Need Help!- Motor stalling... Suggestions needed!!

[tskguy]

Hi all,


I am in th proccess building my second CNC desktop router and Im having an issue. My new Y axis is now moving a much heavier Z axis and during jogging the motor stalls.The motor is very close to this model Minebea-Matsu****a# 23KM-K255-P1V. Here is my question, I am currently only running 12v and I am considering either upgrading the power supply to 24v (the motors max) or replacing the motors all together. Or should I do both! Money is a little bit of a factor in the decision. Any opinions?

Eric

[florins]

Hi tskguy,

In order to get useful advice, you should post here some data about the drivers you are using (what type or what IC's used) and the effective weights you are trying to move.
Basically, running a stepper from 12 V with a simple driver will not help you too much, you need a pwm switching driver powered at much higher voltage in order to push the necessary currents through the motor at high stepping rates - otherwise the motor stalls.

All the best,
Florin

[tskguy]

I figured so much...

The board Im using is from Lightoblect.com and the model is TB6560T3V1
Its a cheaper board but was working fine for some time on my MDF build. I checked my parallel ports voltages and they look fine(5v). Here are the specs of the board.

Specification: * In/Out Interface port: Parallel * Built in relay control for spindle * Support 2/4 phases 4, 6, 8 wires stepping motor * High speed optical isolation coupling * Built in No. 4 Axis interface for expansion * LED indicators for each axis & relay * Current: 2.5A r.m.s (3.5A max) * Resolution (speed): 1/16, 1/8, 1/2, 1 * Power: Single DC12 ~ 32V (no separated 5V needed) * RC7414 auto half bridge current control

The z axis is close to 10 pounds with the router attached. I also am using linear rail that is pretty stiff but smooth so Im sure that is adding to he resistance.

I hope that helps..I can provide more if needed.

Eric

[florins]

I presume that the board is three channel TB6560 based - that should be a fine board if designed correctly.
With this board a 24V PSU will help a lot when replacing a 12V PSU. Otherwise, all seems OK, in my opinion.

[wildwestpat]

Hi Eric

Firstly has the motor enough power to rotate at very slow speed and is this reliable so that say 200 steps forward and then 200 back brings you to exacly the same place or have you lost steps?

Secondly turn off and microstep function as this reduces the torque available.

Try and measure the torque needed to get the axis moving from rest. How does this compare with the stall torque quoted for the motor. The motor needs to have torque in reserve.

The torque of the motor falls rapidly with increasing step speed and increased motor voltage will help to an extent. IMO the PWM of the current by the driver will keep the current down to the recommended value for the motor for single stepping so you can check out the earlier tests above.

Hope thios helps - regards Pat

[Kelinginc]

Hi

What is the size of table?

if you can not solve the problem after changing to 24V power supply
I suggest you to change to a 270 oz-in motor and 425 oz-in motor
or add another motor in y axis

www.kelinginc.net

[tskguy]

Thanks for all the help guys!

Im not losing steps as far as I know. To be perfectly honest Im not sure on how to check that in mach3. But my old machine was accurate. The symptom I get now is the motor stops and has a high pitched whine. Changing the IPM seems to help I can olny get about 25IPM and even then it stops once in a while. My screw is a 16 tpi single start acme lead so that speed isnt really that bad. I did find an 18v power supply and it did improve things. It is only 3 amps though. As for my table its 12inch X 12inch. The new power supply will be orderd tomorrow. Any suggestions on a good one would be great!

[leaveme]

Seems you are low on current requirement.

You can measure current requirement for TB6560 boards in this way:
Steppers current * number of stepprs + 2
Example: 2 * 3 + 2 = 8A

You need a 8A PSU if your steppers are 2A (each).

Just my 2 cents...

[tskguy]

Great stuff!

Thanks for all your help! I'm ordering a 30v 500watt linear ps just in case I need to upgrade motors. Hope it will help.

Thanks again,
Eric

[Torchhead]

Steppers are a constant watt device. The more voltage you have available the less current you need and the faster you can spin the motor. Because steppers loose torque the faster you spin them, they have a stall point (the high pitched scream). For a given load they will only spin so fast before the decreasing torque curve meets the increasing RPM curve (stall point). Lost steps show the edge of a stall. A full stall feeds on itself.
The numbers being given for calculating the power supply current are way off from reality. The motors only draw their rated current at zero RPM (locked rotor) and then only at the applied voltage as constant DC. Since it's pulsed DC the average current is the peak current per pulse times the duty cycle.

If you measure real current with a meter running with a normal 3 axis machine you will find the current demands to be about 1/4 to 1/2 the total nameplate specs. So 3ea 2A motors running at say 50% of their max rated RPM and higher voltage won't pull but maybe 3A total. There will be a lot of screaming and disbelief but do some actual measurements sometime and see what you get. We have included actual Amp and voltage readouts on our products using Gecko steppers that display real numbers on the MACH screen and so there is no "rule of thumb" numbers being quoted. All a bigger (more amps) power supply will get you is more weight and more expense. Speed comes from voltage.

TOMCAUDLE
www.CandCNC.com

[tskguy]

Torchhead,

Your voltage explanation is great! Im glad I chose more volts than amps. I went with a 30v 300 watt ps to save a little dough. It should be here early next week.

Thanks!!

[Torchhead]

Only down side is the Toshiba chip and those drives, although rated to 35V and over 3A, won't handle that for more than a few minutes. I think the sellers of those units just quoted the absolute max ratings of the chip without doing the proper derating and thinking about the nasty inductive kickbacks from larger steppers.

If you have an unregulated DC 30V supply that rating may be under full load. Partially loaded you may see voltages well above the 30V level. You also have to factor in Back EMF (motors are generators when the push on the motor is greater than the power needed to move it like during rapid deacceleration) About 24VDC and 2.5A is all I would trust those units to handle. The same motors running with drives that can handle 48 volts would provide you with almost double the RPM.

Here is the problem: The 16TPI leadscrews means you have too spin the motor at 800 RPM to get 50 IPM. They simply won't do that pushing even a moderate load. You would need voltages in the 65 to 70 VDC range to hit those RPM's and ones that had torque ratings to handle the forces involved.

The voltage/current thing with steppers running from PWM based drives (sometimes called "chopper" drives) is that the more voltage available to charge the coils the faster the motor will move from one poll to another. There are all kinds of parameters that effect the coil charge rate (coil inductance DC coil resistance, rated coil voltage, and the available applied voltage are the most prominent) . Normally motors with lower rated coil volts will operate better than those with higher ratings. It has to do with the impedance of the coil and that determines the rate of charge of the coil at a given voltage. As a general statement the more voltage you have, the faster the coil charges and the faster the motor will spin. That does not mean you can just keep adding voltage. At some point the DC resistance starts to influence the equation in the form of IR losses (heat loss from the resistance of the winding) and increased eddy current losses in the magnetic structure start to define the limit. Numbers of 10 to 25 times the nameplate voltage are often tossed about but there are other factors that can make that only a very rough estimate.

300W should be plenty to run up to 4 motors. The only scary thing will be the popping sound of the drive chips if you run them anywhere close to their published specs

TOMCAUDLE
www.CandCNC.com