April 2011 Archives

CNC - Stepper testing harness

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Well apparently Dr. Pepper has caffeine. So, I'm up later than I want to be on a Friday night. I have had a circuit setup on a breadboard to run some steppers. Tonight I found a scrap of PCB that was big enough to transfer the loose wires to something more permanent.

Stepper test driver

The board is quite simple, a 555 sets up a step pulse (similar to what EMC will send via the parallel port) into RA2 on the PIC16F716 which is programmed to output a full step wave drive to 4 pins. The PIC is programmed to reverse when RA3 is high - I have not yet soldered in a switch to pull that line up, so for now it just drives forward.

This will be used when building assembling the CNC frame / guides while away from the computer to manually drive the various steppers. It is also a test bed for programming the PIC to drive the steppers, and future evenings will have me build a couple of PIC only stepper drivers (no 555, just step & dir input lines).

Fixing things with spare parts - garage doors

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So my wife calls me at work - "The garage door won't stay closed". It goes down, hits the ground, keeps pushing for all its worth and then opens back up. Only, it doesn't open far enough to get the van out.

No problem I think. There's a little pretend garage door inside that travels along a track and at the ends of the track are adjustable sensors. When the little pretend door hits a sensor, the door stops moving. If the motor senses an obstacle before it reaches one of the ends, it reverses.

Most likely threaded rod that the little pretend door travels on popped out of alignment - this has happened to me before.

So, when I get home, I open it up and take a look. The little door seems fine, so I readjust the down sensor and things seem to be working. Then I notice some metal bits around the main gear shaft, and as I take a closer, I realize the gears that connect the main shaft to the pretend garage door are a bit further apart then they should be. That is probably why they slipped.

But why the gap?

Looking closer, I see that the bushing on the main shaft is almost completely worn away!

Garage door opener - broken

Well, that is certainly going to be a challenge to fix. Then I remembered a box of junk I have in the back of the garage. I find the box, and inside, sure enough is a cannibalized garage door opener, with a motor assembly whose bushing is not worn out!

Garage door opener - fixed

Yay! 1 hour later (and with some grease from a neighbour - thanks Mark!) the door opener is reassembled, adjusted and working again!

I love old fixable stuff!