dc motormotor
In trying to understand brushed DC motors, this post has been very helpful but I still have some fundamental questions about the brush mechanism. For instance, what is the purpose of the spring?
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And since a brush looks mostly like a spring, how did the name "brush" even come about?
It's because of the amount of current you need to drive the motor, the arduino can't supply much.
It's not unusual to find that under near-full-power-out conditions the motor will be about 50% efficient. This is a big motor but it still applies: -
Next, you estimate how much mechanical power you need (2 pi n T) where n is revs per second and T is torque in newton.metres. If your dc motor's data sheet doesn't provide this information (like the graph above) then get one that does.
If you don't know how to calculate your mechanical power requirements you need to learn and start with: -
Force = mass x acceleration courtesy of Isaac Newton
Mass is what you want to move and acceleration is final speed divided by time to get to that final speed (i.e. what you want it to do).
Force x distance = work done and work done per second = power.
Don't forget friction as a loss and if it moves fast then there will be other losses due to moving air around.
Best Answer
The purpose of the brushes is to make electrical contact with a rotating conductor (the commutator). Originally, these were bundles of wire that would be dragged across the commutator. At any time, at least a few strands of the wire would be making contact. These bundles, of course, look like "brushes".
Things have improved though, and now we use solid, low-friction, conductive materials for the brushes. It is common to use assorted types of graphite. These brushes must be held against the rotating commutator, and the material eventually wears away and must be replaced. The spring pushes the brush against the commutator, providing good electrical contact as the material slowly wears away.
Here's a representative picture dredged from Google. The dark material is the actual "brush", made of conductive graphite.
Please note that, unlike the brushes in your link, these don't have a wire connecting to the graphite. This is because the springs themselves are conductive! An additional wire can be used in higher-current applications.