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Messages - MN300

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131
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 24, 2020, 06:44:44 PM »
1000 was based on a conservative guess at the maximum stepper speed with a single start lead screw. That would be 2000 with the 2 start leadscrew.
The speeds you actually use for machining will probably be lower but being able to jog at a higher speed would be convenient.
The penalty for going too fast seems to be only the cost of a TIP122 so after you have had a period of problem free running you could raise the speed.
Check the motor temperatures so you have an idea of what's normal and can tell if it increases to much under harder use. The 5718 series motor has a Maximum Case Temperature of 176 °F. Around 130 °F it's hard to keep a finger on an object. Of course an IR thermometer is a better way to check. They're not very expensive these days.
A quick blow fuse in the center tap lead should protect the motor from overheating in case of a shorted transistor. Start at 1 amp and increase it if they blow during normal operation.

Take a picture of the end of the circuit board with the TIP120's. Maybe there is a way to add a better heat sink.

132
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 24, 2020, 07:50:47 AM »
Normally a hobbyist will tune a stepper by finding the acceleration rate or speed that make the stepper stall or lose steps and setting the limits considerably lower. Those values depend on the mechanics of your mill and later the tool loading. It should be safe to experiment with acceleration rate but too high a speed may pop more transistors. That's why knowing the original feed specs would be good.

Once you know the limits, the values you use to actually do useful work are determined mainly the material being machined and the tool. References like the Machinery's Handbook or the Engineers Black book will help you to find appropriate spindle speed and feed rates. The G code generator program that converts your drawing to G code uses such information.

Find online tutorials that you are comfortable with and watch YouTube channels related to CNC. Here is one example.
https://www.youtube.com/user/saunixcomp

133
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 24, 2020, 12:11:56 AM »
200 steps divided by 2.55 mm = 78.4313725 steps/mm, twice the 39.2343239 value you're using. The lower value would make sense if you have a two start leadscrew. (double thread) If that's the case my estimate of max speed would double.

Can you look at the G code and see what feed speeds have you been running?


134
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 23, 2020, 09:41:29 PM »
Perhaps I missed something. Does the X motor now run hotter than it used to before the TIP120 failure?

"Shorting" in this case would mean the insulation between the copper wires inside the motor has broken down allowing adjacent wires to touch so the current can take a shorter path. The motor current would increase causing heating of the motor and transistor.

It's hard to measure low value resistance accurately with a multimeter. I assumed the range of 1.4 to 1.6 ohms was from measuring error. If not that could be an indication of a shorted winding.

I am guessing the highest reasonable speed for X and Y is 1000 mm/min. In your test G1X100 F100  you set the speed at 100 mm/min (F100).
It would be very useful to know the intended maximum feed speed so you can remain within the safety limit. Perhaps Dave from Lin Engineering could supply that information.
When I said your settings are higher than 1000 I was referring to to the information in the images of the motor settings.

Before we knew about the low resistance of the motors I was more concerned about voltage spikes. Except for the voltage rating the specs of the TIP120 and TIP122 are the same.
I think you may be confusing the TIP120 transistors with the microcontrollers PICnnnnn. (I can't read the exact number)
The PICs each have a step and direction input and drive the 4 TIP120s for their axis. There are also 3 signal lines common to the 4 PICs. One is probably an enable, other is possibly a fault output.

If the system is running happily with the transistors replaced maybe running below the maximum feed speed will be enough. The Z axis max will be proportionally lower as it has a different leadscrew pitch.
 

135
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 23, 2020, 10:42:41 AM »
2.55 mm/rev is suspiciously close to 2.54 mm or 0.100 inch. At 200 steps/rev travel would be 0.0005 inches per step.
The Z axis would be 0.000317 inches per step, not as good a match to imperial units.

I tried to find specifications for the maximum feed speeds but had no luck.
A wild guess, back of the envelope calculation says 1000 mm/min is the maximum X or Y speed. That's far less than your MACH settings.
I think the pulse width is programmed in the PIC, not accessible to the user. I estimate it to be about 0.250 millisecond.



136
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 22, 2020, 10:59:53 PM »
Your readings suggest the motors are pulsed rather than powered continuously.

If you were to apply 17 volts to a 1.6 ohm winding continuously it would draw over 10 amps. You may have seen the note on the circuitry drawing showing the max supply input current is 4 amps. 3 motors times 10 amps would be 30 amps, double that if half stepping mode is used.
Also if continuous power is applied to a winding it would receive 170 watts (10 amps times 17 volts). You have not reported any great clouds of smoke, making that possibility very unlikely.

https://www.electronicshub.org/wp-content/uploads/2017/03/full-step-one-and-two-phase-ON.jpg
Full stepping can be done with momentary pulses. Half stepping requires continuous power to hold in the half step positions.

10 amps also exceeds the the current rating of the TIP120. When voltage is applied to an inductor it takes time for the current to build up. The correct length pulse could allow enough current to move the stepper but not exceed the maximum.

The TIP120's are likely failing for one of two reasons. One is if the maximum pulse current is too high. There's little we could change to help that beyond reducing the supply voltage which would reduce power and limit speed.
Another problem is heat build up in the transistors. The more pulses per second, the more heat needs to be removed.
MACH 3 may be moving the motor faster than the original controller did causing more heat. Did the failures happened after long high speed moves?

Reducing the maximum speed may be a way to work around the problem. Better airflow or a fan would keep the transistors cooler.




137
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 21, 2020, 08:04:41 AM »
Your motor control circuit is a unipolar constant voltage type. Most CNC applications use bipolar constant current.
https://www.motioncontroltips.com/what-is-constant-voltage-drive-for-stepper-motor-and-when-is-it-used/

While your motors may be able to be run in the constant current mode the motor control circuit is only unipolar. Unipolar motors are usually used in applications like printers where low cost is important and high speed is not needed. Often those motors are only energized while stepping and depend on the magnetic field of the motor to hold position when stopped. That's why I asked about the voltage readings.

You would get an improved performance from the motors with a better drive. However that's a major cost. There are many posts by  joeaverage  with information about the available choices.

138
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 20, 2020, 09:32:28 PM »
I am waiting to hear what the winding resistance is. Also a few voltage checks would be of interest. With the drives enabled would you please measure the voltage from ground to pins 1,2,3 and 4?. If you have a basic stepper drive two pins will be the nominal supply voltage, about 17.5V and the other two will measure about a volt.

139
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 20, 2020, 06:28:19 PM »
The terminal with the number 5 in TPS's drawing is the center tap.
As I mentioned earlier you can determine the center tap with an ohmmeter, it's the one wire that measures the same resistance to the others.

The brown earthing wire is not counted when determining if it's a 5 wire and 6 wire motor.
I can't find a Lin Engineering diagram for a 5 wire motor. Is there a chance two wires are connected together somewhere between the motor and the board connector?

140
General Mach Discussion / Re: Looking for good DIY controller kit supplier
« on: November 20, 2020, 05:20:12 PM »
If 'Color code 1' in the table mentioned earlier is correct white and yellow are the center taps of the two windings. They should both be connected to a terminal on the board motor connector.
In a 5 wire motor they would have been connected internally to one wire leading out of the motor.

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