Morphing Handcycle Lift System: Decision to Use Dual Gas Shocks & Adjustable Shock Cord

Rory, Graham, Alan and Bill met on Tueday, Feb 2 by screen share. This post will review the decisions made.

Decision 1: Pursue dual gas springs, mounted inside of the two upper morphing arms

There were three choices for the gas shock (we also call it a gas spring.) Choice 1 was a single shock that didn't protrude, but that requires a custom shock. Choice 2 is dual shocks (the choice we picked) and choice 3 was a single off-the shelf shock that would be longer and would have an extension that would hold it down

This sequence will let you create your own animation of the morph up/down sequence showing the action of the gas shock.

This animation shows Choice 3 - a single, longer shock, mounted further along the morphing arm. The good news here is that the total force from the shock can be lower, because the mechanical advantage for lifting is higher. But we didn't like the look of the shock protruding out of the mechanism. Also, Morph 2 uses two shocks, and it has that "magic." We don't know what a single shock would be like.

Custom Shock Side View.

Custom shock top view.

Here we have the custom shock solution. One big, powerful shock mounted at a partial distance along the morphing link arm. But here's the shocker: due to the longer range of Morph 4 compared to Morph 2, this shock needs about 1000 lbs of force for a 250 lb rider. Wow! We don't want a single shock with this much force, and we don't want a custom solution.

Rear view of the dual shock approach. We're going to see if the two shocks can be mounted inboard of the struts, rather than with the small extension. With 500 lbs on each shock, that' creates a lot of moment a the mounting points.

Side 3D view of the dual shocks.

Adjustable Lift System

Adjustable Lift System - This side view shows the idea of some of the lifting force being supplied by an elastomer (shock cord). The cord is shown in red. In the low mode, the cord is stretched, and it is providing significant lifting force. By changing the where the cord is attached to the forward frame, we can instantly adjust the up force. This adjustment will be done when in high mode, where the cord is slack.

An idea for the upper morphing arm. Teardrop shaped tubing with a machined end that is welded on. Not sure this is an ideal design.

Bearings are captured in the clamp?

What Makes a Morph Go Up and Down Like Magic? Animations and Lots of Details Here

This is a big post that will review a wide range of design choices on Morph 4.

First up is the design for the "lift system" - the gas spring and any other elements that make the Morph...well... morph. Here we see a design that uses a single long-stroke gas spring that fits in between the dual arms of the upper and lower link arms. This spring would be rated at about 500 lbs of force. It is an off-the shelf shock from McMaster Carr:

Details on the single shock. Click here to see the gas spring online.

Morph 2 (and its modified version, Morph 2.5) uses two gas springs. We're debating right now which is better. With two gas springs, we can have more force, and the place the springs closer to the hinge point. This means a smaller shock, and maybe a neater look.

Side view animation. Gee, the single gas spring seems like it's hanging out in low rider mode. Is that cool? Or wrong? Note the "extension" that holds it to the upper morphing arm. This member is only in tension. It is like the vertical cables on a suspension bridge.

Rear view animation. Note that the big shock "pokes up" in Morph 4, but in Morph 2/2.5, the gas springs protrude downward and are handled by an extension from the axle tube.

Note the two thin extensions welded to the axle tube. These welds actually failed on Morph 2 because there is about 250 lbs of force acting at a distance on these extensions. But they do serve to allow a longer gas spring to fit into the system. I believe  we could use a similar approach on Morph 4.

We decided to look into this some more, and scheduled another online meeting for Tuesday, Feb 2, 2010. Or calls uses for screen visuals, and we are in Bath, Maine, Cambridge, MA, Somerville, MA, and Santee, CA.

Adjustable Lift System

Let's say you weigh 170 lbs, and the gas shock is sized just for you. You want to show a guy who's 200 lbs exactly how cool the Morph is. Well, it won't work that well, because the 200 lb person is 30 pounds over the design weight. This means that he will sink down fast to low rider mode, and will need to work a bit to get up. He won't have that wonderful "float" that makes the Morph so amazing.

