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sambo2
08-07-2016, 10:19 AM
I'll start with a bit of background. I have an RF-45 style mill that i'm planning to CNC over the next few months. I've got ballscrews and am converting all the axis at the moment, planning to drive the head rather than the quill for the z axis. Probably going to go for a 2:1 reduction on the drives.
On to the drivers... I was thinking for this size mill I should use a Nema34 size stepper, I can't afford to use servo drives at the moment and it's only a hobby machine so I think it'd be wasted too. I've narrowed it down to a digital driver, now do I go for a leadshine EM806, DM870 or the Kinco 2M880N? They are all similar priced at about 100 a piece from Zapp or Motion. The other option is a CWD 872 from cnc4you for 66. I guess my question is are the other drivers worth the extra or will I get good enough results using the cheaper?

I understand the impedance should be used to calc the running voltage. I have seen 34 motors with 6-8mH per phase and approx 8Nm so this would give a voltage of 78-90V based on the square route(impedance) x32 from the gecko drive site. Does this sound right or should I double the impedance as two phase? I would be running at 70-75v as the drivers are only 80V so would loose some motor power and speed. I could however go for a 23 size motor producing 4Nm and gear down further to get the torque. This motor could run at 60v and achieve almost maximum performance.
What do you guys think?

Sorry for all the questions!

Clive S
08-07-2016, 11:23 AM
Hi and welcome to the forum. Nema 23 with AM882 or the 806 drives with a 70V none linear power supply would be fine. Belt drive the screws

m_c
08-07-2016, 11:47 AM
I'd say Nema23 with a good driver.

Nema 34 although they produce more torque, you really need to run via high voltage drives to get good acceleration out of them.

sambo2
08-07-2016, 12:49 PM
Thanks guys. I thought the smaller motors would be fine but after reading all the American conversions where they use big motors I doubted myself.
It doesn't seem like you can beat the AM/EM drivers for the price.

sambo2
08-07-2016, 02:35 PM
Right, I've been window shopping and can't find many places selling EM806 drivers in this country. Zapp has 1 in stock and Motion want 150 each which seems a bit steep at 50% more than Zapp. I also can't find anywhere in the uk to buy the AM882, theres some on eBay for about 50 quid from China but i'd prefer to get from the uk if possible.
Do people usually import or are there more uk suppliers?

What's the consensus on the cnc4you nema 23's at 4Nm too? They seem fairly low impedance but are there better?

Clive S
08-07-2016, 05:00 PM
Right, I've been window shopping and can't find many places selling EM806 drivers in this country. Zapp has 1 in stock and Motion want 150 each which seems a bit steep at 50% more than Zapp. I also can't find anywhere in the uk to buy the AM882, theres some on eBay for about 50 quid from China but i'd prefer to get from the uk if possible.
Do people usually import or are there more uk suppliers?

What's the consensus on the cnc4you nema 23's at 4Nm too? They seem fairly low impedance but are there better?cnc4you is a good place to buy the motors. Zap has them as well.

I would go for the 23's 3.1Nm. I have them running on my Warco WM18 mill that I converted.

I have never had any problems buying the drives from China and will save you a lot of cash. the AM882 is the earlier model of the EM806 but are proven and very good drives.

Have you thought about a motion controller? or are you going down the P.P. route

sambo2
08-07-2016, 09:25 PM
Thanks Clive. Out of interest, what pulley ratio are you using with those steppers?

I've not decided yet. I've read PP can be better for Mach which I will be using, I'd need to get a PP card for my pc but they seem cheap enough on ebay. I'm also on 64 bit but I can load a 32 bit OS if needed. This looks the cheapest way as the PP break out boards are less than a motion controller.
On the flip side, are there any reasonably priced motion controllers? Things like the smooth stepper seem to cost a fortune.

JAZZCNC
08-07-2016, 11:14 PM
I've not decided yet. I've read PP can be better for Mach which I will be using,

Well who ever wrote that is talking rubbish or more likely they never used an external motion controller. Night and Day difference between them.

If you want cheap but good External controller then Pokeys 57cnc is great little board and uses Ethernet which is much better than USB. To be fair most of the current main stream lower end motion controllers like Pokeys, UC100 or UC300, Pmdx 411 are ok and far better than PP.

Regards the drives then don't be afraid of buying AM882 from China I've bought 100's and not had one faulty or problem.

If you go with Nema 34 larger than 6Nm then go with High voltage mains drives.

sambo2
09-07-2016, 09:32 AM
Thanks Jazzcnc. I got that info from some American cnc sites. It's hard to pick out the crap info from the good stuff as there's so much to sift through.
I'll go for one of those motion controllers, thanks for the recommendations.
I'll go ahead and order the drivers then. It's much more cost effective getting them from there even with duty added.

I'm pretty sure I'll go for the 23's as suggested but I do have a pair of old slo-syn nema 34 steppers by superior electric to play with too.

Thanks for all the help guys :)

JAZZCNC
09-07-2016, 11:21 AM
I'm pretty sure I'll go for the 23's as suggested but I do have a pair of old slo-syn nema 34 steppers by superior electric to play with too.

If those are the Old round type then won't compare to modern square type. You'll get much better performance from modern motor.

sambo2
09-07-2016, 07:49 PM
I thought as much. For such a large motor they've got a small output too.