What are Stepper Drivers
Under the hood of every 3D printer, 3D carver, or CNC, there are stepper drivers. They control and cause the coils in stepper motors to trigger, making the shaft of the motor rotate in a precisely controlled manner. Some control boards have the stepper drivers integrated as part of the board, and others have them as swappable and replaceable plug-ins. There’s an advantage and disadvantage to every form, so let’s take a look at what these little guys are capable of.
How they work:
Stepper drivers all have a central chip that processes inputs and outputs them as movements across each axis. Nema17 stepper motors have a certain number of steps per rotation (with most being 200) which is just how many changes in the magnetic field of the coil will it take to completely rotate the motor shaft. By carefully controlling the current that the driver outputs, it will magnetize one side of the motor, causing the shaft to spin, and by constantly and consistently changing which side is magnetized is how the motor spins.
What is microstepping:
Drivers can also do something called “microstepping” where instead of moving strictly one tooth of the gear or step at a time, the driver can apply just enough current to hold the gear between steps, increasing the accuracy of the output motion. As of today, 1/16th microstepping is fairly standard, and has been for a while, but there are some drivers that can go to 1/32, 1/64, 1/128, or even 1/256 microstepping. The more microstepping that a driver outputs, the more current it will need to be able to have the torque to hold those fine positions.
A4982, DRV8825, and TMC2130s are all very common stepper drivers for a 3D printer. In cheap and simple kits you might find the A4982, in an upgrade kit a pack of DRV8825s, and in a newer, higher quality printer the TMC2130s. The A4982 or Allegro drivers are usually pretty cheap, but can be pretty noisy when they’re running and they’re limited to 1/16 microstepping. The DRV8825 or Texas Instruments drivers can use 1/32 microstepping and have been a common choice for stepper driver upgrades, but some have noticed that they tend to have issues making accurate microsteps, meaning that when it’s told to move one microstep, it might skip and move two. TMC2130s are more recently developed and have some pretty neat features like 1/256th microstepping, stealthchop, sensorless homing, and skip detection. However, while it’s capable of doing these things, it’s also up to the firmware to make these things actually happen.
The Different Forms of Stepper Drivers
Stepper drivers come in two different forms: integrated and removeable. Integrated means they are part of the board and are not installed separately; when you buy a mini Rambo, the A4892 chips are soldered directly to the board; on a classic RAMPS, the stepper driver plug into specific ports on the board. If you have separate drivers, that does mean you’ll have to source those as well as the control board if you’re building a 3D printer, however if they ever fail, you only need to replace that single driver (which is usually below $15 each) rather than desoldering a bad driver or getting an entirely new control board if you blow a driver on an integrated board (which could be $150 mistake). With removeable boards, there’s the Pololu footprint and Bigfoot footprint; Pololu is a standardized footprint, whereas Bigfoot is specifically made for Panucatt boards and to allow for more current and larger chips.
Keeping the Drivers Cool
While the stepper drivers are smart enough to shut down if they start overheating, that does mean you’re going to be skipping steps in your print. Some drivers just need a heatsink attached to the chip and call it a day, while others may need that and a fan blowing cool air onto the board.
Stealthchop and Spreadcycle
A staple of Trinamic drivers is StealthChop and Spreadcycle. Stealthchop is for quiet, low-current performance, which means your printer may be completely silent, save for the bearings rolling across the smooth rods, but it also means move too quickly, too abruptly, or snag on some tipped over supports and your 3D printer may skip steps. Spreadcycle is basically the “normal” mode and will power through and perform as you would expect. They’ve also come out with Stealthchop2 which is even better than before, so where before it may skip a step, now it can counter it with no problem at all.
On a base level, that about covers what stepper drivers are, how they work, and should hopefully give you an idea of what you might want in a 3D printer. If you’ve gone ahead and swapped out the stepper drivers in your 3D printer, I’d love to hear what you’ve upgraded to.