Onward and Upward
A quick update to let you know things are still moving, slowly but surely. We’ve yet to receive all of the beta units back, but we’ve refurbed the hardware we have and are waiting for firmware updates before machines can be sent out again.
Solved: Wet Pucks
One of the bigger hardware issues we encountered during beta was that pucks were wet after extraction. We knew we’d get some wetness using the VST baskets, which are known for being very dose-sensitive, but beta testers were seeing a large amount of water remaining in the pucks, regardless of portafilter basket used.
Though the jury’s out on whether wet pucks are actually a problem, it does make for messy cleanup. We determined that excessive wetness is due to the group head screen sitting too high over the portafilter basket, leaving space for water to collect once the brew cycle ends.
To resolve this, we’ve modified the thermoblock/group head assembly to lower the screen about 3mm into the puck, and changed the check valve design.
Solved: Group Head Dripping
Another issue was that the group head dripped after a shot, and dripped water when the steam mode was active. We’ve reworked the plumbing to include a shuttle valve that keeps dripping at bay (pictured below). The shuttle valve opens the block’s water path to the drain valve without opening it to the group head - sort of like two opposing check valves.
Drip = conquered!
In Other News, UL
We’re also still waiting on our UL designation. All of the tests are complete, and we’re assured we’ll have our number by the end of this week. Of course, we thought all of the tests had already been completed. What happened?
After our last update we got a call from the certification agency saying that one of the tests that had been performed needed to be redone. The test in question consists of running a continuous brew cycle for 5 minutes without water in the machine. If the machine overheats (as UL had expected), the machine gets a “pass.” If it doesn’t overheat after 5 minutes, the test is performed 4 more times, and if it still doesn’t cut off, the machine is given a “pass.”
Our machine didn’t overheat but the test wasn’t repeated, and the oversight wasn’t noticed until two weeks ago when we were notified. It then took a week to determine exactly what was needed to complete the test, and get it on the schedule for completion.
As far as we know now, all UL tests have been complete (for real this time), and we should expect our number designation by the end of this week. Fingers crossed!
Something else we’ve discovered in testing (with the gracious help of a few of our trusty beta testers) is that the pressure sensors actually have a slightly parabolic curve response, not a linear one as indicated in their data sheet (which we foolishly believed!).
We had been using 2-point calibration to calibrate the pressure sensors. This means that, for each machine, we use an automated rig to test pressure readings at known values of 0 and 10 Bar, then do the calibration math to write unique code for each machine, based on its sensor’s performance.
We’re now using a 3-point calibration, meaning that we’re using three data points to describe the sensor performance. This means that the testing will take a bit longer (about 3 minutes per machine), but performance will be more accurate.
We’ve also finessed the PID algorithms for better performance across brew, idle, and steam modes.
The gating items now are the revisions to firmware and completion of the calibration automation suite.