Saturday, 3 December 2016

Astrophotography - the mount driver

I am using an old Vixen GP mount with the Vixen MT1 stepper motors.

I am using a raspberry pi with Pololu stepper drivers. I've described this in an earlier post.

Now comes the job of making this work - initially for guiding and hopefully later for 'goto' as well (albeit that will be a bit slow with these motors).

The ingredients are:
  1. pi model B
  2. 2 pololu drivers mounted on a little HAT card as described here
  3. a 24v power supply to drive the stepper motors
  4. CAREFULLY set the current limit on the pololu driver carriers
  5. write a test program to do some basic testing of the drivers / motors
  6. Prepare a second raspberry pi to run this nice autoguiding software
  7. do a quick hack to enable Gordon'd autogider software to talk to my driver software.

I have done a quick video of the test program running the code to slew the scope as fast as the steppers can go here.
and below is the gory details.....

I am running this on a pi model B......
  1. started with clean install of jessie lite (2016-11-25-raspbian-jessie-lite.img)
  2. usual new pi things like enable ssh, expand filesystem and setup nfs server
  3. sudo apt-get install python3
  4. setup pigpio as detailed here
  5. and set it to start at raised priority automatically at boot:
    sudo crontab -e
  6. add this to the end of the crontab file:
    @reboot              /usr/bin/nice -n -5 /usr/local/bin/pigpiod
  7. link up to my file server
  8. STILL *sigh* have to fix the rpcbind - nfs server screw up - from here
I run pigpiod at slightly raised priority as on the model B I am using I was getting occasional stutters of a millisecond or two in pigpio scripts that were enough to throw the stepper motors into freeze buz mode at high stepping rates.

That's the basic setup completed

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