Definition
A direct-current motor that has two field windings on each pole: a shunt winding connected in parallel with the armature, and a series winding connected in series with the armature. In a differentially compounded motor, these two windings are wired so their magnetic fields oppose each other. As load on the motor increases, the series field grows stronger and partially cancels the shunt field, which weakens the total magnetic field and causes the motor to speed up rather than slow down. This produces a motor whose speed remains relatively constant — or even rises slightly — as mechanical load increases.
Plain English
A type of DC motor with two separate sets of field coils wired so they push against each other. The result is a motor that does not slow down much when you put a heavier load on it, and may even run a bit faster.
Context Anchor
Seen in aircraft electrical-system study, especially when comparing types of direct-current motors and how they behave under load.
Derivation
‘Compounded’ here means combined — the motor combines two kinds of field windings (shunt and series) into one machine. ‘Differentially’ comes from the Latin differre, meaning to carry apart or set against. So a differentially compounded motor is one in which the two combined windings are set against each other, with their magnetic fields opposing rather than reinforcing.
Why Pilots Care
Different motor types behave differently under load. A differentially compounded motor holds its speed steady as load changes, which matters when designers select motors for jobs that need consistent rotational speed regardless of how hard the motor is working. Knowing the type helps you understand expected behaviour during troubleshooting.
Analogy
Think of two people pushing on the same cart from opposite sides. The harder one person pushes, the more that push cancels the other person’s effort. In this motor, the opposing “pushes” are magnetic fields.
Grounding Statement
As the motor is loaded more heavily, the opposing field winding becomes stronger and weakens the motor’s overall magnetic field.
Intuition Check
Do not read “differentially” as just “different.” Here it means the magnetic fields oppose each other and subtract from the total field strength.
Example Sentence 1
The technician identified the unit as a differentially compounded electric motor based on how its two field windings were connected at the terminal block.
Example Sentence 2
The actuator motor in the landing gear system is a differentially compounded electric motor chosen for its predictable torque response.