{"id":8074,"date":"2026-11-09T14:25:16","date_gmt":"2026-11-09T14:25:16","guid":{"rendered":"https:\/\/reachsky.co\/"},"modified":"2026-11-09T14:51:16","modified_gmt":"2026-11-09T14:51:16","slug":"motor-desync-high-current","status":"publish","type":"post","link":"https:\/\/reachsky.co\/zh\/%e7%94%b5%e6%9c%ba\/motor-desync-high-current.html","title":{"rendered":"Motor Desync High Current: Causes and Fixes"},"content":{"rendered":"<p><strong>TL;DR<\/strong><\/p>\n<ul>\n<li>Motor desync at high current is a commutation error. The controller loses track of the rotor, fires the wrong phase pair, and the current spike burns hardware that was never undersized.<\/li>\n<li>Current is both trigger and amplifier: it shifts the zero-crossing the controller reads, lengthens the freewheel window after each switch, and shortens the time available to sample.<\/li>\n<li>Fix it cheapest-first \u2014 timing and startup, ramp rate, pack and wiring, then firmware limits \u2014 and prove the fix on a stand where the current step repeats.<\/li>\n<\/ul>\n<p>A drive that loses sync does not announce itself politely. It chirps once at arm-up, or it flies for eleven minutes and then flips a single motor on a punch-out. Motor desync at high current is the version that damages parts, because every lost commutation event dumps stored energy into one phase pair while the rotor sits somewhere else. This guide covers how to recognise it, the six causes worth checking in order, and a bench routine that turns an intermittent fault into something measurable.<\/p>\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1536\" height=\"864\" class=\"wp-image-8075\" src=\"https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured.webp\" alt=\"A drone motor clamped to a thrust stand with three phase leads running to a bare ESC and an oscilloscope probe\" srcset=\"https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured.webp 1536w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured-300x169.webp 300w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured-1024x576.webp 1024w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured-768x432.webp 768w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured-18x10.webp 18w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured-800x450.webp 800w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/01-01-motor-desync-test-bench-featured-600x338.webp 600w\" sizes=\"auto, (max-width: 1536px) 100vw, 1536px\" \/><\/figure>\n<p><em>Bench setup for commutation testing: motor in a thrust stand, three phase leads to a bare controller, scope probe and tachometer on the same timeline.<\/em><\/p>\n<h2>Desync is a commutation error, not a power problem<\/h2>\n<p>A sensorless brushless drive answers one question several thousand times per second: which two of the three phases should be energised now? It answers by watching the back-electromotive force (back-EMF) of the unenergised phase, or by running a motor model in firmware, and it assumes that answer stays valid for the next switching step.<\/p>\n<p>Motor desync high current begins here, when the assumption breaks. The estimated rotor angle drifts more than one commutation step from the real angle, so the controller energises a pair that produces little torque or torque in the wrong direction. The motor now looks like a locked rotor: low impedance, no back-EMF to oppose the bus, current limited only by winding resistance and the FET channel.<\/p>\n<p>A burnt FET is therefore a symptom, not a diagnosis. The damaged device is whichever one happened to be conducting when the estimate failed, and it is usually on the same phase pair every time, which misleads people into blaming that phase. The phase is fine; the decision to fire it was wrong. This is also why more current capacity does not help: a larger controller moves the ceiling and fails in the same place at a higher current.<\/p>\n<p>The distinction separates this fault from its neighbours. A drive that runs hot for twenty minutes and then cuts out is a thermal problem, covered in our <a href=\"https:\/\/reachsky.co\/zh\/esc\/esc-overheating-causes.html\" target=\"_blank\" rel=\"noopener\">ESC overheating causes<\/a> note. A drive that fails inside the first second of a load step is a commutation problem, and heat is not yet part of the story.<\/p>\n<h2>What does desync look like before it burns an ESC?<\/h2>\n<p>It looks like a brief loss of torque with a current spike that does not match it. Every other symptom is a variation on that signature, and the variation tells you which branch of the fault tree you are on.<\/p>\n<ul>\n<li><strong>A chirp or tick at arm-up.<\/strong> One motor twitches, the others spin up cleanly, and the third or fourth attempt succeeds.<\/li>\n<li><strong>A single-motor flip on a punch-out.<\/strong> The airframe yaws hard for a fraction of a second, then the motor catches. Attitude control masks it as a wobble.<\/li>\n<li><strong>A hard start that ends in smoke.<\/strong> The motor never catches, the controller keeps trying, and current stays high because no back-EMF opposes the bus.<\/li>\n<li><strong>A current spike with no RPM response.<\/strong> The clearest log signature: current climbs steeply, RPM stays flat or drops, throttle did not change.<\/li>\n<li><strong>Damage on one phase pair only.<\/strong> Often one low-side FET plus its gate resistor.<\/li>\n<\/ul>\n<p>Two other faults get mistaken for desync. Bearing rumble is mechanical, follows RPM and produces no current spike. Propeller imbalance is a once-per-revolution vibration that never stops the motor. A desync is an event with a beginning and an end.<\/p>\n<h2>Motor desync high current: why it shows up under load<\/h2>\n<p>Because current changes both the signal the controller reads and the time it has to read it. Four mechanisms do the work, and they usually arrive together.<\/p>\n<p><strong>The zero-crossing moves.<\/strong> The phase the controller treats as floating is not at the motor&#8217;s neutral point. It carries the resistive drop of the current flowing through the other two phases, plus the inductive term from the switching transient. Both are negligible at low current and both shift the apparent crossing by a real electrical angle at high current, so the controller commutes early or late in proportion to load.<\/p>\n<p><strong>Freewheel takes longer.<\/strong> When a phase is switched off, its current decays through the body diode of the opposite device. That decay scales with current, so a phase that was floating by the time the controller looked at it at 20 A is still clamped at 120 A. The comparator reads a false crossing, or none, and the step is missed. This is demagnetisation, and it drives most desync events on large low-KV motors with heavy props.<\/p>\n<p><strong>Inductance falls as the stator saturates.<\/strong> Winding inductance is not constant. Push current toward the saturation knee and inductance drops, so current rises faster for the same voltage and the ripple grows. The sampling window is unchanged; the current inside it has moved further.<\/p>\n<p><strong>Torque per amp falls, so the loop asks for more amps.<\/strong> Wrong timing means phase current is not aligned with back-EMF. The motor makes less torque for the current it draws, the speed loop compensates with throttle, and that extra current feeds the first three mechanisms. The failure escalates on its own, which is why events look violent rather than gradual.<\/p>\n<p>Both commutation schemes fail this way. Six-step depends entirely on zero crossings in a signal that current corrupts; field-oriented control (FOC) estimates the angle in a rotating frame and tolerates more, but not when its observer is tuned for an inductance the motor does not have. Our <a href=\"https:\/\/reachsky.co\/zh\/%e7%94%b5%e6%9c%ba\/bldc-vs-foc-escs-uav-control-selection.html\" target=\"_blank\" rel=\"noopener\">BLDC versus FOC comparison<\/a> covers where each earns its keep.<\/p>\n<h2>The causes, in the order you should check them<\/h2>\n<p>Motor desync high current faults rarely have a single cause, and the order matters as much as the checks. Work cheapest first, because each step eliminates a whole class of cause. The first row you can prove with data is the one you fix, even if a later row also looks plausible.