Newsgroups: comp.robotics
Path: cantaloupe.srv.cs.cmu.edu!rochester!udel!gatech!newsjunkie.ans.net!butch!enterprise!news
From: mdenney@hercii.lasc.lockheed.com (MAD)
Subject: Re: Motor selection for micromouse?
Message-ID: <mdenney-120595122653@h2mac102.lasc.lockheed.com>
Followup-To: comp.robotics
Sender: news@enterprise.rdd.lmsc.lockheed.com (News Administrator)
Organization: LASC
References: <D8E9vt.96z@ucc.su.OZ.AU> <3otq1b$b24@handler.Eng.Sun.COM>
Date: Fri, 12 May 95 16:34:15 GMT
Lines: 42

In article <3otq1b$b24@handler.Eng.Sun.COM>, cmcmanis@Sun.COM (Chuck
McManis) wrote:

> Mark Hedley (hedley@ee.su.oz.au) wrote:
> : I am building a micromouse (small mobile robot for finding way through maze),
> : and need help selecting a suitable motor, and a supplier.
> 
> : I presume that a DC motor is best (the microcontroller I'm using is 68HC11K1
> : which has PWM outputs).
> 
> Could be a false presumption. A stepper motor is more controllable, especially
> at low speeds.
> 
> : Is it possible to get motor with good torque at very low speeds (say 100 rpm)
> : or is a gearbox mandatory?
> 
> A gearbox is pretty much required. Basically the speed of the motor is 
> ultimately controlled by the physical properties of the motor. The windings
> exert a force on the armature, the armature accellerates (f = ma) until
> the friction of the bearings and the wind resistance of the armature and
> and the inertia of the load all balance out. Unloaded, a small DC motor
> can easily run at 9000 RPM. There are good decscriptions of this in
> most elecromechanics textbooks.
> 
> A couple of suggestions:
> 	1) Use neutered Radio Control Servos (keep the motor and the
> 	   gearbox.)
> 	2) Build a custom gearbox using gears from any one of the suppliers
> 	   in the FAQ or near you in Australia.
> 	3) Use stepper motors.
> 

Just to add to Chuck M. suggestions:
4) look for an appropriately sized toy R/C car- similar weight etc. at a
yard sale (or in your kids toybox). Even if it's broken all you want is the
motor and gearbox and these often come with a differential.

My $.02 worth.

-- 
MAD
mdenney@hercii.lasc.lockheed.com
