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Roland MDX-15 Mill - Spindle Motor Alternative

Finding an alternative spindle motor or using an external spindle controller on the Roland MDX-15

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The Roland MDX-15 mill is an old product and spare parts are hard to find.
This project aims to find an alternative spindle motor to the stock item.
The best solution I feel would be to take the spindle 'ON' signal from the mill and use this to activate an external spindle driver and motor. This would allow different power and speed alternatives to the original.
The mill's mainboard has signals to check if the spindle cable is attached, powered, and has over-current protection.

I bought a Roland MDX-15 mill from eBay, it came without the spindle motor. I've set about finding a replacement motor.

So far I've found a hobbyist 19V multitool and found the pos/neg pins on the spindle motor connector. The mill has the ability to jog the z-axis directly on the machine using two keys on the control panel. When I jog the z-axis the spindle motor starts (as it should). Easy...

As soon as I release the jog button the spindle stops (as it should), however, this is immediately followed by all LEDs flashing. According to the manual, this indicates the spindle motor connection has been disconnected. After thoroughly checking the connections, the problem persists.

I began to wonder if this has something to do with back EMF and flyback diodes or lack of capacitance.

I've soldered a capacitor across the motor terminals but with no luck. I've also tried loading the motor so that when the motor power stops the rotor will produce a lower kickback voltage, this had worked on some occasions.

When loading the motor I did discover that it can stall very easily, causing a different error on the mill indicating over current.

I reached out to Johan (who has been featured on HaD before), and he supplied me with some images from under the hood of an original spindle motor. It shows something that looks like fuse-links in series with the motor.

I reverse-engineered the spindle control section of the mainboard and added the components from the original spindle motor pcb.

I need help finding how the spindle motor PCB connects to the ground, in case this has something to do with kick-back/emi?

I want to replace the motor in this circuit with some 'dummy' load so the mill thinks a spindle is connected, I then want to use the dummy load to switch an external motor controller on.

Any help here is greatly appreciated.

Adobe Portable Document Format - 239.76 kB - 05/05/2022 at 12:24

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    JackJamesHoward05/04/2022 at 20:18 0 comments

    I bought a Roland MDX-15 mill from eBay, it came without the spindle motor. I've set about finding a replacement motor.

    So far I've found a hobbyist 19V multitool and found the pos/neg pins on the spindle motor connector. The mill has the ability to jog the z-axis directly on the machine using two keys on the control panel. When I jog the z-axis the spindle motor starts (as it should). Easy...

    As soon as I release the jog button the spindle stops (as it should), however, this is immediately followed by all LEDs flashing. According to the manual, this indicates the spindle motor connection has been disconnected. After thoroughly checking the connections, the problem persists.

    I began to wonder if this has something to do with back EMF and flyback diodes or lack of capacitance.

    I've soldered a capacitor across the motor terminals but with no luck. I've also tried loading the motor so that when the motor power stops the rotor will produce a lower kickback voltage, this had worked on some occasions.

    When loading the motor I did discover that it can stall very easily, causing a different error on the mill indicating over current.

    I reached out to ... who supplied me with some images from under the hood of an original spindle motor. It shows something that looks like diodes (possible resistors?) in series.  I need help to figure out what these items are and what purpose these might solve.

    I reverse-engineered the spindle control section of the mainboard and added the mystery components from the original spindle motor.

    I want to replace the motor in this circuit with some 'dummy' load so the mill thinks a spindle is connected, I then want to use the dummy load to switch an external motor controller on.

    Any help here is greatly appreciated.

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casper wrote 05/06/2022 at 06:06 point

They do not look like fuses, but EMI filters. 

  Are you sure? yes | no

paulvdh wrote 05/04/2022 at 20:58 point

Why not just replace the main PCB with something that speaks GRBL?

I had a short peek at the insides of this thing:

https://graviranje.rs/Engraving_PORTAL/machines/roland/pdf/Roland_MDX-15_and_20_Parts_Manual.pdf

and apparently it has quite small stepper motors.

Datasheet of the MTD1120 confirms this. They go upto 80V, but only deliver 1.2A.

Any 3D printer main PCB can deliver those 1.2A, although probably not the 80V. What do these motors actually run at?

  Are you sure? yes | no

JackJamesHoward wrote 05/05/2022 at 09:11 point

I considered this already.

I've been following along with a modification to convert the original board to USB, but haven't been successful yet.
I figured the spindle motor might be stopping the board from accepting any commands, so I want to fix this first.
If I can't get the thing to work via USB after fixing the spindle issue then I may just give up and fit a GRBL board.

This seems a waste of original hardware and the toolset/software the original machine ships with. I have an original scanning probe for the machine that I might be able to get working yet.
Also, the machine doesn't use end-stops for homing, I think it monitors the motor current and looks for when it stalls. So I'd have to fit end-stops for a GRBL board.

All hassle I can't face right now when there's seeming good hardware already in place.


I'll power the mill up tonight and probe some voltages.

  Are you sure? yes | no

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