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Author Topic: Looking for good DIY controller kit supplier  (Read 4052 times)

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Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #30 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.

Offline TPS

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Re: Looking for good DIY controller kit supplier
« Reply #31 on: November 21, 2020, 11:29:16 AM »
anyway, had a look to your Profile file. nothing Special in there, so swapping X and A should  be running like suggested.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.

Offline TPS

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Re: Looking for good DIY controller kit supplier
« Reply #32 on: November 22, 2020, 04:49:21 AM »
today i had a look to your Motor setting's, i think a couple of the setting's are not "real", but this is a Point later on the road.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Looking for good DIY controller kit supplier
« Reply #33 on: November 22, 2020, 09:18:14 PM »
Yes, TPS, that would be good to look at because when all was 'running well' before it ran at a snail's pace.
The X, Y and Z resistances 5/1, 5/2, 5/3 and 5/4 range between 1.4 and 1.6 ohm.
The voltages between pins 6 (earth) and 1, 6/2, 6/3, 6/4 and 6/5, with the power connected and switched on but NOT with the computer attached, are all between 17.4 and 17.6 V. There are no connections between pin 6 and other pins that are below 17.4 V.

Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #34 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.



Re: Looking for good DIY controller kit supplier
« Reply #35 on: November 23, 2020, 01:13:41 AM »
Much to learn.
Originally, the CNC was built to be run on a Mach version called MaxPath42 but I installed Mach3 instead. The machine has never been used to do a job as I was learning to understand the processes. I got as far as setting up the configs, motor tuning, jogging, setting Soft Limits, loading up G Code and "Cycle Start' dry runs in Mach3. It was then that the TIP120 burnt out ......smoke galore. The X Channel had only 3 out of 4 TIP120 installed as the 4th one was loose in the circuitry box. We installed both the loose and a replacement TIP120, tried again and after some 4 hours the same thing happened ..... again plenty of burning plastic, with a very hot X axis motor. The Y and Z channels and motors were fine.
The machine jogged at what to me was a good speed, but when in 'Cycle Start' mode, at an absolute snail's pace.
I have emailed Dave from Lin Engineering to see if the readings are within specs and for more info on motor characteristics with this wiring configuration; I expect an answer hopefully by tomorrow. It'll be interesting to see if the motors are functioning within specs.
So what I understand you are telling me is that with these readings, the motor would draw a current that can not be met by the circuitry without causing some damage to the TIP120 unless the pulse length is controlled. Would that be a circuitry function or an original setting in the MaxPath42 config, which I may not have picked up in the Mach3 settings? If circuitry, no wonder MaxNC went bust.
Heat build up could be a problem with temps here in the good land of Oz reaching the high 30s Celsius, so opening the box an applying more airflow can be arranged.
Limiting or reducing speed further than it already is in 'Cycle Start' mode would maintain a snail's pace or bring it to a virtual stand still. This issue may be related though to the issue TPS has just raised yesterday re the Motor settings not being 'real'. Could we go into that further, TPS?
I would prefer to wait with the trial run till I've received all info, just in case I blow the A Channel now used as the new X Channel up.

Offline TPS

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Re: Looking for good DIY controller kit supplier
« Reply #36 on: November 23, 2020, 05:17:19 AM »
for a correct Motor Tuning we Need to know how the Motor are connected to the machine.
direct via ballscrew ? via teethbelt ?
the we Need to know what one Rotation of the Motor is the real distance of traffel?

than we can further on to get the correct Settings for Motor Tuning.
anything is possible, just try to do it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Looking for good DIY controller kit supplier
« Reply #37 on: November 23, 2020, 06:14:26 AM »
The lead screws are directly attached and in direct line with the motor shafts so one turn of the motor (200 steps) is one turn of the lead screw. The X and Y lead screw pitches are 2.55 mm each and the Z pitch is 1.61 mm. There is some error in this reading as my calipers are quite cheap and loose. The error may be 0.05 to 0.1 mm. I will reduce the error tomorrow as lighting is not great in the shed at night.

Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #38 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.


Re: Looking for good DIY controller kit supplier
« Reply #39 on: November 23, 2020, 08:15:56 PM »
Dave from Lin Engin confirms what we know so far but adds that 'If the motor windings get overheated the insulation on the windings can begin to break down over time leading to shorting or performance issues'. Could be possible that has happened since the TIP120 burnt out; but the motor ran cool before that. What is 'shortening'?

I have averaged the Z lead screw pitch over a few distances and come 1.606 mm, so 1.6 mm is not too far off. This lead screw has the smallest diameter.

MN300, 1000 mm/min travel, should that be 100 mm/min? TPS looked at this issue on a different post and we tested the metric distance travelled against the line  G1X100 F100 starting X at 0; 100 mm or 10 cm took exactly one minute. I must say that I do not really understand the issue with the Mach settings, would either of you please explain them to me.

If the required pulse is determined by the PIC120, would replacing it with a PIC122 change the pulse duration and strength? How would that affect the motor?