Small DC Motors

[MisterFuji]

What kind of RPM do I need for a small DC motor for a 1-2 lb line
following robot? I see a lot of cheap DC motors, but they are
anywhere from 2300 - 5600 RPM, which I suspect is too much RPM. Any
thoughts or recommendations?

Cheers,
Randle

[Randy M. Dumse]

MisterFuji said: Sunday, August 09, 2009 6:04 PM

> What kind of RPM do I need for a small DC motor for a 1-2 lb
> line following robot?

That's really the wrong question. The question is more like:
What gear train do I need given the motor I've chosen?

Almost all DC motors work best at a high RPM. So they will
almost always need a gear train to take them from their high
speed - low torque operating range to a low speed - high torque
application to the wheels. Even the size of the wheels comes
into play in the answer.

Another issue is speed. If you go slow, you can use very little
power, and still get enough torque. If you want to go fast, you
need power.

So generally you start the other direction. How big is your
intended wheel is the starting point. How big is it around? Then
given your desired speed and intended wheel, you can figure how
many RPMs you need to get that wheel to turn that often. Now
with the wheel's operating RPM and your motors operating RPM,
you can figure what gear ratio is necessary.

Next thing is figuring out if your motor has enough power to
attain and hold the operating speed you want. If it doesn't you
either have to get a bigger motor or settle for a slower speed
with a lower gear ratio.

Randy

[Dan Hockey]

For something that small you could try using a servo such as the
following...
http://www.parallax.com/Store/Robots/RoboticComponents/tabid/198/CategoryID/70/List/0/Level/a/ProductID/102/Default.aspx?SortField=ProductName%2cProductName