PVT Update, PVT Changes, Bounty Update, Expansion Specs
The production of various parts for PVT (meaning Product Validation Test - or making a small number of printers first to test all the production processes and the final product) is under way, but still in progress.
We are currently dealing with some corrections to the injection molded parts and testing out some alternative suppliers for the 3D printed parts. We are also looking at whether some of those 3D printed parts can be quickly switched to injection molding - because overall the injection molding has been easier to lock down both in quality and timeline. Injection molding a part has a huge upfront tooling cost, but that is something we can afford for at least a few more parts especially if it means we have those parts when we need them.
We are also waiting on several final parts from suppliers - this includes the Laser module itself for the laser upgrade and the extruder mechanisms - these are both off the shelf components, so we can go to a different vendor if we need to.
PVT is taking longer then we hoped, but the purpose of PVT is to get all the ducks in a row - so we expected there could be delays here.
PVT is about testing the whole product including the production of the product in as near as possible to final form and process. That means that a successful PVT will also have failures and improvements.
Here are some changes that have emerged from PVT so far:
PCB Heating - While we are still working through production of some of the electronics, main board prototypes were tested and showed too much heating especially when subjected to ambient temperatures like they would see inside the full enclosure. We've made some changes to reduce the heat generated by the voltage regulators - switching from linear to switching regulators for the 5V supplies - and we've added a temperature sensor to the PCB itself which can be used to control the enclosure fan to ensure the enclosure doesn't exceed safe limits for the electronics, motors, and plastic.
Plastics Durability - The acrylic structure of the BuildOne and ABS parts remain the main plan - and the temp sensor mentioned above can be used to ensure that full enclosure models stay warm enough to keep the prints looking good without causing any issues with warping the plastic parts or overheating the electronics. However, we are, at the recommendation of our plastic supplier testing Polypropylene in place of both the ABS parts and the Acrylic sheet - if this proves to be a better choice we will consider it as long as it doesn't contribute to any additional delay. Polypropylene can be injection molded into the same molds and comes in sheet form that can be cut just like Acrylic - but it has a much higher temperature resistance for about the same price.
Current Setting - As part of the testing process the electronics factory was being asked to set the current settings for the stepper motor drivers - this is done by a little screw on each stepper driver board. That wasn't very practical and was time consuming and prone to error - and getting one set wrong would be very frustrating for a beginner - because it would not be obvious that was the issue and the effects could be bad print quality. We are solving this by taking a page from the MiniRAMBO 3D printer board design and allowing the main controller to control the current in the stepper drivers - so the firmware will set the current settings, no need for workers with little screw drivers to get it just right. Additionally at the same time, we've moved the micro-stepping settings into firmware control as well. You will still be able to substitute in your own standard driver boards - but our driver boards it ships with will use three extra pins for the current control feature.
Two of the bounties have now been completed by one of our backers - Stephen (@the-real-orca) - this means that when the BuildOne ships the WiFi module in it will be updated to the latest firmware whenever you update the main firmware, no extra work required - and both the WiFi and USB modes for printing can be used without having to change firmwares or even flip a switch. Thanks Stephen!
Want to help us with some code? Check out the bounties here: https://github.com/digistump/BuildOne/issues
While still subject to changes, they are very unlikely at this point and we know that a few people have been waiting to know what the expansion header on the main board will look like - here it is:
A few notes for those interested in building expansions - this will be a right angle 40 pin (2x20) male connector on the side of the main board. Most pins are self explanatory and labeled as either the Port and Pin number from the MEGA2560 MCU or the Voltage they provide - here are some notes about the rest just to get folks started:
- LASERGND - Connected to the Laser's mosfet - can be used for a second hotend or similar load (~3.5A max)
- LED2 - is connected to the output of the WS2812B LED on board, for chaining more LEDS on.
- BED - the logic level signal for the bed heater.
- RESET - The RESET line for the MEGA2560 - we use this in the factory to program the boards.
- HOTEND2 - Logic level pin the Marlin sees as a second hotend heater.
- PB1-3 - There are also the SPI pins.
- X-MIN, Y-MIN, Z-MAX - The BuildOne uses X-MAX, Y-MAX, and Z-MIN so these pins are brought out in case they are needed for customizations.
- THERM3 - Marlin sees this as a 4th Thermistor input - no electronics for it on the main board.
- SDA, SCL - I2C bus to the MEGA2560, already pulled up to 5V
- GPIOs - these are connected to the ESP8266 module on board and correspond to its pins.
- RES - This is the RESET line for the ESP8266 module.
That's all for tonight.
We will continue to keep everyone updated as we work through the PVT. Thank you all for your support.