Messages

21

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

« on: August 31, 2019, 05:10:39 AM »

Hi,

It's quite a strong machine, 4 " Box section frame with the steel frame gantry with large linear guide rails and blocks on all axis. Twin motors on the Y Axis.
I would say I wouldn't want to go much faster than 5 to 6k mm/min in any case and at that the new motors would only be spinning at 375 rpm max at with my set up. Even though we don't have a torque graph for these motors based on the Leadshine graphs that should be well up in the motor torque range should it not?
Hopefully then I want get any stalling or missing steps etc and very good acceleration speeds?

Mark

22

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

« on: August 31, 2019, 04:37:42 AM »

I'm just a little bit jealous now Craig, 

Have you got any pictures of your machine/setup?

I'm going to give those motors a go first, I've negotiated a discount and can get the motors and power supplies for £236 delivered which is a bargain for the upgrade.

As i'm not used to using such a small machine what speed do you think is reasonable with light cuts in say mdf, at work I can run at 8mtrs/minute with a 12mm tool cutting through 19mm thick veneered mdf board in one pass
Of course I'm not looking to do that on my little toy

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

23

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

« on: August 30, 2019, 06:58:30 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.

Many thanks again, 

24

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

« on: August 30, 2019, 06:32:46 PM »

Craig,

One more question, would you leave the Z motor as is, the travel is only 170mm. The reason for asking is if doing a lot of carving work where the z will be changing height rapidly and my xy travel is speed up then I'm thinking I should match all the motors?

25

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

« on: August 30, 2019, 06:20:22 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

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

I'm going to order those motors as they are a direct physical swap for what i have now and also those higher power supplies, my stepper controllers will still be fine...

26

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

« on: August 30, 2019, 06:16:44 PM »

My 3.3 amp power supplies aren't going to cut it either are they 

this is the one that is packaged with those motors

27

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

« on: August 30, 2019, 06:09:51 PM »

That's fantastic thank you for an excellent explanation, i always say everyday is a learning day.

I've just checked my voltage supply and stepper motor drivers see attached

28

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

« on: August 30, 2019, 05:34:13 PM »

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


This product contains/This item includes: 3 pieces/PC act NEMA34 34HS9456 stepper motor with dual flat shaft (threaded)
Step Angle/Step Angle: 1.8 °
Voltage/Rated Voltage: 2.1 V
Rated Current/Rated current: 5.6 A/phase
RESISTOR, CHIP resistance: 0.39 OHM/phase
Induk Dance/Inductance: 3.76 MH/phase
Securing moment/Holding Torque: 7.5 N.m
Locking Catch moment/Detent Torque: 9.6 N. cm Max
Torque/Rotor torque: 1700 g/cm²
Cable slots/Lead Wires: 4
Thread diameter thread/shaft diameter: 14 mm
Dual flat dimensions: Male thread/Dual Flat Size of shaft: 13 mm (1 mm for flat)
Length/Motor Length: 98 mm
Weight/Motorised, Weight (kg): 3.0
Cable connection/Lead Wires Connection: 4 lines/4 leads: red - a +, Green - A - B + - Yellow Blue - B channel

29

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

« on: August 30, 2019, 05:27:09 PM »

A selection of longs motors attached, the one I've highlighted seems to be a better specification, much lower Phase Inductance , Phase Resistance and slightly more holding torque?

30

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

« on: August 30, 2019, 05:20:35 PM »

I didn't increase the steps per just the velocity. I bought the machine second hand because the size and build of the structure and its capacity was exactly what I needed, unfortunately finding out that the cutting feed rates are a little low now is a pain yes but if it is an issue I'll have to change the motors.

I have attached a graph for these motors.

Hi,

So you you believe 312.5 rpm is far to fast for these motors and at that speed there will be no torque?

Without some published data from the manufacturer I cannot tell for sure.

You stated that you tried to increase the max velocity and they started stalling......doesn't that tell you exactly that?
They work OK at 125 rpm but stall out at 312.5 rpm.

Longs Motors make stepper motors with really high torque but also very high inductance. They sell to first time buyers
who think the higher the torque the better but what they don't realize is that high inductance kills a motor at speed.
Savvy buyers want to know both the torque AND the inductance, or to be technically correct, time constant.

Until I mentioned 'time constant' in this thread had you ever heard of it? Would you consider making a buying decision on
the basis of a time constant?

Now that you have heard of it and seen torque/speed curves that illustrate what a 'time constant' means in the real world
what would be your decision today?

May I suggest that if a company/supplier cannot provide either a torque/speed curve, or a time constant or an inductance
then walk away....they are selling to first time buyers.

Craig