Episode 130 — DC Motors

In this episode of The Engineering Commons, we discuss an electromechanical component commonly used to achieve physical motion; the ubiquitous direct-current (DC) motor.

  • Carmen admits to getting turned on by electricity… and sugar!
  • Although differences between engines and motors can be argued, at least one definition claims that an engine converts chemical energy to mechanical energy, while a motor converts electrical energy to mechanical energy.
  • DC motors are powered with direct current, while AC motors are powered with an alternating current.
  • Carmen mentions an app note (pdf) on Brushless DC motors by MPS (Monolithic Power Systems).
  • Although linear motors will not be covered in this episode, their operation is similar to that of rotational motors.
  • The two major categories for DC motors are brushed and brushless; the two major categories for AC motors are synchronous and induction (asynchronous).
  • When describing a motor’s mechanical components, the portion that rotates is the rotor, while the portion that remains stationary is the stator.
  • Brian notes that Nikola Tesla’s induction motor may be his most significant invention.
  • In induction motors, slip is percentage difference between the rotational speed of the magnetic field and that of the rotating shaft.
  • A homopolar motor was developed by Michael Faraday in 1821.
  • Joseph Henry created an electo-magnetic “rocker” in 1831.
  • In 1832, William Sturgeon produced the first practical DC motor.
  • An H-bridge is an electronic circuit that allows a DC motor to run forwards or backwards.
  • In many cases, a pulse-width modulation (PWM) signal can be used to control motor speed. This is accomplished by turning motor power on and off at a high frequency, while maintaining a desired ratio of “on” time to “off” time.
  • When describing a motor’s electrical components, the portion that carries the current is called the armature, while the portion that generates the magnetic flux is called the field.
  • An electrical charge passing through a magnetic field is subject to a mechanical force, known as a Lorentz force. A conductor (wire) carrying current through a magnetic field can thus be levitated by this force.
  • DC motor behavior is described by several motor constants, including the torque constant and the back-EMF constant.
  • A commutator periodically reverse the flow of current through an external circuit. In a brushed DC motor, this is accomplished mechanically.
  • Brushes deliver voltage to the commutator, and are often spring loaded against the commutator segments.
  • In mechanical systems, rotational power is the product of torque and angular velocity.
  • Brushless DC motors often use Hall effect sensors to detect when power should be switched to a different armature winding.
  • A stepper motor advances by a fixed rotational angle each time it receives an input pulse.
  • Enterprising engineers can play music with stepper motors!

Thanks to Les Chatfield for use of the photo titled “At speed!” Opening music by John Trimble, and concluding theme by Paul Stevenson.

Episode 129 — Noticing

We are joined once more by Dave Goldberg, author of A Whole New Engineer, to discuss the critical engineering skills of noticing, listening, and questioning.

Thanks to Flavio~ for use of the photo titled “Before it Started Barking.” Notice any similarity between the dog’s nose and the ironwork? Opening music by John Trimble, and concluding theme by Paul Stevenson.

Episode 128 — Industrial Academic

Dr. Dave Vandenbout offers up his insights on choosing between academic and industrial careers in this episode of The Engineering Commons.

  • Carmen wastes no time in revealing his secret method for stress-testing CMOS chips.
  • X-ray systems can be useful in locating bad solder joints hidden underneath a ball grid array (BGA) integrated circuit.
  • Our guest is Dave Vandenbout, an electrical engineer who founded XESS Corporation twenty-three years ago. Dave also has experience as an engineering professor and industrial researcher.
  • In Episode 103, Ones and Zeros, Dave explained the various types of programmable logic devices available to electronic designers.
  • Our guest notes that, in his experience, industrial organizations tend to be hierarchical and well-funded, while academic organizations tend to be relatively flat and less well-funded.
  • In academic circles, an overhead rate is the percentage of research funding that goes directly to the university to pay for supporting services that are not directly related to the research effort.
  • Jeff notes similarities in the experiences encountered by entrepreneurs and newly-employed professors.
  • Carmen notes a blog and podcast by Jon Ellis (a.k.a. Prof. Gears) that discusses the ups and downs of life as a tenure-track academic.
  • Two of the larger funding agencies in the United States are the National Science Foundation (NSF) and the Defense Advanced Project Research Agency (DARPA).
  • On average, Dave found a student’s grade point average (GPA) to be a poor predictor of research performance.
  • Although once rare in the engineering field, more and more engineering PhDs are taking jobs as postdoctoral researchers (post-docs) in preparation for academic careers.
  • In the United States, most tenure-track academics start their careers as Assistant Professors.
  • Tenure is a contractual right, granted by an academic organization, that provides legal protection against dismissal without just cause.
  • After six years, assistant professors not granted tenure are asked to leave the university (normally after a one year appointment). Those receiving tenure are often promoted to the position of Associate Professor.
  • Full Professor (or just Professor) is the top academic rank at most universities.
  • An h-index is a numerical ranking that attempts to measure an academic’s influence and contribution within a research field.
  • Dave comments that every graduate student wants to be a professor, and every professor wants to be a graduate student.
  • A recent Science Magazine article notes that only two of five influential cancer studies could be replicated.
  • Donald Knuth is a professor emeritus at Stanford University, and the author of a multi-volume text on algorithms, The Art of Computer Programming. He also developed the TeX language for typesetting mathematics.
  • Dave is excited by clustered regularly interspaced short palindromic repeats (CRISPR) techniques that allow for precise genome editing.
  • Our guest can be reached on Twitter as @dvbeisme.

Thanks to U.S. Army RDECOM for use of the photo titled “Army scientist bolsters nanomaterials research with Singapore.” Opening music by John Trimble, and concluding theme by Paul Stevenson.

Practical insights for the engineering crowd