# How-To: Motors

## Step 2: DC Motors

DC motors are in many ways the simplest electric motors. Most DC "brushed" motors operate in the same way. There is a stator and a rotor. The magnets on the stator and a coil on the rotor which is magnetically charged by supplying current to it. The presence of brushes (static, permanent mechanisms) within the motor, which propel the electromagnetic rotor forward.

Utilizing a DC power source, very few controls are needed. Speed of the motor can be controlled by the amount of current reaching the coils from the battery to the commutator.

If you reverse the leads, or wires, coming off of the motor - the motor will spin the opposite direction as it was previously.
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skrubol2 years ago
The brushes are just part of the commutator. They're the switch that keeps the coil at the right polarity to keep spinning. They don't propel anything.

Also I agree with Clemtasm. A constant voltage across an 'ideal' motor will give constant speed with varying load. In real motors the speed drops with higher load due mostly to the resistance of the windings.
2 years ago
When the load on the motor increases the current consumed by the armature will also increase hence the flux will increase. Speed in inversely proportional to flux. So the speed of the motor has to decrease with increase in load over a constant load. Even in case of an ideal DC motor. Please let me know if I am wrong.
2 years ago
It's been a long time since I've dealt with theoretical emag, so I'm not sure. In an ideal motor model with zero ohm windings (I think even in an ideal motor, sometimes you will account for winding resistance, depends who considers it ideal..) speed is strictly proportional to voltage and torque is strictly proportional to current.
In a simple motor model (where you do take winding resistance into account, but do not take reactivity or friction into account,) it's pretty easy to deal with the winding resistance. Speed will just be (Vin - Tout/Ka*r)*Kv. Or if you know V and I, just (Vin - I*r)*Kv.
Clemtasm2 years ago
I believe you mean speed of the motor can be controlled by controlling the amount of voltage across the motor?

My understanding is- A DC motor fed a constant voltage will have a fairly constant speed over a range of loads. A motor fed constant current will produce fairly constant torque over a range of speeds