The speed I expected from a working motor at 5 Hz was on the order of 0.6 µm per second, scaled from the source design's published performance [first_motion_playbook.md §1]. Watched with perfect attention for thirty seconds, that motor accumulates about 18 µm of travel (Derived), a fraction of the width of a hair, with no reference mark that an unaided eye could use. A dead motor watched the same way accumulates zero, so at this scale a working motor and a dead one look the same to a human eye.
An experiment is blind when its outcome looks identical whether the hypothesis is true or false. I ran experiments like that for about a month, mostly without understanding that I was doing so, and I think this is the mistake somebody else is most likely to make too.
A month without results
From the outside, and from the inside too, the month was ordinary [builder, 2026-08-07]. With the stack ticking at 5 Hz (§M7), I set a preload with the calibrated screw and watched the slider, then added a tick on the screw and watched again, and each time I saw nothing. Over these sessions I walked the preload across the whole plausible working range, zero to 5.5 N [first_motion_playbook.md §1; my recollection said "about five," and for once memory and the record agree], which on paper is a systematic sweep of the parameter that stick-slip physics is most sensitive to.
Every null result felt like information because it was tedious to produce. By the end I was close to certain the motor didn't work [builder, 2026-08-07]. But given the arithmetic above, "no visible motion at this preload" was compatible with a broken motor and equally compatible with a working one.
How much of that is fair to me depends on one number, how long a single trial ran. Thirty seconds of watching is blind at this speed, but the same motion becomes visible when it is watched long enough against a fixed mark. So some of what I am calling blindness was a detector problem and some of it may have been a patience problem.
Eliminating variables
Since I could not read the output, the only move I had was to eliminate suspects feeding the input, and §M9 told that story from the hardware side. The commercial rail, whose breakaway drag I had every reason to think exceeded the entire drive budget, was replaced with the bearing-bolt rail built to be as close to frictionless as printed parts allow. §M9 is blunt that neither rail's breakaway was ever measured, so this suspect was removed on strong suspicion rather than on evidence.
Removing the rail still mattered, because if nothing moved on the freer rail either, the drag explanation was finished [builder, 2026-08-07]. That moved the drive to the top of the list, and it was the suspect I had been vouching for on paperwork alone. It was not the only one left, as §M11 would eventually make clear, but it was the only one I could put a scope on.
Instrumenting the input
With the mechanics cleared as far as I could clear them, I put the oscilloscope on the drive signals at the stack, expecting just to double-check that everything made sense [builder, 2026-08-07]. It did not, and a careful reading of the signals found the drive's faults, which per the records had been there the whole time. The board's real output was half of what the documents claimed, its waveform fell apart if asked for anything much faster than the bench's 5 Hz, and one channel was underperforming its neighbor (§M7 covers each of these faults).
So the blindness ran in both directions. The sweeps were output-blind because micrometer motion is invisible to the eye, which I understood in principle by mid-month, when the first-motion playbook formalized the arithmetic [first_motion_playbook.md §1, 2026-07-13]. They were also input-blind because I had assumed the drive was healthy on its documentation's word.
The feeling
When the scope finally named a culprit, I felt extreme relief [builder, 2026-08-07]. It had been a long time since the bench had given me an answer to anything, and this was one, even though it amounted to "your drive has been lying to you for weeks." It felt like the project restarting.
Instrumented measurement
The playbook's one-line verdict was "Your no-motion test is almost certainly blind, not broken." Its advice was to fix the readout, not the speed [first_motion_playbook.md]. The playbook's two inequalities, µN > F_drag for the stick phase and m·a_flyback > µN for the slip [first_motion_playbook.md §2], double as a list of ways this motor can fail with no visible sign. My preload sweep was a fine experiment, but it was judged by a detector (me, squinting) with no sensitivity to the effect.
Two instruments replaced the eye, and a third is built and waiting. One is the oscilloscope on the input, and the other is accumulation, which needs no instrument at all. When a slow motion runs long enough against a fixed mark, even a naked eye becomes an instrument again, and that is how first motion was caught, with a strip of masking tape and ten minutes (§M11). The third is the Michelson interferometer on the output (§M8), built so that 260 nanometers of travel becomes one countable fringe, though it has not yet been pointed at the motor.
I now define an experiment as something whose outcome can change what I believe, rather than something done at a bench. For about a month, my experiments could not do that. Everything downstream of this chapter, the validation battery and the controls that go with it, exists so that no result in this project is ever that uninformative again.