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Third party software and hardware support forums. / Re: Help with Stepper Motor Tuning and Setup
« on: April 03, 2009, 05:48:50 AM »
Hi again Prof,
I fully understand what you are trying to do here, you have explained that well in other postings, but I can’t help thinking that you are ‘re-inventing the wheel’. We have moved on a lot since the early days of CNC and the advent of chips with computing powers have simplified controlling the drive requirements of stepper motors considerably. If we consider a basic CNC machine it all comes down to the need to move an axis from one place to another. Because any axis has mass this then requires a greater force to accelerate and decelerate it than it does to maintain it at a constant speed. Just considering mass and acceleration at the moment and ignoring the many other forces involved, then the greater the mass the greater the force required likewise the greater the acceleration / deceleration the greater the force required. Now steppers have the characteristic of being able to provide high torque (force) at slow speeds and low torque at high speeds which pretty much meets the requirements for moving a CNC axis. When a stepper is stationary, the torque is high so the current through its windings can, within limits, be reduced without compromising its performance (holding torque). So to drive a CNC machine well and efficiently the current through the steppers must vary in accordance with the task. Minds greater than my own have tackled this problem and for example chips, such as the Alegro SLA7024M series for unipolar and the A3982 for bipolar steppers implement the requirements to a tee. There are, of course, many other makers and chips to choose from and I recommend that you proceed in this direction. After all we must learn from and build on others experience because, as others have said, life is just no long enough to make all the mistakes yourself.
Sorry for rambling on a bit but if your ultimate goal is to build a working CNC machine why not concentrate on the mechanicals and purchase Gecko drives for the steppers – it may be a lot cheaper in the long run.
All the best,
Tweakie.
I fully understand what you are trying to do here, you have explained that well in other postings, but I can’t help thinking that you are ‘re-inventing the wheel’. We have moved on a lot since the early days of CNC and the advent of chips with computing powers have simplified controlling the drive requirements of stepper motors considerably. If we consider a basic CNC machine it all comes down to the need to move an axis from one place to another. Because any axis has mass this then requires a greater force to accelerate and decelerate it than it does to maintain it at a constant speed. Just considering mass and acceleration at the moment and ignoring the many other forces involved, then the greater the mass the greater the force required likewise the greater the acceleration / deceleration the greater the force required. Now steppers have the characteristic of being able to provide high torque (force) at slow speeds and low torque at high speeds which pretty much meets the requirements for moving a CNC axis. When a stepper is stationary, the torque is high so the current through its windings can, within limits, be reduced without compromising its performance (holding torque). So to drive a CNC machine well and efficiently the current through the steppers must vary in accordance with the task. Minds greater than my own have tackled this problem and for example chips, such as the Alegro SLA7024M series for unipolar and the A3982 for bipolar steppers implement the requirements to a tee. There are, of course, many other makers and chips to choose from and I recommend that you proceed in this direction. After all we must learn from and build on others experience because, as others have said, life is just no long enough to make all the mistakes yourself.
Sorry for rambling on a bit but if your ultimate goal is to build a working CNC machine why not concentrate on the mechanicals and purchase Gecko drives for the steppers – it may be a lot cheaper in the long run.
All the best,
Tweakie.
