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Author Topic: Motor tuning, please take it easy on me I'm new to this :)  (Read 1323 times)

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Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #10 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,

Quote
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
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #11 on: August 30, 2019, 05:25:22 PM »
Hi,
just as an illustration:

Leadshine 86CM80 (4mH,0.63 Ohm) time constant=2.5ms
Longs 34HST9805 (15mH,3.2 Ohm) time constant=  48ms

Thus for the same input voltage the Leadshine motor would run 19.2 (48/2.5) times faster at the same
percentage torque reduction.

That's nearly 20 times faster!!!!

Craig
My wife left with my best friend...
     and I miss him!
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #12 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?
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #13 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
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #14 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
My wife left with my best friend...
     and I miss him!
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #15 on: August 30, 2019, 05:49:10 PM »
Hi,

Quote
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
My wife left with my best friend...
     and I miss him!
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #16 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
My wife left with my best friend...
     and I miss him!
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #17 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
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #18 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
« Last Edit: August 30, 2019, 06:17:13 PM by joeaverage »
My wife left with my best friend...
     and I miss him!
Re: Motor tuning, please take it easy on me I'm new to this :)
« Reply #19 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
My wife left with my best friend...
     and I miss him!