On Friday 10 July 2020 22:26:12 Ken Strauss wrote: > "You need more gearing with the DC motor." Correct and this could be > considered an advantage since a very small DC motor + gearing > (multiple planetary stages) would have sufficient torque to move the > scope. I have no idea if a RPI can keep up with 3 quadrature encoders > and control 3 motors and manage a UI. However, you could make a > compact unit at low cost containing a microprocessor that takes > step/dir, tracks encoder position and generates PWM to run the motor. > Rather like a low power, low RPM, high torque version of a Clearpath > servo.
The rpi4 w/2gigs, and a mesa 7i90HD controller would be an expensive overkill, but consider that it could not only run the telescope but the rest of the building its in. One of the firmwares that can be loaded into the 7i90 gives 4 stepgens, 4 encoders and 4 pwmgens. And still leaves you about 60 other gpio pins to keep track of the whole environment, like a motorized sliding roof, or even the whole building over the scope that could take protective action based on wind velocity exceeding a set limit value, or sensing rain, parking the scope, bringing the roof or building back over it and even starting a small heater and vent fan to dry it out until the humidity is safe. My hal files have quite a bit of "gingerbread" that runs in a 200 hz thread doing lots of stuff, like tracking the z position and running the x in and out to correct for several thousandths of bed wear. The jog dials that replace the hand cranks all work in this slower thread. It also tracks the distance it overtravels at spindle reversal due to the mass of a 40 lb chuck, sending back to the driver gcode if you want to use it, to shorten a rigid tap stroke after the first hit on the hole, giving me the ability to set the depth of a hole to be tapped, but reducing the stroke to prevent the overtravel from hitting the bottom of the hole and breaking the tap. Even with all that, I still have around 40 gpio pins that are not committed. Two of those gpio's control the AC power via 40 amp ssr's so that when motion is disabled, the only power left on is the raspi's and monitor. Thats about 15 watts, so its on 24/7. My ability to do stuff around that lathe is limited only by my imagination, which I have a reputation for allowing out to play without a chaperon. :-) Running an 8" Dob would be a piece of cake. Might have to teach stellarium how to drive a scope thru an spi interface. Serial, very high speed. Installed and ran stellarium but didn't find an interface as it seems to need ASCOM drivers, and they give very limited control. I'm disappointed. Looks like a new wheel will need to be written. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
