lots of power till 300 rpm then stops is this normal?

[mike10]

I'm using vextra 620 oz 2.8v 4.5amp 2phase 0.66 oms resistance motors.
my power suply is 12v 18amps i have one for each motor.
my resistors are 160w 2 ohms
im using mach2 software

the motors have lots of torque up to 300 rpm then they just stop turning and make a zzzzzzzzzzz sound if that helps lol

i raise the kernel value to 45000 mhz and was able to double my speed (150 rpm to 300 rpm) 45000 mhz is the highest selection available

id like to get 500 rpm from these motor is there any sugestions?

my board is from dellargrage techlonogy very nice board and good people to deal with
http://www.dtllc.com/

[murphy625]

Ok.. Im a newbie (probably newer than you!) but I'll give it a try..

Every drive I have seen so far has a maximum current limit for the motor it is driving. Seeing as speed and torque are related, I am wondering if there is a "max current" setting in your setup and if there is, you may be exceding it.

But I barely know what I am talking about.. <<Not a joke.

Murphy

[MrBean]

I think you would benefit from a chopper, type drive. They are much more efficient than an L/R drive. With an L/R drive the torque will drop off more rapidly than with a chopper drive. A chopper will allow you to reach higher RPM's before the torque drops off to an unusable level.

Regards Terry.....

[Mac T. Knife]

And The drive you are using is a unipolar drive,,, where coils are switched onand off,,a bipolar drive would give you more torque, as the controler is switching the polarity back and forth instead

[Dr.H]

as rpm rise your amps decrease and torque will depend on amps so if you wnat to reach 500 rpm you need more than 12v but if you run at low speed with more voltage you may burn your motor so you need a power supply that is adjustable or a chopper drive

[CJL5585]

Stepping motors have areas at which the motor practically (or does) stops rotating and the pulses to the motor cause it to have a whining sound.

It is caused by Resonance which is caused by the saturation of the motor windings. I just replaced a Superior Electric MO93 500 in/oz motor for the same reason. It would just stop at about 550-600 RPM's. I tried different current levels from 1 amp to 7 amp settings (via dipswitch), different accleleration levels, and could not get past the resonance problem.

You may be able to accelerate through the resonance frequency band. I have not been able to lay my hands on a graph for my motors that shows the resonance bands in the steppers, but you may have better luck.

I don't have a cure for your problem, but think that you are on the right track with resonance.

Hope this helps.
Jerry

[CJL5585]

After re-reading all the posts about bi-polar drives and switching drives (PPM)
which is pulse position modulation, and about power supply voltages, let me say that micro-step drives are usually able to minimize the properties of resonance to a point where it is a problem.

In my case, I have 48 VDC supplies and commercial Superior Electric microstepping drives, and could not get around the problem. It was just too big of a struggle. Smaller steppers with lower inertia factors work just great for my application, so that is what I am going to do.

The best of luck,
Jerry

[ger21]

Generally, you'll double your top speed by doubling your voltage. So, if you can get 300rpm with 12V, you should be able to get 500rpm with 24V.

[fyffe555]

Mike10,

You've some inconsistencies here.

Your ZZZZZ noise is the stepper stalled, either because it's load has exceeded it's torque curve at that speed, the driver can't provide the power at that speed and so the motor is running at less than its rated maximum at that speed, or as Ger suggested the your driver voltage isn't high enough and so you're not getting the necessary power at the speeds you expect. Whatever the cause you're 'missing' steps and the motors ar stalled. It's not necessarily related to the Mach 2 frequency setting.

Do you have a torque curve for this motor? If it's close to other Vextra's of the same rating then the torque, even when run at optimum voltage and Amps will be under 30% of rated at 300rpm.

Do you have a spec for the drivers listing rates, amps, etc. I assume these are unipolar?

Mach2 can produce 45000hz max or 45000 pulses per second. 45000mhz is 45000 *million* pulses per second which is something else entirely.

What PC are you running this on ? You will need a substantial PC to produce 45000hz, or 45000 step's per second reliably. You also need a serious driver to be able to use step signals at that rate. In other words do you know what speed pulse train your PC is actually producing and whats the rated speed for your drivers? I'd suggest that you might be trying to overdrive the stepper pulse rate and the drivers might not be able to keep up.

How do you know it's making 300 rpm? What model drivers do you have? What lead leadscrew are you using? Since the driver supplier lists at best a 1/2 step driver and your motors are 200steps per rev then for 300rpm your motor needs a max pulse stream for step of 2000hz for 1/2 step and 1000hz for full step.

12v for a 2.8v stepper is too low, especilly for a L/R or resitor limited drive. Try 24vdc at least, 28, 36, 48 or what ever the max driver limit is would be better. Is your supply linear or switching? A linear supply would be preferable - switchers are not ideal and can get upset when a load has variable loads and some emf such as a stepper and driver would produce.

Your driver uses a power resistor to limit current. This can be both wasteful in power and limits the high speed performance. It is slower to fully energise the motor coils for faster step rates, so less power is actually produced in each coils as the speed increases and so reducing the torque produced below the motors rated. The higher the speed the less effective a resister limiting driver becomes. A chopper driver is much better for higher step rates.

You can most easily counter this by increasing the power supply voltage.

Andrew

[H500]

You undoubtedly need more voltage if you want more speed.