Why CarveWright Uses Servo Motors Instead of Stepper Motors

CarveWright’s CNC systems from the early models to the new RAVEN are the only CNC machines in size capacity and price range using servo motors. You usually only find servos on large, expensive industrial machines that require accuracy and high torque at high speeds. To understand why we use this technology in our machines rather than stepper motors like our competitors, it’s necessary to understand the differences between the two motor types.

Stepper Motors

Stepper motors are a basic motor design that uses electromagnets to divide a full rotation into a number of equal steps. Basically, they are commanded by a controller to move a certain number of steps at a specified speed. There isn’t much more sophistication to the motors than that.

Their advantage lies in their simplicity. However, this simplicity has a few serious drawbacks. Most importantly, stepper motors do not utilize position feedback and cannot react or adjust to changes in load. The motor torque in a stepper motor also decreases as its speed increases, requiring very slow speeds and shallow cuts. Moving too quickly or with too deep a cut will result in missing steps, and without any feedback, the controller has no way of compensating for it.

For these reasons, stepper motors are not well-suited to the sophisticated project and material types of high-end CNC operations demanded by our community of users.

Stepper Motor CNC
PROS	CONS
• Generally lower in cost • Good low speed torque and accuracy • Low duty cycle	• No feedback to report positioning • Cannot sense or react to changes in load • Prone to losing position and crashing if not run at slower speeds • Requires shallow cuts in multiple passes • Torque decreases as speed increases

Servo Motors

The servo motors found in CarveWright CNC’s are high-torque DC motors with an encoder mounted on the back shaft to detect the position and speed of the rotor. The feedback from the encoder enables high-resolution, high-response positioning operations.

This sophisticated motor design offers some real advantages over stepper motors. Unlike steppers, servos can apply peak torque on demand at any speed. Our ServoSmart Controller monitors and regulates the motor’s current for more precise torque control, allowing the machine to adapt to changes in load in real time without stopping. Furthermore, the machine’s position is constantly being reported by our high-resolution encoder (1296 PPR), allowing the machine to detect and auto-correct any errors. The result is that CarveWright CNCs offer faster, more precise carves than competing CNC machines.

Servo motors allow our machine to carve a lot faster because excess load or backlash situations are automatically compensated for. Our machines produce different commands based on feedback from the three-axis servo motors. This makes servo motors a superior choice for variable-load systems like a CNC machine, which is why all professional-grade CNC machines use servo motors just like CarveWright does.

Servo Motors
PROS	CONS
• Feedback loop for real-time sensing • Senses slips and auto-corrects • Reports issues instead of crashing • High torque at high speeds • High resolution encoder ensures accuracy	• Generally higher in costs • Proprietary to specific controller

Feeling a little lost? Understandable! Here’s what you really need to know: Thanks to our ServoSmart controller and servo motors, CarveWright offers the fastest and most precise consumer CNC routes in the world. That’s why the performance of CarveWright CNC machines is unmatched.

Have questions about how our machines work? We’ve got answers! Contact us today for more detailed information on how CarveWright machines outperform the competition.