Machsupport Forum

Third party software and hardware support forums. => PoKeys => Topic started by: boskap on October 26, 2017, 04:52:12 PM

Title: Change Stepper to Servo
Post by: boskap on October 26, 2017, 04:52:12 PM
Hi
Is it Possible to change my StepperMotors  to this Servo with integrated Driver
http://www.jmc-motor.com/products.php?cid=249&id=162

How i must them Connect to the Pokeys57cnc ?
Settings ?

thx Peter
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 26, 2017, 06:04:02 PM
Hi,
yes its possible to run these motors.

While they are advertised as servos I suspect they are in fact stepper motors with encoder feedback, good
to be sure, but still have the same essential limitations of a stepper, poor torque at high speed.

I would insist that I were provided torque/speed diagram before I parted with any money. Don't be taken in
by advertising hype.

Craig
Title: Re: Change Stepper to Servo
Post by: boskap on October 26, 2017, 06:47:44 PM

over posteps ?
or posteps are didnt needed because this servos have the driver implemented

but how i connect them direct to pokeys57cnc
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 26, 2017, 07:29:34 PM
Hi,
you can connect them just like you would an open loop stepper, Step, Dir and Enable.
You can also monitor the fault output signal from the servo/driver if you wish.

Craig
Title: Re: Change Stepper to Servo
Post by: boskap on October 27, 2017, 01:40:07 AM
sorry i dont not know howbto vonnevt it directly to the pokexs device
whivh pins from the 8pin vonnector

sometimes i read i need then poblocks
or not

can you make a short wiring diagramm

thx
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 01:46:25 AM
Hi,
how have you connected your stepper drivers? These servos should connect the same way.

Craig
Title: Re: Change Stepper to Servo
Post by: boskap on October 27, 2017, 01:53:23 AM
hmmm
my steppers are conmected ofer the posteps driver
but need i the postebs driver when the servo have there own
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 02:25:11 AM
Hi,
page 16 of the 57CNC manual shows the pinout of the 8 pin motor sockets.

You will need the Enable pin1, Dir pin3, Step pin5 and if you want the servo to be able to signal an error back to Mach then Error pin7.
Pins 1,3,5 are all DO5 type pins, 5V output, 100Ohm impedance, 8mA max current per page 19 of the manual. Should be able to drive the input opto couplers
directly. The Error input is DI5P type, 5V tolerant, pulled high by 10kOhm, page 19, and can be connected to the Alm+ output of the servo driver.

The connection is simple.

Do you really want those servos? Get a torque vs speed diagram before you buy them. If they can't supply one then stay away from that brand.

Craig
Title: Re: Change Stepper to Servo
Post by: boskap on October 27, 2017, 04:40:16 AM
well now i have open loop steppers
and when i see what closed loop cost and this servo cost then my option ist servo
a friend from germany already hat it and is super happy with them
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 04:49:39 AM
Hi,
then get a torque vs speed diagram for it. If they're good that is the evidence, they could be recommended by God himself but I still want to see the torque vs
speed diagram BEFORE I spend anything!

Craig
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 05:18:11 AM
Hi,
whats wrong with the open loop steppers?...are they losing steps or too slow? Many people seem to think that a closed loop is going to solve 'lost steps',
certainly that's the advertising hype,  if a motor is loaded to the extent its losing steps then feedback is going to try to overcome that but feedback
DOES NOT make a motor any more powerful. If it was losing steps because it lacked the torque to do the job, it will still lack the torque, lose steps and
then fault out 'following error' feedback or not.

Servos, either brushed DC or brushless AC maintain their torque at high speed and beat stepper motors hands down above 1000 rpm or so. Stepper motors
have lots and lots of torque, for their size, at low speed. In fact steppers beat servos hands down at low speeds, for torque anyway.

Steppers and their drivers are way cheaper than good servos and except for high speed are as good or better than servos of the same size. If you really really
need your machine to go fast then pay up....and for your high speed production machine you'd be stupid to buy cheap crappy servos, you need good ones which
will last.

I repair welding equipment for a living and I see cheap Chinese electronics all the time...don't go there....they can and do make good stuff but its not cheap!

Craig
Title: Re: Change Stepper to Servo
Post by: boskap on October 27, 2017, 09:04:49 AM
ggg
no i am ahobby user only
i mill now with my second milling machine the third bigger and massive one
for the new machine i need stronger motors
so if i take steppers then i need new driver

i can take the postep 60 but i then prefer i closed loop system
or i take the servos
a friend have them and have good experience with it
(https://www.youtube.com/watch?v=O_PR7S4j1og&t=94s)

which stepper cloes loop can you advice

thx
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 09:42:21 AM
Hi,
34 size, that is 80mm square motors can be had in various lengths upto about 2000 oz.in (10 ft.lb or 15Nm). Low inductance windings promote
high speed torque in conjunction with a high voltage driver, ie minimize a steppers disadvantages.

