Newsgroups: comp.robotics
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From: pmalenfa@kitkat.webo.dg.com (Paul Malenfant)
Subject: How to choose a motor
Sender: usenet@us.dg.com (Usenet Administration)
Message-ID: <1994Apr20.183656.25350@us.dg.com>
Date: Wed, 20 Apr 94 18:36:56 GMT
Reply-To: pmalenfa@kitkat.webo.dg.com (Paul Malenfant)
Organization: Data General Corporation, Westboro, MA
Lines: 38

With the Hartford Ct candle contest behind me, I can start thinking
about my next robot.  This time, I want to have good motors.

Ideally, I'd want a motor that comes with a gearbox and has an integrated
shaft encoder, but the gearing is more important.

How do you go about sizing your motor?  I know the speed I want it to
travel, and can guess the size of the wheels, so I can estimate the
rpm's I need (around 240).  However, how do you estimate the
torque needed?

Since the robot doesn't exist yet, I don't know its weight, or friction.
But I do know that it should be able to produce my top speed (240rpm)
on a surface like concrete.  It should also be able to travel indoors
on thick carpeting at a reduced speed (>120rpm).

Some motors have specs like:
   300 rpm    no load    xxx ma
   250 rpm    15 oz-in   xxx ma
   200 rpm    30 oz-in   xxx ma
     
	etc.

Others say something like 300 rpm, 50 oz-in, xxx ma without any mention
of other loadings.

How do you evaluate the specs so that you can choose an appropriate motor.
Servo Systems has one for $29, which I'm willing to pay, but I need to
ensure it meets my needs first.


Paul Malenfant
pmalenfa @ kitkat.webo.dg.com (508-898-7153)

-- 

Paul Malenfant
pmalenfa @ kitkat.webo.dg.com (508-898-7153)
