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17-06-2017 #1
Thanks for all the advice from members of this forum. Finally bought 3 AM822s - http://www.ebay.co.uk/itm/330782929553 - worked out at about £62 each including UPS shipping (one week) and VAT etc.
Very pleased with these except that they're not driving the direct coupled Astrosyn Nema 34 4.8Nm (8 wire series connected) motors above about 500mm/min terribly well. Plenty of torque at low speeds but losing steps at anything over 500mm/min on the X-axis. This is a very high quality Swiss made mill-drill with 4mm pitch ball-screws and coated cast iron dovetail slides - the coordinate table weighs in at around 100kg. The machine specs state that the maximum rapid traverse was 4000 mm/min. The original motors were massive Superior Electric 11A 2.1Nm jobs, so the Astrorsyns should be up to the job.
The motors have a nameplate current of 2.8A. The best match to that on the driver is 2.57A. They do perform better at the next setting (3.29A), but they get too hot to touch (just warm at the lower setting).
I've got the micro-steps set to 32/6400 and Mach3 set to 1600 steps/rev which seems to give reasonable smoothness.
I'm using a 36v 9.6A switch mode power supply to power all three drivers. I suspect that this is the weak point and that 60 or 72v supply would improve higher speed performance.
Any observations welcome.Last edited by Agathon; 17-06-2017 at 12:32 AM.
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17-06-2017 #2
Wire them bipolar parallel, with double the current.
And yes, double the voltage.
Also try 1/8 or 1/16 microstepping.
Note that with the Protuner Software, you can set the current to any value you want, and are not limited to the default settings.Gerry
______________________________________________
UCCNC 2022 Screenset
Mach3 2010 Screenset
JointCAM - CAM for Woodworking Joints
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17-06-2017 #3
I would certainly agree with Gerry - run the drivers at 68-70V, and go to parallel connection. Series connection is fine but is more suited to lower-speed operation. One of the important things about steppers and speed is to look for low inductance. In effect, this is a kind of electrical inertia that slows the rate at which current can build up through the motor windings and as it's current that gives driving torque, current and fast change of current is what you want. Series connection adds the coil inductances together; parallel connection halves the inductance. Much better!
I'm a bit surprised as well that you are using NEMA 34. Given that the original motors were 2Nm or so (were they steppers or servos?) I would have guessed that you could get away with NEMA23 4Nm. Smaller, lower inertia, lower inductance. If the NEMA23 has enough grunt, it will typically give better performance than a NEMA34, which is contrary to expectation but it can be true. Max useful speed is about 900-1000RPM, which would give close to your nominal 4000mm/min with those ballscrews.
I would have slight reservations about a SMPS as well. These can current-limit under peak load conditions, just when you need the current most. A simple linear power supply with big capacitors on the output can cope much better with peak loads in this situation. People use SMPS quite happily, but they need to be well-specced to make sure.
I'm a little confused about your microstep settings. Again, Gerry has given the usual advice - 8 to 16 microsteps is generally a good compromise between resolution, smoothness and torque. So, x8 gives 1600 microsteps/rev. That's 4mm of movement, so Mach3 should be set to 400 steps per mm.
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17-06-2017 #4
Many thanks for your replies Gerry and Neale.
I have three Astrosyn motors on the machine two L709s (x&y) with an inductance of 7.7mH and one L259RE (z) with 3.5mH - both physically the same and both with the same torque (2.8 and 4.3 amps respectively). I've used Nema34 motors as that's what the original stepper motors were and these bolt straight on with no modification.
I've changed over to parallel connection and set the driver to 5.86A rms and it's much, much better. Motor heating much lower too.
I had the drivers set to 32 microsteps since this seems to give the best compromise between speed and smoothness. Just to address Neale's point about steps - the feedscrew is 4mm pitch. 200 steps = one rev/4mm travel. At x32 = 6400. 6400/4 = 1600 = 1/4 rev or 1mm travel.
Having it set at 32 microsteps means that I can't go faster than around 1000mm/min which is a bit slow for rapids, but I can live with it. I've just knocked the drivers down to 8 mcstps and set the travel at 1800mm/min and this works well except that the "sensorless stall" protection trips from time to time. I'm guessing this is down to the power supply not being up to it.
Any recommendations for a source of an unregulated power supply?
Finally, I'm keen to use the Protuner software, but my computer doesn't have an RS232 serial port - any advice on how to connect?
Thanks again David
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17-06-2017 #5
I bought the Leadshine RS232 cable, and a USB to RS232 adapter cable, and run Protuner on my laptop. It works fine.
With ProTuner, I set my current reduction to 30%, to keep my motors even cooler.Last edited by Ger21; 17-06-2017 at 02:33 PM.
Gerry
______________________________________________
UCCNC 2022 Screenset
Mach3 2010 Screenset
JointCAM - CAM for Woodworking Joints
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17-06-2017 #6
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17-06-2017 #7
Not sure. I posted the pinout info in another thread. http://www.mycncuk.com/threads/10842...1052#post91052
Last edited by Ger21; 17-06-2017 at 02:55 PM.
Gerry
______________________________________________
UCCNC 2022 Screenset
Mach3 2010 Screenset
JointCAM - CAM for Woodworking Joints
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17-06-2017 #8
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There is no problem making your own if I remember correctly there is only 4 wires. I am away at this time but I seem to think the pin out was on the website leadshine
Edit https://oceancontrols.com.au/LSK-001.htmlLast edited by Clive S; 17-06-2017 at 03:02 PM.
..Clive
The more you know, The better you know, How little you know
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17-06-2017 #10
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