The title of  my last post on this subject had the word ‘Finished?’ with a question mark, because I suspected that John and I weren’t really ‘finished’ with this project (and for that matter, may  never be!), and sure ’nuff, the ‘finished’ version came back to me with some suggestions for improvements.  However, as has happened at every stage of this journey, lessons learned with each trial opened up avenues for improvement.  One of the many cool things about the current 3D printing world is that a single individual or a small group (in our case, a ‘group’ of two!) can traverse the complete trial, re-design and re-implement cycle  in a very short time at essentially zero cost.  This short cycle time and low incremental cost means that failure isn’t only an option – it’s an expected and accepted way of rapidly stepping through many design variations in the quest for truly useful and cool ‘things’.  After all, who would have thought that a clay model of a joystick-mounted ClearNav remote caddy created by one pilot long ago would have evolved so rapidly into a detachable and rotatable flap handle mounted caddy at all, much less in the 2-3 months we have been working on the project (and this time includes several ship/return cycles to move trial pieces from my lab to John’s glider and back again!).

So, anyway, back to the current design cycle:  At the conclusion of last week’s episode, I had completed a new version and sent it off to John for testing.  This version included the following improvements:

• Deleted the cable channel in the flap grip piece
• Resized the rectangular slot in the flap grip piece
• Removed the finger scallops on the front of the grip
• Offset the caddy piece slightly forward of the flap handle centerline, and rotated it about 20 degrees up’ relative to the top surface of the flap grip
• Used a round vs rectangular post to couple the caddy to the flap grip to allow for rotation
• Added protection walls for the RJ-11 remote connector

Although this version was a decided improvement over the last one, I still wasn’t happy with it, for a number of reasons:

• First and foremost – the way that I had implemented the rotation feature meant that John could no longer remove just the caddy portion from the flap grip when entering/exiting; now he had to remove the entire system, flap grip and all, from the flap control bar.  I didn’t think this would work as a long-term solution.
• The transition piece from the flap grip ellipse to the remote caddy rounded rectangle was clunky and ugly, to say the least

So, even as the previous version was on its way down to John, I was already working on ideas for the next version to address the above issues.

Rotatable and Detachable:

I wanted a way to have my cake and eat it too – a way to make the remote caddy easily (and repeatedly) detachable from the flap grip  and easily rotatable about the axis of the flap grip  and  fixable at the desired  rotation angle.  Whatever solution I came up with had to also be implementable as a plastic 3D-printable shape – no cheating allowed!

Option 1 – Snap Ring:  Maybe I could design a snap ring setup, where the post on the bottom of the caddy piece would snap into some sort of groove in the flap grip so it would rotate freely but not just fall out – some force would be required to detach it?  I decided to experiment with this a bit and see if I could come up with something workable.  Another of the many cool aspects of 3D printing is that I can  rapidly design and print small parts to test just the current idea, without wasting time with non-relevant structures.  In this case, I designed and printed several pairs of ‘buttons’ just to test the snap ring idea.

What I learned from this series of experiments is that a) I’m not that good of a Mechanical Engineer, and b) The snap ring idea is  great for a semi-permanent rotational coupling, but not so much for a system that must be connected and disconnected many times. The plastic is just too hard – it’s just as likely that the part will fail before the snap ring disconnects!  The good news is that I was able to learn this lesson quickly and cheaply! ;-).

Option 2 – Separate the rotation feature from the attach/detach feature:  The snap ring exercise convinced me that I needed to separate the rotation feature from the attach/detach feature.  Conceptually, this meant that I had to partition the system into three  parts rather than two; the flap grip, a ‘converter’ piece that would attach/detach from the flap grip on one side, and would form a rotational surface with the remote caddy piece on the other, and the caddy piece itself.  Separating the design into three pieces vs two wasn’t really much of a conceptual leap anyway, as I had already done most of this in the previous incarnation when I used the 123D Design’s ‘Loft’ feature to transition from the flap grip ellipse to the caddy rectangle.  All I had to do was to make that transition into it’s own separate piece, with some sort of attach/detach mechanism on the bottom, and a rotation feature on the top.  Of course I still had to figure out what those  mechanisms were, but details, details, details! ;-).