American made Gecko drivers have a very good reputation, their 80V 7A models are around $150. Some experienced CNCers recommend Leadshine
AM 882 80V 8.2A drivers which are good value for money at $75.
Title: Re: Change Stepper to Servo
Post by: boskap on October 27, 2017, 10:04:56 AM
ok that are the drivers
but motors ?
and can i connect this leadshine to the pokeys
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 10:31:39 AM
Hi,
there are lots to chose from, Leadshine 86HS85 are 8.5Nm units  for about $80, even bigger 86HS120 which are 12Nm are about $200.

Note these with the AM882 are open loop systems. Closed loop systems tend to cost more yet not really get any advantage, they are still stepper
motors, a closed loop driver done not make them any more powerful or faster. They will try to make up for lost steps if there are any but in most cases
if they lose steps they can't make them up because they're just plain overloaded so the drive faults 'following error' and shuts Mach down.

An 8.5Nm motor and drive would cost about $155 plus shipping. A 400W Delta servo is rated for only 1.27Nm and servo and drive cost about $380
and a 750W is still only 2.39Nm with servo and drive about $600. The servos will be much faster but also way more expensive. Used within their
limitations the open loop steppers will work well for a fraction of the price.
Title: Re: Change Stepper to Servo
Post by: boskap on October 27, 2017, 11:20:51 AM
thx for your detailed description
but thats the point
this servos with implemented encoder and driver cost 130€ + shipping
i need 4
x y z and a

gecko 150$ + Leadshine 86HS85 80$ are cost more
and i think servo are the future
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 11:48:20 AM
Hi,
get some proper information about those servos. They sound too good to be true.....and therefore probably aren't true.

130 for proper servos....yeah right! Good luck.

Craig
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 27, 2017, 11:10:42 PM
Hi,
found these on Ebay:
https://www.ebay.com/itm/200W-3000rpm-0-64N-m-NEMA24-Economical-AC-servo-motor-driver-kit-36VDC-1250-line/263174349390?hash=item3d4669e24e:g:vl0AAOSw7ZlZpTq8 (https://www.ebay.com/itm/200W-3000rpm-0-64N-m-NEMA24-Economical-AC-servo-motor-driver-kit-36VDC-1250-line/263174349390?hash=item3d4669e24e:g:vl0AAOSw7ZlZpTq8)
which is pretty cheap, note that its only 0.64Nm.

https://www.ebay.com/itm/200w-60mm-0-64Nm-3000rpm-AC-Servo-Motor-drive-kit-absolute-20Bit-AC220V-JMC-CNC/263257457182?hash=item3d4b5e021e:g:jXYAAOSw6b9Z3bjT (https://www.ebay.com/itm/200w-60mm-0-64Nm-3000rpm-AC-Servo-Motor-drive-kit-absolute-20Bit-AC220V-JMC-CNC/263257457182?hash=item3d4b5e021e:g:jXYAAOSw6b9Z3bjT)
This unit is made by the same company that you linked to but these are the real deal AC servo and note the price, $300 plus shipping. And like the
previous model I linked to still only 0.64Nm.

If you want Mitsubishi, Panasonic or Yasakawa double and triple and more those prices and still only 0.64Nm.

I think 130 EUR is highly optimistic or alternately very  very low powered 50 or 100W either way insufficient for a decent size router/mill.

Craig
Title: Re: Change Stepper to Servo
Post by: boskap on October 28, 2017, 03:36:45 AM
Hi
the holdingtorque of the stepper like leadshine is 8.5nm
but when you drive 500 revolution you only have about 3nm
at 1000 only 1nm

this servos have about 1.8kn at 300%
and when its right konfigured the have also much power at low feed rates
Title: Re: Change Stepper to Servo
Post by: joeaverage on October 28, 2017, 04:28:49 AM
Hi,
you're right steppers lose torque at speed, low inductance units like these lose less than most but still only have a 1/4 of their torque at 1000 rpm, so
about 2Nm or 305 oz.in.

I've found a spec for the largest of the integrated servos from JMC, 180W and 0.57 Nm or 87 oz.in. The servos can temporaily do three to four times their
continuous rated torque but they'll fault out in 20-30 seconds. If you expect to run them in excess of their continuous rating you'll be disappointed.
Quite frankly I doubt 87 oz.in is enough for a substantial machine. If they lag behind because they don't have the torque to maintain the position/velocity
profile of your Gcode trajectory they will try to keep up and either overheat and fault 'over temp' or lag behind the position required and fault 'following error'
Closed loop feedback does not make servos immune from being overloaded and when overloaded they perform just as badly as any other overloaded motor.

Quote
and when its right konfigured the have also much power at low feed rates
wrong...they have 0.57Nm torque from 0 to 3000 rpm, they do not
have more torque when going slow.

You might be advised to get one and try it out before you buy the whole lot.

Craig