[Grimgnaw]

Hello everbody,

Im a noob to CNC, so i will try to post the problem as clearly has I can. I have a couple of questions regarding Linuxcnc, electronics interface, and stepper motors so i don't know where to post this, anyway here it goes. The first question might not be related to Linuxcnc but eventually it comes to that, so sorry for the inconvenience.

1. I have designed a fixed gantry machine with a moveable Y axis along the Z axis, and of course I have two stepper motor in each corner of the gantry and two ballscrews to provide lift. When i was talking to some of the suppliers for machine, they said that two motors could because a problem eventualy with time. If one motor breaksdown the gantry could fall apart, twist, bend, or whatever happens when something like this happens. So my question is how often do people use two steppers for the moveable Y axis, or any axis, and how catastrophic would be if one of the steppers fails completly. It seems that people use two motors on the same axis frequently, although i don't know if they are prepared for this kind of failure of one the steppers. Is there special circuitry to prevent one of the motors from moving if the other fails? can Linuxcnc detect this? or i am worried with something that just doens't happen?. Does anyone has experience when one of the steppers completly breaksdown?

2. Continuing with the previous problem, I read that encoders in the steppers can account for the position and it is possible to interface with Linuxcnc. However there are a lot of opinions on this matter. Some say it is impossible because you need special hardware to read the encoders at the speed that is required, some say that it could only trigger the E-stop, but to trigger you need to read the encoders, right? if its only a matter of reading the encoders properly, If i reduce the speed of cutting will this make the encoders readable in real time? If so, how much lower would the cutting speed be?

3. Another question is regarding stepper drivers, specially the digital ones. Some have the stall detection system, but i don't understand what they do except to say "MOTOR STALLING". I don't know if its easy or very dificult to manually detect stall, but i supose that many people use drivers without the stall detection because you can hear or see if its missing steps, right? Do these digital drivers provide the stall signal to Linuxcnc for further processing, or is this just a LED that blinks in the driver to give a warning?

I feel that planning is everything when you have a project like this, so any answer will be greatly appreciated.
Thanks everyone

[urbnsr]

The only thing I can comment on is the first part. I run single motors for each XYZ axis, but there are many designs using dual motors per axis. There are pros and cons to either way. Single motor is less expensive and easier to configure, but doesn't offer any help to continually keep the axis squared-up. Dual motors cost more and require more setup when configuring, but could be used to square the axis regularly. Of course, if one motor looses steps in a dual motor setup and you don't catch it right away, your axis gets out of square. That's probably the main reason I designed my table with single motors - Takes more to make sure it's running true, but once set, it's harder to get out of square.

Your motor size and table design will decide how much damage occurs if a motor fails. If the table is heavy enough, the other, working motor will start loosing steps when the axis gets into a bind. Strong motors will go further and the table design will then determine if the motor goes too far and starts breaking the table.

HTH
Paul

[Grimgnaw]

Thank you for the reply urbnsr, I thought that single motor design would be easier, but apparently its not just a solution but also offers some disadvantages. How easy is to square the axis with dual motor system?
What about a solution with a single motor to drive a belt and pully that is connected to both ballscrews. This is probably crazy, but am I solving a simple problem with a complex solution?

If anybody as some comments on this, and to the previous questions in the original post, I would greatly appreciate.

Thanks everybody.

[Al_The_Man]

Have you looked at Dynomotion for true closed loop for servo's?
Dynomotion Motion Control Boards for CNC Manufacturing and Robotics Applications
If you use Kanalog, you can use the commonly available