Quarter-Turn Latch For Attach-Detach:  While I was doodling around trying to figure out a good mechanism for latching/unlatching the center ‘converter’ section to the flap grip, my wife happened to look over my shoulder and casually say  “what about a quarter-turn fastener?”.  My first thought was “nah – WAY too hard”, but the more I though about it, the more is seemed like that might not be such a crazy idea after all.  One of the many cool things about 3D printing is its ability to form internal structures that aren’t possible via normal milling/machining techniques, another is its ability to convert a solid shape to a cavity and vice-versa, and  another is the way it facilitates rapid experimentation.  The combination of these three things allowed me to design complementary plug/socket designs, and then rapidly iterate through several versions to improve the design.

I started with a circular base for both the ‘plug’ and ‘socket’ version of the quarter-turn latching mechanism, but rapidly changed to an elliptical base that exactly matched the cross-section of the flap grip. I knew I would eventually need to transfer the mechanism to the top of the flap grip and the bottom of the identically-shaped bottom of the center transition section, so using the same shape for the experimental parts would make the transfer a LOT easier.  The first set of trials were pretty clumsy, as I had no real idea what a good mechanism looked like, how to determine the amount of rotation from locked to unlocked, and which direction I wanted the locking rotation to go.  Version 1 used a rectangular tongue for the latch, but I discovered this didn’t work very well, so this evolved to a pie-section tongue shape, and the complementary internal socket channel evolved to match.

By version 3, I had also started adding ‘engraved’ version number and orientation reference marks to the experimental pieces as an aid for getting the lock/unlock orientations right (after having screwed this up a couple of times without the reference marks).  I had also gotten smart enough (after some more screwups) to extract  the design of the quarter-turn mechanism  into its own file, so it could be added to whatever structure required it (and making it available for completely different future projects!).

Doing this made it MUCH easier, for instance, to reverse the lock/unlock rotation direction when I discovered that the original orientation made the mechanism too easy to unlock inadvertently during normal use (50/50 chance and I blew it – again!).  The finished (as much as anything gets finished in this project) product is shown below

Rotational Feature:  Based on earlier feedback from John, I wanted the remote caddy to be able to rotate with respect to the flap grip.  In an earlier incantation, the piece that transitioned from the flap grip ellipse to the semi-rectangular remote caddy was integrated into the remote caddy, and the entire piece rotated about the top of the flap grip.  This was OK, but the transition/caddy section could not be easily removed from the flap grip, making glider entry/exit potentially awkward.  In the new setup the idea was to separate the transition section from  the remote caddy so it  could rotate around the top of the transition section, while the combined caddy/transition sections would attach/detach from the flap grip via the quarter-turn fastener.  So, I needed a rotation mechanism, preferably with some sort of detent arrangement so John could try different rotation angles in flight.  The detent requirement led to another series of  experiments with snap-ring buttons, with a small protruding tip one button that engaged a set of radially distributed grooves on the other.  The result, unfortunately, was that if the tip was sufficiently large to properly engage the grooves, it was also large enough to  make it nearly impossible to ‘click’ from one groove to another.  In other words, it turned out to be pretty much an ‘all or nothing’ kind of thing.  Fortunately I still had a couple of the McMaster-Carr ball-spring plungers left over from the last go-around, and I replacing the protruding tip with a spring-loaded ball did the trick very nicely!

OK, so now we had the desired quick-release feature so John can  easily remove the remote caddy (with its attached cable to the ClearNav) from the flap grip for glider entry/exit, AND the desired ability to rotate the caddy with respect to the flap grip axis!  All it took was a little persistence, a genius wife, and about a million design/implement/test cycles ;-).  The following photos show the various experimental parts generated, and the ‘final product’ (but of course, ‘final product is what I said the last time!)

