1 / 11

Motor Dynamics

This lab focuses on the principles of pulse width modulation (PWM) and its application in controlling DC motors. It covers topics such as duty cycle, maximum current estimation, incompatible motors, motor characteristics, and motor performance plots.

helentaylor
Download Presentation

Motor Dynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Motor Dynamics Lab 2 Spring Quarter

  2. Pulse Width Modulation • Pulse Width Modulation (or “PWM”) is the manner by which most of today’s DC motors are controlled • Rather than varying the voltage supplied to the motor to control the speed (or power level), the voltage to the motor is simply switched on and off at a very high rate • This rate is expressed as the “Duty Cycle” or the ratio of “on-time” versus “off-time” • Example: a motor with a 50% Duty Cycle is only on half of the time, and therefore only runs with 50% of the power Spring Quarter

  3. The Handyboard • Designed for motors operating at: • 9.6 V • 1 A (maximum current) Spring Quarter

  4. When does Max Current Occur ? • A motor will typically draw the maximum amount of current when it is stalled (i.e. not turning or stopped) • This current is known as the “stall current” • A large spike in current (approaching the level of the stall current) will also occur whenever a motor is started Spring Quarter

  5. How to Estimate Max Current • Measure the motor’s internal resistance using a multi-meter • Set the multi-meter to its most sensitive scale (typically 0 to 200 Ω) • Apply the probes to the motor terminals and gently rotate the motor shaft by hand until the smallest possible reading is obtained Spring Quarter

  6. How to Estimate Max Current • Apply Ohm’s Law ( V=IR ) to find the current draw based on a voltage of 9.6V • A reading of 9Ω would mean a 1A draw (the maximum the Handyboard can deliver) Spring Quarter

  7. Incompatible Motors • Typically the Handyboard will not run properly with: • 3V-4.5V toy car motors • They are too electrically noisy and may draw several amps of current • High end radio controlled car motors • They draw large amounts of power and require 25, 50 or more starting amps • Drawing too much current from the Handyboard will lead to a board reset or possibly a lot worse Spring Quarter

  8. Motor Characteristics • The output properties of primary interest for a DC motor are shaft torque and speed • Typically these quantities are represented as a plot of Torque vs. Speed • The type of DC motors commonly used in this lab will exhibit an operating characteristic known as “negative speed regulation” – which just means that the motor’s speed decreases as the load connected to its shaft increases Spring Quarter

  9. Motor Performance Plots • The maximum speed with no load attached is called the “no-load” speed (nr) • The load that stalls the motor is called the “stall torque” (also the starting torque) Spring Quarter

  10. Lab Guidelines • BE SURE TO PRINT OFF EXTRA COPIES (one per team) OF YOUR TABLE AND TORQUE vs. SPEED GRAPH • Lab Report Guidelines: • Due one week after lab • Individual lab reports • Five pages maximum (including cover page, sketches, attachments) • See Lab Write-Up for more specific instructions Spring Quarter

  11. Questions ? Spring Quarter

More Related