I bought a Mellow Fly-SB2040 board and the FLY-UTOC-3 to go with it (I think I should have bought the UTOC-1 though). But why buy another set of boards for the Voron, when it already comes with the Pi and the Spider mainboard? These two boards will allow me to reduce the number of wires going from the Spider mainboard to the toolhead by using them as a CANBUS bridge to communicate and control the components on the toolhead. This means the UTOC-3 (or UTOC-1) board will be located in the electronics area under the printer, and will connect to the Pi via USB. There will be only 4 wires (24v, Ground, and 2 CANBUS signal wires) between the UTOC and the SB2040 board located on the Stealthburner. This cuts out all the stepper, fan, LED and hot end wires, and will make cable routing simpler and more resilient. The SB2040 board will break out the individual components like fans, thermistors, hot end and LED's right on the Stealthburner tool head.
I have read however that there are some issues with the SB2040, including some unprotected (non level shifted) inputs for the Pi controller on the Mellow board, which could result in a magic smoke release if 5V is sent to a Pi input on some pins. What that means is that I cannot use my tappety tap tap without putting it's light sensor on the so called "HV Endstop" (aka GPIO 25), which is also helpfully called out in the listing for the SB2040 on AliExpress now. Not a big deal, except that the Voron Stealthburner is very tight in the area where the "HV Endstop" connecter is located when the SB2040 is installed, meaning there could be issues with wiring. There is also a potential issue with either the Pi rp2040 chip, or the TMC2209 stepper driver chip overheating in some conditions, even with heatsinks. Fortunately for me, and anyone else using the Fly-SB2040, Printables user Paul Trautner has posted a cool solution. I wanted to add a fan guard to his design, and while I was at it, opened up the fan bump out just a bit to allow fewer supports and possibly some more room for wiring. The fan grill also acts as a fan clip. I'm printing the parts now, and will use them when I assemble my Stealthburner, which uses the Tap Probe Mod, a Mellow SB2040 board, and maybe a Rapido hot end. If things work out, the modified files will be posted to Printables as a remix of Paul Trautner's design.
Update 5/4/2023: I decided to go with a BTT EBB SB2209, but I am gonna modify this design to fit that board as well (will fit both the SB2209 and SB2040), and am printing a model to test it now.
Update 5/5/2023: The new remix is completed, though I cannot test it with a 3007 fan. I tried the 3010 fan and it is very tight, and may not give enough clearance for wires. The print is not the best but it fits everything very well and I think it is ready to post when I get the time to write it up. The changes made to fit the BTT SB2209 board were very minor, but necessary since the original design was made for the Mellow SB2040 board, which is a bit smaller. The fan shroud is also remixed but with very minor changes to allow for a fan guard and printing without any supports (if your printer is able to handle some overhangs on the hole for the fan). These parts were printed in Monoprice ABS+, which aside from requiring a very low flow (81.5%), it printed very easily and there were no lifting issues when using the "Tab Anti Warping" plugin for Cura.
I also switched out the gears for some helical gears which just arrived. The method I use to align it, is to install the gear loosely on the main shaft, but with the set screw tightened just enough that it can move a bit but cannot rotate. I added a very small amount of blue threadlocker as well. Then, with a filament installed through the stepper, I removed the tensioning arm and used a long allen wrench to set the grub screw in the correct position. Having the filament going through sort'a helps to see where the gear should be. Once it was tight, I just re-installed the red tensioning arm and set the max travel set screw. I did manage to over stress the latch though, it has a stress mark on it and I will probably need to swap it out soon.
Update 6/3/2023: I uploaded a fanless remix of Paul Trautner's original design to Printables. It only has some minor changes where I removed some holes to make it easier to print.