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)

Photos of the Morphing Handcycle Test Rig

Here are all the photos from our August 17th meeting at John Baron's shop, with Alan Ball. Sorry, no time to do nice organizing.

 Here's what we were looking at:

 1. Can we replace the expensive, heavy gas spring with shock cord "spring".

 We tried this with a few bungee cords, and it worked rather well. See the videos in the next post. We will refine the approach this week by testing with shock cord set to balance John's weight. Note that without the gas spring in the way, flanking members on the frame work better, and the frame travel is much longer. The bike goes a little higher, but gets a lot shorter, and it can also go much lower, practically touching the ground if you let it. (we may have a removable stop for that)

 2. Could we get the damping and locking of the frame by using a standard bike brake hub?

 Again, we think the answer is yes. The internal drum hub would go on the joint under the seat and would allow firm locking of the morphing frame, at low weight, low cost. We think this control, along with some "end of travel" bumpers, may work well with the shock cord lift system.

 3. The seat bottom is from an office chair. Real seat won't be that big.

 4. The automatic seat adjusting system works like a charm. I didn't even realize it was happening. It just felt right.

 5. When you don't worry about weight, things really do get heavy. This test rig weighs about the same as a small refrigerator. (We knew that, but still interesting.)

 6. The adjustment mechanism for the gas spring didn't work the way we want. Turns out you have to adjust TWO attach points, not just one. This is because by changing only one point, you adjust travel AND pre-load at the same time, and they tend to cancel each other out. The shock cord lift system is actually much easier to adjust.

 7. As designed, the bike has a huge moment arm where the axle meets the morphing frame. If you ever hit one wheel and not the other, you'll twist the frame and it will be easy to make it go out of alignment.

 8. We discussed separating the rear flanking members to be closer to the wheel. This will triangulate the rear frame and will eliminate the moment arm. It will also let us use smaller tubes and save weight. Some of the sketches are related to this.

 9. John has a detailed spreadsheet that shows the calculations to maintain weightlessness at every angle of the frame, and for any rider weight.. (we should post it later)

 10. The pictures of Bill (in purple) on the test rig are meant to be a sequence, but they may be out of order in this post.

 11. Alan is going to make some very rough concepts for review next week when Rory returns.

 12. John is going to work on the shock cord lift system.

 13. The items we talked about could make the morph lighter, stronger, cheaper, more reliable, easier to adjust and easier to build.