<\/p>\n<div style=\"margin: 26px 0; border: 1px solid #E3E7ED; border-radius: 8px; overflow: hidden;\">\n<div style=\"overflow-x: auto; -webkit-overflow-scrolling: touch;\">\n<table style=\"width: 100%; min-width: 620px; border-collapse: collapse; margin: 0; font-size: 16px; line-height: 1.55; border: 0;\">\n<thead>\n<tr>\n<th style=\"width: 25%; background: #1F4E79; color: #ffffff; text-align: left; font-weight: 600; padding: 13px 16px; border: 0; border-right: 1px solid rgba(255,255,255,0.16);\">Symptom<\/th>\n<th style=\"width: 25%; background: #1F4E79; color: #ffffff; text-align: left; font-weight: 600; padding: 13px 16px; border: 0; border-right: 1px solid rgba(255,255,255,0.16);\">Likely cause<\/th>\n<th style=\"width: 25%; background: #1F4E79; color: #ffffff; text-align: left; font-weight: 600; padding: 13px 16px; border: 0; border-right: 1px solid rgba(255,255,255,0.16);\">How to verify<\/th>\n<th style=\"width: 25%; background: #1F4E79; color: #ffffff; text-align: left; font-weight: 600; padding: 13px 16px; border: 0;\">Fix<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top; font-weight: 600; color: #14263d;\">Chirps at arm-up, then runs clean<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Startup power too low for the prop, or timing too retarded to catch the rotor<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Arm up twenty times from cold at low throttle and count failures<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; vertical-align: top;\">Raise startup power in small steps; keep timing low until it catches reliably<\/td>\n<\/tr>\n<tr style=\"background: #F7F9FC;\">\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top; font-weight: 600; color: #14263d;\">Desync only on a hard throttle step<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Ramp faster than the estimator can track, or demag compensation too weak<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Step 0 to full throttle in one frame, ten times, logging current and RPM<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; vertical-align: top;\">Cap acceleration in firmware; enable or raise demag compensation<\/td>\n<\/tr>\n<tr>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top; font-weight: 600; color: #14263d;\">Desync at sustained high current, motor hot<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">PWM frequency too low for the motor&#8217;s inductance, or the stator is saturating<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Log phase current at maximum sustained thrust and compare with the motor&#8217;s rated current<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; vertical-align: top;\">Raise PWM frequency one step; if saturation is confirmed, change prop or motor class<\/td>\n<\/tr>\n<tr style=\"background: #F7F9FC;\">\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top; font-weight: 600; color: #14263d;\">Desync on one arm only<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Solder joint, bullet connector or damaged phase lead<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Move the ESC to a known-good arm and repeat; the fault follows ESC, motor or harness<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; vertical-align: top;\">Re-solder the pads, replace the lead, replace the connector<\/td>\n<\/tr>\n<tr>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top; font-weight: 600; color: #14263d;\">Desync after a prop change<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Operating point pushed past the motor&#8217;s continuous current<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Compare hover and max-thrust current against the motor&#8217;s published thrust table<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; vertical-align: top;\">Step the prop back one size, or move up a motor class<\/td>\n<\/tr>\n<tr style=\"background: #F7F9FC;\">\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top; font-weight: 600; color: #14263d;\">Desync near the end of a pack<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Bus voltage sagging under load, or long DC leads ringing at each commutation<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; border-right: 1px solid #E3E7ED; vertical-align: top;\">Log voltage at the ESC pads, not at the pack, at the moment of the event<\/td>\n<td style=\"padding: 12px 16px; border: 0; border-top: 1px solid #E3E7ED; vertical-align: top;\">Use a pack with more headroom, shorten the DC leads, add bulk capacitance<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<h2>Why the row order is cost, not frequency<\/h2>\n<p>Row order is about cost and speed, not frequency: on large airframes the pack and wiring rows are more common than expected, because nobody instruments the DC path. The rows also interact, since a saturating motor looks exactly like a timing problem.