Messages

2071

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 31, 2019, 05:01:27 AM »

Hi,
I would guess that the ultimate speed limit will be the rigidity of the machine or possibly the power, or lack
thereof, of the spindle.

As the speed goes up so do the cutting forces and any flexure in the machine can badly degrade the work.

I have two spindles, one German made 24000 rpm asynchronous spindle with ER11 manual tool holder and
a home made Rego-fix ER25 cylindrical in P4 angular contact bearings powered by my Allen Bradley 3500 rpm 1.8 kW
6Nm servo. The high torque slow speed spindle I made so I could machine steel and stainless steel. It works great
but the cutting forces are high. Despite my machine being made of cast iron it still flexes, the rate of metal removal
depends on the amount of flexure I can tolerate with a given operation.

As I said earlier acceleration is the key, less important is the speed. The steppers you have ordered will be an order
of magnitude faster than what you have currently. I suspect they will be faster than the machine can safely and reliably
handle.....machine flexure will determine the limits....not the steppers.

Craig

2072

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 31, 2019, 01:27:14 AM »

Hi Marky88,
I have been wanting to swap out my steppers for servos for a while. I have just (10 minutes ago) ordered a Delta B2
series 400W servo, drive and cables, price $460USD including shipping to New Zealand. I still have to pay 15% tax
when it enters the country so will cost $872NZD by the time I get it.

When I built my machine I bought secondhand 23size 5 phase Vexta steppers with low lash (less that 3 arc min) 10:1
planetary drives. Despite the small motors the 10:1 reduction means I get great torque, just over 700 oz.in. They drive
directly a 20mm diameter 5mm pitch ground ballscrew which gives a stall thrust of over 1400kg force or 14kN.
The only downside is the gear reduction means its slow, I have them tuned for 1200mm/min. I can get them to do 2000mm/min
but I have to run them at max current (1.4A per phase) and they get hotter than I like. So I run them at 1.1A per phase.
The vagaries of 5 phase steppers is that four phases are energized at any one time so 1.4A phase rated is equivalent to 2.8A
in a 2 phase stepper. At reduced current and consequent less torque I've found that 1200-1500 mm/min is reliable.

At 1200mm/min the ballscrew rotates at 240 rpm and so the stepper is rotating at 2400 rpm. You might ask 'can a stepper
do that speed' given the nature of this thread. 5 phase steppers are a bit specialist. Among the advantages they have over regular
two phase steppers is smooth operation without the vibration propensity of two phase steppers, high speed operation
and 500 full steps per revolution compared to 200 full steps per revolution for a two phase stepper.

The drivers I use are specialist Vexta 5 phase drivers. They don't require a power supply, you wire them directly to 230VAC.
I have measured a peak output voltage at the stepper of 150VDC. So you can see that Vexta drives have a very high voltage output
which goes a long way to secure the high speeds that can get.

Even secondhand the steppers and drives were not cheap, $278USD each plus shipping for the motor and gearbox and $147USD
each plus shipping for the drivers.

These steppers have been absolutely superb....once I had them tuned they never missed a step (except when I crash!) and I get
repeatable resolution of 1um. They have been so good I don't think I'll sell them....I'm so impressed with them. I'm sure I'll
find other uses for them. Of course I've only ordered one servo so far...I'll have to save a few more pennys before I can
buy another two!

Craig

2073

Mach4 General Discussion / Re: Mach 4 Licencing Question

« on: August 30, 2019, 07:32:15 PM »

Hi,
to get a licence for any given PC you have to supply the unique PCID. Normally you would do this by saving the PCID to the
clipboard, logging on to the NFS wesite Licencing page and paste the PCID. If you don't have an internet connection for the
PC you are trying to licence you could save the PCID (of the target machine) on a thumb drive, and then on another PC that
has a connection paste the target PCID into the licencing page. You would then receive the licence files on your connected
PC which would have to be transfered by thumb drive back to the target machine.

You should be able to run your machine from your laptop even if only in demo. Provided you can hook the ESS to the laptop
and have it communuicate it should run your machine. In demo it will only run for six minutes before requiring a restart.

Note that you can have up to five PCs licenced for one Mach4Hobby purchase. So you can have both your machine licenced
and your laptop.

