2007/08/09 - Re: A motors question [TANKS [TANKS] (Micah Leibowitz)

"a high wattage motor can be run slower with less reduction with gears to give the same torque and rpm as a less powerful motor running faster with a higher gear reduction meaning that the shaft in the motor is spinning slower producing less heat."

somewhat, but there pieces of the puzzle you are missing.

Firstly, let me be clear this only applies to Permanent Magnet Direct Current Motors (PMDC) which I will assume that it what almost everyone uses.

A PMDC motor produces all its torque at stall condition (shaft not turning at all) it also draws the most amps at stall. With no load it spins at its maximum Rpm, produces virtually no torque, and draws the fewest amps. If you chart these figures out where the torque and rpm cross is the maximum power. In most cases that rough point is 1/2 the no load rpm (and 1/2 the stall torque), however, while producing maximum power the motor is also no more than 50% efficient.(most motors are much less than 50% eff. at this point)

Given these laws if you have a less powerful motor that is run closer to its maximum output it will be less efficient than a more power full motor run with more "head room". That says that the physical size of the motor doesn't play a big part in the game.... In the real world size matters. A smaller motor will heat faster simply because it has lower thermal mass, and heat is the enemy of efficient. Smaller motors usually need to turn much faster to produce the same output as a larger slower motor, there is the added inefficiency of the steep gear train.

I like to compare the two motors to a hopped up honda engine with NOS and a Detroit diesel. They produce the same output but one is light, fast, and built for short runs. The other is big, heavy, and built for a lifetime of use

sasquevaneach-at-aim.com wrote:

from what i can see from motors is that the larger the motor the less work it has to do to move the tank so it shouldn't get as hot as fast

a high wattage motor can be run slower with less reduction with gears to give the same torque and rpm as a less powerful motor running faster with a higher gear reduction meaning that the shaft in the motor is spinning slower producing less heat.

matthew

----- Original Message ----- From: <funkyneroc-at-ntlworld.com>
To: <tanks-at-rctankcombat.com>
Sent: Wednesday, August 08, 2007 11:19 PM
Subject: A motors question [TANKS]

> I`ve been wondering for a while about my motors ,I dont know the wattage,
> Im guessing lower than 100w and my tank moves as fast as i
> would ever want it to.
> However they do get warm quickly. Is that one of the reasons for using > high wattage motors?
>
> Neil "Electricly clueless" R
>
>
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From:	Micah Leibowitz <bbandit97-at-yahoo.com>
Subject:	Re: A motors question [TANKS [TANKS]
Date:	Thu, 9 Aug 2007 13:35:59 -0700 (PDT)
Reply-To:	tanks-at-rctankcombat.com