Help - Current For Stepper Motor Driver AM882 - ProTuner

[PaulP]

Thanks for the replies gentlemen,

OK so I've been popping on most of the day for short burst to see what's been said but was unable to reply as I hate using my phone to do any forum posts. I've got back to my laptop to read your replies properly without the mither of a sugar loaded 4 year old.

I ran the program twice more this evening with the dust boot on and got the same results in both Trespa (HPL) and MDF. I nipped up the grub screws on the carriages to see if they were causing any issues ran the programs and had exactly the same deviation in the tool path at the same 2 locations. I'm concluding that there are two issues at play here. One I expected the other I didn't. Firstly it's definitely losing steps in both the x and y, the x was out by 0.23mm and the y was out by 0.18mm, I'm now going to change the wiring to parallel. I'll include the wiring diagram that I translated into english, if someone could confirm I got this right I'll try to get start on doing that tomorrow.

The second issue which is a bigger worry is the flexing on the Z axis. Those bristles are 0.6mm diam. the layer of bristles is about 6-7mm thick and when pressing down and sideways when it's machining it's flexing the Z axis at certain points because of the geometry of the part it was cutting. Bristles are easy to bend if the layer is only 2-3mm thick but 2 rows of a 6-7mm channel was enough to cause the z axis to bend enough to show up in the finished part. The bristles are already 15-20mm past the bottom of the cutter and when it's cutting 20mm deep they are forcing the z axis in 3 different directions, plus sometimes they go into the slot and get caught by the cutter. I'm opting for a single 0.6mm layer of skirt printed out in a strip to be fastened on to the rim. This should eliminate the forces acting on the z axis and contain the dust/chip spray when cutting. It's also much easier to make as it's 3 layers of PLA printed rather than cutting bristles off an old draft excluder and glueing them in vertically. We'll see how that goes. I'll include the sketch of what I mean below.

I didn't know it until tonight but I zero'd the tool to the work piece on both the x and y sides and pushed the neck of the spindle and on the side of the spindle to see what was going on. When I could see light passing between the workpiece and the tool I knew what was up. It was evident in both the x and the y but more so the y. This was disappointing but at least I know what was causing the movement. I'll measure the flex tomorrow/today but I'd estimate it's about 0.3mm in the Y and a little less in X. I should say that this machine is built from 20mm thick Trespa TopLab and uses supported 20mm rails. I was never meant to be a brute of a machine and was only for light materials such as MDF, foam, balsa and any other material used in pattern making. It is pretty tough though it cuts ali pretty nicely but you can't go too deep with it. The gantry design does allow me to lower it for more rigidity but I'm unsure if the flexing is the gantry upright plates or the combination of the Y carriage plate and Z axis assembly. For now I'll be using it for light machining and drilling ops for the MK2 version which will be a totally different design, mainly ali frame and components.

Without the dust boot it does cut MDF, Trespa and Ali to within 0.02mm to 0.04mm so I'm happy about the fact I can make the parts for the next machine on it. Hopefully with the wires in parallel and the printed skirt it should do what it needs to do without any more cock ups.

In your wiring diagram, connect A to C, -A to -C (can't replicate the exact terms in your diagram but I'm sure you can see what I mean), and then A/C to A+ on the driver, -A/-C to A- on the driver. Ditto for B&D. I think you know that you only then need four wires back to the driver.

I did have a strip of draught excluder brush with long bristles for my dust shoe but it was a pain to make - getting the groove right was tricky with the balance between too tight/too loose and bending the strip to fit was just a bit fiddly. My cheap and cheerful solution works at least as well and costs nowt into the bargain! That's an engineering solution...

My bristles came from a draft excluder but your milk bottle idea made me think of the printed skirt idea, it's hands off and much less tedious to do. As for the wiring I think Kitwn confirmed what I thought when I read that so below is the schematic I'll follow when I rewire my motors...

The printed skirt...




The wiring schematic...

Yes twin screws so 4 steppers.

That's good news as I'm now reassured that there's enough power there.

The noise you are hearing is normal and if you haven't done the auto-tuning they will even scream/squeal sometimes.

I did the tuning but wasn't too sure what I was doing or what the Kp and Ki settings were about but found a decent guide in a Leadshine ProTuner manual, out of curiosity I'll try it again before I go parallel. They do squeal a bit which is noticeable when the ENA is not active (as in powered down) but I'll try them again when I'm back on the machine.

Your motors are Nema 34 so running them in parallel becomes even more important for a router. Large motors like these have a higher inductance than smaller NEMA 23 motors which means you require more volts to get the same rpm. Torque drops away much sooner up the curve with NEMA 34's so if you have them wired in series this compounds this even more which is why higher volts are needed to get high speeds out of nema34s.

What does bother me and makes me wonder if you have an issue is that while they won't spin fast when wired in series they shouldn't easily stall at lower RPM and no way should a few bristles from a dust shoe cause missed steps.? A series wired NEMA 34 with 68V should rip that dust shoe off the machine and not even know it's done it.!

These motors are NEMA 23, I got them from Zapp a few years back but either they've discontinued them or for some reason, I may be wrong they seem to be listed as NEMA 24. Either way the frame size is defo 23. I might have used the wrong diagram but I wasn't brave enough at the time of buying to get the 34s. I bought all the electronics before I'd designed the machine. I was 10 years younger back then and didn't know exactly what I was doing or getting into.

If you wire the motors in parallel and set the current to 4.2a then with 68Vdc you should expect to get approx 900 to 1100rpm before torque starts to drop away at any significant rate. So if you have a 5mm pitch and are getting 6000mm/min without stalling then your about right, but if you have a 10mm pitch then you should be seeing roughly double that.!

The setting is per phase so just set protune to the spec sheet per phase rating ie: 4.2a

As for speeds I think they stalled when rapiding at 7500mm/min so I brought it back down to 6000mm/min which is pretty quick over the size of bed I'm on, it's 915 in x and 515 in Y so not that far to go but I cut MDF at 4-5000mm/min, Trespa at 3000mm/min but shallow cuts only. I knew when buying the ballscrews that I should go with 10mm pitch but corona had started to go mental this time last year and the ballscrews were a bit of a panic purchase. The next machine is having 10's where needed and changeable pulleys for high res work.

As for the setting per phase or for motor total your last comment has really settled my mind. It's been bugging me for a while now with regards to what it meant. Not just on the router but on any stepper system. Anyway I can rest my mind on that one.

OK I'll see what happens with the new skirt tomorrow or Tuesday. Rewiring motor plugs, checking all the fasteners and re-tuning should see me good for a couple of days, I'll then report back.

Thanks again for your responses, I'd be goosed without this forum.