Craig

2074

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 06:39:11 PM »

Hi,
I would change the Z axis motor also. It may not have to travel far but it does need to accelerate fast, otherwise
the X and Y axes have to slow down to allow the Z axis to keep up.

Overall acceleration is the most important tuning objective. High acceleration promotes accurate toolplath following
without corner rounding that happens with CV tooplaths. Additionally most Gcode jobs spend more time accelerating
than actually at full speed. Therefore cycle times are commonly more favorably affected by high acceleration than
high max velocity but low acceleration.

Craig.

2075

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 06:29:59 PM »

Hi,

Wow, but this is getting expensive with servo motor suggestions, it's just for a bit of hobby fun in my little garage

Understood. What I would like exceeds my budget also. Good servos have come down in price however. You don't
need multi turn encoders etc, even 'plain old 16 bit incremental encoders' will still outperform any stepper ever made.

Some time ago I bought a second hand Allen Bradley (US made-quality) 1.8kW servo and servo drive to make a spindle motor.
Its power and flexibility has to be experienced to be appreciated.

A stepper is like a horse and cart......a modern AC servo a high power 4x4 truck!

I would still recommend a toroidal power supply. For example:

https://www.automationtechnologiesinc.com/products-page/torroidal-power-supplies/unregulated-1300w-65vdc20a/

This has 20A output so would do all your steppers with just the one supply.

Craig

2076

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 06:14:57 PM »

Hi,
that power supply is too whimpy for the 5.6A stepper.

You would be advised to get a toroidal transformer type power supply, that are much more rugged and forgiving than
switch mode supplies like the one you have pictured.

Craig

2077

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 06:11:43 PM »

Hi,
by the way if you look at the Delta A3 series they have a 24 bit multiturn absolute encoder with battery backup.
Thus you can use 8 bits of the encoder for the number of complete revolutions (+- 127) and still have 16 bit resolution (131071
count per rev) within any one turn.

When you turn the machine on the battery backup means you don't even have to home the servo, it just picks up from
where you left off at the last session.

These are the latest and greatest from Delta but all the major manufactures are going that way, that is multiturn high
resolution encoders.

Apparently DMM have, although not widely publicized, a 30 bit multi turn absolute encoder option for their servos....amazing!

Craig

2078

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 06:01:38 PM »

Hi,
if you want your machine to run at production speeds and duty cycles then you need AC servos.

Stepper motors have great torque at low speeds but are limited in resolution and speed and run hot all the time.
Servos have somewhat lower torque for the same size motor but maintain that torque right up to rated speed
and have usually a 3-4 fold temporary overload rating, they run quietly and coolly, with superb (100 fold better)
resolution.

The DMM 400W, 200V servos I linked to earlier with the 200V driver and cables is about $450USD. Note that the driver is
wired directly to 230VAC, ie no external power supply is required.

A Delta A2 or B series 400W servo, driver and cables (again 230VAC input) are about $500USD.

Either of these servos will 'eat your steppers for lunch.....any time any where'.

Craig

2079

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 05:49:10 PM »

Hi,

If these are much more suitable Craig can i use my existing drivers?

Provided they can handle the much increased current (5.6A vs 2A) then yes. Note it maybe you don't even require full current,
motors tend to run really hot (50⁰C) when at rated current. If you back off a bit to 4-4.5A they will run cooler
and most likely still have enough 'grunt' to do the business.

Craig

2080

General Mach Discussion / Re: Motor tuning, please take it easy on me I'm new to this :)

« on: August 30, 2019, 05:43:31 PM »

Hi,
yes that is a vastly superior motor. In fact so is the model above it.
Compare:

34HS9840 (3.5mH, 0.8 Ohm) time constant=2.8ms
34HS9456 (3.76mH, 0.3 Ohm) time constant=1.128ms

Verses your existing:
34HST9805-37B2 (15mH,3.2 Ohm) time constant=48ms.

The 34HS9456 is the hands down clear winner and the 34HS9840 not an unreasonable second place whereas the
34HST9805-37B2 is really just nowhere for CNC purposes.

Note that while the 34HST9805-37B2 is poor for your machine say for slewing a telescope where it might turn  1 or 2 rpm
through a reduction box it would be perfect.

CNC demands high torque at high speed.....a performance requirement that does not favor stepper motors.

Craig