 

Stay Tuned!

Frank

 

 

 

 

 

 

 

 

In Part 5 of this journey, I described our paradigm shift from a joystick mounted ClearNav remote caddy to a flap grip mounted version.  When John received and tested the first try at this approach, he agreed we were on the right track, but there were some ‘issues’ (there are *always* issues!).

• The cable channel in the flap grip piece is unusable, as routing the cable this way interferes with opening the canopy.  Instead, John just used the single tie point on the caddy piece, and simply detached that piece when entering/exiting the glider
• The rectangular slot in the flap grip piece was a bit too roomy in the forward/aft direction.
• The finger scallops on the front of the grip didn’t really fit John’s fingers – oops!
• The caddy piece would work better if it was offset slightly forward of the flap handle centerline, and rotated about 20 degrees ‘up’ relative to the top surface of the flap grip (i.e. toward the glider centerline)
• The way that the caddy piece was attached to the flap grip prevented it from being rotated slightly to accommodate John’s actual thumb position; he suggested a round stud rather than a rectangular one.
• The remote connector (a RJ-11 phone-style connector) sticks out the front of the caddy and is vulnerable to damage; John suggested I design in some protective walls for this.

Incorporating all the above elements into a new design involved some head-scratching, and quite a few  4-letter words, as I found that none of the 3D design tools I have so far employed (TinkerCad, 123D Design, and MeshMixer) would do the whole job.  I wound up working with all of them at one point or another in order to get what I wanted.  In addition, I was in the process of upgrading my PrintrBot 3D printer with a heated bed to accommodate future plans to print with ABS plastic in addition to PLA, and this turned out to be a  lot more complicated than I had envisaged (I eventually reverted to my original hardware configuration, as I could not get consistent prints with the heated bed).

The first three items above were trivial to solve – just deleting the relevant ‘hole’ structures from the design, and modifying the rectangular slot dimension slightly.

The last three, however, required a complete re-thinking of the way the caddy piece coupled to the top of the flap grip piece.  The flap grip has an elliptical cross-section, with a top surface that is parallel to the glider centerline, while the caddy piece has a rectangular cross-section that needed to be tilted up 20 degrees to the flap grip piece.  In addition, the front portion of the caddy piece needed to have significant material added to support a side wall protection structure for the RJ-11 connector.  I ran through several TinkerCad versions but ultimately realized that TinkerCad just kind ran out of horsepower to handle the complex surface morphing I was looking for.  I just couldn’t get any kind of a smooth transition from the elliptical flap grip shape to the essentially rectangular caddy shape *and* provide for connector walls.

 

However, I had been playing with 123D Design as a possible alternative to TinkerCad, and realized that it’s ‘sketch lofting’ feature might be just what I needed (assuming I could get past all the 123D Design frustrations and actually make the *%$@!#%$#* thing work!  The way the ‘lofting’ feature works is to take a ‘base’ 2D sketch in an  X-Y plane (in my case, an ellipse representing the top of the flap grip), and morph it into a ‘top’ 2D sketch (an outline representing the bottom of the caddy section) over the Z-axis distance between the two sketches.  By doing this I hoped to  get a much smoother transition from one surface to the other.  After playing around with this in 123D design for a while, I actually got this feature to work (an unusual occurrence with this program!). The following two images show the basics of the feature – here I have ‘lofted’ an ellipse in the Z=0 plane to a rectangle in the Z=50 plane, rotated about the Y-axis by 20 degrees.

For my purposes, I imported the flap grip and caddy pieces into 123D Design, and used them as patterns for the required 2D sketches.  I still needed to add the connector-guard section onto the front of the caddy section sketch, but this was fairly straightforward using the 123D Design ‘2D polyline’ feature.  Once I had the two surfaces mapped out and placed at the desired heights/angles, I could use the ‘loft’ feature to create a transitional 3D structure.  The first run at this is shown in the following screenshot.

