So, on the theme of the old “Got Milk?” ad campaign, and at the risk of sounding absurd, Got Brushes? No? That’s okay. But don’t be surprised if a lot of the toys you have around you do!
From my narrow slice of the world in industrial motion control, we have long since abandoned the brush motor, or brush servo, to the boneyard of antiquity. Like the single phase SCR drive, or dare I say the old GE vacuum tube (yes you read that right) motor drive of yesteryear, gone and almost completely forgotten.
But as I meander into other markets for motor technology, to my utter surprise, this stalwart technology is still alive and kicking. When it comes to price and performance it’s hard to beat. Single phase means lower cost of electronics. Variable speed is intrinsic, no special measures needed, unlike AC. And when the drive quits, you can hook it up to a battery and it will still run.
From its humble inception with Michael Faraday in 1831 the homopolar motor was just a curiosity and demonstrated the unique qualities of electromagnetism. Some more developed versions had the ability to do meaningful work in the 1850’s, but without a power source it was impractical to apply to commercial use, much as the electric car is today without a suitable battery technology. Then came the spark (pun intended) that caused the revolution in lighting, a DC brush motor driven by a steam source could generate electricity. And suddenly the light age, and the motor age together are born.
The starter motor that replaced the hand crank of the old Model T engine? A brush motor. As is every starter on every combustion engine. Check around the house and you’ll probably find that your vacuum cleaner is a brush motor, because a small series wound brush motor will run on AC power at very high speeds. Power screwdriver? Brush motor again. Kid’s toys? brush motors.
In fact I recently found out that many of the air operated actuators in cars are being replaced by electric motors because people are keeping their cars longer and the electric actuators last 10 times longer than the air ones. Power windows? Power seats? All brush motors.
And after 30 to 40 years of development of the brushless DC technology, we are just now seeing control pricing drop, magnet pricing drop, to the point where brush motors and brushless motors are reaching serious competitive levels. A truly amazing accomplishment. The beauty of the brushless motor is that its life expectancy is that of the bearings themselves, and if the lessons of the hard disk drive industry can be applied, even the bearings can be replace by fluidized bearings to make things even more reliable and more cost effective.
In the age of increasing energy costs, the efficiency of some of the newer designs is reaching levels that were unimaginable 10 years ago (check out the Novatorque article in Design World July 2008). And it is my sense that further innovation is around the corner. There a lot of brilliant engineers working on extending the performance of this relatively recent technology. I can’t wait to see what the next couple of years will bring.