Steppers and Pulleys

So it’s not getting any warmer and finding time is getting hard with my co-op term coming to a close. I could prepare myself for the beginning of 2nd year, or I could finish my mill in another week to make more parts for my electric car conversion. CNC it is.

I’ve had the steppers, drivers, and power supplies sitting for a while now and finally figured them out. Currently the electronics are mounted on a temporary mdf panel for testing, until I have time to do a proper enclosure. The steppers are 425 oz-in from Wantai motor off Ebay and the drivers are also Wantai model number DQ542MA. The power supplies are TDK-Lambda part number “LS150-36” 36v and 4.3A. I’ve never had confidence in cheap power supplies which could kill me, always go for brand name and CSA approved or UL listed products. The IEC power connectors have built in fuse holders which I’ve fitted 2A fuses to, in case something interesting happens.

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After some wiring and flipping dip switches every which way, I was able to get the steppers to move predictably. Initially I didn’t notice the ON label accompanied by an arrow pointing the opposite direction I assumed was ON, so the motors were doing all sorts of strange things like rough stepping, missing steps and heating up. I had intended to use 1/2 micro-stepping (400 pulses/rev) and the lead screws on my mill were 10 turns/inch, and I had calculated 4000 steps per unit. After getting the dip switches right, steppers did move 1 full tern per 0.1″ and 10 turns for 1″, close enough for now.

wiredsteppersI had been using Mach3 on an old laptop with windows xp for debug and initial setup, although a few stability issues are driving me away. The long term plan is running LinuxCNC on some recycled print servers. The print servers are running a Celeron D with 1 gig of ram and will shortly had a pci parallel port card. I also plan on using the cases of truly dead print servers for an enclosure for the electronics.

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IMG_20131202_172053 Back to the mechanical side now, for some reason i thought 1/4-20 socket head cap screws would fly for mounting the steppers, probably should have double checked some measurements before I tried reaming out the holes:

IMG_20131201_195109That said, I may try to redo the face plates on the motors once things are CNC. Only one of the 12 holes I reamed actually cracked. The face plates were cast aluminum and looked simple enough to replicate from the inside.

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Since 11/12 holes went thru no problem, I test fitted the x and y axis mounts, the z axis will probably wait for a new motor face plate because of the higher load.

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I’ve received the timing pulleys to replace the hand wheels but not the belts or pulleys for the stepper yet. Minor modifications included counter boring one side of the pulleys so a nut could still thread onto the end of a lead screw and also adding a keyway. Boring was rather unexciting and relatively painless. To make the keyway however was a bit more sloppy. I don’t have a broach set, but a 1/8″ end mill was close enough. To get the keyways deep enough, I did have to create some relief for the shank of the 1/8″ bit so it could plunge down without any problems.

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The pulleys were a nice snug fit after some filing and hammering, because if you can’t achieve a precision fit with a hammer, don’t force it.

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Hopefully I’ll have my belts for next weekend and have functional CNC positioning that will be more accurate than keeping track of hand wheel rotations in my head.

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