Hey Tom,
what exactly are the reasons for you to want the Masso Controller? Or, is there something why you think the Onefinity Original Series/Buildbotics Controller is not matching your requirements?
I plan to use another controller too, but that is only for certain reasons. Nonetheless I bought a Onefinity Controller because I think the Buildbotics and its derivate, the Onefinity, is really a very complete and capable controller, it’s a piece of soft- and hardware to be fascinated of if you think of the fact that it was programmed mainly by one person. And for a stand-alone CNC controller, the price is unbeatable.
The open-loop steppers as found on the Onefinity Original Series are used widely everywhere, both in the hobbyist area and in the professional and industrial area too, they are the standard motor for CNC machines. The open-loop stepper motor is an ingenious piece of technology that has the steps there in hardware, and controlling it is something that has been established and improved over many decades. Well-evolved integrated stepper driver chips like the Texas Instruments DRV8711 are available at very low cost. The secret of having open-loop steppers work reliably is simply to dimensionate them correctly for the application.
Closed-loop steppers as found on the Elite/Masso have an encoder (usually a glass disk with marks on it that are read by a photo sensor) that reports back every movement to the driver, so if the motor does not execute the steps which the driver received from the CNC controller, the driver can try to repeat them and catch up the position, and should this fail, will report an alarm to the CNC controller which can then stop the program.
If you should say e.g. as a luthier you have sometimes workpieces worth $3000 then I know exactly what you are talking of. But when judging on the correct motors to choose for your CNC machine, it is important to consider two things:
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Do the open-loop steppers really are a cause of possible malfunction to have a danger of damage on a workpiece? Or did I encounter damage because the machine did something wrong but that had in fact other causes? Aren’t open-loop steppers, a well-used standard motor for CNC, reliable enough to not be the cause of problems?
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A closed-loop stepper does not report missed steps to the CNC controller either. It just sends an alarm if the amount of divergence between received step commands and steps executed becomes too high and it cannot catch up and compensate this anymore, so the controller can stop the program. But what could be the cause of a stepper not executing the steps? In daily use, this could be e.g.
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a too high feed, plunge or depth of cut rate so that the motor is not capable to cope with it
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a failure of the milling motor or of the electric parts that ensure its functioning so that the bit does not rotate anymore
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Other errors you could encounter, that would not make loosing steps, but disturb the operation are:
- a bit that breaks
The question is now: Would a closed-loop stepper have avoided a damage to the workpiece, more than when using an open-loop stepper system? I think it’s about a closed-loop stepper bringing a different machine behaviour: It would not proceed milling the program after having lost too much steps. But would the event that triggered the error, e.g. a too high feed rate, with a bit stuck in the workpiece, or a workpiece shifted out of its position by the too high feed force when bit is partially broken or stalled, have prevented that the machine made a damage to the workpiece? I think, you can’t be sure. If you mill the f-hole of a violin top that was dried for twenty years, I think perhaps you cannot tolerate even a single millimeter damage, that could occur even when using a closed-loop stepper. So in short, the moment when a closed-loop stepper signals the alarm to the CNC controller, often it is when a damage is already done. The controller then just won’t proceed stupidly with the entire rest of the program.
If I personally plan to use something superior to open-loop steppers, that would not be the closed-loop steppers as found on the Masso/Elite, but servo motors, because they have not the typical stepper speed limit and can run twenty times faster. They are closed-loop too, but as they have no hardware steps, they need extremely sophisticated algorithms in their driver and those drivers are more expensive.
But even servos would not change anything on the danger of the user selecting too high cut rates, or routers failing, or bits breaking.
What I think you need in the first place is to retrofit a professional cable management (drag chains) to your machine, to get rid of the known possible causes of errors on this machine, and, if you want, additionally proximity sensors as limit switches which can be added to the Onefinity/Buildbotics controller, to get rid of stall homing.
Besides that, to use the Onefinity/Buildbotics Controller with open-loop steppers, it would be enough to
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have enough experience with CNC milling wood to always select an appropriate feed, plunge and depth of cut rate matching the wood type,
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to use high-quality bits and to make sure they’re always sharp, and
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to have a reliable electric system around a reliable millling motor.
So far my thoughts on that, hope it gave you some inspiration.