We would like to have a fast, easy way to adjust the lift system. One idea is to have the gas spring handle part of the weight, and have an adjustable elastomer system handle the rest. Those are the red cords in the picture above.

X-ray view.

You can see the elastomer cord bisecting the "diamond" of the frame, and then going inside the main tube, then emerging to a hook. What hook you set it on determines how much supplemental force you get for the lift system. Want to change it? just move the hook when you are in high rider mode and the cord is slack.

This is one proposed supplemental lift system. Just hook it to get the lift you want. We're still working on other ideas. The silver item below the cord is the coupler that lets the front and back of the bike come apart for getting the Morph in a car.

We're debating aesthetics vs ease of construction. Here is an upper link arm with straight tubes. Much easier to make, but will it have that "cool" look that gets people excited? Other arm has the cuts/and welds shown.

Aye, she's a beauty, but oh, the work to make this part. Cuts, welds, and precision machining for the bearing races that mate at either end.

This design avoids having to seat bearings at each end. Uses ball joints. Hmmm.

Here's another way to complete the tube. A machine insert that is welded on. We're also thinking about teardrop tubes which would look much better than rectangular.

In the previous post, we had an issue with seat clearance to the main tube. The new design moves the cross-member further forward, so the horizontal supports can straddle the main tube.

A look at an assembled version using ball joints. I like the ball joints for the little seat adjusters. Not sure they're great for the main morphing joints.

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

The Gas Strut Challenge - Single Large Gas Shock

The hard part about this new design is the gas strut.

Last time we did this, we had an inkling of the strut that we were likely to use as we were designing the frame and morphing geometry, which made it relatively easy to fit.

The challenge now is a little more complicated:

 1. We are traveling through a greater range of morphing motion, so
    the range of motion of the strut (Stroke length) has to be much
    greater unless we are to overload the frame.

 2. The geometry now lends itself nicely to a single strut.  This,
    however means that we will need twice the force out of a single
    piston.  It also means that you only need to purchase one per

So the result is that we need a substantially longer shock that is almost twice as stiff.

Figuring this out was something of an iterative process:

I know that we will potentially need to lift at least 250lbs in the seat of the handcycle, and that the geometry of the strut with respect to the linkage arms in low rider mode would affect the mechanical advantage and thus the strength of the spring that was needed.   The spring could only fit a few ways, so I found the strongest spring available off the shelf, and then designed the geometry to provide the appropriate force.

This spring has 562lbs of force.  The barrel is 1.1 inches in diameter, and a stroke of 11.81 inches.  It is also a reducible force gas shock so it can be tuned down to lower forces.

Based on this I calculated where the pivots needed to be to generate 250lbs of lift.  It turns out that this point is almost half way along the upper linkage.  Then to fit the shock in I had to create an extension linkage to create some extra room for the longer shock.

This sounds very simple but fitting it into the geometry was really tricky.  Check out the attached screen shots.  Pay attention to clearance issues that limit the positioning of the shock.

Single large shock design.
Low rider. Note large shock retainer to give room for long single shock.
Mid rider 1

Mid rider 2
Almost all the way up.
Morphed up to high rider mode.
Closeup of single shock and lower link arm in high rider
Single shock rear oblique view.
Single shock side view.
Closeup of ball joint morphing joint.

Photos: Quick Release "Easy On" System

[From Graham Butler, Janaury 31, 2011]

Here are the pictures of the quick release system for the front end.

They guy who bought this bike loves it.  Hasn't had any problems and has just ordered a second one the same to keep at his cabin.

Morph will use similar release mechanism to make it easer to get on the bike.
Press button to release.
Front end pulls away
Pleanty of clearance to bring feet over. Not that this bike (like the Morph) is fitted with a coupler to allow the bike to break down for travel and stowing in a car.
Then replace strut for riding by clicking it in the receiver.

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.

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....