Servo - January 2011

Featured This Month:

Features

22 PARTS IS PARTS: Identifying Unknown Brushed DC Motors by Kevin M. Berry

23 Affordable 2. 4 GHz by Pete Smith

27 The Safe Use of Lithium Polymer or Lithium-Ion Batteries in a Combat Robot by Steven Kirk Nelson

30 RioBotz Combot Tutorial Summarized – DC Motors Summarized by Kevin M. Berry

35 Hello Bradley – Why Gambling Doesn’t Pay by Bradley Hanstack

36 Melty Brains Cartoon by Sean Canfield and Kevin Berry

Events

35 Oct 18th – Nov 10th 2010

Results and Jan/Feb 2011

Upcoming Events

PARTS IS PARTS

Identifying Unknown Brushed DC Motors

● by Kevin M. Berry

This month’s column is blatantly stolen (Editor’s note: “researched,” not stolen!) from Professor Marco Antonio Meggiolaro’s popular book, the RioBotz Combot Tutorial. Marco’s book is available free for download at www.riobotz. com.br/en/tutorial.html.

If you bought your motor from a junkyard or found it forgotten somewhere in your laboratory and you don’t have any clue about its characteristics, you can follow these steps:

• Seek any identification on the motor, and look for its datasheet over the Internet.

• Make sure it is a DC motor. If there are only two wires connecting it, there is a good chance it is DC. Otherwise, it could be an AC, brushless, or step motor.

• Measure the electrical resistance between the terminals, obtaining Rmotor.

• Apply increasingly higher voltages, such as 6V, 9V, 12V,

18V, and 24V.

Wait for a few minutes at each level while checking if the motor warms up significantly. If it gets very hot even without loads, you’re probably over the nominal voltage, so reduce its value.

• Most high quality motors can work without problems during a three minute match with twice their nominal voltage; this is a technique used in combat (such as the 48V Etek powered at 96V). The 24V Magmotors are exceptions. They are already optimized for this voltage, tolerating at most 36V. Even so, the current should be limited in this case.