[Coco] Raspberry PI preference

[gene heskett]

On 1/12/23 01:58, Rich Mellor via Coco wrote:
> At the moment, the choice is more about what is available.
> 
> I have experience of the Odroid C1, Banana Pi and Raspberry Pi (all 
> various models) and it depends what you want to use them for.  The 
> USB-OTG port on the Odroid C1 and Banana Pi are better at being used to 
> emulate a USB printer for example in my experience.  The Raspberry Pi 4 
> (and the Pi Zero) were the only models of the RPi which allow you to use 
> the USB-OTG port as a host (previously it was just used for power!).  I 
> am not sure if the Banana Pi M5 is good for that now as the 
> specifications do not refer to an OTG port.
> 
Yes, that is how the bpi5's are powered. I'm using them for running 
octoprint and klipper to manage a small farm of 3d printers. Neither 
octoprint nor klipper can drive 2 printers so one per printer.

I started out with an rpi3b running the now 80+ yo Sheldon lathe I have 
converted to cnc, I wanted to see if it could be done, but the roi3b was 
dragging its tongue on the floor a bit, so when the 4 came out I got one 
and its as happy as a clam. I wanted to see if I could do it with 
linuxcnc, and it is happily doing tricks with only two motors replacing 
the hand cranks and all those hard to find gears. The compound was 
damaged beyond repair by a fallover that also bent the spindle as this 
sheldon was the service truck model and had fallen over going around a 
corner too fast, so the compound is a block of sprue cut off a large car 
wheel hub to replace the missing compounds height, LinuxCNC is a more 
accurate compound than a mechanical one. I reground the mt5 in the 
spindle and refaced the chucks backing plates so everything runs true 
again. Switchable in gcode from inch to metric, cuts internal/external 
threads of any pitch w/o any gear changes, no gears to change. Tricks it 
could not do when it left Chicago in the 1940's.

I had to re-calibrate it a bit 2 years ago as I replaced those 2 motors, 
2 phase steppers that if pushed too fast can lose their home position, 
with 3 phase stepper/servo's that signal if they cannot get to where 
they are told to go, and will shut down linuxcnc in a millisecond in 
that event. They measure the error and adjust the coil current, so they 
run cooler than the 2 phasers ever did. Electrically much more efficient.

That works when tested, has never happened when at work. It now moves 
like Casper the ghost, and with a VFD driving the spindle I don't use 
the 4 speed belt changer at all, I can slow the vfd to 5 hertz or run it 
up to 200 hertz for speed changes. The vfd can go to 400hz, but that old 
1hp century motor's inductance would need a 480 volt supply, and all I 
have is 250 single phase, so motor coil current, 3.9 amps a coil, is 
below 1 amp at 200 hz. The vfd is set to not boost the currents at 
underspeeds above the motors FLA, so while the motor does heat some, its 
in no danger of burning it up. Best of both worlds.

Losing home is a favorite way to fail on a 3d printer, so the ones I'm 
rebuilding are getting these new "can't lose home" motors too.  The 
biggest problem is that what I want to build, needs to be made with PETG 
plastic, and PETG needs around 50C more heat, which destroys a consumer 
grade hot end in a week. Or less. When I get done, a 60mm speed rated 
printer will do at least 250mm a second.  Maybe more, depends on how 
fast the hot end can supply liquifyed plastic.

Take care and stay well all.

Cheers, Gene Heskett.
-- 
"There are four boxes to be used in defense of liberty:
  soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
  - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>