# How a Single Coil Powers Multiple Motor Armatures Simultaneously

> A 1973 design for an electric motor that uses a single central coil to power several separate armatures arranged in a circle.

- **Patent:** US 3723796
- **Original title:** Multi-armature motor
- **Owner:** Individual
- **Granted:** 1973
- **Status:** Public domain (expired)
- **Times cited:** 22
- **Field:** mechanical, energy

## What it does

This patent describes a motor assembly where multiple armatures are placed in a circular pattern between two disks. These disks have interlocking finger-like projections that act as magnetic poles. A single central electromagnetic coil sits between the disks, creating a magnetic field that flows through these fingers to drive all the armatures at once. Essentially, it allows one power source to run multiple rotating parts simultaneously within a compact, integrated housing.

## What it does NOT cover

- Does not cover motors using permanent magnets instead of an electromagnetic coil.
- Does not cover linear motors where the armatures move in a straight line.
- Does not cover single-armature motors.
- Does not cover motors where the armatures are not arranged in a circular, parallel array.

## The clever bit

The use of interdigitated finger portions creates a shared magnetic flux path, allowing one coil to effectively energize multiple independent armatures without needing individual coils for each one.

## Real-world examples

1. Early multi-spindle industrial drills
2. Compact automated assembly line actuators

## Why it matters

This design represents an early attempt at high-density motor packaging. By sharing a single magnetic field source across multiple armatures, it aimed to reduce the weight and complexity of multi-motor systems, which is a common challenge in robotics and automated machinery.

## Frequently asked questions

### What does How a Single Coil Powers Multiple Motor Armatures Simultaneously cover?

A 1973 design for an electric motor that uses a single central coil to power several separate armatures arranged in a circle.

### Who owns patent US 3723796?

Individual owns this patent, granted in 1973.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 3723796 cited by?

This patent has been cited by 22 later patents that build on its ideas.

### What problem does this patent solve?

This design represents an early attempt at high-density motor packaging. By sharing a single magnetic field source across multiple armatures, it aimed to reduce the weight and complexity of multi-motor systems, which is a common challenge in robotics and automated machinery.

### What does this patent NOT cover?

Does not cover motors using permanent magnets instead of an electromagnetic coil.

**Full plain-English explainer:** https://patentbrief.org/patent/us/3723796/mri-cancer-tissue-detection

**Original patent:** https://patents.google.com/patent/US3723796

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


## Related patents

Semantically similar inventions in the PatentBrief corpus:

- [How to Make Electric Motors Run Smoother and Last Longer](https://patentbrief.org/patent/us/RE48399/action-camera-waterproof-housing) — A design for electric motor armatures that uses a specific ratio of winding slots to commutator bars to reduce electrical sparking and improve motor efficiency.
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- [How Nikola Tesla Invented the Modern AC Electric Motor](https://patentbrief.org/patent/us/382280/tesla-ac-motor) — Nikola Tesla's 1888 patent for an induction motor that uses rotating magnetic fields to convert electricity into mechanical motion without needing physical brushes.
- [How Early Hard Disk Drives Accessed Data Quickly](https://patentbrief.org/patent/us/3503060/hard-disk-drive) — A 1970 patent detailing a mechanical system for moving read-write heads across magnetic disks to retrieve stored information rapidly.
- [How Nuclear Power Plants Reuse Fuel Between Multiple Reactors](https://patentbrief.org/patent/us/10818403/inter-module-fuel-shuffling) — This patent describes a method for nuclear power plants with several reactors to efficiently reuse partially used fuel by moving it between different reactor cores across multiple operating cycles.