Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: oregondane on October 08, 2013, 11:45:57 AM
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I have added a 4th axis to my machine. Am having no luck getting Mach3 to recognize the A-axis as rotational (or angular) instead of linear. I have searched the forums and thought I found the answer several times but no joy. I have enabled the a-axis, set the a-axis as angular in the config screen, checked the 'x-axis as the axis of rotation' and 'A rotations enabled' in the Rotations dialog in the ToolPath dialog. Nonetheless, the added a-axis just turns and turns up to 360 when the g-code line commands A to 360. I have tried many different numbers in the motor tuning and haven't felt totally comfortable with any of them.
My board is a Xylotex board at 1/8 and a Xylotex 2.5A 269 stepper.
I have screen pics for verification if you need them.
Could someone help with what I am missing or doing wrong.
Thanks for your help.
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Here are pics to support the text.
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How do you have your tuning on the A axis? IIRC it is 360 on a rotational axis.
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If you type
G00 A1. do you get 1 rotation?
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It would require A360 for a full rotation
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It should require A360 for full rotation is setup right, but he said "added a-axis just turns and turns up to 360 when the g-code line commands A to 360". I remember seeing a mode where A1 equals a full rotation somewhere. Just wanted to eliminate that as a problem.
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Thanks for your replies.
Did the G00 A1 test. With the Steps Per in Motor Tuning set at 1600, the A-Axis turns a full 360. If the Steps Per is set to less than 1600, the revolution is less than 360. I just experimented to arrive at the 1600.
When I do the math for Steps Per, I get 13.333. That is 200 x 8 microsteps x 3 (I am using a 15-tooth .2 XL pulley on both the motor and the a-axis) = 4800 divided by 360 = 13.333. The motor will virtually not respond at this setting. It is invisible on the Motor Tuning graph. That is why I experimented to get up to the 1600 Steps Per.
By the way, the a-axis responds the same whether 'A-Axis is Angular' is checked or un-checked. Which leads me to believe this isn't the right setting to make the a-axis rotary, but then where is the correct place to make this change?
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G00 A1 should get you 1 degree, if you are getting 1 rotation something is wrong. Is this what you're getting?
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Is your axis direct drive? Otherwise I would think 200x8 (microstepping)x360 or either 200x8x reduction value.
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Thanks for the reply.
No - G00 A1 gets a full 360 revolution. Yes, I agree. It should provide only 1 degree. I used the Automatic Calculation of Steps Per - it gave me back 1600.
I feel strongly that the problem lies with the fact that Mach3 isn't doing anything with the A-Axis is Angular check box. There is no different behavior whether the box is checked or not. I wonder if there is any code behind it??
The manuals make frequent reference to setting A-axis to Rotary but nowhere can I find where that is at. I am using R3 revision of the software, which is relatively new I think. I am wondering if this new version eliminated the A-axis to Rotary setting or put in some place other than the General Configuration page.
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Yes - the drive motor is connected to the a-axis shaft via two timing belt pulleys and a XL belt. Both are 15-tooth at .2 pitch. That would mean the distance of travel for one revolution of the motor would be 3 inches.
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"The manuals make frequent reference to setting A-axis to Rotary but nowhere can I find where that is at. I am using R3 revision of the software, which is relatively new I think. I am wondering if this new version eliminated the A-axis to Rotary setting or put in some place other than the General Configuration page."
On the General Config. Page - A Axis is Angular. Top left of page.
John Champlain
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Yes - the drive motor is connected to the a-axis shaft via two timing belt pulleys and a XL belt. Both are 15-tooth at .2 pitch. That would mean the distance of travel for one revolution of the motor would be 3 inches.
How can you translate degrees into linear distance? If both pulleys are 15 tooth there is no gearing. It should be microstepping value 1/8 the you said. 200x8=1600 steps per revolution of the stepper. Is there a picture of this set up? The actual A axis?
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Does it have a worm gear?
