Zack, Check out K3NG's Arduino rotator control project. It incorporates the proper sensors and should, with the proper interface hardware, drive your hardware. I'm in the process of a build myself. Norm n3ykf
On Wed, Aug 7, 2013 at 9:58 AM, Zach Leffke <zlef...@vt.edu> wrote: > Hello Everyone, > > I recently came into possession of a Pelco PT170-24P > tracking pan tilt pedestal designed to support large security cameras. My > intent with this new acquisition is to repurpose it as a "low cost" (got it > on Ebay for ~$75 + S&H) alternative for an antenna tracking pedestal for > amateur satellites. It uses 24VAC induction motors to move the azimuth and > elevation assemblies, pretty much just like the G5500s that I'm sure so > many > of us are familiar with. It definitely cannot support the same amount of > weight as the G5500, but I'm looking to construct a small, portable > satellite ground station node and this thing is plenty beefy enough to > handle a couple of Arrow style antennas. Here is the problem, it provides > absolutely no feedback. > > > > My question to the group is does anyone know of a non-mechanical method for > getting relatively accurate feedback for azimuth and elevation. I'm > looking > for an all electronic means that I can mount somewhere outside of the > actual > pedestal assembly (like perhaps on the cross-boom) that will be able to > provide measurement of the az/el (or pan/tilt, or yaw/pitch, whatever you > want to call it) position. I'm using an arduino microcontroller for the > tracking controller. Originally I intended to find a way to mount > potentiometers in inside the unit and simply use the ADCs on the arduino to > read the position feedback voltage from the pots, however, there is barely > enough space to mount an elevation feedback pot inside the unit, and there > is virtually no space for an azimuth feedback pot. Hence I'm looking for a > non-mechanical method. > > > > My first thoughts for the elevation feedback was to use the old > potentiometer plus nice heavy weight method mounted out on the boom. This > idea doesn't appeal to me very much as other factors can now affect the > position feedback (such as high winds). I then thought of something along > the lines of an accelerometer. I also tossed around the idea of a 2-axis > gyro for both Az/El. My issue is I have limited experience working with > these types of sensors, and was hoping to get advice from everyone in this > group. I know for example that the gyro will provide rate of motion around > an axis and thus I have to integrate over time to get the actual position. > This becomes cumbersome because now I have to keep track of time in the > Arduino while executing movement commands (certainly do-able, just more > complicated than reading an ADC voltage). Additionally, I believe these > devices suffer from drift and require frequent calibration (although there > may be a scheme of starting from a known position, say at one of the limit > switch contact points, for each pass that might work). I also toyed with > the idea of an electric compass for azimuth feedback, but I'm worried about > distortion of the magnetic field near the pedestal due to the AC induction > motors or when the antennas are radiating. In theory the motors are housed > inside the metal pedestal enclosure and thus are shielded from the outside > world, but I can just see it now, nice steady feedback when the pedestal is > stopped and as soon as I execute a motion command the azimuth feedback > starts dancing all over the place. Since the motion stop command is based > on achieving the target position, system instability is sure to occur. > Even > if I solve the AC motor EMI problem, I still worry that when transmitting > the fields could potentially be distorted if near the antenna (remember my > goal is a compact design) and taint the position feedback. > > > > Any ideas from the group would be greatly appreciated. I'm looking for a > "sparkfun" type solution here and if anyone has experience working with > accelerometers, gyros, electric compasses, etc. I would love your advice on > which might be the way to go for the position feedback. If you think I've > hit on a good idea above and should go with it please let me know. Again > I'm using an Arduino, so analog voltage feedback, I2C, SPI, and UART serial > are all on the table for communicating with the sensors to get the feedback > info. > > > > Thanks in advance! > > > > Sincerely, > > Zach, KJ4QLP > > > > _______________________________________________ > Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
