Neobotics Foundation Inc.
Motor jitterNEORACER DOCS
NEORACER DOCS
These docs are public and open source.Edit on GitHub
TROUBLESHOOTING / MOTOR

MOTOR JITTER.

Three causes account for nearly all motor jitter, and working through them in order tends to be the fastest path. A fresh motor trim catches the first two, and a careful look at the rear wiring catches the third.

~0 minutesCommon after a crashFixed in software 80 % of the time
// YOU SEE
At rest, the motor hums or briefly pulses. Under control loops, the car oscillates left-right or chugs forward-back instead of holding a smooth speed.
// WHAT SHOULD HAPPEN
A trimmed motor is silent at zero command and tracks smooth speed curves cleanly. Control loops should converge without visible shake.
01 / FIRST, POWER AND SURFACE

POWER AND SURFACE.

Jitter at rest is almost always power or mechanics, not software. The motor neutral is fixed in the driver at the 's 1500 microsecond center, so there is nothing to re-trim. A low or sagging pack, a warm motor, or an uneven surface are the usual causes, and a charged pack on flat hardwood clears most of them. Confirm a zero command really is silent:

python
import racecar_core

rc = racecar_core.create_racecar()

def start():
    rc.drive.stop()

def update():
    rc.drive.set_speed_angle(0, 0)   # should be dead silent at rest

rc.set_start_update(start, update)
rc.go()

If it still shakes at exactly zero on a charged pack and a flat floor, the cause is the ESC neutral or mechanical drag, covered on the motor trim and drivetrain pages. Read on.

02 / IF TRIM DIDN'T FIX IT

PROBABLE CAUSES.

01

Control gain too high

The script is fighting the car.
A car that overshoots and corrects on every tick reads as motor jitter, even though the motor itself is fine. If a wall-follow or script is oscillating, halving your proportional gain is a good first move.
Kp /= 2 # try this first
02

Pinched motor wire

A rough crash can shift the rear loom.
Any insulation damage, or a wire touching the metal frame, causes jitter under load. The three motor wires leave the ESC under the chassis, so lifting it for a look is easiest with the pack disconnected first.
visual check · no crimp damage
03

Worn pinion gear

Gear teeth missed at top end.
A high-mileage car can develop a flat spot on the small pinion gear. Symptoms: a regular click every full motor rev, jitter only at high speed. A new pinion is a five- minute replacement.
click freq ∝ motor rpm