Motor on the thumb-turn
A geared motor clamps over the existing cylinder body on the inside of the door and turns the thumb-turn (or a key left in the cylinder). The lock case, cylinder, faceplate, keys and door prep are all untouched.
Applies to these lock types
Euro profile cylinder in a mortise case (DIN) · UK oval cylinder (uPVC and composite doors) · Multipoint locking system (uPVC / composite)
Measurements this architecture needs
- Cylinder total length and halves (e.g. 35/35)
- Cylinder protrusion past the escutcheon
- Interior thumb-turn / turn-piece size and profile
- Door thickness
- Cam type and clock position
Adapter interfaces to design
- Clamp inner diameter range and clamping force that does not mark a brass cylinder
- Turn-piece adapters: knurled knob, lever knob, key-slot carrier
- Axial compliance so the drive train absorbs cylinder length tolerance
- Rotation range and hard-stop detection (current spike or encoder)
Design targets
Targets marked "from standard" come from the cited document. Targets marked "practice" are our engineering guidance and must be verified for your design.
| Target | Value | Basis |
|---|---|---|
| Output torque at the turn-piece | ≥ 1.2 N·m continuous, ≥ 2.5 N·m stall |
practice A156.36 caps key/turn torque at 1.2 N·m for a compliant new lock; existing worn or stiff locks need margin above that. |
| Rotation range | ±180° typical, 360°+ for multi-throw |
practice |
| Cylinder protrusion needed | 3–10 mm past the escutcheon |
practice |
| Back-drive resistance | Must not be back-drivable by hand from the outside knob |
practice |
Known blockers
- Cylinder without emergency function: a key left inside blocks the outside key. Specify a double-clutch (emergency/hazard) cylinder.
- Flush or recessed thumb-turn gives the clamp nothing to grip.
- Multi-throw and multipoint gearing needs several turns — check rotation range and battery budget.
- Cylinder total length over ~90 mm pushes the motor body far off the door face.
Design checklist
- Measure the cylinder halves and confirm the clamp fits the largest and smallest in the family.
- Confirm the cylinder is emergency-function before shipping the kit.
- Test on a lock at end of life: dirt, worn cams and cold weather all raise torque.
- Design a mechanical free-wheel or clutch so the manual key always works when the battery dies.
- Keep egress legal: the inside must still open by hand without a tool or a phone.