This actually worked pretty well, but I realized that the connector-guard portion of the transition structure wasn’t going to be nearly deep enough (in the Z-axis direction) to actually do any connector guarding – bummer!  So I tried again using a 3-surface model, with a middle surface using the non-rotated caddy outline plus the outline of the connector guard.  With this setup, I got a much more radical initial transformation from the ellipse to the caddy outline (not so good), but much more available bulk in the Z-axis direction for the connector guard (very good).  On balance, the need for the additional connector guard material outweighed the aesthetics of the smoother transition, so I wound up with a transition section that looked a bit like some prehistoric alligator (minus the legs)  but…

The next step was to import the transition section created in 123D Design back into TinkerCad for additional work and tuneup prior to 3D printing.  It was right in here somewhere that TinkerCad (a ‘cloud-based’ application) mysteriously went away for about 24 hours, causing a major hiccup in my project and correspondingly major damage to my Wa (I had upwards of 80 design revisions in the TinkerCad cloud, and if they all went away…).  Fortunately for me and my Wa, TinkerCad came back several hours later, and I was back in business.  The following screenshots show the ‘final’ (as if this project will ever end!) version of the remote caddy section.  The holes in the remote caddy bed were intended to accommodate the remote’s mounting screws (so they could be retained in the remote and not lost), but unfortunately the measurements were a bit off :-(.  The side view shows the tie-wrap attachment ring on the front undersurface, and the mounting plug on the bottom.  Both the mounting plug and the front portion of the caddy underside were shaved off a bit to create a larger attachment area for 3D printing

So now it was time to fire up my 3D printer and start making parts.  Unfortunately, in the interim between this version and the last one I had decided to do the long-awaited upgrade to a heated print bed so I could eventually transition to stronger and more resilient ABS plastic instead of only PLA.  The downside to a heated print bed is the much higher power requirements, and a host of other secondary problems associated with heated-bed printing.  As it turned out, I couldn’t get a consistent print of the caddy piece with ABS or PLA using the heated bed, so I eventually had to downgrade my hardware setup and revert back to the original unheated bed, at least for these prints.  The following screenshot shows the problem with PLA on the heated bed.  The heat from the bed causes the PLA filament to stay soft too long and curl upward, even with forced air cooling.

Anyway, after getting the hardware restored to its original unheated configuration, I started making trial prints of the remote caddy.  The first several tries were failures for one reason or another.  The first few trials failed because I had inadvertently disabled the ‘generate support structures’ option, and the next few failed because the support structures, when enabled, were too tightly bound to the main structure to remove when the print was finished!  It took some tweaking and print re-orientation to get to a configuration that produced useful results, although I’m still not happy with the ‘final’ (see above) product.   After the caddy piece, the flap grip piece was “a piece of cake”, as its geometry was much less complicated, although physically much bigger.  The final caddy piece took about 1.5 hours to print, while the flap grip piece went for more than 4 hours!

 

After getting both parts printed, there was still quite a bit of work to be done, especially on the caddy piece.  As it turned out, the cylindrical post on the bottom of the caddy piece was much too long for the matching hole in the top of the flap grip (measurement goof on my part), so the post had to be cut down by hand.  Then I had to drill and tap the post for a 4-40 screw so John can tighten the caddy down on the flap grip when he gets  the rotation angle correct for his hand placement.  Then a 4-40 clearance hole had to be put into the top of the flap grip piece, and the 4-40 screw threaded up into  the rectangular slot, through the clearance hole, and then screwed into the caddy mounting post (let’s hear it for double-sided tape and long, skinny screwdrivers!).  Also, the bottom surface of the caddy was a  lot rougher than I liked (printer misconfiguration?) so I had to spend some time with a file and a sanding block to get this surface even remotely acceptable.  I think I’ll try some more experiments to see if I can do a better job at this, so I’ll be ready when John comes back with the next batch of ‘issues’! ;-).

Stay tuned!

Frank