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Topic: Drawing Machine - CNC Shield with additional stepper motors (Read 283 times) previous topic - next topic

LemmyC

Hi all,

I have made a drawing machine which runs the GRBL software, using an arduino with a CNC shield like this one: CNC Shield. It has drivers for 4 stepper motors.

I have a stepper motor attached to each of the X and Y axis, and have a servo motor attached to additional pins to control up/down movement of the pen.

I would like to revise my design to have two stepper motors each for X and Y. So my questions are:

1. Can I run pairs of the stepper drivers in sync, e.g. X and Y for X-axis, Z and A for Y-axis?
2. Alternatively, is there a way to add additional stepper motors while still keeping the Z stepper driver free, as I would like to look at adapting it to control the pen movement, instead of using the additional servo. (This is mainly so that I can use existing G-Code for my drawings. At the moment I have to add additional commands to my G-Code to implement pen up/down commands.)

I am happy to consider other boards or shields to achieve this...


Thanks for any suggestions!

Robin2

IMHO the best option would be to send the same step and direction signals to two stepper motor drivers - but that would probably mean that some of the drivers could not be connected to the CNC shield.

Or you could connect two stepper motors to a single driver - but they need to be connected in series so that the same current flows through both of them. And with the two motors in series you may need a higher voltage power supply.

If you are using two motors for the same job it would probably be best if they are firmly coupled mechanically to avoid any risk of them getting out of step with each other.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

Or you could connect two stepper motors to a single driver - but they need to be connected in series so that the same current flows through both of them.

Note this means each winding individually in series, the A winding from motor1 in series with the A winding
of motor2, and ditto for the B windings.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

LemmyC

Thanks for your reply!

And with the two motors in series you may need a higher voltage power supply.
Would this mean a loss of torque? Do you think 'normal' performance could be restored by providing higher voltage, and if so, any ideas on how best to quantify the amount needed?

Robin2

With a suitable voltage from the power supply I would not expect any loss of torque. Stepper motor torque falls off with speed due to the inductance of the coils and back emf. And of course two motors in series doubles the coil resistance as well as other things. A higher voltage counteracts that. Of course it is essential to set the driver current limit correctly to protect the motor. If the motors are in series the current will be the same as for a single motor.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

Thanks for your reply!

Would this mean a loss of torque? Do you think 'normal' performance could be restored by providing higher voltage, and if so, any ideas on how best to quantify the amount needed?

Double the voltage if in series, then each motor sees exactly the same as before.

You may not need too, worth testing before committing to a new power supply, and check the limit of the
stepper driver you have.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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