Another busy couple of weeks here, largely starting the whole UL process. Our initial "digital review" (online) flagged an issue with our interlock system and what would happen if it failed (it could fail in reverse in a way that caused the grinder to seize up, which fails as the grinder must always be able to spin in reverse). Specifically, if the grinder was heavily loaded in reverse, the interlock swing mount would bind on one of the interlock gears.
The original interlock. Notice how both are full plates - but there is significant evidence of binding around the middle gear hole from when it would get caught on the mount.
We quickly hacked together a new mount design, and tested it briefly over the weekend at Maker Faire Ottawa, where it failed almost immediately - it turns out in our haste we'd forgotten to ensure the rigidity of the new mount, and the gear that does the "locking" fell out of it's housing!
Our original solution to solve the binding was to just remove the part that kept catching...but then the mounts no longer had enough strength, and failed within a weekend!
We re-designed the mount again, properly this time, to address the failure points. The "hasty" design used only two small shafts to hold the two mounting plates together, while the "proper" design uses a third offset plate. When the two shafts bend, it allows misalignment between the two mounting plates, and gears can bind / pop out - but with the offset plate, there is no more room for play. We've tested it with some 100% infill objects to verify the design, and then submitted it to UL for our in person review...and it passed! While it's important to note that this is not the final stamp of approval (which can only go on an "as manufactured" product), it's great to know that we shouldn't have any further design changes with the grinder.
The final chain drive, in all it's glory!
The interlock "engaged" - note the solenoid position, gears all in contact. Above the gears is the offset plate that adds all of the strength.
The interlock "dis-engaged" - again, note solenoid position, and gears obviously no longer in contact. Offset spacer plate now very evident!
Things have not all gone totally smoothly with UL so far, however - two of our components, our solenoid and snap discs, did not pass testing and will need to be re-sourced. Specifically, the solenoids could reach dangerously high temperatures (>140 C) if they were engaged for an extended period - something we hadn't considered in all of our drill powered testing. The snap discs, while labelled as "certified for thermal control", did not actually have the correct classifications for our product type. It's also been decided that the auger is too dangerous to be touchable, so we'll have to add a grate of some form over the main hopper.
After 10 minutes our solenoid had gotten to 91 C...
...and a little later, it reached a max temp of almost 150 C!
And, finally, they're concerned about our nozzle being accessible. The safety standards for 3D printing are incredibly new and so don't specify many details on what the max safe nozzle temperature is, what warnings are required, etc. They're worried that because our nozzle can reach temperatures above most printers, is prominently displayed and accessible, and "is more involved with the user experience than in 3D printing", that we might be subject to more thorough safety standards (we'd have to shroud the nozzle fully, instead of only partially). We've appealed this decision and are waiting to hear back from them, as we believe quite strongly that the nozzle of ProtoCycler is no more dangerous than the nozzle of a good 3D printer, and should not be subject to "extra" safety constraints that aren't currently part of the standard.
Of course, all of this affects our timeline. To move things along as quickly as possible, we'll be working with UL to re-source the solenoid and the snap discs, and we'll be moving ahead with the rest of the design as these components are relatively small and have little impact on other parts of the product. However, we do have to source the new components and add the grate to the main hopper before we can go ahead with the testing and begin production, and at this point it's going to be very hard to do all of that by December 7th. We're hoping to have the new components sourced and couriered by the end of next week at the latest, at which point we can re-begin the UL testing. With some luck, we won't hit any other delays, and can finish testing by the 18th, a delay of roughly 2 weeks. Being forced to re design the nozzle shroud would likely add another week to that estimate, as it's in house and a relatively easy design change. This brings the new timeline to Start / End of Jan for Early / Campaign units, respectively, as opposed to the middle of December / Middle of Jan previously hoped for. As always, we apologize for the ongoing delays - we're hoping UL will cut us some slack and not force a nozzle shroud re-design as well, but at this point we're pretty much at their mercy until we get the green light to begin production.
That's pretty much it for this update - a huge "Thank you!" as always to our supporters and backers, and we'll be back at the start of December with some more news :)
-The ReDeTec team