TILTFORGE
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Drivetrain

How the encoder knows where your slats are.

An absolute encoder needs a shaft end, and a blind's tilt rod does not give you one — it runs straight through the housing. A 12-tooth spur fused beside the worm wheel drives a 16-tooth crown gear onto a vertical axis, which creates that shaft end. The crown sits under the rod, beside the worm, teeth up at the spur — and the magnets lie in a recess on its top face, with a hole down through the middle so the AS5600 below can see them. Drag the rod: every rotating part carries the same reference mark, so the ratios are something you watch rather than something you take on trust.

Tilt rod

20T wheel + 12T spur · the bar is the slat plane

0°

NS

Crown gear

seen from above · magnets flat in the top recess

0°

12T spur Ø14.0on the rod, pitch dashedmagnets, flat in the recesson the crown's TOP faceAS5600 below, facing upboard goes in inverted 16T crown gear, teeth UPsame mark, at 0.75× the rodbrim flares out to the rimboss Ø13.0, at the board Looking down the tilt rod, drawn to scale. The spur and the crown carry the same reference mark, so 12 into 16is the thing you can see: the crown turns three quarters of a turn for the rod's one, and the mark goes hollowonce it has gone round the back. Crown drawn on axis; its own axis really sits 8.00 mm to one side.
N S 2 × 3 × 6 × 1.8 mm, FLATside by side, poles opposed6.00 mm across the pairprinted floor, ~1.03 mmwhat the blocks rest onØ6.25 hole through itthe field path down recess Ø12.38 × 2.00the bore inside the teeth1.05 mm + clearancemagnet face to sensor topU2 · AS5600, faces upbody nests in Ø7.06 × 1.77 Rev D — the AS5600 is on the bottom copper, and the board goes in inverted, so it faces up U2 sits 0.295 mm off the board centreline; register the shelf bore on U2, not on board centre Detail — 4.3× the view above, cut material hatched
Rod
0°
Crown
0°
Encoder
768 / 1536
Motor
2.50 rev
Per count
0.117° at the rod
Wrap headroom
2.67×
tiltforge-5110.local

TiltForge

Direct LAN control

▲ closedopenclosed ▼

Position 50% · open

encoder 768 / 1536 counts

State IDLE · Calibrated yes

Or drag either dial. A full sweep runs 5.0 s, the real tilt time.

A simulation of the page the firmware serves, driven by the gear ratio — not a live device.

Why these numbers

  • 12 into 16 is a 0.75 step-down. A full 180° tilt turns the crown 135°, which is 1,536 of the encoder's 4,096 counts. That leaves 2.67× headroom before the absolute reading wraps, so no count in the travel is ambiguous.
  • 0.117° per count at the rod. Finer than a blind needs — backlash and clutch hysteresis will limit you long before the encoder does.
  • The magnet is two magnets. Not the Ø6 × 2.5 mm diametric disc every vendor sells as “the AS5600 magnet”. Two standard 3 × 6 × 1.8 mm blocks lie flat side by side, poles opposed, in the Ø12.38 × 2.00 mm recess inside the crown's tooth ring — 6 × 6 mm in plan. That runs the field across the bore the way a diametric disc does, out of parts any supplier stocks. An axial disc of the same size gives a reading that looks alive and means nothing.
  • The printed part sets the air gap. The magnets rest on a thin printed floor 2.80 mm above the crown's bottom face, and that bottom face carries a Ø7.06 × 1.77 mm pocket — a SOIC-8 body is 4.90 × 3.90 × 1.75, so the sensor nests up inside the crown. The gap is 1.05 mm plus the crown's running clearance over the board, which lands mid-window on the 1.0–2.5 mm the sensor wants without anyone holding a shelf height to a tenth. The firmware prints the AGC on boot; mid-scale means the gap is right, and that beats any calculation.
  • The board goes in inverted. The AS5600 is on the board's bottom copper, which is a fab fact, not an assembly one: installed, that face points up, through the crown's Ø6.25 bore, at the magnets above it.
  • The recess does not locate the magnets. Ø12.38 around a 6 × 6 mm stack leaves about 3 mm of slack in every direction, against an AS5600 misalignment budget of ±0.25 mm. Wherever the pair gets glued is where the encoder's zero lives, so that one assembly step, not the print, is what the accuracy now rests on.
  • The worm is why it holds. A 2-start module-0.8 worm, Ø30.584 at the tip, sits under the 20-tooth wheel on 22.48 mm centres: 10:1 with a 3.21° lead angle — self-locking, so the blind stays where you left it with the power off. Five motor turns cover the whole tilt, in 5.0 seconds. It is not in the drawing because you cannot see it looking down the rod, which is the view the drawing takes.

The part that decides the accuracy

The crown gear is the most important printed part in the set, because its tooth quality is the angle noise floor. Print tolerance, the printed journal, the PCB stack-up and the footprint RSS to 0.274 mm of misalignment against the ±0.25 mm AMS allows — about ±1.5° at the rod. Invisible on a window blind, and measured rather than hoped for.

The long version, including the trap where the sensor die sits 0.295 mm off the board's centreline, and how the magnets turned out to sit, is in Where the Magnet Goes. The board itself is at Rev D.