Unexpected Motor Travel on Initial Setup
Posted: Sat Oct 03, 2020 9:06 am
Hello, I was wondering if someone would be able to provide a little support to get me milling again?
I have recently started the process of retrofitting an old ShopBot table with the BuildBotics CNC Controller. Following the Getting Started documentation was a breeze. I rewired the existing motors from Unipolar to Bipolar in order to use the BuildBotics drivers, booted up, and boom, it just plain worked with the existing settings using the supplied gamepad. Kudos to the BuildBotics team here as I was expected a little more work to see my first movements!
The default settings are not ideal for my motor configuration, so I made the recommended adjustments. At least, what I think are the correct adjustments.
Here is some general information about my setup:
M0 = X-Axis (Reversed through wiring) - PK296A1A-SG3.6
M1 = X-Axis - PK296A1A-SG3.6
M2 = Y-Axis - PK296A1A-SG3.6
M3 = Z-Axis - PK266-02A
In the BuildBotics UI I entered the following values:
For the (2) X Motors and the Y Motor I set the Drive Current to 2. I did this because the motor specs show 1amp/phase and this is a 2-phase motor. I left the idle at 0 (default). I set the step angle to .5 to match the motor specs.
For the Z Motor I set the Drive current to 2.8 as the motor specs show 1.4amps/phase and this is also a 2-phase motor. Again, I left the idle at zero. I verified that the step angle matched the motor specs (1.8).
I made no other changes to the motor configurations other than reversing the motors so that positive X, Y and Z values moved the machine in the correct direction.
I pulled the post processor from github for Fusion 360 and exported a tool path with it to cut out some small shapes to validate sizing. This is where things went a little crazy….
The program ran, started a tool change sequence, I continued, and the machine started moving. And it moved A LOT and at a speed I am unused to. This machine has never had limit switches but believe me, after this experience, they have been ordered. I stopped the program quickly to avoid any damage. The shapes I am cutting out are 1x1” and the machine bed is 4x8’. There is no logical reason that I can think of as to why the machine would need to move several feet in order to run a program where the stock size is less than 4x4 inches.
I started a little experimentation at this point and jogged the machine around and watched the position values on the controller. The CNC Controller would show a movement of a millimeter, but the machine is moving much more. This leads me to believe I have goofed something in the configuration, and this is likely not an issue with the tool path itself.
This machine setup is obviously a little more complicated than my Shapeoko running Carbide Motion so I could be missing something. My best guess is that this has something to do with the travel per revolution and/or gear ratio for these motors, but I really don’t want to continue guessing on what I need to do especially if this machine can effectively destroy itself or worse, come out of alignment, lol.
It would also be awesome if I could put on some “training wheels” and slow the motors down a bit while I'm still learning. I assume this is done in the max velocity value for the motor but again, I will defer to the subject matter experts.
Thank you so much for any support you can provide. I’m happy to provide any additional details that may be required!
Motor Specs:
PK296A1A-SG3.6 - https://catalog.orientalmotor.com/item/ ... 6a1a-sg3-6
PK266-02A - https://catalog.orientalmotor.com/item/ ... /pk266-02a
I have recently started the process of retrofitting an old ShopBot table with the BuildBotics CNC Controller. Following the Getting Started documentation was a breeze. I rewired the existing motors from Unipolar to Bipolar in order to use the BuildBotics drivers, booted up, and boom, it just plain worked with the existing settings using the supplied gamepad. Kudos to the BuildBotics team here as I was expected a little more work to see my first movements!
The default settings are not ideal for my motor configuration, so I made the recommended adjustments. At least, what I think are the correct adjustments.
Here is some general information about my setup:
M0 = X-Axis (Reversed through wiring) - PK296A1A-SG3.6
M1 = X-Axis - PK296A1A-SG3.6
M2 = Y-Axis - PK296A1A-SG3.6
M3 = Z-Axis - PK266-02A
In the BuildBotics UI I entered the following values:
For the (2) X Motors and the Y Motor I set the Drive Current to 2. I did this because the motor specs show 1amp/phase and this is a 2-phase motor. I left the idle at 0 (default). I set the step angle to .5 to match the motor specs.
For the Z Motor I set the Drive current to 2.8 as the motor specs show 1.4amps/phase and this is also a 2-phase motor. Again, I left the idle at zero. I verified that the step angle matched the motor specs (1.8).
I made no other changes to the motor configurations other than reversing the motors so that positive X, Y and Z values moved the machine in the correct direction.
I pulled the post processor from github for Fusion 360 and exported a tool path with it to cut out some small shapes to validate sizing. This is where things went a little crazy….
The program ran, started a tool change sequence, I continued, and the machine started moving. And it moved A LOT and at a speed I am unused to. This machine has never had limit switches but believe me, after this experience, they have been ordered. I stopped the program quickly to avoid any damage. The shapes I am cutting out are 1x1” and the machine bed is 4x8’. There is no logical reason that I can think of as to why the machine would need to move several feet in order to run a program where the stock size is less than 4x4 inches.
I started a little experimentation at this point and jogged the machine around and watched the position values on the controller. The CNC Controller would show a movement of a millimeter, but the machine is moving much more. This leads me to believe I have goofed something in the configuration, and this is likely not an issue with the tool path itself.
This machine setup is obviously a little more complicated than my Shapeoko running Carbide Motion so I could be missing something. My best guess is that this has something to do with the travel per revolution and/or gear ratio for these motors, but I really don’t want to continue guessing on what I need to do especially if this machine can effectively destroy itself or worse, come out of alignment, lol.
It would also be awesome if I could put on some “training wheels” and slow the motors down a bit while I'm still learning. I assume this is done in the max velocity value for the motor but again, I will defer to the subject matter experts.
Thank you so much for any support you can provide. I’m happy to provide any additional details that may be required!
Motor Specs:
PK296A1A-SG3.6 - https://catalog.orientalmotor.com/item/ ... 6a1a-sg3-6
PK266-02A - https://catalog.orientalmotor.com/item/ ... /pk266-02a