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Thanks for the replies.
Here is a pic of the '4th-axis'.
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Ok no mechanical advantage or reduction. I was just verifying as the problems seem odd.
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As Fasttest1 stated:
“200x8=1600 steps per revolution of the stepper.”
Note the units are steps per revolution
I think what you are wanting is actually steps per degree.
So divide the 1600 steps per rev by 360 to get 4.4444 steps per deg.
al
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Hi, Thanks for the reply.
I have used the 4.444 step per setting but the movement of the a-axis was virtually imperceptible, although I was able to hear a tick-tick-tick-... which was likely each degree. The velocity line was not visible on the motor tuning graph, probably below the range. Nonetheless, maybe I can jack up the Acceleration to compensate.
Thanks again for your help.
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Can you attach your xml please
Hood
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Looks like your Steps per Degree is resolved and you have now run into a feedrate issue.
Here again the problem is the different units. As an example say you have a feedrate of F10. A feedrate of 10 in/min would be quite reasonable for the linear axis but 10 deg/min for the A axis would barely go tick, tick, In fact it would take over half an hour to go only one rev. To obtain say 10 RPM on the A axis would require an F3600.
If your project will allow keeping the linear and rotary moves on separate lines, then enter the desired feed on the line for each axis. Make sure your A axis velocity is set high enough.
If not, it gets a little trickier. Mach has a feature called ‘Rotation Radius’ on the Settings page. This will allow Mach to calculate internally a deg/min that will result in the requested linear feed at a given radius.
You may find this calculator helpful:
http://www.machsupport.com/forum/index.php/topic,16315.0.html
Hope this helps.
Al
Hi, Thanks for the reply.
I have used the 4.444 step per setting but the movement of the a-axis was virtually imperceptible, although I was able to hear a tick-tick-tick-... which was likely each degree. The velocity line was not visible on the motor tuning graph, probably below the range. Nonetheless, maybe I can jack up the Acceleration to compensate.
Thanks again for your help.
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Thanks for the replies.
Here is the XML file.
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Oh, the joy!
Changed the Steps Per to 4.4.
I tried an MDI of G00 A360 F3600 but that didn't change the behavior of the a-axis. Al, is this what you meant by controlling the feedrate in your F3600 comment? I didn't see another way to change the feedrate for a particular axis.
Next, I set the Velocity to 3600 in the Motor Tuning (see attached pic). Now the a-axis rotates to the proper angle! (I do need to add more decimal values to the Steps Per like 4.4444.) The drive belt chatters or vibrates a bit on ramp up, but the motor sounds normal.
So, due to everyone's help, I am making progress.
Thanks a ton.
The spreadsheet is very helpful as well.
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Slow the accel rate down to lessen the chatter.
Are you using a G540? It sounds like you must be running a 10x microstep value. I just went back and read you are running a Xylotex on 1/8th. The math isnt working for me.
3600 steps per?
Yes F in a gcode does pertain to feed rate. On a rotational axis F360 would be 1 revolution per minute, 3600 would be 10 revs. If that is what you were asking.
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A bit of clarification. The G00 is a rapid command, that is it ignores the F word programmed feed rate. It will move at the max feed as designated by the velocity set for that axis in the Motor Tuning.
A G01 will move at the programmed F feed rate, (as long as it does not exceed the max set in Motor Tuning).
You will need to determine the max velocity and acceleration for each axis in Motor Tuning. To do this, increase each parameter (velocity and acceleration) one at a time until the max is found. The max is where the stepper stalls, (it will not move, just buzz). Then back off 15% or 20%.
You are getting there!
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Thanks for your helpful replies.
My next step now is to learn more about g-code programming.
Problems are really good because they help (with all of your advice/assistance) advance my understanding. I've made leap in knowledge as a result of working through this situation.
Thank you.
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Here are two pics of the now-working A axis. Thanks to you folks on the forum this upgrade to my 3 axis machine is working well.
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Good Show!