I usually like to have my cake and eat it! Last week, I tried to do exactly that: test further Autodesk 123D, build a testbed for my joule telemetry application, and learn to print in 3D. I think I made it, and I am ready to share with you some of my learnings. Let’s start with the CAD software. My testbed is not very complex, but the honeycomb structure requires to handle hundreds of objects. Well, 123D doesn’t seem to be able to use the computer resources available to its advantage, and struggles a lot at each operation I did. To be true, it’s been a while I hadn’t had to wait on my computer. Since I ditched my 286! It took literally 10-30 s to apply a simple transformation. I had to reapply my leanings from the good old times: think ahead of every operation to carry out, and more importantly, be patient and don’t touch the mouse until the software finished to work. This is a killer when you want to use the trial-error approach in an interactive way. This is like batch processing vs. using a GUI!

Rapid as a snail

And it is too bad because, with 36 cores and 128 GB of RAM available in my workstation, this should really not be so painful/long. Or, maybe, Autodesk is reserving the optimized (multi-threaded?) code for the paying customers. Fair enough, we are not supposed to look into the mouth of a gift horse. Besides few epic crashes of 123D – but it was able in many cases to retrieve some history out of the local drive on re-start –, my biggest complaint is the lack of an object browser (a tree view of the 3D project, where you can select a sub-object and edit only that one). To be fair, it is possible that there is a secret key sequence to hit to display one. But I am afraid that such a browser simply doesn’t exist. Dommage! (Please make me wrong and tell me how to do that if you know ;-)). Nonetheless, I could design my testbed after spending way too much time.

On the 3D printing, I am now at a point where I think I understand what to do to get a good result (using PLA and PVA). The most important point in my case is to have a … dirty print bed! Up to now, when I cleaned the tempered glass thoroughly, removing all traces let my previous prints as well as any palm grease between each print, the initial layer delaminated, and the print was somehow crocked. If I print a build plate adhesion (and extra single-layer border to the object on ~1/2 cm), the damage in such a case is minimal. Keeping the glue residue of previous prints (yes, plural), makes it perfect! The second learning of the week was to curb my enthusiasm and grandiose plan.


When dirty is good

By this I mean that very quickly I learned that the size of the print is of major concern – even with a beast like the Ultimaker 3 Extended. So, either you build your model up (Z-axis) and you have to fight with the support structures, or you print the object in pieces and glue them together. For the rocket project – the main goal –, I will definitively have to build such a puzzle, but with some serious concerns regarding the rigidity of the assembled object and the pick of the best glues to use (based on the materials… super cool, more learning to come!). For my testbed, I still wanted a single piece object, so I had to shrink considerably my initial design. To a point, where some component placing will be challenging.

Last but not least, I started to populate the testbed with the 1.4Ah LiPo battery, the UBEC (Universal Battery Elimination Circuit), the power bus, the Joule computer, and the XBee. Some cable management – and maybe some new cables – is definitively required, but all should fit snuggle at the end of the day.

On my way to the launchpad

Once the components fixed and connected together, I should be able to carry the setup all over the place and test the battery autonomy and the telemetry software – still to be designed and implemented. These experiments also helped me to refine my initial design for the rocket’s electronic bays. I will have to build multiple parts and assemble them. I will need to carefully think about cable management. And will definitively have to use a dual-sided platform (indeed, the rocket has only a 4” diameter body). Overall, I lagging behind my initial plan, but learned so much in two fields I had no experience with up to now, that I am happy. Have a great WE.