<\/p>\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1600\" height=\"900\" class=\"wp-image-8076\" src=\"https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart.png\" alt=\"Flowchart for motor desync troubleshooting: one symptom, four branches by when the fault appears, and the measurement that confirms each cause\" srcset=\"https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart.png 1600w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-300x169.png 300w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-1024x576.png 1024w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-768x432.png 768w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-1536x864.png 1536w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-18x10.png 18w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-800x450.png 800w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/02-03-desync-troubleshooting-flowchart-600x338.png 600w\" sizes=\"auto, (max-width: 1600px) 100vw, 1600px\" \/><\/figure>\n<p><em>Same order as the table, drawn as a decision path: the branch narrows the cause, the measurement confirms it, the fix is the last line of each row.<\/em><\/p>\n<h2>Timing, ramp rate and motor inductance<\/h2>\n<p>Timing advance defines the electrical angle by which the controller leads the detected crossing, and every motor has an angle where torque per amp peaks. Below it, current lags the back-EMF and the motor makes less torque for the same amps, so the speed loop asks for more. Above it, phase current peaks early, the FETs carry more loss, and the drive runs hotter for the same thrust.<\/p>\n<p>At high current the useful lead angle creeps upward, because resistive and inductive terms in the phase voltage grow with current and push the useful part of the waveform later. A fixed value tuned at hover is therefore slightly retarded at full load. That is why a motor often desyncs only when the airframe is heavy: timing was set light.<\/p>\n<p>Ramp rate is the setting people ignore, and the more common cause on multirotors. Winding current cannot change instantly; it rises at a rate set by bus voltage minus back-EMF, divided by inductance. Low-inductance motors \u2014 large stator, few turns \u2014 rise fast, and a throttle step the flight controller treats as instantaneous becomes a current step the estimator has one or two switching periods to interpret.<\/p>\n<p>A ramp limit is therefore not a comfort setting. It is the interval in which the controller can keep its angle estimate valid while load changes. If the airframe needs an aggressive ramp for attitude control in wind, the answer is usually more inductance or a better estimator. At the top of a 12S or 14S build the commutation period is short enough that a fixed sampling delay becomes a large angle error by itself; our <a href=\"https:\/\/reachsky.co\/zh\/%e7%94%b5%e6%9c%ba\/motor-kv-battery-cell-count-heavy-lift-build.html\" target=\"_blank\" rel=\"noopener\">KV and cell-count matching<\/a> note covers how electrical frequency scales with RPM.<\/p>\n<p>One mechanical check: prop inertia and mount flex let the rotor lag the commanded acceleration, so the estimate runs ahead of reality.<\/p>\n<h2>Pack sag, wire length and ground return<\/h2>\n<p>A pack sags under load in proportion to current. That is a performance problem on its own, but it becomes a desync cause through the controller&#8217;s sensing.<\/p>\n<p>Zero-cross detection compares phase voltages against a reference derived from the bus or a virtual neutral. During a load step the bus collapses and both move, at different rates: the reference follows bulk capacitance, the phase signal follows the winding. The comparator then sees a crossing that is not there, or misses one that is. Long leads worsen it, because cable inductance rings at every commutation and the ringing lands on the supply rails.<\/p>\n<p>Ground return is the third part of the same problem and the one most often missing from the drawing. Signal ground, logic ground and power ground are one net on a small board, but the join point matters. Return heavy current through a path that shares no copper with the signal reference, and join the two once, near the input capacitor. On a long airframe with the pack in the nose and ESCs in the arms, a shared return puts switching current in series with the throttle signal&#8217;s reference.