Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!noc.near.net!howland.reston.ans.net!usc!elroy.jpl.nasa.gov!decwrl!netcomsv!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Picking an RC car motor for 6.270 'bot.
Message-ID: <nagleCCuG4C.1sp@netcom.com>
Keywords: motor 6.270
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <181@ultrix.uhasun.hartford.edu>
Date: Sat, 4 Sep 1993 19:14:36 GMT
Lines: 37

jcook@uhasun.hartford.edu (== John David Cook ==) writes:
>Can someone offer some advice on picking a pair of drive motors for
>a 6.270 'bot?  I just got Tower Hobbies catalog and its got some large
>lists of motors for electric RC cars.  These are typically high speed
>and high torque DC motors, but also high current.
>I'm not up on RC racing terms like "wet magnets" and "breaking in motor"
>so I'm confused about what I'm looking for.  I'd like a high torque motor
>that doesnt draw _too_ much current that doesnt require tweaking or 
>adjustments.

      The R/C car racing crowd uses motors that are running near the limits
of performance.  They also have a dollar limit on motors in some racing
classes.  Racing motors thus require "tweaking".  This usually takes the
form of advancing the brushes to the maximum torque point for forward
rotation.  Full-power MTBF can be measured in minutes.  

      "Breaking in" refers to running the motor enough to get the brushes
to wear to fit the commutator.   Replacing and fooling with brushes is
part of dealing with these motors when used for racing.

      They're definitely high-current devices.  Those things often have,
say, only 15 turns in the motor armature.  They're also high-RPM devices.
But you can run them at low RPMs if you have a good speed control, a 
shaft encoder, and a suitable control loop.  If you're running them at
25% of rating, they should be reasonably trouble-free.

      One option is to look at motors designed for model "monster trucks".
These tend to be more rugged and less tweaky.  A mid-priced monster truck
motor is probably a good choice for a robot.

      AstroFlite has a line of motors designed for model helicopters.
Cobalt-neodymium magnets, ball-bearings, shipped broken in.  Expensive,
though.  Probably the best choice if you want this speed/torque range
and intend to use the machine for a while.  

					John Nagle
      
