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CNC SPINDLE :
Brushless Motors

Bigger stationary machines that use belts to transfer power to rotating tooling like saw blades and shaper bits are brushless. They are also called induction or AC motors. They do NOT use brushes at all, so don’t look for the holes to replace them.

These motor must be electronically commutated instead of mechanically commutated like brushed or universal motors. The actual motors themselves are not really any more expensive to produce but the circuitry to control them is more complicated and expensive. This is even more so when variable speed is required as complicated and expensive variable frequency drives (VFD’s) are required to achieve this.

Having said that, I’ll also suggest that with CNC applications becoming more prevalent and the need for variable speed control, the price off all the circuitry including VFD is falling drastically compared to 10 year ago. (That’s a comment from my electrician that is even seeing this technology in municipal pumping stations etc., that’s how big this is becoming)

Advantages of Brushless Motors:

• Motors are more efficient because there are no brushes to create friction
• No brushes also means that maintenance is greatly reduced and life is increased…
• Torque burst (of short duration) of 2 or more times the normal operating/design torque are possible with this type of motor without causing damage to the motor… as would be the case when hitting a knot or cutting cross grain for short periods of time without the need to slow down the feed rate….
  
  In comparison, torque bursts are NOT possible with a permanent magnet UNIVERSAL motor. Attempting to get more than the designed torque from the motor by pumping excess current into the motor could lead to permanent damage.. 
  
  
• Brushless motors can achieve even higher rpm's than traditional universal motors because speed is not limited by heat build-up and friction between brushes and communtator.

Disadvantages:

• Cost: Require electronic control so although motor is not that much difference in price the extras are.
• More complex to wire.

For a complete table of comparison between the basic woodworking router style of universal motor and its more sophisticated brushless cousin, click on the next page in this series

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