Tag: M2

Using and tweaking a Makergear M2 3D printer

Portable AC Vent Plug

This plug for a portable air conditioner’s window vent may be un-buildable with my current state of 3D printer-fu. The top view shows the recess for a disk of insulating foam:

The side view shows the thread profile and the groove for the O-ring seal:

Portable AC Vent Plug - solid model - side — Portable AC Vent Plug – solid model – side

The bottom view shows the hemispheric finger grip recess:

Portable AC Vent Plug - solid model - bottom — Portable AC Vent Plug – solid model – bottom

Basically, that design requires extensive support material no matter how it’s laid out. I tried the obvious way without any support, but that huge flat surface popped off the glass:

AC Vent Plug - flat build — AC Vent Plug – flat build

The thread and groove overhangs in that orientation would require support and then extensive cleanout. Slic3r doesn’t do a good job of supporting internal layers, so the bottom of the recesses tend to flop into the hexagonal infill. I’m not sure building internal support all the way up the inside of the threads would be a Good Thing, though.

Rotating by 90 degrees and cutting it in half failed because the automagic support structure popped off the platform:

AC Vent Plug - split build — AC Vent Plug – split build

Admittedly, that was before I started using hairspray (on the platform!), but both orientations require far too much support. In fact, the rotated version might weigh half a kilo…

I’m also generating the thread elements incorrectly; the joints don’t meet smoothly at the junctions. I think tapering each element so the smaller end nests inside the larger end will work better. Perhaps using a scaled hexagonal element would be better / faster than the current extruded 2D shape?

I think the correct way to proceed will be a 3D print of the finger grip and flange section, oriented so the hemisphere points upward, with the threaded section made from a length of PVC pipe with lathe-turned threads and O-ring groove, butted against the flange around the grip section.

Problem: that’s an 8 mm pitch thread and my inch-size lathe doesn’t do metric:

Need: 8 mm = 0.315 in → 3.175 TPI
Closest: 3-1/4 TPI → 0.308 in = 7.82 mm
Worse: 3 TPI → 0.333 in = 8.47 mm

The plug needs about three turns, which means the 3-1/4 TPI = 7.82 mm pitch thread would be off by 0.54 mm, roughly a third of the thread form’s crest. That might actually work, as the “thread” on the inside of the pipe this thing fits into is actually a thin ridge, rather than an actual thread shape, and the plug is supposed to jam against the flange anyway.

Maybe a four-axis setup in the Sherline, with the rotary table holding the PVC pipe (or whatever) aligned with the X axis? It would just barely fit under the spindle with the end mill in a collet.

The pipe rack doesn’t hold any suitable plastic pipe.

The OpenSCAD source code:

// Portable AC Vent Plug
// Ed Nisley KE4ZNU - June 2013

Layout = "Show";			// Show Build Grip Helix HelixUnit Ring Plug Stiffener
//-------
//- Extrusion parameters must match reality!
//  Print with +0 shells and 3 solid layers

ThreadThick = 0.25;
ThreadWidth = 0.40;

HoleWindage = 0.3;

Protrusion = 0.1;			// make holes end cleanly

function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

//-------
// Plug Dimensions

PlugLength = 53.0;
PlugOD = 128.0;

FlangeThick = 5.0;
FlangeWidth = 4.0;
FlangeOD = 2*FlangeWidth + PlugOD;

HelixPitch = 8.0;
HelixOffset = 29.0 - HelixPitch/2;		// add half turn to ensure snug fit against flange
HelixLength = PlugLength - HelixOffset;
HelixDepth = 3.0;
HelixBase = 3.5;
HelixTip = 1.8;

ORingDia = 3.4;
ORingDepth = 0.75 * ORingDia;
ORingOffset = ORingDia/2;

GripOD = 90.0;
GripDepth = 20.0;
GripBar = 15.0;

AlignDia = 3.0;
AlignDepth = 5.0;

FoamOD = PlugOD - 4*HelixDepth;
FoamDepth = PlugLength - GripDepth;

NumSides = 12*4;
$fn = NumSides;

echo("Flange OD: ",FlangeOD);
echo("Overall length:",(FlangeThick + PlugLength));

module PolyCyl(Dia,Height,ForceSides=0) {			// based on nophead's polyholes

  Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

  FixDia = Dia / cos(180/Sides);

  cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//-------
// Recessed finger grip
// Includes Protrusion below Z=0 for clean removal from plug

module GripShape(Length,Width,Depth) {

Radius = (pow(Depth,2) + pow(Length,2)/4) / (2*Depth);

	difference(convexity=2) {
		intersection() {
			translate([0,0,(-Radius + Depth)])
				sphere(r=Radius);
			translate([0,0,(Depth/2 - Protrusion)])
				cube([2*Radius,2*Radius,(Depth + Protrusion)],center=true);
		}
		translate([0,0,Depth/2])
			cube([2*Radius,Width,(Depth + Protrusion)],center=true);
	}
}

