Upgrade stepper. Go for Keling?

Hallo guys, I need to upgrade my system, made now of one chinese tb6560 4ch stepper driver, 4 nema23 175oz/in motors powered by a 24V 15A switching p.supply.
I need more power (but not so much..), because by now i can move (it's an inverted tetrapod) objects of about 3kg, but i need to hung objects a little bigger without losing steps. let's say 10-12 kg.
Another problem is that i cannot go to nema34, because my motors-drums frames are built for nema23 and modifying them is not so simple..then also my budget for this mod is not so big, let's say 5-600$

I have found only two solutions for now:
one is an offer from Modelshopcnc for 4 steppers (nema23 3,5A 6,4mH 620oz/in) combined with a gecko 540, which gives 3,5A/ch at max 50V. and i should add power source. (is a breakout board needed?)
the other is the Keling kit with 4 steppers (nema23 5A 2,5mH 570oz/in) combined with 4 KL-6852 drivers (5,2A/ch, max 68V) a switching p.source 48V 12,5A and a breakout board (chosen between C10 and C35 from CNC4PC).

some questions i'd like to ask you, before buying, apart from costs, obviously:
-Which of these configs can be more powerful? I mean, what i need are real oz/in at the higher speed possible.
-Do you know of other better-working combinations? i mean, staying into nema23 size. (or any suggestion will be appreciated..)
-My motors are 20mt far from the pc, what do you think is best, to have a breakout board near pc and drivers near motors, or also drivers near pc and only motors far?
-Do you know between C10 and C35 breakout boards which is better? other suggestions?

another issue is that i only have found these things in US. If you know a good deal also in Europe it will be very appreciated!

Thank you very much, Davide.

dab77 wrote:

some questions i'd like to ask you, before buying, apart from costs, obviously:
-Which of these configs can be more powerful? I mean, what i need are real oz/in at the higher speed possible.
-Do you know of other better-working combinations? i mean, staying into nema23 size. (or any suggestion will be appreciated..)

It is important to know that developed torque falls off sharply as speed increases.
The exact torque vs. speed curve depends on the motor, drive and power
supply voltage. More voltage generally moves the torque falloff to higher
speeds, but also increases motor heating.

Lower motor inductance is generally better, so the 620 Oz-In 6.4 mH motor may
well have less running torque than the 570 Oz-In 2.5 mH motor.
But, you;d need to use Gecko 201-series drives instead of the 250-series
drives in the Gecko 540.

-My motors are 20mt far from the pc, what do you think is best, to have a breakout board near pc and drivers near motors, or also drivers near pc and only motors far?

20 m of cable is not likely to affect motor performance greatly. Possibly
there could be interference in the step and direction commands to
drives located remotely from the PC, although proper wiring design
could solve that.

Jon

Thank you Jon for answering. are you saying that is possible to buy Gecko540 with 201series modules inside? or i misunderstood?
ok for the mH considerations, i will take that in mind..
is there a formula to undestand approx how many volts can i send thru the motor? or do i have to use a hand-heating sensor?

So you suggest is better to let drivers near the pc, in every case..

I'd like very much to use your Geckos, but costs for this ampere request will go to far for me, i think.

thank you again, or if you have other suggestions, you're welcome!

davide.

dab77 wrote:

Thank you Jon for answering. are you saying that is possible to buy Gecko540 with 201series modules inside? or i misunderstood?

Nope, they physically won't fit inside.

ok for the mH considerations, i will take that in mind..
is there a formula to undestand approx how many volts can i send thru the motor? or do i have to use a hand-heating sensor?

Mariss has a formula on the geckodrives web site for estimating the best voltage
for a particular motor. It should be in the data shet for the drive, or maybe in a
white paper on there.

So you suggest is better to let drivers near the pc, in every case..

No, not really. If you are experienced in installing digital systems for tolerance
to interference, then putting the drives and power supply on the machine is
probably best. But, poor wiring design will cause interference to the step and
direction signals, and then it can be hard to troubleshoot. But, a poor wiring
plan will cause trouble no matter where the drives are placed. Using twisted
pair wiring to the step and direction inputs between PC and Gecko drive
is required. Unfortunately, the Geckos have a common terminal which
partially defeats the current loop control.

I'd like very much to use your Geckos, but costs for this ampere request will go to far for me, i think.

MY Geckos? I don't have any relationship with Gecko, except that I know they make a
VERY good stepper drive.

Jon

In my experience, one of the tricky parts about matching a motor to the drive is the maximum supply voltage. The recommendation from Gecko is:

Supply Voltage = sqrt(inductance) * 32
Supply Current = Number of motors * Motor Current * (2/3 for parallel motors, 1/3 for series motors, most are parallel)

That maximum voltage will give you the most torque at high speed possible, without killing the motor from heating. The problem with most lower current motors is that motors under 3.5A (so they would work on a Gecko G540 or G251 drive) have a higher inductance, meaning they need way more than the 50V maximum from those drives. 6.4mH, for example, needs a max supply voltage of 80VDC to achieve their maximum capabilities - too high for the G540.

I would recommend one of these two routes:

Gecko is selling their own steppers right now, and they are a very good deal, in my opinion, and well matched to their drives. Only two options, and both are NEMA 23. That is limiting for some people, but ideal for you. www.geckodrive.com

1. Use their 280 oz-in stepper, a Gecko G540 (no breakout board needed, the G540 is basically 4 G251 drives and a simple breakout board in one enclosure), 10A, 48VDC supply
2. Use their 400 oz-in stepper, 4 Gecko G201X drivers, a simple breakout board and a 13A, 48VDC supply

Neither is the cheapest possible option, but both are relatively inexpensive, and very well supported combos.

-Sam

andypugh wrote:

However, for high speed applications like this, servos really would work a lot better. And cost 20x what you have already spent.

Well, no, not 20X. Keling has some great brushless servo motors, the KL23BLS series,
about $52 without encoder. You can get some decent basic encoders from US Digital,
Avago or others, although the 1/4" diameter shaft limits choices a little.
My brushless servo amp is $150 per axis. And, for servos you do need a controller/
interface like my Universal PWM Controller.

So, a 3-axis system runs about $1000. Not great if you have already bought a system that
doesn't meet your expectations. But, not hugely more expensive if you went with such a
system from the start. A Universal Stepper Controller plus 3 Gecko 201 drives and
3 decent stepper motors will still run $750 or so.

Jon

to be precise, this is my kit: www.ebay.co.uk/itm/CNC-Kit-4-Axis-TB6560...&hash=item415ef2d479
I have to say i never had problems, other than noise from motors (and there are instructions on a forum to modify this driver to make it really better..), so considering that i buied this kit to play and understand if it was possible to build an inverted tetrapod and make it run, i think it was the best deal! now i need two higer steps: the first is just increase power with stepper system for medium flying objects (max 10-15kg, considering now i can with 3-4kg), and with a little budget.
next one, in the future and with a bigger budget, will be with servo motors, new frames, mesa drives for big power, generally a really more serius thing...
Considering your suggestions (thanks) i think i'll have the best balance with keling or with cnc4you. Have you ever had experience with their drivers and bobs?