Servo center calibration sounds trivial until your AGV pulls slightly left at full speed. The integrator swore the trim was set correctly. But he had calibrated the servo on the bench, unloaded, and never rechecked it after bolting the linkage on. A 2 µs offset at the servo tester translated to a 3-degree steering bias under load.
Here are three methods that actually work when the machine is already assembled.
Why Bench Calibration Lies
A servo tester sends a 1500 µs pulse, the servo centers, and you bolt on the horn. But every linkage adds asymmetric load. The horn pulls slightly harder in one direction, the gear train deflects, and the true mechanical center shifts by a degree or more. You have to calibrate under load, not in free air.
Three Practical Methods for Servo Center Calibration
The fastest approach uses a programmable servo tester with a rotary knob. Send 1500 µs, install the horn, then manually sweep ±50 µs while watching the load. Find the position where the linkage sits at true mechanical midpoint. Mark that pulse width and set it in the controller firmware.
For multi-servo systems — a pan-tilt head with two axes, or a quadruped with eight joints — skip the manual method. Use a USB servo controller and script a calibration sequence. Sweep each channel independently, log the center offset for every axis, and write the offsets into the motion controller. This takes ten minutes instead of two hours.
The mechanical backup method works when you have no electronics at all. Power the servo, let it center on the default signal, and loosen the horn screw. Rotate the linkage to true center by hand, then re-tighten. It is crude, but it works on a downed machine when the only tool within reach is a hex key. Every field technician should know this one.1