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?

Morphing Handcycle - Important Breakthroughs - See the uncut video

This post shows the uncut video from our design session at Baron Engineering on Monday, August 17, with John Baron and Alan Ball. Bill Warner mans the camera.
This video tips the scales at a Titanic length of 8 minutes, which in the "dog minutes" of the Internet translates to a major time committment (is that 56 "Internet" minutes?)
But there's a lot of interesting stuff here, including how you can make a morphing handcycle using bungee cords. (no kidding. Shock cord works great)

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.