//-------
// One section of the screw thread helix

module HelixUnit() {

UnitAdjust = 1.25;

	linear_extrude(height=UnitAdjust*PI*PlugOD/NumSides,center=true)
		polygon(points=[
				[0,0],
				[-HelixDepth,(HelixBase - HelixTip)/2],
				[-HelixDepth,HelixBase - (HelixBase - HelixTip)/2],
				[0,HelixBase],
				[Protrusion,HelixBase],
				[Protrusion,0],
				[0,0]
		]);
}

//-------
// Helix Element Shape

module HelixShape() {

    Turns = HelixLength/HelixPitch;
    Slices = Turns*NumSides;
    RotIncr = 1/NumSides;
    PitchRad = PlugOD/2;
    ZIncr = HelixLength/Slices;
    helixangle = atan(HelixPitch/(3.14159265358979*PlugOD));

    for (i = [0:Slices-1]) {
		translate([PitchRad*cos(360*i/NumSides),PitchRad*sin(360*i/NumSides),i*ZIncr])
			rotate([90+helixangle,0,360*i/NumSides])
				HelixUnit();
	}

}

//-------
// O Ring Shape

module ORingShape(MajorDia,MinorDia,Recess) {
	rotate_extrude()
		translate([MajorDia/2,0,0])
			polygon(points=[[0,0],
							[-Recess,0.25*MinorDia],
							[-Recess,0.75*MinorDia],
							[0,MinorDia],
							[Protrusion,MinorDia],
							[Protrusion,0],
							[0,0]]);
}

//-------
// Overall plug shape

module PlugShape() {

	difference(convexity=5) {
		union() {
			cylinder(r=FlangeOD/2,h=FlangeThick);
			cylinder(r=PlugOD/2,h=(PlugLength + FlangeThick));
		}
		translate([0,0,(PlugLength + FlangeThick - FoamDepth)])
			cylinder(r=FoamOD/2,h=(FoamDepth + Protrusion));
		translate([0,0,(ORingOffset + FlangeThick - ORingDia/2)])
			ORingShape(PlugOD,ORingDia,ORingDepth);
		GripShape(GripOD,GripBar,GripDepth);
/*		for (x=[-1,1])
			translate([(x*PlugOD/4),AlignDepth,(FlangeThick + PlugLength/2)])
				rotate([90,0,0])
					PolyCyl(AlignDia,2*AlignDepth,6);
*/
	}
}

//-------
// Plug assembly

module PlugAssembly() {

	difference(convexity=5) {
		render(convexity=5) PlugShape();
		translate([0,0,(FlangeThick + HelixOffset)])
			HelixShape();
	}
}

//-------
// Build it!

ShowPegGrid();

if (Layout == "Plug") {
	PlugShape();
}

if (Layout == "Show") {
	PlugAssembly();
}

if (Layout == "Build") {
	difference() {
		intersection(convexity=10) {
			translate([0,0,FlangeOD/2])
				cube([2*FlangeOD,3*PlugLength,FlangeOD],center=true);
			union() {
				translate([0,10,0])
					rotate([90,0,180])
						PlugAssembly();
				translate([0,-10,0])
					rotate([-90,0,180])
						PlugAssembly();
			}
		}
	}
}

if (Layout == "Grip")
	GripShape(GripOD,GripBar,GripDepth);

if (Layout == "Ring")
	ORingShape(PlugOD,ORingDia,ORingDepth);

if (Layout == "HelixUnit")
	HelixUnit();

if (Layout == "Helix")
	HelixShape();

2013-06-12

TC4Server: Eagle HAL Device

Dan Newman’s TC4Server turns the TC4 thermocouple board into a USB HID input device that’s compatible with HAL’s hal_input module:

For simplicity (i.e., to avoid writing a special driver), TC4Server misrepresents itself as a nine-axis joystick-like device suited for RC airplane control:

halrun
halcmd: loadusr -W hal_input +A Leonardo
halcmd: show
... snippage ...
Component Pins:
Owner   Type  Dir         Value  Name
     5  s32   OUT          2941  input.0.abs-rudder-counts
     5  s32   IN           4095  input.0.abs-rudder-flat
     5  s32   IN            255  input.0.abs-rudder-fuzz
     5  bit   OUT          TRUE  input.0.abs-rudder-is-neg
     5  bit   OUT         FALSE  input.0.abs-rudder-is-pos
     5  float IN        32767.5  input.0.abs-rudder-offset
     5  float OUT    -0.9102464  input.0.abs-rudder-position
     5  float IN        32767.5  input.0.abs-rudder-scale
     5  s32   OUT          2947  input.0.abs-rx-counts
     5  s32   IN           4095  input.0.abs-rx-flat
     5  s32   IN            255  input.0.abs-rx-fuzz
     5  bit   OUT          TRUE  input.0.abs-rx-is-neg
     5  bit   OUT         FALSE  input.0.abs-rx-is-pos
     5  float IN        32767.5  input.0.abs-rx-offset
     5  float OUT    -0.9100633  input.0.abs-rx-position
     5  float IN        32767.5  input.0.abs-rx-scale
     5  s32   OUT         65535  input.0.abs-ry-counts
     5  s32   IN           4095  input.0.abs-ry-flat
     5  s32   IN            255  input.0.abs-ry-fuzz
     5  bit   OUT         FALSE  input.0.abs-ry-is-neg
     5  bit   OUT          TRUE  input.0.abs-ry-is-pos
     5  float IN        32767.5  input.0.abs-ry-offset
     5  float OUT             1  input.0.abs-ry-position
     5  float IN        32767.5  input.0.abs-ry-scale
     5  s32   OUT         65535  input.0.abs-rz-counts
     5  s32   IN           4095  input.0.abs-rz-flat
     5  s32   IN            255  input.0.abs-rz-fuzz
     5  bit   OUT         FALSE  input.0.abs-rz-is-neg
     5  bit   OUT          TRUE  input.0.abs-rz-is-pos
     5  float IN        32767.5  input.0.abs-rz-offset
     5  float OUT             1  input.0.abs-rz-position
     5  float IN        32767.5  input.0.abs-rz-scale
     5  s32   OUT         65535  input.0.abs-throttle-counts
     5  s32   IN           4095  input.0.abs-throttle-flat
     5  s32   IN            255  input.0.abs-throttle-fuzz
     5  bit   OUT         FALSE  input.0.abs-throttle-is-neg
     5  bit   OUT          TRUE  input.0.abs-throttle-is-pos
     5  float IN        32767.5  input.0.abs-throttle-offset
     5  float OUT             1  input.0.abs-throttle-position
     5  float IN        32767.5  input.0.abs-throttle-scale
     5  s32   OUT          2957  input.0.abs-wheel-counts
     5  s32   IN           4095  input.0.abs-wheel-flat
     5  s32   IN            255  input.0.abs-wheel-fuzz
     5  bit   OUT          TRUE  input.0.abs-wheel-is-neg
     5  bit   OUT         FALSE  input.0.abs-wheel-is-pos
     5  float IN        32767.5  input.0.abs-wheel-offset
     5  float OUT    -0.9097581  input.0.abs-wheel-position
     5  float IN        32767.5  input.0.abs-wheel-scale
     5  s32   OUT          2942  input.0.abs-x-counts
     5  s32   IN           4095  input.0.abs-x-flat
     5  s32   IN            255  input.0.abs-x-fuzz
     5  bit   OUT          TRUE  input.0.abs-x-is-neg
     5  bit   OUT         FALSE  input.0.abs-x-is-pos
     5  float IN        32767.5  input.0.abs-x-offset
     5  float OUT    -0.9102159  input.0.abs-x-position
     5  float IN        32767.5  input.0.abs-x-scale
     5  s32   OUT          2942  input.0.abs-y-counts
     5  s32   IN           4095  input.0.abs-y-flat
     5  s32   IN            255  input.0.abs-y-fuzz
     5  bit   OUT          TRUE  input.0.abs-y-is-neg
     5  bit   OUT         FALSE  input.0.abs-y-is-pos
     5  float IN        32767.5  input.0.abs-y-offset
     5  float OUT    -0.9102159  input.0.abs-y-position
     5  float IN        32767.5  input.0.abs-y-scale
     5  s32   OUT          2940  input.0.abs-z-counts
     5  s32   IN           4095  input.0.abs-z-flat
     5  s32   IN            255  input.0.abs-z-fuzz
     5  bit   OUT          TRUE  input.0.abs-z-is-neg
     5  bit   OUT         FALSE  input.0.abs-z-is-pos
