Hi Denny, Sorry for the late reply, have been doing some traveling. I have my fair amount of experience, although mostly in power electronics and I'm also a little bit rusty. i like your idea of using the LM2596 at each servo location, powering the Mini maestro USB servo controller (https://www.pololu.com/product/1352) servo power input with 24V from this power supply: http://www.mpja.com/24-Volt-Adapter-Power-Supply-25A-Phihong/productinfo/30= 254%20PS/ I think I will be fine on signal shapes this way, pulses will be sent from 0-24v and translated to 5V range at the end of each wire with the LM2596 to feed the servo. My only doubt would be actual servo powering; do you think a LM2596 would hold near to 5V the V+ rail for these 20 meters distances? Regards, Carlos. 2015-05-07 14:06 GMT-04:30 Denny Esterline : > > > > > > On a related matter, I will have to run the controlling lines for the > sevos > > around 10 to 20 meters from the base controller so I believe I will nee= d > > some sort of line enforcing buffer/booster device to avoid mis-shaping = of > > waveforms and/or voltage drops that could lead to bad controlling of th= e > > servo. > > > I do not know your experience level - forgive me if I over simplify. > > Standard servo has three wires, two for power and one for signal. > Servos were conceived in a world where it was "normal" to power > them from four AA batteries. So about 6 volts. Later various 1.2V > rechargeable cells became popular and 4.8v became the nominal > standard. Basically it comes down to "about 5 volts". Current can > vary widely for different servos and various loads, but with the > S3003 you mentioned, plan for an amp or so while under load. > Notice I did not say "while moving". Servos can draw a lot of power > to hold still if thy have to fight the load - something to address in > the mechanical side if you can. > > The signal is a simple square wave - 0 to 5v. The data is encoded > in the ON time of the signal and there is a very loose spec for the > repeat rate. This varies a bit for brand and version, but about 1mS > on time is fully one direction and about 2mS on time is fully the > other direction, and yes 1.5mS is about center. Different manufacturers > made different decisions about which one is clockwise and exactly > where the ends are. This signal needs to be repeated about 20-50 > times a second. > > So... Lots of ways to drive this, but 20m of wire adds some wrinkles. > The one I would be most concerned about isn't so much "noise" on > the wire, it's voltage drop. With that much wire, 0v on one end is > not 0v on the other end. Not only does that reduce the available > power for the motor, but it also eats into the level available on the > signal line. You could probably find some success using a twisted > pair (ground and signal) and a second twisted pair (ground and power) > > I'd seriously consider a point of load switching power supply. Something > along the lines of. > > http://www.mpja.com/LM2596-Step-Down-Adjustable-15-37V-DC_DC-Converter/pr= oductinfo/30148%20PS > Then you can run higher voltage (say 12-24v) over the 20m of wire and the > end > result is considerably less voltage drop. > > The other non-obvious thing I would be concerned with is how to drive > the signal line. 20m is a long antenna and I can imagine various > events killing the transmit side of the system. Lots of ways around it > but at these data rates you should be ok with a single transistor to > pull the line low and pull up resistors on _both_ ends. Plan it for 10s o= f > mA when pulled low. > > -Denny > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .