I have been gathering components for a cnc pcb mill. so far im in the preliminary steps of gathering parts. i started with the electronics part of the build and will build the machine itself later. im gathering the parts slowly, rail systems are kind of expensive but i got some spare 3d printer parts left over from a bed upgrade, and i got some spare linear bearings. i got a rather thick piece of acrylic salvaged from a dead monitor which would serve as a good base plate, since i have a lot of other salvage displays i figure much of the structure would be build out of acrylic and 3d printed parts. will probibly use a dremel flexi shaft as the buisness end with the dremel elsewhere to reduce the mass that needs to move around. anyway its going to be a small machine, so long as i can mill a 4x4" pcb with it.
anyway i got an old arduino (i tried building an stm32 version of grbl but had trouble flashing it to the board, using arm has some advantages, more memory and has an fpu and hardware divide that the atmel chip doesnt have) running grbl with a 4 channel cnc shield. i only have a few steppers salvaged from junk, several laser actuators from dead cd/dvd drives, and a couple mitsumi motors from an old sewing machine. at some point im going to get me some nema 17 motors like the ones on my 3d printer. not sure whether im going to use lead screw drive or belts, but im concerned that belt drive wouldnt have the torque neccisary, but that extra torque costs speed, but its going to be a small machine so thats not a big issue. anyway i cobbled up some wiring harnesses and im using some lithium ion batteries for power. anyway they are unipolar 4-wire motors. i did find a data sheet on the motors, but they didnt cover the electrical connections. the drivers have 2 channels and its not hard to trace out the two coil sets in the motors, each pair of wires to one of the chanels. but im not sure if polarity matters. the channels are powered by an h bridge and will alternate between positive and negative between steps.
anyway i connect the motors, load up bCNC with an svg file and initially i get them to spin. one motor is holding its position just fine, at least up to the limit of its hold torque. the other seems to be freely rotating at a significantly lower torque. this made me question my assumption that polarity didnt matter. maybe they are like encoders and operate with a grey code, maybe having reversed polarity on one of my coils is breaking that grey code. i rechecked my harneses and noticed that i had the coils flipped on one of them so i made them identical, matching the better of the two and im still getting one to spin freely, swapped motors/cables, controllers same difference. i tried lubricating the motors since they are all sleve bering type and have been in my junk bin for awhile. so long story short is there a right way to wire these things?is there some secret sauce that im missing?
anyway i got an old arduino (i tried building an stm32 version of grbl but had trouble flashing it to the board, using arm has some advantages, more memory and has an fpu and hardware divide that the atmel chip doesnt have) running grbl with a 4 channel cnc shield. i only have a few steppers salvaged from junk, several laser actuators from dead cd/dvd drives, and a couple mitsumi motors from an old sewing machine. at some point im going to get me some nema 17 motors like the ones on my 3d printer. not sure whether im going to use lead screw drive or belts, but im concerned that belt drive wouldnt have the torque neccisary, but that extra torque costs speed, but its going to be a small machine so thats not a big issue. anyway i cobbled up some wiring harnesses and im using some lithium ion batteries for power. anyway they are unipolar 4-wire motors. i did find a data sheet on the motors, but they didnt cover the electrical connections. the drivers have 2 channels and its not hard to trace out the two coil sets in the motors, each pair of wires to one of the chanels. but im not sure if polarity matters. the channels are powered by an h bridge and will alternate between positive and negative between steps.
anyway i connect the motors, load up bCNC with an svg file and initially i get them to spin. one motor is holding its position just fine, at least up to the limit of its hold torque. the other seems to be freely rotating at a significantly lower torque. this made me question my assumption that polarity didnt matter. maybe they are like encoders and operate with a grey code, maybe having reversed polarity on one of my coils is breaking that grey code. i rechecked my harneses and noticed that i had the coils flipped on one of them so i made them identical, matching the better of the two and im still getting one to spin freely, swapped motors/cables, controllers same difference. i tried lubricating the motors since they are all sleve bering type and have been in my junk bin for awhile. so long story short is there a right way to wire these things?is there some secret sauce that im missing?