     5  float IN        32767.5  input.0.abs-z-offset
     5  float OUT     -0.910277  input.0.abs-z-position
     5  float IN        32767.5  input.0.abs-z-scale
     5  s32   OUT          2941  input.1.abs-rudder-counts
     5  s32   IN           4095  input.1.abs-rudder-flat
     5  s32   IN            255  input.1.abs-rudder-fuzz
     5  bit   OUT          TRUE  input.1.abs-rudder-is-neg
     5  bit   OUT         FALSE  input.1.abs-rudder-is-pos
     5  float IN        32767.5  input.1.abs-rudder-offset
     5  float OUT    -0.9102464  input.1.abs-rudder-position
     5  float IN        32767.5  input.1.abs-rudder-scale
     5  s32   OUT          2947  input.1.abs-rx-counts
     5  s32   IN           4095  input.1.abs-rx-flat
     5  s32   IN            255  input.1.abs-rx-fuzz
     5  bit   OUT          TRUE  input.1.abs-rx-is-neg
     5  bit   OUT         FALSE  input.1.abs-rx-is-pos
     5  float IN        32767.5  input.1.abs-rx-offset
     5  float OUT    -0.9100633  input.1.abs-rx-position
     5  float IN        32767.5  input.1.abs-rx-scale
     5  s32   OUT         65535  input.1.abs-ry-counts
     5  s32   IN           4095  input.1.abs-ry-flat
     5  s32   IN            255  input.1.abs-ry-fuzz
     5  bit   OUT         FALSE  input.1.abs-ry-is-neg
     5  bit   OUT          TRUE  input.1.abs-ry-is-pos
     5  float IN        32767.5  input.1.abs-ry-offset
     5  float OUT             1  input.1.abs-ry-position
     5  float IN        32767.5  input.1.abs-ry-scale
     5  s32   OUT         65535  input.1.abs-rz-counts
     5  s32   IN           4095  input.1.abs-rz-flat
     5  s32   IN            255  input.1.abs-rz-fuzz
     5  bit   OUT         FALSE  input.1.abs-rz-is-neg
     5  bit   OUT          TRUE  input.1.abs-rz-is-pos
     5  float IN        32767.5  input.1.abs-rz-offset
     5  float OUT             1  input.1.abs-rz-position
     5  float IN        32767.5  input.1.abs-rz-scale
     5  s32   OUT         65535  input.1.abs-throttle-counts
     5  s32   IN           4095  input.1.abs-throttle-flat
     5  s32   IN            255  input.1.abs-throttle-fuzz
     5  bit   OUT         FALSE  input.1.abs-throttle-is-neg
     5  bit   OUT          TRUE  input.1.abs-throttle-is-pos
     5  float IN        32767.5  input.1.abs-throttle-offset
     5  float OUT             1  input.1.abs-throttle-position
     5  float IN        32767.5  input.1.abs-throttle-scale
     5  s32   OUT          2957  input.1.abs-wheel-counts
     5  s32   IN           4095  input.1.abs-wheel-flat
     5  s32   IN            255  input.1.abs-wheel-fuzz
     5  bit   OUT          TRUE  input.1.abs-wheel-is-neg
     5  bit   OUT         FALSE  input.1.abs-wheel-is-pos
     5  float IN        32767.5  input.1.abs-wheel-offset
     5  float OUT    -0.9097581  input.1.abs-wheel-position
     5  float IN        32767.5  input.1.abs-wheel-scale
     5  s32   OUT          2942  input.1.abs-x-counts
     5  s32   IN           4095  input.1.abs-x-flat
     5  s32   IN            255  input.1.abs-x-fuzz
     5  bit   OUT          TRUE  input.1.abs-x-is-neg
     5  bit   OUT         FALSE  input.1.abs-x-is-pos
     5  float IN        32767.5  input.1.abs-x-offset
     5  float OUT    -0.9102159  input.1.abs-x-position
     5  float IN        32767.5  input.1.abs-x-scale
     5  s32   OUT          2942  input.1.abs-y-counts
     5  s32   IN           4095  input.1.abs-y-flat
     5  s32   IN            255  input.1.abs-y-fuzz
     5  bit   OUT          TRUE  input.1.abs-y-is-neg
     5  bit   OUT         FALSE  input.1.abs-y-is-pos
     5  float IN        32767.5  input.1.abs-y-offset
     5  float OUT    -0.9102159  input.1.abs-y-position
     5  float IN        32767.5  input.1.abs-y-scale
     5  s32   OUT          2940  input.1.abs-z-counts
     5  s32   IN           4095  input.1.abs-z-flat
     5  s32   IN            255  input.1.abs-z-fuzz
     5  bit   OUT          TRUE  input.1.abs-z-is-neg
     5  bit   OUT         FALSE  input.1.abs-z-is-pos
     5  float IN        32767.5  input.1.abs-z-offset
     5  float OUT     -0.910277  input.1.abs-z-position
     5  float IN        32767.5  input.1.abs-z-scale

... snippage ...
Parameters:
Owner   Type  Dir         Value  Name
     5  s32   RO          65535  input.0.abs-rudder-max
     5  s32   RO              0  input.0.abs-rudder-min
     5  s32   RO          65535  input.0.abs-rx-max
     5  s32   RO              0  input.0.abs-rx-min
     5  s32   RO          65535  input.0.abs-ry-max
     5  s32   RO              0  input.0.abs-ry-min
     5  s32   RO          65535  input.0.abs-rz-max
     5  s32   RO              0  input.0.abs-rz-min
     5  s32   RO          65535  input.0.abs-throttle-max
     5  s32   RO              0  input.0.abs-throttle-min
     5  s32   RO          65535  input.0.abs-wheel-max
     5  s32   RO              0  input.0.abs-wheel-min
     5  s32   RO          65535  input.0.abs-x-max
     5  s32   RO              0  input.0.abs-x-min
     5  s32   RO          65535  input.0.abs-y-max
     5  s32   RO              0  input.0.abs-y-min
     5  s32   RO          65535  input.0.abs-z-max
     5  s32   RO              0  input.0.abs-z-min
     5  s32   RO          65535  input.1.abs-rudder-max
     5  s32   RO              0  input.1.abs-rudder-min
     5  s32   RO          65535  input.1.abs-rx-max
     5  s32   RO              0  input.1.abs-rx-min
     5  s32   RO          65535  input.1.abs-ry-max
     5  s32   RO              0  input.1.abs-ry-min
     5  s32   RO          65535  input.1.abs-rz-max
     5  s32   RO              0  input.1.abs-rz-min
     5  s32   RO          65535  input.1.abs-throttle-max
     5  s32   RO              0  input.1.abs-throttle-min
     5  s32   RO          65535  input.1.abs-wheel-max
     5  s32   RO              0  input.1.abs-wheel-min
     5  s32   RO          65535  input.1.abs-x-max
     5  s32   RO              0  input.1.abs-x-min
     5  s32   RO          65535  input.1.abs-y-max
     5  s32   RO              0  input.1.abs-y-min
     5  s32   RO          65535  input.1.abs-z-max
     5  s32   RO              0  input.1.abs-z-min
... snippage ...

Dan’s program assigns the outputs thusly:

Wheel – ambient temperature as measured on TC4 board
X Y Z Rudder – thermocouples – channels 1 through 4
RX RY RZ Throttle – thermistors – channels 5 through 8

I created a huge Eagle device that encapsulates the whole thing. A simple demo schematic includes the constants that make the temperatures come out in °C:

TC4Server - Eagle Schematic — TC4Server – Eagle Schematic

That picture produces this HAL file:

# HAL config file automatically generated by Eagle-CAD ULP:
# [/mnt/bulkdata/Project Files/eagle/ulp/hal-write-2.5.ulp]
# (C) Martin Schoeneck.de 2008
# Charalampos Alexopoulos 2011
# Mods Ed Nisley KE4ZNU 2010 2013
# Path        [/mnt/bulkdata/Project Files/eagle/projects/LinuxCNC for M2/]
# ProjectName [LinuxCNC M2 - TC4Server Test]
# File name   [/mnt/bulkdata/Project Files/eagle/projects/LinuxCNC for M2/TC4Server.hal]
# Created     [20:03:16 03-Jun-2013]

####################################################
# Load realtime and userspace modules
loadusr -W hal_input -A +Leonardo
loadrt threads name1=servo-thread period1=1000000
loadrt constant        count=4
loadrt conv_float_s32        count=2

####################################################
# Hook functions into threads
addf constant.0        servo-thread
addf constant.1        servo-thread
addf constant.2        servo-thread
addf constant.3        servo-thread
addf conv-float-s32.0        servo-thread
addf conv-float-s32.1        servo-thread

