Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
… of course don’t fit the Baofeng radio. This being in the nature of a final fix, I chopped off enough protrusions to make the remainder fit snugly into the recess.
Based on one ride, both Baofeng batteries have very little capacity left after several years on the shelf, which comes as absolutely no surprise whatsoever.
The DW660 collet grabs a length of 1/8 inch drill rod jammed into a hole positioned to put the switch actuator directly in line with the spindle axis when it trips the switch, so as to measure a known and useful location:
Z Axis Height Probe – MBI endstop – Slic3r
After mulling things over for a while, I fired up the Sherline, drilled a #54 hole in the actuator, and epoxied a 3/32 inch bearing ball in the hole:
MPCNC – Endstop Z probe – bearing
A #54 drill hole is half the diameter of the ball and, with a bit of luck, enough of the ball will stick through into the epoxy on the underside for a good grip:
MPCNC – Endstop Z probe – bearing – detail
The general idea is to convert the stamped steel actuator into a single, albeit not particularly sharp, contact point that can glide over the platform / PCB / sheet-of-whatever to measure the surface. The actuator pivots as it depresses, so the ball must slide horizontally just a bit. I prefer a rod-in-tube probe poking a linear button switch, but those weren’t getting me anywhere.
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I have often asserted, in public, in writing, that you can’t change the speed of a fan’s BLDC motor by varying its voltage, because the fan controller generates the waveforms responsible for the motor speed based on its internal timing.
A pair of BLDC blowers recently arrived and a quick test showed I’m pretty much completely wrong:
BLDC Blower – RPM I P vs V
The data points come from this blower:
Blower label – 24V 0.2A
The blower specs from the eBay listing:
75MM 24V Brushless DC Blower Cooling Fan Exhaust Fan
Dimension:75(L)x75(W)x30(H)mm
Connector:2Pin-PH2.0
Rated Voltage: DC24V
Rated Current: 0.2±10% Amp
Rated Speed: 3800±10%rpm
Air flow:1.8CFM
Noise: 23±10%dBA
Bearing Type: Sleeve
Life: 35000 hours
Cable Lenght: 32cm(12.5in)
Weight: 75g/pcs
The case is about 75 mm × 75 mm × 30 mm, so the generic part number seems to be 7530, with many variations. However, they all seem to resolve to the same blower with different models drawing different current at specific voltages (clicky for more dots, JPG blurriness in original):
GDT7530S12B BLDC blower parameter table
The blower in hand roughly corresponds to the bottom line of the 24 V section:
0.21 A
4000 RPM
16.3 CFM
1.1 inch H2O pressure
43 dBA
There’s a gross discrepancy between the eBay 1.8 CFM and the chart 16.3 CFM, but the other parameters seem within handwaving distance and, yo, it’s from eBay. ‘Nuff said.
The graph up top shows the results with an unrestricted output opening.
For more realistic results with some resistance to air flow, I taped a small anemometer to the blower output:
Blower air flow test
Which produced:
BLDC Blower – RPM Flow vs V – anemometer
In very round numbers, the anemometer aperture is 400 mm², so the 9 m/s air flow at 24 V works out to 3.6×10-3 m3/s = 0.13 CFS = 7.6 CFM. Which is maybe half the 16.3 CFM spec, but they’re surely using a fancier anemometer with much lower back pressure. Close enough, anyway. Fer shure, 1.8 CFM is wrong.
Completely blocking the inlet with a plastic sheet to simulate the blower pulling air from, e.g., a vacuum table:
BLDC Blower – RPM vs V – blocked inlet
The RPM varies more linearly with voltage when the blower isn’t accelerating any air.
Some current waveform show why you really shouldn’t run fans in series to “split the power supply”, as seems common in 3D printers with 24 VDC power supplies.
From a 24 V supply, the current drops to 50 mA every 75 ms (200 mA/div):
BLDC 24V Blower – 24 V – 200mA-div
From a 12 V supply, even weirder things happen (50 mA/div):
BLDC 24V Blower – 12 V – 50mA-div
Note that you can’t reduce the fan’s supply voltage by applying PWM to the current, as happens in essentially all 3D printers for “speed control”. Basically, PWM turns the fan off several hundred times every second, which does not modulate the voltage.
