John tells me that the latest and greatest flap handle ClearNav remote caddy version is alive and doing well in his glider. The flap grip section fits over the metal flap control handle nicely, and the redesigned remote caddy section with its beefed-up quarter-turn fastener seems to be holding up OK so far. The ‘caddy garage’ piece also seems to be working to hold the remote caddy in an out of the way place when not in use, allowing John to enter/exit the glider without worrying about damaging the caddy or breaking a cable. Only time will tell, but for now it looks like I might be DONE!!!
In our last episode of the Flap Handle Follies, I was sure I had all the bases covered.
- Larger set-screws in grip – check!
- 1/4 turn locking latch connecting flap grip to remote caddy assembly – check!
- Rotatable remote caddy with spring-plunger detent every 10 degrees – check!
Unfortunately, one essential item for success with this version was missing from my checklist, and its absence spelled doom:
- Non-gorilla pilot – check!
A few days after sending the latest version to John, I got an email with some photos and suggestions, and a few days after that I got my folded/stapled/mutilated flap handle assembly back – boy was I embarrassed! What I had thought was a *brilliant* solution to a problem turned out to be not-so-brilliant when exposed to a pilot who expected things to go together in a particular way. I had designed the 1/4 turn locking mechanism so the locking direction was opposite the normal “righty-tighty” direction because by doing so, the pilot’s normal thumb position on the remote caddy tended to hold the caddy locked onto the flap grip, as opposed to tending to unlock it. Unfortunately, I had forgotten to mention this feat of brilliance to my friend, who expected everything to conform to normal lock/unlock conventions – oops!
Ah, well – it wasn’t a total failure, because we learned some things in the process:
- The 3-piece assembly (flap grip, grip-to-caddy converter, caddy) was too long; John couldn’t reach the CN remote’s buttons with his thumb while his hand was comfortably placed on the flap grip.
- The 1/4-turn locking mechanism was way too fragile (jokes about gorilla pilots notwithstanding)
- The dimensions of the rectangular slot in the grip piece seemed to be just about right.
So, back to the drawing board yet again. hunting through the forest of design possibilities for just the right combination.
- Minimize or eliminate the grip-to-caddy converter to reduce overall length
- Enlarge/strengthen the 1/4-turn locking mechanism (but keep the opposite direction actuation)
Minimizing or eliminating the converter piece required that I drop the caddy rotation feature. This was kind of overkill anyway, as John had marked the correct (for him) rotation much earlier in the game; I was trying to generalize his preference into something other pilots could use as well. I just needed to think about the rotation feature as something ‘baked in’ to the design, rather than something pilot-adjustable.
Enlarging/Strengthening the 1/4-turn locking mechanism shouldn’t be too much trouble, as the latch parts were available in their own separate design files, so a simple scaling operation should do the trick there. The only limitation on size being that the latching mechanism has to fit into the top of the flap grip and the bottom of the converter piece.
Based on my now extensive experience with printing parts on my PrintrBot, I also added the requirement that each part be printable in a way that preserves the quality of the mating surfaces. I have come to understand that there is a right way and a wrong way to print parts; the right way result in very clean and smooth mating surfaces, while the wrong way results in ugly, bumpy surfaces that no amount of sanding can make right. Fortunately, the combination of careful design and clever positioning of the part on the print plate seems (so far) to be effective. The trick here is to make sure that parts are positioned so the mating surfaces are either perfectly parallel or perfectly perpendicular to the print plate; in either orientation the result is nice, clean surfaces. In the case of the converter part, the mating surfaces aren’t parallel to each other, so it was placed vertically on the print plate so the larger mating surface (remote caddy interface) was perpendicular to the print plate, and the smaller (flap grip) surface was tilted 20 degrees from the vertical. Near-vertical surfaces also print very well, so this resulted in both mating surfaces printing nicely, but the cost was a much longer printing time (2 -3 hours vs about 15 minutes!).
In the previous version, the thickness of the grip-to-caddy converter part was driven by the need for the caddy to rotate on the converter-to-caddy mating surface, which required that the converter have a hole deep enough to accommodate a reasonably sized axle post on the caddy part. Eliminating the rotation feature allowed me to eliminate much of this thickness. I still had the following requirements:
- The caddy has to be rotated about 25 degrees CCW with respect to the fore-and-aft centerline of the flap grip, when looking at the top of the caddy. This value was measured from John’s marks on an earlier version.
- The caddy has to be tilted vertically about 20 degrees with respect to the flap grip mating surface (again taken from John’s feedback).
To implement the ‘minimized’ grip-to-caddy converter piece, I went back to Autodesk 123d Design’s ‘sketch loft’ feature. This is a very cool capability, and makes it (just) worthwhile to deal with 123d Designs many other ‘non-linear frustrations’ (see 2014/10/tinkercad-vs-123d-design-vs-meshmixer-pick-poison/). I started with a 2D ellipse that matches the flap grip cross-section, and then added a 2D sketch of the caddy. Then I tilted and rotated the caddy sketch as defined above, and then ‘lofted’ the ellipse sketch into the caddy sketch – voila!
Now that I had the grip-to-caddy converter design worked out, all I had to do was to insert the scaled up 1/4-turn latching mechanism into the top of the grip and the bottom of the converter, and print all the parts. Scaling and inserting the latch parts turned out to be pretty easy, as I already had all the latch geometry issues worked out from the time before, and all I had to do was use Tinkercad’s uniform scaling feature to ‘grow’ the latch about 150% or so. After scaling the parts, I latched and unlatched them in Tinkercad a couple of times to make sure that Part A did indeed fit into Part B, and then simply copy/pasted them into the grip and converter designs.
There was one complicating factor; due to printing concerns, I decided to print the converter and caddy parts separately, and then screw them together using 2ea 4-40 screws. I designed matching 2mm pilot holes in both the caddy and converter mating surfaces, and I added thickness to the bottom of the caddy so I could countersink sufficiently (about 3mm) to hide the screw heads below the bottom surface of the caddy. However, when I got everything done, I wound up just gluing the parts together with gap-filling superglue from my local hobby shop, and this seemed to do much better than screws.
In summary, I was able to quickly design and implement a new flap-grip version with ‘baked-in’ caddy twist and tilt, and was able to get the caddy about 12mm (about 1/2 inch) closer to the flap grip than in the old design.
As an added amenity for the pilot, I decided to design and implement a ‘caddy garage’ so John would have a place to store the caddy when it wasn’t in use. As part of the original testing program for the 1/4-turn latch, I had built some thin test pieces with the same cross-section as the flap grip – one with a plug, and one with a socket. I did the same thing for the larger latching mechanism, so all I had to do was to put some mounting holes in the socket test piece and throw it in the box with the completed flap grip/caddy assembly. John can mount the ‘garage’ in some convenient location in his cockpit, and simply latch the caddy assembly to the ‘garage’ after unlatching it from the flap grip.
OK, off to the Post Office tomorrow to mail the new stuff to John. I hope this new version will survive the ‘Gorilla Pilot’ test in better order than the last one did! 😉
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!)
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’! ;-).