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From: William and Melissa Johns <gizmology-at-gizmology.net>
Subject: Re: Electric Motor
Date: Fri, 05 Sep 2003 19:57:36 -0400
Reply-To: tanks-at-rctankcombat.com

By the way, this assumes it's a permanent magnet DC motor.  If it's 
series-wound or whatever, then all bets are off.


(I'm replying to myself.  Is that like talking to yourself?)

At 07:45 PM 9/5/2003 -0400, you wrote:
>Well, according to my EXTREMELY SUSPECT calculations, your motor is best 
>run at around 12,000 rpm, where it should draw around 13 amps.  Assuming 
>that the motor is 50% efficient, it should be generating around 0.05 
>ft-lbs of torque and 0.10 horsepower.  If the motor is 75% efficient, it 
>should be generating 0.07 ft-lbs of torque and 0.15 horsepower.
>You can tell how efficient a motor is by measuring the stall torque - the 
>higher the torque, the more efficient.  In your case, 0.23 ft-lbs works 
>out to about 50% efficient, and 0.35 to 75%.  (Efficiency is good not just 
>for battery life, but also HEAT - potentially enough to let the smoke out.)
>I hope this helps.  (I also hope it's right!)
>At 05:08 PM 9/5/2003 -0500, you wrote:
>>I would like to see if any of you could help me with some electric motors 
>>I bought at a local surplus store. They are 12 volt ,  4.100"  overall 
>>length ,  2.030" Dia. ,  5MM (.1969) Dia. shaft.,  Internal fan 
>>cooling   , 14,500  RPM free speed. It pulls 3.4 Amps at no load. Pulls 
>>50 Amps at stall. Any idea what an average load RPM and AMP draw might 
>>be? Given a gear reduction of 25 to 30 to 
>>one.                                                          Thanks Randy
>"Forgive your enemies, but never forget their names" -- John F. Kennedy


"Forgive your enemies, but never forget their names" -- John F. Kennedy