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Recommended Encoders
« on: November 30, 2015, 02:13:06 PM »
Hello, I've read that one can buy a stepper motor driver with a built-in encoder to ensure that we can close loop on a target position. I've seen "Gecko" and "Romax" mentioned in these posts. They cost somewhere around $200, or so. I don't mind the cost, but I don't want to experiment and buy a controller that won't work with Mach3, or my system. I saw a 4-axis controller that is compatible with Mach3, but I only need 1 axis (the one giving me trouble).

Can someone please recommend some Mach3 compatible encoders/motor drivers? I'm using a 1.8 degree/step stepper motor (24 V, I think). My system is very small, so I don't want to buy one that is more expensive than necessary.

Thank you, Richard V

Offline Tweakie.CNC

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Re: Recommended Encoders
« Reply #1 on: December 01, 2015, 02:09:30 AM »
Hi Richard,

For what it is worth, my view is that you would be wasting your money.

You really need to sort out the problem of your Z axis loosing steps on the way up. Is your Z axis motor getting hot ?? ( approx.60 deg.C ).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline RICH

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Re: Recommended Encoders
« Reply #2 on: December 01, 2015, 05:03:41 AM »
Rich V
I agree with Tweakie's reply.
Sometimes we should consider what others have recommended rather than looking for a different solution.

RICH
Re: Recommended Encoders
« Reply #3 on: December 01, 2015, 01:22:56 PM »
An encoder on an axis that has a problem will just provide you with a new way for the machine to tell you it can't do what you want. Is that your goal?
Re: Recommended Encoders
« Reply #4 on: December 06, 2015, 09:12:00 PM »
Hello Tweakie, thank you for your advice. I've explored the options. I found a way to improvise an "encoder" with a Sharpie marker. I set my position to ideal height and then marked the sprocket that drives the Z-axis and a stationary point. I can tell now that I truly am losing position of my Z-axis. I am able to use this to re-zero the Z-axis, and that seems to work well.

To answer your questions:
No, my motor is not getting hot; it's cold to the touch. I also measured the temperature of the driver boards for all three axis'; They each measured about 83.6 degrees F (using an IR thermometer).
In the motor tuning section, I set the delays to maximum (5 uS for each). I can't say this helped, but it seemed that I did not have to "re-zero" the z-axis as often as before.

New Question:
Just to rule out Mach3, I'd like to know if the system waits for a command to finish being executed before moving onto the next line? Maybe this is what "Dwell" is for?

Please look at the following made up code below (an example similar to my actual code). Some of my commands are short moves in X-Y, then Pen-Up, Pen-Down. I'm wondering if my Z, axis is being RE-commanded to another position too fast. For instance, I do "G00 Z0", then "G01 F4 Z-0.01" immediately after.

Also, some of my Pen up commands come after only doing a short X, or Y translation, then another Z translation (pen up). For example:
G00 Z0
G01 F4 Z-0.01
G01 F60 Y40  (presume it was only a short move from Y=39)
G00 Z0.5


This is just simple Made-up code:
G00 Z0.5
G00 X23.6 Y36.2
G00 Z0
G01 F4 Z-0.01
G01 F60 X30
G01 F60 Y40
G00 Z0.5
G00 X25.2 Y39.5
G00 Z0
G01 F4 Z-0.01
G01 X26 Y35

Offline RICH

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Re: Recommended Encoders
« Reply #5 on: December 06, 2015, 11:40:04 PM »
I do not think Mach is your problem.

Post your xml file.
What kind of machine are you using? Post info on it like the drives, stepper info, power supply, etc.

It's a real pain to try to help someone when they keep posting different implied questions and trying to solve the problem.

Did you tune the motors as suggested in other replies? ie; trying different velocity, accel values, find where they skip and set appropriately.

RICH

Offline Tweakie.CNC

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Re: Recommended Encoders
« Reply #6 on: December 07, 2015, 02:00:24 AM »
If your Z axis motor is running cold to the touch then increase the current (Amps) setting for this axis. That will increase the motor torque and may resolve the issue. Stepper motors should be run at or near their rated current and as a guide a case temperature of up to 60 deg.C is to be expected.

Quote
New Question:
Just to rule out Mach3, I'd like to know if the system waits for a command to finish being executed before moving onto the next line? Maybe this is what "Dwell" is for?

When using Exact Stop mode (G61) each line of Gcode will be completed before the next is begun but when using Constant Velocity mode (G64) there can be some overlap. Dwell is more usually used to allow synchronization with external devices (gives everything time to catch-up).

