Motor timing

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In order to get best performance out of a motor, the delivery of power must be correctly synchonized with the rotation of the motor. This is known as Motor timing or ignition timing.

Conceptually, motor timing is very similar for both internal combustion engines and electric motors:

  • In an internal combustion engine, as the piston compresses the air/ fuel charge, it is essential that the mixture does not fully combust until the the piston has begun its journey back down the cylinder; that is, the piston must be past "Top Dead Center" (TDC). Combustion before this will serve to oppose the piston's movement.
  • Similarly in an electric motor, as the commutator (in a brushed motor) or ESC (in a brushless motor) energizes the next set of windings, the motor must have advanced sufficiently that the generated magnetic field will be pulling towards or pushing away from the correct permanent magnet; similarly, leave the winding energised too long, and the rotor will be braked as the armature is attracted towards the magnet it has just passed.

Nitro engines adjust their timing automatically to a large degree. As the motor runs faster, the glow plug tends to become hotter, and so ignition is advanced. Timing can be controlled to some degree by choosing a hotter or colder glow plug, or changing the compression ratio by shimming the cylinder head.

Gasser engines have their ignition spark generated either electronically or by a magneto. Magneto timing is usually not dynamically adjusted, so the timing is a compromise between good running (advanced/ early ignition) or easy starting (retarded/ late ignition).

Electric brushed motors can have their timing altered by rotating the commutator brushes by moving the end bell of the motor. Small changes can have dramatic effects.

Electric brushless motors have their timing altered by programming the electronic speed controller. Some advanced ESCs use an "electronic freewheeling circuit" to automatically adjust the timing.

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