How to Calculate VREF?

by Mike Brooks | Last Updated: May 4, 2022

3D printing enthusiasts often find this subject pretty technical to understand.

However, the article takes you through how to calculate VREF. First, you need to understand what a stepper motor does in a 3D printer.

Equally, you may want to appreciate how the stepper motor works, the voltage reference speed, and the ideal setting value.

Stepper Motor

Stepper motors are critical in a variety of applications ranging from different industries. Notably, 3D printers, scanners, floppy discs, aircraft industry, among others, are the primary applications of stepper motors.

In 3D printing, stepper motors come in handy in 3D printer parts that are mobile. The extruder assembly uses stepper motors to pull plastic into the extruder.

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Also, the extruder or build plate must move along the X-Y and Z-axis during printing. It’s the stepper motor that enables the movements to take place.

More significantly, these stepper motors require a power supply to function. VREF stands for voltage reference.

As a result, you need to be familiar with the VREF calculation formula to ensure your VREF settings are correct for optimal 3D printer functionality.

What Is VREF on 3D Printer?

Landing Configuration

Pilots consider VREF as the aircraft’s speed in a stated landing configuration, more so when it descends through 50 feet seeking a landing distance. However, VREF refers to the voltage reference speed required for proper stepper driver workings.

Thus, in 3D printing, VREF stands for the amount of energy that the stepper motor drivers release, the voltage or current required to power the stepper motor speed.

Another way of looking at VREF is the calibrations conducted on the stepper motor drivers.

What’s VREF Speed?

In the 3D printing industry, VREF refers to obtaining reference voltage for the stepper drivers.

Why Is This Important?

It lets you know and determine the amount of power or current you should supply to stepper motor drivers.

VREF is the calculated reference speed for the aircraft’s final approach performance in aviation.

Stall Speed

The aircraft operating manual defines the VREF speed required as 1.3 x stall speed with selected landing configurations.

The CPL flight test guide provides the following formula for calculations of VREF; 1.3 VSO KCA (Maximum Gross Weight) x Square root (Landing Weight/Gross Wt).

If the pilot calculates the correct VREF values, he meets the landing runway threshold for a safe landing.

How Do You Adjust a VREF Stepper?

Adjusting the stepper driver current remains a simple undertaking. Use a multimeter on the DC voltage settings. First, you need to locate the position of the potentiometer. Then, adjust VREF by turning the potentiometer using a tiny flathead screwdriver.

You turn it clockwise if you want to increase the VREF value, or turn it anticlockwise if you’re going to lower the current.

Importantly, you need to turn the potentiometer carefully; you can easily damage your terminals if you short your screwdriver on them. Also, some stepper drivers tend to have a fixed position, meaning they can only turn at a maximum of 270 degrees.

Other stepper drivers rotate without limitations, turning back to zero after reaching 100%. Notably, don’t force it if it stops turning.

If you turn the potentiometer and realize it doesn’t move, check out for a reason. If overheating is the cause, then you won’t hear any sound. Conversely, insufficient power supply causes audible grinding and chunking sounds.

Also, if you skip steps by accelerating the motor too fast or if you misconfigure extruders, you will hear a “buzz” sound during retraction movements.

Why Is VREF Important?

VREF is vital for efficient motor or driver operations, measured in voltage. Significantly, it regulates the amount of power that reaches a stepper motor driver.

If insufficient power gets to the stepper motor or driver, the machine tends to skip steps when operating. Skipping steps makes the device less effective, more so in precision. It causes visible layer shifts in your 3D print products.

On the other hand, if you supply too much current to the stepper motors or drivers, it results in overheating. Still, overheated engines and drivers are prone to damage, especially over long periods of use.

Notably, various drivers boast of different maximum power ratings that they can withstand. Therefore, surpassing stipulated top current ratings causes overheating, leading to motor and driver damages.

Furthermore, it would help appreciate that the correct VREF setting leads to optimal stepper driver calibration.

Is VREF the Same as Vapp?

The reference speed is 1.3 times the stalling speed in the required landing configuration in the aviation or aircraft industry. Also, at the stated aircraft weight.

On the other hand, Vapp refers to the approach speed or operational speed required by the aircraft during landing. The primary Vapp speed determinant remains the aircraft flaps in a landing configuration.

More importantly, Vapp is the reference speed with the addition of the wind factor. Also, note that VREF is the speed over the threshold, not the aircraft touchdown speed required. The touch-down rate is lower.

Significantly, the pilot moves VAPP to VREF during the threshold approach. He only gets to VREF at the threshold.

TMC2208 / TMC2209 VREF Calculator

Trinamic Motion Control company manufactures both TMC2208 and TMC2209 VREF calculators. The two types of calculators are quiet and support 1/256 micro-stepping.

They are modern drivers that work using VART or Standalone operating modes.

Setting a VART mode stepper current needs a computerized process. On the contrary, the standalone mode works manually.

TMC2208

The TMC2208 is an ultra-quiet VREF calculator with a two-phase motor drive. Its continuous drive current stands at 1.4 A, reaching 2A. The voltage range is between 4.75 V to 36V, and it boasts 256 subdivisions.

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Additionally, it’s compatible with most 3D printers available in the market. Thus, it reduces costs by eliminating the need to redesign.

Furthermore, it’s easy to use and can replace the TMC2100’s lower heat in 3D printing.

TMC2209

The TMC2209 enjoys a drive current of 2A and a peak current of 2.8A. It has a voltage range of between 4.75 V and 29 V. Also, it hosts 256 subdivisions.

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One of its primary strengths remains its excellent heat dispensation. It lowers up to 30% of heat than other stepper motor drivers.

At the same time, TMC2209 is readily available in the market at a pocket-friendly cost, and it remains pretty easy to use.

How to Calculate VREF

Various stepper motor drivers react differently and require calculations and formulas to get a perfect voltage setting.

Additionally, the maximum stepper motor drive current you can set is 2.0A. However, the practice when calculating VREF is to use a lower value like 0.8A.

The TMC2208, for instance, has a maximum output value of 1.2A RMS.

Therefore, using the formula:

VREF= Amax X RMS

VREF=0.8 X 1.2

VREF=0,96V

Conclusion

Stepper motor drives remain essential parts of a 3D printer. They primarily control movable parts of your 3D printer, and you’ll like them to work well to get quality prints.

Notably, insufficient power in the stepper driver causes the driver to skip impacting the quality of the 3D product.

Excess current heats the stepper motor drive, damaging it in the long run. As such, get the correct VREF settings by using the formula VREF=Amax X RMS.

Michael Brooks is the founder of M3DZone.com. He sees a very bright future for 3D printing that's why his mission is to try and make this easy for everyone. Discover your hidden talent and creativity. You can follow here: Facebook, Twitter & Pinterest.