<\/p>\n<p>What to measure, cheapest first:<\/p>\n<ol>\n<li><strong>Loop resistance<\/strong> from pack terminals to ESC input pads, system off. A joint that has been hot will read high, and higher when warm.<\/li>\n<li><strong>Voltage at the ESC pads during a load step<\/strong>, not at the pack. The difference is the drop you feed the controller.<\/li>\n<li><strong>DC bus ripple<\/strong> on a scope, AC-coupled, same load. Large ripple with a healthy pack points at lead length and missing capacitance.<\/li>\n<\/ol>\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1536\" height=\"1024\" class=\"wp-image-8077\" src=\"https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint.webp\" alt=\"Macro view of heavy-gauge silicone wires soldered to tinned pads on a green ESC board, with heat-shrink ending above the fillets\" srcset=\"https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint.webp 1536w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint-300x200.webp 300w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint-1024x683.webp 1024w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint-768x512.webp 768w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint-18x12.webp 18w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint-800x533.webp 800w, https:\/\/reachsky.co\/wp-content\/uploads\/2026\/11\/03-02-motor-phase-wire-solder-joint-600x400.webp 600w\" sizes=\"auto, (max-width: 1536px) 100vw, 1536px\" \/><\/figure>\n<p><em>Inspect all three pads, not just the one that failed: a cold fillet or a discoloured lead adds resistance exactly where current is highest.<\/em><\/p>\n<h2>Firmware limits and protocol settings<\/h2>\n<p>Firmware can create desync, hide it, or tell you it happened. All three are useful if you know which one you are looking at.<\/p>\n<p>The limits that matter shape current rather than throttle. A motor output limit or current limit caps demand before the ESC sees it, which avoids the last few percent of throttle where the estimator is weakest. Low-voltage cutoff, if set aggressively, produces a mid-climb throttle reduction that looks like a desync in the log but is a protection feature working; rule it out early, because it is a configuration change, not a repair.<\/p>\n<p>Protocol changes how a corrupted command is handled. Legacy PWM carries a pulse width with no integrity check, so noise on the signal wire becomes a real throttle change. DShot frames carry a checksum, so a corrupted frame is discarded, and bidirectional DShot returns eRPM per motor \u2014 the cheapest desync detector available, because you can compare commanded throttle against measured RPM and find the moment they diverge.<\/p>\n<p>The parameters we change, in order:<\/p>\n<ul>\n<li><strong>Demag compensation<\/strong>: raises the commutation limit during fast throttle changes. Turn it on before touching timing.<\/li>\n<li><strong>Startup power<\/strong>: fixes arm-up chirps. Too high and the hard start becomes the event.<\/li>\n<li><strong>Timing advance<\/strong>: adjust last, in small steps, re-testing the failing load case each time.<\/li>\n<li><strong>PWM frequency<\/strong>: one step up helps low-inductance motors hold a clean waveform; too far raises switching loss without fixing anything.<\/li>\n<li><strong>Firmware target and board revision<\/strong>: a build compiled for a different gate driver can arm and spin while switching at the wrong dead time; check the <a href=\"https:\/\/www.st.com\/en\/motor-drivers.html\" target=\"_blank\" rel=\"noopener\">gate driver reference<\/a> for the silicon on the board.<\/li>\n<\/ul>\n<p>Record the parameter set against the airframe serial. A replacement ESC arrives at defaults, and those defaults are often the cause of the second failure.<\/p>\n<h2>How do you reproduce desync on a test stand?<\/h2>\n<p>You reproduce it by making the current step repeatable: same prop, same pack state of charge, same command, and instrumentation that shows the estimate failing. A fault that only appears in flight cannot be fixed, only guessed at.<\/p>\n<ol>\n<li><strong>Mount and guard.<\/strong> Clamp the motor with the prop fitted and a guard in place. The rules still apply on the bench: <a href=\"https:\/\/www.faa.gov\/uas\" target=\"_blank\" rel=\"noopener\">FAA UAS<\/a> \u4ee5\u53ca <a href=\"https:\/\/www.easa.europa.eu\/en\/light\/topics\/drones\" target=\"_blank\" rel=\"noopener\">EASA drones<\/a> define what a civil operator may do. Desync produces torque reversals, and a prop that lets go is the expensive part of the test.