A bit of background first...
The motors I currently have on my milling machine are only 1Nm, with a Unipolar driver which I've just sold to raise money for the new stuff. These motors are mounted to the side of each screw and connected via timing belts etc to give a ratio of about 1:2 (I tried various ratios). With this setup the maximum feedrate I could get was 1.4mm/s, and that was pushing it. This is with the standard 2.5mm pitch ACME screws that came with the machine.
Anyway, I've finally decided to buy 3 (or 4) new stepper motors and drivers from Zap so that I can get a higher feedrate. I was about to buy them yesterday but thought I'd just check first:
I'll be running them at 72V. I'll probably experiment a bit with the pulleys to see what works best.
My question is what feedrate can I realistically expect to get with this setup (without ballscrews), and are those motors/drivers a good combination? I'd like maybe 25mm/s.
Might these 3.5Nm motors be better? I'm guessing not as Nema 34 are generally slower, being bigger?
(I live just a couple of miles away from Arc-Euro so those would be pretty convenient.)
Here's a link to me using the machine to turn something, just to show which milling machine I have (skip to the end of the video):
Thanks in advance...
for 25mm/s (1500mm/min) you need to spin those motors at 300rpm. At 72v those motors have a corner speed of 1023rpm so you will be near optimal as regard their torque curve, indeed you might be better off with 1:1 gearing (motors running at 600rpm). Assuming a 20mm screw then you should get pretty close to your goal.
The 3.5Nm motors have a higher inductance and are more marginal than the 3Nm ones at the speed you require with 1:1 gearing... stick with the 3Nm
The Following User Says Thank You to irving2008 For This Useful Post:
We sell the PM752 with the SY60 and they work well together.
Also 72V is a bit too high for the PM752 driver, it will work, but is a bit close to the max voltage.
At a high voltage the Arc motor should perform well, but will not spin as fast as the Sy60, but will have a lot more torque at the slower speeds.
I would also point out that the datasheet is wrong, and if connected in parallel the current would be 6A not 4.2.
It is odd that they say the motor is rated as 4.2A in parallel because parallel current would be double the series current.
All i can think of is that the motor has a problem running at 6A, so if you decide to use this motor, i would ask the question to them.
The Following User Says Thank You to Gary For This Useful Post:
Those 3Nm motors you sell Gary will do fine for this application at 60 - 65v with no meaningful loss of torque as even at 60v the corner speed is 850rpm so he'll still be in the flat region... in fact it would still just be ok at 48v but I wouldnt go any lower than that..
How did you work out the corner speed of the motors?
When I said 1:2 earlier I meant smaller pulley on the motor to double the torque...the 1Nm wouldn't move without.
The screws are about 25mm I recall, though that's a guess...
Based on a corner speed of 1023rpm, and 1:1, would if be reasonable to expect 40mm/s for traversing? I guess this is difficult to say since there are so may factors.
If 72v is a bit high what would you advise? 60v?
I'm still not sure what to use for the power supply, rewinding a microwave transformer I've got seems an attractive (i.e. cheap) option, so does putting 5 or 6 computer power supplies in series, isolated, for the same reason.
If I buy the motors and drivers tomorrow how soon will you be able to post them. I ask because your website says the PM-752 isn't in stock?
Thanks again for the help...
The PM752 is running low, but have about 15 in stock and another 100 cominig in in about 2 weeks.
I've been waiting for money to transfer to my bank account from paypal. I didn't pay with paypal directly as I don't think it's fair to make a website pay paypal fees when I can pay using a debit card. Now I've just found that the stepper drivers have gone up from £44 to £50 today :( Now I've not got enough pocket money...
How much difference will getting the PM542 and running the lower voltage make?
Last edited by Jonathan; 21-05-2010 at 06:08 PM.
The price has gone up because of the exchange rate, out of my control im affraid.
have a look at the torque curve in the datasheet, and this will give you an indication of the difference in power.
My mum lent me £20 so I was able to buy them on Friday :).
Order was dispatched on Monday and arrived yesterday - excellent service, thanks!
Been doing some testing...
I've not got round to making pulleys for a 1:1 ratio, so for the moment the closest I can get is 22T on motor, and 42T on screw.
The motor stalls above 1250rpm (no load), yet it still has enough torque to drive the X-axis at 25mm/s (1150rpm). Trying higher feed-rates than this gets a bit dicey.
I think this means that if I put a 1:1 ratio, then above 25mm/s is almost certainly attainable since the motor will only have to run at 600rpm to get the 25mm/s. Having said this the current speed is pretty scary! I had to put a lot of tension in on the belt to stop it slipping.
Currently I'm using 1/4 microstepping. I've tried 1/8 but it doesn't seem to make much difference. What do you recommend I use? The computer I'm using is only 1.4ghz, this might be a limiting factor? I'm using Mach3 at the moment, I intend to change to EMC.
Also, I've set the port frequency setting in Mach3 to 25Khz. I tried 35Khz but it seemed worse, should one be better than the other? I've set the pulse width to 5us, is there any reason to change this? I guess not unless I start using 10000pulse/rev...
Thanks for all the advice so far.
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