View Full Version : motor vs servo, reed relay

02-20-2010, 05:39 PM
Sorry for the sloppy title and overlook these questions if they have been asked a million times prior. http://forums.parallax.com/images/smilies/smile.gif I have been reading and can't find a clear answer to a few questions.

What is the advantage of using a motor over a continuous rotation servo? I do not have to have a motor controller with the CRS, so why pay more for a simple design that requires rotation?

Another question: I have a reed relay bought from Radio Shack. It can handle 120ac. Do you know of any tutorials / PDF documentation that shows how to use the relay? I am usually ok with diving right in and doing hands on test to figure something out... in this case I would rather not harm the bs2. lol

Thanks in advance for the help guys. Bare with me and maybe one day I'll be on here answer peoples questions. http://forums.parallax.com/images/smilies/smile.gif


What is the best component for sizing objects up? I have been playing around with ping and a motion detector. Finding objects in a room and determining if they are moving or not is fairly easy. What about determining size of an object? I have some bits of code poking around in my head but I am wondering if there is an easier method, or a more common method.
(By size, I of course mean size given by visible edges)

Post Edited (we2r1two008) : 2/20/2010 11:16:53 AM GMT

02-20-2010, 07:54 PM
For the relay, it would help if you specified what you were planning on using it for. BE CAREFUL WITH 120-VOLT AC AND BASIC STAMPS!!!!!
For the motor, I'm not sure because I have only ever used servos in robotics.
To size an object, perhaps you could put the ping on a panning head and pan it until you find the edges.
Or, you could turn the robot 90 degrees either direction, point the ping sensor towards the object, get to one edge, and use dead-reckoning to get the distance to the other. So the robot would do this:

Find an object
Turn 90 degrees either way
Turn the PING towards the object
Follow the side of the object until the distance reading increases sharply
Turn the robot and ping 180 degrees
Get to the side
start following the wall, counting the pulses sent
detect the other edge, stop counting
divide the number of pulses to get to the other side by the number of pulses to travel whatever unit you feel like using
store value in EEPROM (this value is the width at the base in whatever unit you used earlier)

This isnt exact, but is pretty close (be sure to update the pulses-per-unit often to reduce the effects of battery drainage)

Post Edited (legoman132) : 2/20/2010 1:00:13 PM GMT

02-20-2010, 08:04 PM
See the "member supported faq" for more info on driving a relay

02-21-2010, 12:03 AM
One major difference between motor and servo is servo codes are built into the stamp and are easy to control while motors can be huge and far outperform servos.

- Stephen

02-21-2010, 01:13 AM
Generally speaking...if speed and/or torque are important using a motor is the way to go. But for a small roaming robot using servos is simpler.

"A complex design is the sign of an inferior designer."