Sunday, May 19, 2013

Foster Family Day at Fort Knox (Maine)

Saturday was Foster Family Day at Fort Knox, an event that recognizes the families who step up to care for Maine's abused and neglected children.

Due to the nature of the event, I don't take pictures of the adults or children in attendance.

This is the second time I've been down for this annual event and I'm just in awe at all the happy kids and families that come together for this.  We had a beautiful spring day with plenty of sunshine, so the kids could explore the Fort, jump in the inflatable jump-castle or enjoy the entertainment.

R2-D2 was set and raring to go once we got there...

Mid-way thru the event, while moving R2's dome around, I heard a "thunk".  I took a peek thru one of the dome panels and expected to see something simple.  Perhaps the power lead that goes from the dome plate to the dome got snagged, or the dome drive sprocket had worked itself loose, hitting the dome plate.   

Those all looked fine.  Hmmm.

Once I thanked the hosts and packed R2 up, I checked more carefully for the metallic clunking I was hearing.  The motor was spinning and the dome gear would move slightly.  So, that told me the issue was likely the motor itself.  This dome gear and motor/sprocket setup is still a bit new, having just gone in a few weeks ago.  I have had a very busy May, already doing four events this month.  The dome drive had worked perfectly in those events.

While driving home, I decided to stop over at Fred's house, my machinist friend.  I knew he'd enjoy taking the motor apart and helping play detective with me.

With the Pololu 37D motor removed from R2, Fred carefully unscrewed the motor assembly.  He didn't have to look far to see that some of the teeth were sheared off....

The diagnosis is a sheared gear, as you can see in the image.

What probably caused it is the back and forth motion from having R2-D2's dome moving around with the music being played.  That's a popular request so it looks like the Pololu motor won't be the best for this dome gear & sprocket setup.  If I were using a rubber wheel pressed against the rockler bearing, that would work fine, since the wheel would just spin until having enough traction to reverse direction.

The Pololu motor cost $25, so this isn't a disaster by any means.  I simply need to find a motor that is stronger and able to withstand the rapid direction changes the dome gear & sprocket.  With any luck I'll find something small and comparable in cost.  And of course, with any luck, minimal changes to the motor mount and sprocket....but, we shall see!