This is the link to the system I described in the earlier email
http://www.cbk.waw.pl/~mstolars/projekty/rotor/index_en.html 73 El 07/08/13 19:01, Ing. Pavel Milanes Costa escribió:
Yes, me to... I do have a old Japanese tracking camera mounting also with 24 AC motors here... 360 degrees azimuth with stop switch on 0 and 360 degrees and about 0 to 120 degrees of elevation (0 ~ horizon, 90 ~cenit) Pretty good construction, a ham here in Havana have one the uses to move 2 phased yaguis of 5 elements for 2m... the brake system is primitive but works fine... Pointing is by eye and as in your case no means of feedback... recently after completing some TODO-IN-THE-FUTURE projects with Jal/JalLib (Just Another Language and libs for PIC devices) and pics I get hands on this project A couple o months or so (maybe more) there was a thread on the list about this... I find the arduino project from K3NG, but no arduino here, only Microchip PIC (PIC18F4520) so I have to re-invent the wheel... I was thinking on gray encoding the position with 7 bits, but this is A LOT of cables to run.. Then I see on the specs of the arduino a feedback mechanism of pulse counting... and find on the internet a project from a polish? ham that uses this mechanism wit a ATMEGA MCU but with a trick... (I have the link on my work place... link will be tomorrow) I explain, he uses several magnets glued on the edge of an intermediate gear in the reduction mechanism... then get a magnetic switch (or a hal sensing device if you like) close to the edge where the magnets are... This mechanism do about 500+ pulses for each 360 degrees... pretty neat an simple... with only 2 cables... The only thing is you have to reset the mechanical position of the antennas at each power-on to reset the internal count in the pic/arduino/atmega MCU... I'm on the ideas-on-the-boad part of this project for making it 450 degrees instead of only 360 and how to deal in software with the 0 to 90 degrees restriction on the elevation part... Just another idea to the brain storm... 73 de CO7WT. PS: control will be serial emulating a RS232B protocol from Yaesu... El 07/08/13 09:58, Zach Leffke escribió: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! 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