Custom Rotary Solenoids

A rotary solenoid uses the same principle as a linear one, a coil that magnetizes a steel frame and attracts an armature, but turns that pull into rotation. In the most common construction, the armature rides on balls in inclined races: as the coil pulls the armature toward the pole, the balls roll along the races and the armature rotates, with a small axial movement as well. Other designs use a shaped rotor and stator, or a permanent-magnet rotor, to produce rotation with no axial movement at all.

Rotation ends at a defined stop, so the output angle is set by the design rather than by a controller. That makes a rotary solenoid a simple, fast, and robust way to move something between two positions.

A rotary solenoid moves between end positions; it does not stop at arbitrary angles or rotate continuously. When the job is to flip, turn, or index between two defined positions, it is usually smaller, faster, simpler, and less expensive than a motor with a gearbox and feedback: no encoder, no motion controller, and no gear backlash. When the job needs intermediate positions or continuous rotation, a motor-driven actuator is the better choice.

Most rotary solenoids are monostable: they rotate while energized, and a return spring brings them back when power is removed, a fail-safe default. Bistable rotary solenoids use permanent magnets to hold each end position with no power and switch on a short pulse, which suits battery-powered devices and mechanisms that hold a position for long periods. Bidirectional designs drive the rotor in both directions, by reversing the current or energizing a second coil.

Rotary solenoids typically fall within these ranges. Torque depends on the rotation angle and on the duty cycle, so the extremes do not occur together. Every design we build is custom to your specification across this range.

• Torque: under 0.01 N·m to about 5 N·m.
• Rotation: about 1° to 110°.
• Supply: typically DC.

These are the details that decide whether a rotary solenoid performs in the product, and the ones we design and test for:

• Torque across the full angle. Torque varies through the rotation, so we size the design against your load at every point, including the friction and inertia it must overcome at the start.
• Angle and end stops. The rotation angle is set in the design, and the end stops are engineered to absorb the impact energy over the required cycle life.
• Speed and settling. Fast rotation ends in a hard stop; where bounce or noise matters, we tune the drive and damping so the output settles cleanly.
• Axial movement. Ball-race designs move axially as they turn; where the mechanism cannot accept that, we use a construction with pure rotation.
• Duty cycle and heat. A spring-return rotary solenoid needs current to stay rotated, so holding time is limited by coil heat. Peak-and-hold drive or a latching design removes that limit.

Because Cerebrus develops embedded systems in-house, we design the drive alongside the actuator: peak-and-hold or PWM current control for long holds, polarity switching for latching and bidirectional designs, controlled drive to soften end-of-travel impact, and position feedback where the product needs it.

Development starts from your torque, angle, response, duty-cycle, envelope, and power requirements. We model the magnetic circuit, then build prototypes in our own shop and characterize them on the bench: torque versus angle, response time, temperature rise, and holding behavior. Prototypes are built in-house in two weeks, and once the design is approved we manufacture production units ourselves under our ISO 9001:2015 quality system.