Changes for the shutter

The shutter is still having trouble closing. Opening is always fine, but sometimes the close operation fails. The lower shutter gets power, but never moves. The Arduino goes into reboot mode, as though power was re-applied to it.

My theory is that firing up the motors maybe causes a momentary power surge / voltage drop, so the Arduino thinks power has been cycled. Perhaps the shutter in the closed position requires more power/torque from the motor to get started, due to the angle of the activator pulling the shutter closed.

Connecting power directly to the shutter (bypassing the “brush/ring” mechanism) works.

Things to try:

  • Perhaps the copper tape on the track, used to distribute power to the Arduino, is torn or worn. I replaced the tape in the park position area. The brush/tape system now has a resistance of around 5-10 ohms.
  • I notice that the shutter failure occurs when the park position does not place the dome in the exact correct spot. The Foster is often off by 6-12 inches when it parks the dome. In fact, I am seeing potential problem here – sometimes the position is 3 feet off! Oh, boy, another Foster problem to debug.

On the other hand, the home sensor is fairly accurate since it works by detecting the sensor magnet. It will be a couple of inches off depending on which direction the dome turned to find home, but it is consistent. So, I moved the home sensor so that home is in the same position as park. Foster version 3.2.3 has a checkbox that indicates Home is the same as park, but Parking does not use the magnet. It just goes to where it thinks the home sensor should be; this position can be off several inches.

Incidentally, the inaccurate positioning started happening with version 3.2.2. Updated software/firmware to 3.2.3, same problem.

I re-synced the telescope so the rotation is consistent with the new home sensor position.

  • I changed the Arduino code to ramp the pulse width modulation (PWM) from 512 (doesn’t move the motor) up to 1023 (full speed) in steps of 64 every 50 msec. I thought maybe this would help avoid the power drop. I can hear a slight change in the motors starting up.
  • If these things don’t work, my last idea is to install 2 large capacitors on the the Sparkfun MonsterMotor board. They leave spots on the board for these capacitors, but I can’t get any information from them on what they are for or how one would size them. Maybe these capacitors would avoid the power drop. If one even exists:)

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