didn't get much of a rise out of sudo-doscuss... steve i have a 2-axis compass chip that is earmarked for rover use. excellent point about the cloudy day problem - i gave derek my paired arduino/processing utility for passing servo instructions from PC to microcontroller and my understanding is that he is going to port the PC side to python using the GPIO pins of a raspberry pi for serial connection with arduino to do the low-level actuation since it runs at 5V like servos and some ICs, with the end goal of pointing a webcam. I will take a look at your code when i get back to town and try to find a schematic for driving those HVAC servos. we can fabricate whatever mount we need, but for starters it looks like we could get away with some 1/2" or 5/8" square tube through the servo, with holes drilled for attaching plywood to which we could duct tape some small panels (i have 2 5-watt car charging panels for testing purposes). any interest in sensing the battery voltage and having the computer enter sleep mode during the night? Not sure how to do that on the rpi but there's some documentation for the arduino. The whole rpi could be turned off and on with a single power transistor, as could individual transmitters ------------Forwarded message------------ From: steveberl(a)gmail.com Date: Mar 31, 2013 09:29:23 AM Subject: Re: robotics: 2-axis pointing To: hol(a)gaskill.com Cc: patrikd(a)gmail.com, sudo-doscuss(a)lists.sudoroom.org On Sun, Mar 31, 2013 at 9:07 AM, Steve Berl steveberl(a)gmail.com> wrote: I've already got the "calculating the daytime paths" part. I have python code using pyephem that given a latitude, longitude, and time, gives back the altitude and azimuth of the sun. For a fixed platform, that you can align once, that should be all you need. For a portable or moving, rotating platform, you need a way to know the orientation of the platform, which might be a magentometer, or even better, a 9DOF IMU like  https://www.sparkfun.com/products/11486 Dithering around the sun would probably be OK for solar panels, but on cloudy days, it might spend a lot of time hunting for a peak that doesn't exist.  For radio astronomy, it would add noise to the system which you would need to figure out how to filter out somehow. -steve On Sat, Mar 30, 2013 at 9:13 PM, hol(a)gaskill.com> wrote: +1 on using a geared DC motor with encoder.  we will basically wind up with a custom servo.  i have some IR sensors that i got with the intention of making a photo interrupt type encoder - just need to print some dartboard-esqe patterns on transparency sheet and center it on the shaft or a coupler.  steve i am very interested in building a sun-tracking mount for solar panels and those servos we have at sudo room would work for that application...i think there are also a few boxes that have geared stepper motors too, from the same batch of parts which i think was an overflow from AMT.  two main options fro pointing as i see it are calculating the daytime paths geometrically, or using closed loop control to dither the panels around the sun like the thermopile on a sidewinder missile.  also would be interested in one where the yaw axis of the panels is actuated by virtue of being mounted on a rover chassis (roomba???) with 2-axis magnetometer as feedback on pointing. Mar 29, 2013 04:44:09 PM, patrikd(a)gmail.com wrote: If you want something precise and slow, you probably want to go with a > > > > > >> >> >> >> >> >> >>> >>> >>> >> >>>> >>>> >>>> >>>> >>>>> >>>>> >>>>> >>>> >>>>> >>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>>> >>>>> >>>>> >>>> >>>>> >>>>> >>>> >>>> >>>> >>> >> > > > > > -- -steve -- -steve