####################################################
# Set parameters

####################################################
# Set constants
setp constant.0.value    10
setp constant.1.value    2732
setp constant.2.value    0
setp constant.3.value    0

####################################################
# Connect Modules with nets
net n_2 constant.2.out conv-float-s32.1.in
net n_3 constant.3.out conv-float-s32.0.in
net tc4-ambient input.0.abs-wheel-position
net tc4-flat input.0.abs-wheel-flat input.0.abs-x-flat input.0.abs-y-flat input.0.abs-z-flat input.0.abs-rudder-flat input.0.abs-rx-flat input.0.abs-ry-flat input.0.abs-rz-flat input.0.abs-throttle-flat conv-float-s32.1.out
net tc4-fuzz input.0.abs-throttle-fuzz input.0.abs-rz-fuzz input.0.abs-ry-fuzz input.0.abs-rx-fuzz input.0.abs-rudder-fuzz input.0.abs-z-fuzz input.0.abs-y-fuzz input.0.abs-x-fuzz input.0.abs-wheel-fuzz conv-float-s32.0.out
net tc4-offset input.0.abs-wheel-offset input.0.abs-x-offset input.0.abs-y-offset input.0.abs-z-offset input.0.abs-rudder-offset input.0.abs-rx-offset input.0.abs-ry-offset input.0.abs-rz-offset input.0.abs-throttle-offset constant.1.out
net tc4-scale input.0.abs-wheel-scale input.0.abs-x-scale input.0.abs-y-scale input.0.abs-z-scale input.0.abs-rudder-scale input.0.abs-rx-scale input.0.abs-ry-scale input.0.abs-rz-scale input.0.abs-throttle-scale constant.0.out
net tcouple-1 input.0.abs-x-position
net tcouple-2 input.0.abs-y-position
net tcouple-3 input.0.abs-z-position
net tcouple-4 input.0.abs-rudder-position
net tmistor-5 input.0.abs-rx-position
net tmistor-6 input.0.abs-ry-position
net tmistor-7 input.0.abs-rz-position
net tmistor-8 input.0.abs-throttle-position

Fire it up with halrun to see the temperatures (alphabetically by the pin name):

halrun -I -f TC4Server.hal
halcmd: start
halcmd: show pin *position
Component Pins:
Owner   Type  Dir         Value  Name
     5  float OUT          20.9  input.0.abs-rudder-position ==> tcouple-4
     5  float OUT          21.5  input.0.abs-rx-position ==> tmistor-5
     5  float OUT        6280.3  input.0.abs-ry-position ==> tmistor-6
     5  float OUT        6280.3  input.0.abs-rz-position ==> tmistor-7
     5  float OUT        6280.3  input.0.abs-throttle-position ==> tmistor-8
     5  float OUT          22.5  input.0.abs-wheel-position ==> tc4-ambient
     5  float OUT            21  input.0.abs-x-position ==> tcouple-1
     5  float OUT            21  input.0.abs-y-position ==> tcouple-2
     5  float OUT          20.8  input.0.abs-z-position ==> tcouple-3

The sensors do not correspond to the picture at the top: only the first thermocouple and first thermistor are connected ; the ADC returns bogus data for disconnected inputs, which means you must be careful about tightening the wires and checking the result. Dan’s firmware has the ability to disable unused sensors, in which case you get a huge value; when used for heater control, a sensor failing high means the heater will turn off, but, should you use this gadget in a freezer, you might want them to fail low (so modify the code for your own use).

The ambient temperature reported for the board runs 1 or 2 °C higher than the actual ambient air temperature, probably because of all those components doing useful things up close to the sensor chip. That particular ambient temperature serves as the cold junction reference for the thermocouples; the other temperatures don’t change very much as the board warms up, so it’s all good.

Remember to issue the start command in halrun, because otherwise nothing changes.

Also remember that you must configure TC4Server with the thermistor characteristics before you use it as a hal_input device.

2013-06-10

UDEV Rules for M2’s HAL Devices
Rather than have a bunch of separate rule files for each USB HID device I’ll be using with LinuxCNC on the M2, here they are in one lump:
```
cat /etc/udev/rules.d/hal-input.rules
# Rules to configure input device permissions for hal_input

ATTRS{product}=="Nostromo SpeedPad2",GROUP="plugdev",MODE="0660"
ATTRS{product}=="Arduino Leonardo",GROUP="plugdev",MODE="0660"
ATTRS{product}=="Logitech Dual Action",GROUP="plugdev",MODE="0660"
```
The strings are case-sensitive and must match exactly. That post (among others) describes the whole dance required to get all the information.

