Sunday, June 26, 2011

Cat feeder coupler

Tonight I built a really crappy coupler to connect the motor on the cat feeder mechanism to the drive screw on the slide. I was having some difficulty getting anything to work and started on a new slide with a scotch yoke design, but, not surprisingly, I had trouble connecting to the motor shaft for that too. So I poked around a bit and found a grub screw in the junk box that I figured would work to secure an adapter to the motor shaft. To make the adapter I cut a short length of aluminum rod which I then needed to bore out to the diameters of the two shafts.

Since I don't have the equipment to properly bore a shaft, I did it improperly, and with really poor quality. To do this I mounted the rod in the drill press chuck, put a drill bit into the vise, and made an attempt to set the bit vertical and on center, then drilled away. This technique can be used to put a hole exactly in the center of the rotating shaft, give or take a few inches. Flip and repeat with the smaller bit for the motor shaft.

I tapped the larger hole for the screw, then mounted it up and marked where the motor shaft flat was so I could drill a hole for the grub screw. I didn't have a tap small enough for the grub screw, but since the screw is steel and the shaft is aluminum, it can self-tap. I ground the outside of the shaft a bit to remove some of the worst of the imbalance from the crappy, off-center boring job, dripped some loctight in it, and mounted it all up. I'm too impatient to wait for loctight to dry though, so I crushed the threaded portion to secure it to the shaft.

It's working pretty well. I'm not sure how much torque this motor generates, but at stall it generates a reasonable amount of linear force through the screw, a pound or two. At stall the motor draws 2.5A, so I'll need to scrounge up some appropriate transistors for the h-bridge.

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