed to 28 for Nitrogen) Both N and Ar are readily available and relatively cheap (nitrogen is used for laser cutting). It comes in a cylinder compressed to 2000psi. If you were to fill this shock with either gas at 2000psi , it would generate ~1700 lbs of force. This begs the question. Why not create a method to fill and bleed the piston. This solves our variable weight problem especially if it can be done on the fly. You could even have a small canister of gas on the bike permanently linked up to adjust the pressure in the piston. Inert gas is relatively cheap....

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.

The Morph Begins the Move From Wood to Metal: Initial Frame Designs From Graham Butler - Looking Great!

Graham Butler sent along a series of screen images in advance of todays online meeting of the minds between Morph inventor Rory McCarthy, design and manufacturing engineering from Graham Butler, industrial designer Alan Ball, and design consultant and project manager Bill Warner.

Above is the initial frame design for Morph 4. Wow, that is looking great!

This image shows the metal frame model on the left. The red members provide the flanking design needed for Morph 4. The green area just shows the chain path...there won't be any "green thing" on the chains!

Rear view of the initial Morph 4 frame design. 

Side view of Morph 4 initial frame design. Note that some of the wood structure is still shown for comparison on the front.

Wireframe shows the wood model.

The new frame will use an SNS coupler so the frame can be taken apart to fit in a car. This coupler requires steel or titanium, so this means the main tube will likely be thin wall chrome molly steel tubing. (Graham already uses this on his current handcycles.)

A closeup of the morphing arms. Not sure what these will be made of...probably aluminum. We're taking a cue from suspension mountain bikes, and we plan to use bearings on all the morphing joints, rather than bushings. Mountain bikes have moved away from bushings as they have been unreliable.

A closeup of the assembled morphing joint. I think there is a single bearing on each side, since there is a thru-axel.

Graham proposes using tie-rods for the automatic seat adjusters. This allows us to adjust their length to suit the user's preferences, and they already take care of 8 points of rotation at very low cost.

Tie rods under the rear portion of the seat bottom. These linkage cause the seat to move not with the main tube, but with the lower morphing arm. This provides the self-adjusting magic that make the Morph work just right.

How many joints? How many bearings?

Upper and Lower Link Arms :  4 joints, 8 bearings total

Forward seat tilt hinge, similar bearings to morphing joints? Thru axel? Probably 2 bearings.

Forward Seat Tilt Hinge: 1 joint, 2 bearings

Seat back articulation:  Just above red link arm on the bottom is a rotation point for automatic seat tilt.

Seat Bottom Pivot: 1 joint (maybe this one is a bushing.) Just above red link arm on the bottom is a rotation point.

Total joints and bearings:  

Upper and Lower Link Arms :  4 joints, 8 bearings total

Forward Seat Tilt Hinge: 1 joint, 2 bearings

Seat Bottom Pivot: 1 joint (maybe this one is a bushing.) Just above red link arm on the bottom is a rotation point.

Automatic Seat Tilt Tie Rods - 8 joints, 8 bearings

TOTALS:      Joints:  14 joints total (sounds like a lot, but suspended mountain bikes have many also.)

Bearings: 18 (wow), 8 are in the tie rods, 10 outside of tie rods

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

A Detailed Video Review of the Morph 4 Wood Model Before It Goes to Metal

This is a detailed video review of the Morph 4 wood model. It shows each joint in detail, and gives an overview of the mid-morph lock that I'm proposing. This video is intended as input to Graham Butler, who is starting on the frame design for Morph 4. The wood model shows the location of all the joints, and demonstrates how it all moves. The actual frame design will keep this same geometry. Of course, all the rest of the decisions still need to be figured out -- the mechanics of the lift system, the foot rests, the seat adjust, the mid-morph lock, and the frame design and materials. Over to you, Graham. We have another online design session on Wednesday, January 20, 2010.

Morphing Handcycle: Morph 4 e-Drawings Model - View the Reference Model in 3D

Side view of reference model for Morph 4.

Rory, Graham, Alan, and Bill are planning an online design session for Wednesday, Jan 13. These e-Drawings models along with the earlier drawings showing dimensions will be useful for the discussion.

Our man's name is "Slim Flatstock"

He disappears in front view.

Isometric view.

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

Comparison Drawings: Morph4 vs Morph 2 Do the Numbers Match Up? Yes.

Before we go into detailed design for the actual Morph 4 prototype, I asked Alan to check the key dimensions of Morph 4 against those for Morph 2. Everything looks good in the drawing above.

Trail in Low Rider: 2.5" (okay, a bit more trail than Morph 2's 1.3")
Trail in High Rider: -1.3" (same as Morph 2)

Wheelbase High Rider: 42.46 inches (1/2" more than Morph 2)
Wheelbase Low Rider: 59.37 inches (3/4" more than Morph 2)

Height to seat joint, low rider: 9.83 inches vs 12.03 Morph 2
Height to seat joint, high rider: 23.67 inches (.4 inches higher than Morph 2)
Seat height delta: 13.84 inches (2.63 more than Morph 2...very important for low CG in low rider)
Eye height delta: 16.21 inches (extra is due to change in seat back tilt?)

These are the measurements for Morph 2. Note that Morph 2 doesn't have the automatic seat adjustment system, and that it doesn't come down as far.

All of these dimensions and angles look good. Nice drawings, Alan. Very clear and simple.