Remember to add yourself to the plugdev group, too.
2013-06-06
Marlin Firmware: Stepper Interrupt Timing
Based on the discussion attached to the post on Z axis numbers, I wanted to take a look at the points where Marlin switches from one step per interrupt to two, then to four, just to see what the timing looks like. The RAMBo board has neatly labeled test points, to which I tack-soldered a pin for the scope probe poked through one of the ventilation slots, and an unused power connector on the left edge of the PCB that provided a ground point (admittedly, much too far away for good RF grounding, but it suffices for CMOS logic signals). The Tek Hall-effect current probe leaning in from the top right captures the current in one of the X axis windings:

X axis Step and Current probes

I’ve reset the Marlin constants based on first principles, per the notes on distance, speed, and acceleration, so they’re not representative of the as-shipped M2 firmware. Recapping the XY settings:
- Distance: 88.89 step/mm
- Speed: 450 mm/s = 27000 mm/min
- Acceleration: 5000 mm/s², with the overall limit at 10 m/s²
The maximum interrupt frequency is about 10 kHz and the handler can issue zero, one, two, or four steps per axis per interrupt as required by the speed along each axis, up to a maximum of step rate of 40 kHz. There are complexities involved which I do not profess to understand.

The maximum 10 kHz step rate for one-step-per-interrupt motion corresponds to a speed of:

112.5 mm/s = (10000 step/s) / (88.89 step/mm)

The maximum 40 kHz step rate produces, naturally enough, four times that speed:

450 mm/s = (40000 step/s) / (88.89 step/mm)

Assuming constant acceleration, the distance required to reach a given speed from a standing start or to decelerate from that speed to a complete stop is:
x = v² / (2 * a)

The time required to reach that speed is:
t = v/a

Accelerating at 5000 mm/s²:
- 112.5 mm/s = 6700 mm/min → 1.27 mm, 22.5 ms
- 150 mm/s = 9000 mm/min → 2.25 mm, 30 ms
- 450 mm/s = 27000 mm/min → 20.3 mm and 90 ms
An overview of a complete 6 mm move at 150 mm/s shows the acceleration and deceleration at each end, with a constant-speed section in the middle:

X Axis 150 mm-s 6 mm – overview

The bizarre patterns in the traces come from hp2xx‘s desperate attempts to discern the meaning of the scope’s HPGL graphic data where the trace forms a solid block of color; take it as given that there’s no information in the pattern. I described the trace conversion process there.

The upper trace shows the X axis motor winding current at a scale of 500 mA/div, with far more hash than one would expect. The RAMBo drivers evidently produce much more current noise than the brick drivers I intend to use.

The lower trace is the X axis step signal produced by the Arduino microcontroller. You can barely make out the individual step signals at each end, but there’s not enough horizontal resolution to show them when the motor moves at a reasonable pace.

In round numbers, the acceleration and deceleration should require about 30 ms each. The overall move takes 63 ms, so the constant-speed section in the middle must be about 3 ms long. That’s probably not right…

Here’s a closer look at the step pulses as the motion starts from zero on the way to 150 mm/s:

X Axis 150 mm-s 6 mm – 1 ms-div 0 ms dly

Over on the right, the 5 kHz step rate after 8.5 ms suggests a speed of 56 mm/s and counting 28 pulses says it moved 0.32 mm. Plugging those numbers into the equations:
- a = v/t = 6600 mm/s²
- a = (2 * x)/t² = 8900 mm/s²
It’s not clear (to me, anyway) whether:
- The firmware accelerates faster than the alleged 5000 mm/s² limit
- It’s accelerating near the overall limit of 10000 mm/s²
- The acceleration isn’t constant: starts high, then declines
- The measurement accuracy doesn’t support any conclusions
- I understand what’s happening
In order to see the double- and quad-step outputs, here’s a 50 mm move at 450 mm/s, with a 19 ms delay to the point where the interrupt handler transitions from single-step to double-step output:

X Axis 450 mm-s 50 mm – 200 us-div 19 ms dly

The interrupt frequency drops from just under 10 kHz to a bit under 5 kHz, with the doubled pulses about 16 μs apart. At the transition, the axis speed is 112.5 mm/s, pretty much as predicted.