<\/li>\n<li><strong>Instrument the DC side.<\/strong> Current clamp or ESC telemetry for phase current, plus a voltage sense wire at the ESC input pads \u2014 not at the pack, not at the distribution board.<\/li>\n<li><strong>Instrument the AC side.<\/strong> One phase to a scope against the PWM input, plus an optical tachometer or eRPM telemetry, so the electrical event and the mechanical response share a timeline.<\/li>\n<li><strong>Fix the pack.<\/strong> One pack at a known state of charge for the whole baseline. Changing packs between runs changes the variable you are trying to hold.<\/li>\n<li><strong>Baseline.<\/strong> Ten seconds at 30% throttle, ten at 60%. Record current, voltage, RPM and any stutter. If the baseline is already unstable, fix that first.<\/li>\n<li><strong>Step test.<\/strong> Ten repetitions of 0 to full throttle in a single frame, with rest between. Count events, not impressions.<\/li>\n<li><strong>Ramp sweep.<\/strong> Repeat at 1 s, 0.5 s and 0.25 s ramp. The duration where the event first appears sets your firmware limit.<\/li>\n<li><strong>Sag test.<\/strong> Repeat at successively lower states of charge until the event appears. That tells you whether the pack is part of the cause.<\/li>\n<li><strong>Swap test.<\/strong> Substitute a known-good ESC, then motor, then lead set, one at a time. The fault follows one of the three.<\/li>\n<li><strong>Re-run the failing case.<\/strong> After the fix, run the exact step that failed twenty times. Surviving one run is not a test.<\/li>\n<\/ol>\n<p>Write the numbers down with the configuration. A ramp limit or timing value without the prop, pack and ambient attached is not reproducible, and the next engineer starts from zero.<\/p>\n<h2>Procurement notes<\/h2>\n<p>Desync is cheap to prevent at specification and expensive to discover after the airframe is built, so the useful question is not which controller has the highest rating. It is which combination of motor, controller and firmware was characterised together.<\/p>\n<p>Ask for four numbers before ordering, and treat a datasheet that omits them as a warning:<\/p>\n<ul>\n<li><strong>Winding inductance and rated continuous current<\/strong> for the motor, not just KV and weight. Inductance decides which PWM band the drive must work in.<\/li>\n<li><strong>Continuous current at the voltage class you will actually run<\/strong>, not one headline figure. Our note on <a href=\"https:\/\/reachsky.co\/zh\/uncategorized\/esc-amp-rating-continuous-vs-burst-current-explained.html\" target=\"_blank\" rel=\"noopener\">continuous versus burst current ratings<\/a> explains why they are measured differently.<\/li>\n<li><strong>Firmware and protocol as shipped<\/strong>, including whether bidirectional telemetry is supported. That feature makes desync visible instead of mysterious.<\/li>\n<li><strong>Whether current is logged internally<\/strong>, and at what rate. A 10 Hz log cannot resolve a commutation event.<\/li>\n<\/ul>\n<p>For heavy-lift work we specify the <a href=\"https:\/\/reachsky.co\/zh\/product\/mad-ampx-esc-200a-12-24s-hv\" target=\"_blank\" rel=\"noopener\">AMPX 200A 12-24S HV<\/a> where the pack is large and the DC path long, and the <a href=\"https:\/\/reachsky.co\/zh\/product\/mad-pulsar-bl32-8s-100a-single\" target=\"_blank\" rel=\"noopener\">MAD PULSAR BL-32 8S 100A<\/a> for single-motor applications in the 8S class. Both ship with the settings sheet recorded against the unit, which shortens the first bench session. Motors across the AM50 to AM160 range and the M50C35, M60C50 and M60C60 PRO IPE series sit on the <a href=\"https:\/\/reachsky.co\/zh\/product-category\/%e7%94%b5%e6%9c%ba\" target=\"_blank\" rel=\"noopener\">motor category page<\/a> with their thrust tables.<\/p>\n<p>Commercial terms as we quote them: samples from one piece, stock units at 3 to 10 business days, samples at 7 to 15, OEM builds at 25 to 40. Warranty is 12 months and engineering replies within one business day. Model cost as three lines rather than one \u2014 the controller, the spares you carry, and airframe downtime per event. On a commercial airframe the third dominates, which is why the specification work pays for itself. Units are supplied to ISO 9001, RoHS and REACH.