I have no way to measure pressure, but if the 1.1 inch H2O number comes close to reality, the blower can produce 1.5 lb of clamping force per square foot. Which isn’t a lot, granted, but it might suffice for paper and vinyl cutting.
Because the OLED driver came from the pip package manager, not the Raspberry Pi’s system-level apt package manager, it (or they, there’s plenty of code under the hood) don’t get updated whenever I do system maintenance. The doc says this should do the trick:
sudo -H pip install --upgrade luma.oled
However, it turns out the new version has a slightly longer list of pre-requisite packages, causing the update to go toes-up at a missing package:
Could not import setuptools which is required to install from a source distribution.
Please install setuptools.
So update (or install, for the new ones) the missing pieces:
Doing so produced a backwards-compatibility error in my Python code:
... change ...
from luma.core.serial import spi
... into ...
from luma.core.interface.serial import spi
The motivation for all this fuffing and fawing came from watching some OLEDs wake up completely blank or become garbled in one way or another. Evidently, my slower-speed SPI tweak didn’t quite solve the problem, although it did reduce the frequency of failures. I have decided, as a matter of principle, to notembrace the garble.
Soooo, let’s see how shaking all the dice affects the situation.
It’s entirely possible the OLED controllers don’t quite meet their specs, of course, or have begun deteriorating for all the usual reasons.
Yes, the SSR negative output goes to the Protoneer + Power Input.
I should drive the SSR from the Motor Enable output (in the external motor control header), rather than +5 V, to let GRBL control the motors, with a manual E-Stop override. The A4988 drivers require -Enable, so:
-Enable to SSR -Control input (replaces GND)
+5 V to BRS to SSR +Control input (as before)
The SSR Control input draws 13 mA at 5 V, suggesting I should drive the AC SSR (for the spindle motor) from the DC SSR output, rather than paralleling the two on a single Arduino output pin.
I belatedly recognized the E-Stop BRS as an instantiation of an SCP-001-JKeter-class anomaly; it is now appropriately labeled:
MPCNC EStop as SCP-001-J
I can attest to its effect on rational thought; a molly-guard may be required.
After a year of fairly light use, the lens holder (and “attack ring”) of my J5-V2 flashlight worked loose and began to rattle. The ring holding the lens in place turned out to be finger-loose, but that wasn’t the entire problem, so I removed it and looked inside:
The aluminum ring holding the LED assembly in place was also finger-loose, so I unwound it to take the whole front end apart:
J5-V2 Flashlight – front parts
Reassembly with a few dabs of Loctite in appropriate places should prevent future rattles.
Given the number of … issues … accompanying this thing, I’d say it’s not been a good cost performer. The Anker LC40 and LC90 flashlights work much better.
So I intended to shrink the Autolevel probe with 1/8 inch drill rod and a tactile membrane switch:
MPCNC – Simple Z probe – pogo tactile switch
Unfortunately, it didn’t work nearly as well as I expected, because the switch membrane requires slightly less than the 180 g of pressure that pushes the P100 pogo pin entirely into its housing, leaving no overtravel worth mentioning. The membrane switch mechanism itself has much less than 1 mm of overtravel after the dome snaps, which left me with an uncomfortable feeling of impending doom.
I managed to figure that out before completely assembling the thing, saving me a bit of time.
The end of the pogo pin initially sported a dot of epoxy to spread the load over the switch dome:
Pogo pin with epoxy switch-pusher drop
I dismantled the pogo pin to see whether I could substitute a more forceful spring how it worked. As expected, a teeny spring drives the probe up against a trio of indentations in the brass housing. I didn’t expect the probe to have such an intricate shape, but it’s obvious in retrospect.
The OpenSCAD code for the housing required minimal tweakage from the larger version, so it’s not worth immortalizing.
The Smell of Molten Projects in the Morning 