If that’s the case, the overall acceleration to the transition works out to:

5800 mm/s² = (113 mm/s) / (19.5 ms)

Delaying the traces to 41.9 ms after the motion starts shows the double-to-quad step transition:

X Axis 450 mm-s 50 mm – 100 us-div 41.9 ms dly

Once again, the pulse frequency drops from 10 kHz down to 5 kHz. The speed is now 225 mm/s, half the maximum possible speed, which also makes sense: at top speed, the pulses will be essentially continuous at 40 kHz.

The average acceleration from the start of the motion:

5300 mm/s² = (225 mm/s) / (42.1 ms)

That implies the initial acceleration starts higher than the limit, but it evens out on the way to the commanded speed.

Those scope shots come from moving only the X axis. Moving both the X and Y axes, with Trace 1 now showing the Y axis output, for 50 mm at 450 mm/s, produces similar results; the Y axis output lags the X axis by a few microseconds:

XY 450 mm-s 50 mm – 100 us-div 19.5 ms dly

Once again, that’s at the single- to double-step transition at 19+ ms. The overall timing doesn’t depend on how many axes are moving, as long as they can accelerate at the same pace; otherwise, the firmware must adjust the accelerations to make both axes track the intended path.

None of this is too surprising.

For a motor running at a constant speed just beyond the single-to-double step transition at 112.5 mm/s or the double-to-quad transition at 225 mm/s, the rotor motion should have a 5 kHz perturbation around its nominal position: it coasts for nearly the entire period, then a pair of steps kicks it toward the proper position. At those transitions, the rotor turns at:

3.2 rev/s = (10000 step/s) / (3200 step/rev) 6.4 rev/s = (20000 step/s) / (3200 step/rev)

The perturbation should look like a 5 kHz oscillation (not exactly sinusoidal, maybe triangular?) superimposed on the nominal position, which is changing more-or-less parabolically as a function of time. I expect that the overall inertia damps it out pretty well, but I’d like to attach a rotary encoder to the motor shaft (or a linear encoder to the axis) to show the actual outcome, but I don’t have the machinery for that.

In any event, LinuxCNC’s step outputs should behave better, which is why I’m doing this whole thing in the first place…
2013-06-04
Makergear M2: Platform Stabilization

The M2’s build platform consists of an 8×10 inch glass slab atop an aluminum spider, all supported by a trio of fairly stiff springs. Back when I was experimenting with excessive acceleration, I inserted some silicone rubber cylinders to boost the spring constant and stabilize the platform

The same vibration isolators that provided the vacuum cleaner’s floor brush rollers came through again:

Silicone rubber pads for M2 platform – punching

I removed the screws and springs one by one, tucked a cylinder inside the spring, and reinstalled it:

Silicone rubber pads for M2 platform – installed

The trick is to park the nozzle near the edge of the platform where it will rise without the screw holding it down, measure the distance twixt nozzle and platform, lower the platform by a (known!) 50 mm, install the cylinder, raise the platform, then tweak the screw to put the same distance between the nozzle and the platform as you started with.

This probably doesn’t make much difference with the default 3 m/s² acceleration, but up around 10 m/s² it seemed wobbly. No suprise: that’s over 1 G of lateral acceleration and the platform weighs a pound or so.

2013-05-31
Hexagonal Chain Mail

Everybody at the Squidwrench Show-n-Tell loved the chain mail. I printed up a sheet of Ablapo’s hexagonal chain mail before the show (because it takes forever) and it came out very nicely on the M2’s larger platform:

Hexagonal Chain Mail – on platform

The first layers sprinkle a bazillion little shapes all over the platform:

Hexagonal Chain Mail – first layer

It makes a nice doily for my desk lamp:

Hexagonal Chain Mail – lamp doily

The odd blue coloration must be an optical effect, because it’s not visible on the black PLA.

2013-05-30
3D Printing Show-n-Tell

So the local hackerspace put on a show in Highland and, being the guy with the 3D printer, I volunteered for a few hours of stand-up comedy.

A pile of stuff provided talking points:

3D Printing This Way – with clutter

Four pages of solid model images on nice glossy photo paper let me talk about what must happen before the plastic emerges:

Nisley – Solid Models – Demo Sheet 1

Nisley – Solid Models – Demo Sheet 2

Nisley – Solid Models – Demo Sheet 3

Nisley – Solid Models – Demo Sheet 4

I loves me some OpenSCAD modeling, yes, I do…

Signage festooned with sample critters dragged ’em in off the street:

3D Printing This Way – signs on post

The printer produced a steady stream of tiny owls:

M2 – Mini owl on platform

And the ever-popular whistle:

M2 – Whistle on platform

A good time was had by all!

2013-05-29