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Author Topic: Looking for good DIY controller kit supplier  (Read 4054 times)

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Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #40 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.
 
Re: Looking for good DIY controller kit supplier
« Reply #41 on: November 23, 2020, 10:53:38 PM »
I only noticed a hot X axis motor the last time the TIP blew up. The Y and Z motors were cool. I did not feel the X motor temp the first time the TIP blew up.
All three motors measure a resistance of 1.4 ohm across 5/1, 5/2, 5/3 and 5/4. So if the X motor is shorted, then the Y and Z would be as well ..... I hope not.

I have sent another email to Dave, but he seems very reluctant to give specifics on this motor as it is a proprietary product. I have asked him for the name of the manufacturer for whom they manufacture this product, hope he'll give it to me.

Yes, I was confusing the TIP120 with the PIC16F84A-201/P. Good to know I could still swap the TIP120 with a 122.

The motor settings have always been a mystery to me. How is it possible for instance for 200 steps (1 full revolution, 360 degrees) to move the X axis 2.54 mm (screw pitch) and yet the 'X Axis Motor Movement Profile' states that the 'steps per mm' is 39.2343239, which is approx 5.1 mm per full revolution. I've always just accepted it as a Mach3 internal mystery. Now if, as TPS says, the settings are not 'real' than the velocity, acceleration and other settings would also be unreal. What are the generally expected values in motor tuning; how do I arrive at correct values?

Unless you have real misgivings and would like me to check the resistances or anything else with a different instrument, I will assume that the motors are still functioning normally. So then the only issue to be resolved before I 'fire up' is the speed; maybe in the Motor Tuning setting ...... I need help there. The 'steps per (mm)' in the 'X Axis Motor Movement Profile' window are arrived at automatically by 'Calibrating the Axis' under the 'Settings' tab in Mach3.  I follow the steps after activating the 'Steps per Unit' button, and the calculator inserts the 39.---- value. I do this a few times to reduce the error as far as I can and then tweak the acceleration and velocity till the gantry movement is smooth. Is this the correct procedure; could there be an error elsewhere in the settings??

And then there is the 'working' speed' ... it seems so very slow. Is that because it is a unipolar slow machine?

Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #42 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?

Re: Looking for good DIY controller kit supplier
« Reply #43 on: November 24, 2020, 02:20:14 AM »
The 78.---- value makes sense. I've only been playing with roadrunner.tap, the file that comes with Mach3. I am so far not up to speed with what the codes mean. There is an F60.000000; would that be it?
Re: Looking for good DIY controller kit supplier
« Reply #44 on: November 24, 2020, 04:57:35 AM »
Aaaaah, MN300, just got educated on thread starts .... thanks for that. Took the other 2 motors off and lead screws out and had a look at the ends of all the lead screws. Both the X and Y lead screws have two thread starts and the Z lead screw has 4 thread starts.
So the steps per mm for the X and Y axes are 200/2.54=78.74 divided by 2 (thread starts) = 39.37 steps per mm.
For the Z it is 200/1.6=125 divided by 4 (thread starts) = 31.25 steps per mm
Fairly close to the present profile figures.

So X and Y speeds double and Z speed quadruples.

How should I configure the axes motor movement profiles; just enter the steps per minute as calculated?
And what velocities and accelerations would be best; tune them so that the motors and gantries run smoothly?
Are there other config adjustments to be made?

Now to Feed Rate; once again a steep learning curve. Please correct me if I'm wrong.
So the G code for Feed Rate is F, say F20, F60, F1500 etc, and the F value is always per minute: i.e. in my case F60 is 60 mm per minute or F125 is 125 mm per minute etc.
Is that correct?

So I can set the Feed Rate (F value) to reflect the speed my motors can handle and that is why you are questioning which max speed they can handle .... is that correct?

Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #45 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
Re: Looking for good DIY controller kit supplier
« Reply #46 on: November 24, 2020, 05:42:46 PM »
I'll reset the stepper values and set the max speed at 1000 as you suggested and re-assemble the machine for a trial run. I'll follow up all your suggestions. Dave was not able to give me the info required so I'm flying blind on original feed specs.
Will let you and TPS know how things went.
Much thanks and appreciation.

Offline MN300

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Re: Looking for good DIY controller kit supplier
« Reply #47 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.
Re: Looking for good DIY controller kit supplier
« Reply #48 on: November 24, 2020, 08:18:41 PM »
will do all that.
Following the same rationale, could I set the Z axis speed at 4000?
Re: Looking for good DIY controller kit supplier
« Reply #49 on: November 24, 2020, 08:33:43 PM »
Let's try