As Rich has said, it would be helpful if you post your .xml file - you will need to copy it then rename it to something unique (ie. rrsquez.xml) to be able to attach it (Additional Options...) to your reply.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Recommended Encoders
« Reply #7 on: December 07, 2015, 11:04:55 PM »
Hello Tweakie and RICH. Per your suggestions I have included the .xml file that I am using.

I do not know how to set the motor current with Mach3. I presume you (Tweakie) are asking me to set it directly with the CNC driver. I have attached a picture showing what my controller board for 1 axis looks like (there are 3). I have already tried tuning my motor to run painfully slow or blazing fast. I saw very little change in problem for either speed. Slowing down the motor did not improve the situation. I also made sure to use slow feed rates for the G01 commands to Z axis. This had no effect at all.

I would really like to correct my problem with software if possible, however, I suspect that I have a bigger problem; hardware issues.

My driver boards are a simple cheap boards (picture). I see the name "TONSEN CNC", but I don't know anything else about them. My system is a cheapy CNC from China (you get what you pay for). I took the board off and found that the IC driving the motors is P/N A3977SEDT. I looked it up on Digikey.com and found that it is indeed a stepper motor driver chip capable of driving up to 2.5 amps. There are no adjustments on these boards, so I cannot set the current manually. I see a large 3 watt resistor, but I dare not change it out for a lower value.

I honestly believe that my problem lies with these cheap CNC driver boards (it's a red flag that I can't give you a part number). The X&Y axis' work well, and they use larger motors (Vexta 103H7124-1142, 2.4 x 2.4 inches). The Z-axis motor is slightly smaller (Vexta C8513-9012K, 1.7 x 1.7 inches), but seems appropriately sized for the job. Listening to this motor in action, it does not seem to be struggling with the given load.

Sorry, but I can't identify the motors any better than to provide the part number. I don't know where to find where these motors came from (aside from knowing they came from China). There is no "Vexta" website breaking down these part numbers. The same is true of the driver boards; Another "red flag".

I am willing to replace the motors and motor drivers, but I need a recommendation. For example, do I need a "4th" axis to activate the spindle motor, or can I use my existing breakout board to do that? What do other users do to turn on the spindle? I need to make sure that whatever driver/motor combination I get is compatible with Mach3. I currently use the LPT port to drive my controller. Should I get a CNC driver kit that supports encoders? I'm not sure if Mach3 can use them.

One last thing, I know Mach 3 is open loop. Does Mach 4 support closed loop operation using encoders?

Thank you very much for taking the time to help.

Best regards, Richard V
« Last Edit: December 07, 2015, 11:07:49 PM by rrsquez »

Offline Tweakie.CNC

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Re: Recommended Encoders
« Reply #8 on: December 08, 2015, 05:29:00 AM »
Hi Richard,

I agree with you, I think the problem lies with those drivers and it looks like a fight you cannot win. It seems that the actual current is set with (what should be a potentiometer) R14 which has been replaced with two resistors. Perhaps bite the bullet and look towards a replacement such as the Gecko G540 (or similar) that way you are guaranteed a high quality product and full back-up service etc.
Spindle on/off is just a matter of connecting a relay - perhaps check out the Gecko site, there is lots of useful information there http://www.geckodrive.com/support.html
Variable spindle speed control is a bit more complicated but it's not rocket science.


Mach is not a 'closed loop' system and my advice is to forget about encoders - I have been using various systems 'open loop' for over 10 years now and I don't get lost steps so there should be no reason your CNC should not work perfectly once it is all set-up correctly with the right components.

Hope this helps.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Spindle Motor logic
« Reply #9 on: December 11, 2015, 12:28:37 AM »
Hello RICH. Thank you very much for that part number. I am happily willing to invest in my system (my time is more valuable to me). It's not very much ($300) considering what it can do.

Do I use the "4th-axis" to activate the spindle? If not, how do others?

Explanation:
My spindle motor is activated by a simple digital logic level from the LPT port (not sure if Mach 3 drives this as a PWM signal). The LPT port is connected to a breakout board (one of my pictures shows it) that switches on the spindle motor. 

last question:
Will this controller provide me that logic signal that I need for the spindle motor?

Thank you for your time and advice. I am getting very excited to see my CNC working properly for once!

Best regards, Richard V
« Last Edit: December 11, 2015, 12:41:11 AM by rrsquez »