Thursday, January 06, 2011

Inching forward with the CNC project, my screws and some hardware have arrived.

Here's a quick mock-up of my X axis, well, hardly a mock-up, but I digress. Framework and data handling aside, these are the important parts.

X axis is to ride on THK linear bearings, driven by a Pacific Scientific Powermax II stacked stepper turning a screw, powered through a GeckoDrive G201X which will receive commands ala dedicated desktop PC running Ubuntu/EMC2. Having all these components laid out in front of me means I really need to address the power supply sooner than later (now).

Front and center sits 112 pounds of power supply, waiting for me to lug it to the bench.

It's only after executing that little juggling operation that I remember this is the unit with a faulty breaker on the DC side and what I'm really after is the 107 pound power supply that was sitting next to it.

After a brief inspection confirming that the power transformer is strapped for 120 volts and nothing is visibly leaking, bulging or dead inside the case, I fire it up. The hum of operation borders on a buzz, but no smoke or sparks thus far... good.

There's a standard cassette tape at upper right for scale.

There's a point of concern with this PSU, the DC breaker. I've gathered that it's inadvisable to to switch the DC side of the power at the drivers, as they will face back EMF from the motors which can burn them up, setting me back replacement costs on up to four G201X, which isn't something I'm interested in.

The supplies are also tailored to battery charging, which has a different set of operational parameters than driving motors. My Y axis will have two motors working in hard sync to move each leg of the gantry, the two stacks of each motor are going to be wired in parallel, offering a path rated at 7 amps per motor. So the last thing I want is some battery configured current sniffer to crowbar output voltage when I most need it.

In short, I came to the realization last night that my best tactic is to gut the logic/regulator portion of the power supply, reconfiguring it into a primitive rectified DC beast, which, as I understand it, is best for this brute force application to begin with. I guess I could have stayed with the heavier supply after all.

No comments: