Wobblycogs CNC Mk2

[JAZZCNC]

I was thinking about maybe getting the parts water jet cut by a local company that could also supply the aluminium for the job. Unfortunately I have no idea how much water jet cutting costs, I'm guessing it's not cheap though. The other option would be to find some kind soul around these parts that would cut them for me.

Only do this for non critical parts has water jetting can leave slight angle on the edges so any plates the mate to each other can end up at and angle.

[Wobblycogs]

I've been reading up on the system electronics recently and I'm a bit confused about the current settings for the drivers. I'm using AM882 drivers and 60BYG301B steppers from CNC4YOU. The steppers will be wired in parallel and the stepper data sheet lists the current for that configuration as 4.2 Amps - all well and good so far.

The problem is that the manual (I have) for the AM882 under "Connections to 8-lead motors > Parallel Connections" it says:

...Multiply the per phase (or unipolar) current rating by 1.96, or the bipolar current rating but 1.4, to determine the peak output current.

That seems to imply that I should set the driver to 4.2 * 1.4 = 5.8A (dip switch settings SW1 = On, SW2 = On, SW3 = Off gives 5.5A or set exactly using ProTuner). That feels wrong to me though. I think the AM882 manual is assuming that the stepper data sheet will give the RMS current but it's not clear from the data sheet if that is the case.

What I think I should do is use ProTuner to set the peak current to 4.2A as the nearest dip switch setting is SW1 = On, SW2 = Off, SW3 = On which only gives 3.6A. Sound right?

[EddyCurrent]

From your data sheet the unipolar current is 3A so 1.96*3=5.88
the bipolar current is 4A so 1.4*4.2=5.88
the nearest setting is 5.5A with switches 1,2,3 set to ON,ON,OFF, this setting also supplies 3.93A RMS according to the AM882 manual.

That's how I would set them anyway but seeing as my setup is very similar AM882 + 60BYGH401 I'll be interested to see other replies.

[Wobblycogs]

Thanks Eddy, last thing I want to do is fry a stepper as soon as I switch it on.

The AM882 drivers can be connected to a PC for set up. This lets you set an exact current limit (0.1A resolution it looks like from the screenshots) amongst other things.

[Jonathan]

The correct current is the current at which the motors don't get too hot, i.e. above 80°C. Generally the easy way to find this, as you've done, is to use the datasheet, but if you're not sure then you can just start with a lower current and work up.

[EddyCurrent]

There's also this to set first.

"Auto configuration by SW4
Change SW4 two times in one second to identify the motor parameter after
power-up if it is the first time installation. Please note that the rotation
switch position must be 0 when using this function. "

Also to set the microstep resolution and current using Pro Tuner then switches 1,2,3,5,6,7 all need to be set to ON and switch 4 OFF

[Wobblycogs]

Thanks Jonathan, that was basically the approach I was going to take if necessary.

Eddy, I don't know why but I was under the impression that the auto-detect would only work for Leadshine steppers. I suppose if it's measuring the steppers response to given input signals though it could work for any make of stepper. I'll give it a go to see what it comes up with, I think the auto-detect can be triggered from software as well which is probably the way I'd go.

[Wobblycogs]

I had some time off over Christmas so got cracking with putting together the electrical cabinet. I've literally just achieved "first rotation" as it shall forever be known in our house.



My main inspiration was Eddy's recent build but there are some of my own ideas in there too. The case is a 600x600 and I've left space for an additional driver if / when I add one. The power supply was proving difficult to fit in until I had the burst of inspiration to go vertical. The clear perspex cover (I call it the idiot guard) was a secondary addition after I got a first hand experience of quite how much power the capacitor bank holds:



The capacitors were almost completely discharged when I probed the top to see what voltage they still held. One slip with the positive probe and a bright flash and bang later and I need a new probe.

The builds not quite finished yet but as you can see I've got a stepper attached and had it rotating using the test mode of the PMDX. Some how, despite measuring everything ten times I've still managed to make it a bit tight around the BOB. I must have been having an off day or something but fortunately I've got just enough space.

I'm going to look at building a soft start for the transformer. As I mentioned in another thread I'm getting some nuisance trips off a 6A Type D breaker. I might give a slow blow fuse a go if I remember to buy one next time I need some parts but I can't imagine it's good for the transformer to be getting whacked with 100A+ at start up. What I can't decide is whether to build a timer circuit to disconnect the soft start thermistor or to just leave it in all the time. The power supply is delivering a steady 71V, many thanks for the help with that so far guys :D.

Anyway, the one thing that surprised me about the set up was that the stepper wasn't silent when it was stationary. It makes a sort of kettle just going off the boil sound if that makes any sense. Is this normal? When it's turning it's quite quiet although I've only had it turning at one speed. I should probably say I've not fine tuned the current for the steppers yet, I just quickly selected a setting that was well below the maximum the steppers can handle.

[EddyCurrent]

"First Rotation", sounds like a maiden flight.

Looking great, 600x600 seems a good size as there's plenty of room in there. Perspex cover is a good idea, it's always best to aim for IP2X with a panel.
I also found stepper a bit noise upon first fire up, used Pro Tuner to set the current and now very quite indeed.
I don't know what the requirement are for that inverter but mine specified 75mm free space both top and bottom for cooling, must be installed upright, no requirement for free space at the sides.

[Clive S]

I don't know what the requirement are for that inverter but mine specified 75mm free space both top and bottom for cooling, must be installed upright, no requirement for free space at the sides.

Eddy Is that to stop the electric from falling out.