<\/p>\n<h2>\u5e38\u89c1\u95ee\u9898\u89e3\u7b54<\/h2>\n<p><strong>What causes motor desync at high current?<\/strong> Demagnetisation of the floating phase is the usual cause. At high current the phase being switched off takes longer to decay, so the controller reads a false zero crossing and fires the wrong pair. Timing, ramp rate and pack sag make it worse.<\/p>\n<p><strong>Can one desync event destroy an ESC?<\/strong> Yes. A single event can put locked-rotor current through one phase pair, and the two conducting devices absorb it. Units often survive with a gate resistor or one FET degraded, which is why a controller that desynced once should be inspected before it is trusted.<\/p>\n<p><strong>Does a higher current rating stop desync?<\/strong> No. A larger controller has more margin for the spike, so the failure is less likely to be destructive, but the commutation error is unchanged and recurs at the same operating point. Fix the estimate, not the rating.<\/p>\n<p><strong>How do I tell desync from a motor stall?<\/strong> A stall has no recovery; the motor stays stopped until throttle is removed or the controller cuts out. Desync is a brief loss of sync followed by a catch. A stall usually follows a mechanical jam, desync follows a current step.<\/p>\n<p><strong>What timing setting prevents desync?<\/strong> There is no universal value. Set timing at the low end of the motor&#8217;s range, prove stability at maximum sustained current, then advance in small steps only if torque is short. Record the value with the prop and pack it was tuned on.<\/p>\n<p><strong>How do I detect desync in a flight log?<\/strong> Look for phase current rising while RPM stays flat or falls, with no matching throttle change. With bidirectional telemetry, compare commanded throttle against measured eRPM per motor; the divergence is the event. Yaw or roll transients on the same timestamp confirm it.<\/p>\n<p><strong>Should I use PWM or DShot to avoid desync?<\/strong> DShot is the better default because a corrupted frame is discarded rather than acted on, and bidirectional DShot gives the RPM telemetry that makes desync visible. Protocol reduces the chance of a bad command; it does not correct a bad commutation estimate.<\/p>\n<hr \/>\n<p><strong>About the author<\/strong> \u2014 REACHSKY Engineering Team, Changsha, Hunan. We specify, test and support propulsion hardware for commercial UAV programmes, including commutation and thermal validation on our own benches. Airframe questions go to <a href=\"https:\/\/reachsky.co\/zh\/contact?intent=oem\" target=\"_blank\" rel=\"noopener\">\/contact\/?intent=oem<\/a>; the <a href=\"https:\/\/reachsky.co\/zh\/product-category\/%e7%94%b5%e6%9c%ba\" target=\"_blank\" rel=\"noopener\">motor category<\/a> lists the full range with thrust tables.<\/p>\n<p><em>All products are supplied for civil end use only.<\/em><\/p>\n<p><strong>\u6700\u540e\u66f4\u65b0\u65f6\u95f4\uff1a<\/strong> 2026-11-09<\/p>\n<hr \/>","protected":false},"excerpt":{"rendered":"<p>Why a motor loses commutation exactly when current climbs, the six causes in the order worth checking, and a bench routine that makes desync repeatable.<\/p>","protected":false},"author":6,"featured_media":8075,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[27],"tags":[1199,1201,1200,1202,1198],"class_list":["post-8074","post","type-post","status-publish","format-standard","has-post-thumbnail","category-motors","tag-bldc-commutation","tag-drone-motor-troubleshooting","tag-esc-timing","tag-high-current","tag-motor-desync"],"_links":{"self":[{"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/posts\/8074","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/comments?post=8074"}],"version-history":[{"count":2,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/posts\/8074\/revisions"}],"predecessor-version":[{"id":8090,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/posts\/8074\/revisions\/8090"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/media\/8075"}],"wp:attachment":[{"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/media?parent=8074"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/categories?post=8074"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/reachsky.co\/zh\/wp-json\/wp\/v2\/tags?post=8074"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}