Quick guide · 5 minutes

How to reverse motor direction
(parameter $3 GRBL)

Motors running backwards? Press arrow and carriage goes opposite. Not a defect — fix it in 2 minutes by changing one number.

It happens often: press arrow and the carriage goes the opposite direction. It's not a defect — it's just the motor rotation direction that needs to be reversed.

In GRBL (the firmware of our machines) this is controlled by parameter $3. You can change it in two ways:

  • Method 1 — Via WiFi (easiest) → use the machine's WebUI from your browser. Recommended for almost everyone.
  • Method 2 — Via USB → with cable and Serial Terminal. Only if you don't have WiFi or prefer cable.
First of all

How the CostyCNC machine moves

  • X axis = right and left (the carriage slides along the rail)
  • Y axis = up and down (the hot wire goes up and down)
⚠️ WARNING — READ CAREFULLY ⚠️
On CostyCNC: up arrow (Y+) = wire GOES DOWN down arrow (Y-) = wire GOES UP

It's not a mistake. It's designed this way — so images are cut straight as you see them on screen.

Y movement: up arrow (Y+) = down, down arrow (Y-) = up

So if on your machine:

  • Press up arrow (Y+) and the wire GOES DOWN → ✅ PERFECT, IT'S CORRECT (don't change anything for Y)
  • Press up arrow (Y+) and the wire GOES UP → ❌ then Y is reversed (you need to fix it)

🧠 Almost all new customers think up arrow (Y+) should go up, but on CostyCNC it's the opposite: up arrow (Y+) = DOWN!

For the X axis instead:

  • Press right arrow (X+) and the carriage goes RIGHT → ✅ correct
  • Press right arrow (X+) and the carriage goes LEFT → ❌ X is reversed
X axis: right arrow (X+) and left arrow (X-)
Method 1 — WiFi

Via WebUI MKS-DLC32 (easiest)

With the machine already connected to WiFi and WebUI open in your browser:

1 Go to the "Control" window

In the top menu, click on "Control" — that's where manual commands and the console are located.

WebUI menu with Control highlighted

Once in the Control window, scroll to the bottom of the page — you'll find:

  • A window at the top: shows the strings the machine sends and receives
  • Below, a text box with the "Send" button next to it
Control window with console and Send box

2 Read the current value

In the text box, type $3 and click "Send".

In the top window you'll see the response: a number (0, 1, 2, or 3). Note it down.

$3 command and response in console

3 Change the parameter

In the same text box, type the command you found (e.g., $3=1) and click "Send".

The top window responds with ok — done.

$3=1 command and ok response

4 Test

Alternate movements (up arrow (Y+) → down arrow (Y-) → up arrow (Y+) → down arrow (Y-)) to see if they now move as described at the beginning.

Practical table

Which value to use

Find your current value and what you want to fix:

If you have...And you want to fix...Type
$3=0right arrow (X+) goes left$3=1
$3=0up arrow (Y+) goes up (instead of down)$3=2
$3=0both axes are reversed$3=3
$3=1right arrow (X+) goes left$3=0
$3=1up arrow (Y+) goes up (instead of down)$3=3
$3=1both axes are reversed$3=2
$3=2right arrow (X+) goes left$3=3
$3=2up arrow (Y+) goes up (instead of down)$3=0
$3=2both axes are reversed$3=1
$3=3right arrow (X+) goes left$3=2
$3=3up arrow (Y+) goes up (instead of down)$3=1
$3=3both axes are reversed$3=0

4 Change the parameter

Type the command you found (e.g., $3=1) and press Enter. The machine responds with ok.

$3=1 command and ok response
⚠️ WARNING ⚠️

After changing the parameter, test like this:

🎯 Alternate movements several times:

  • Press up arrow (Y+) (watch)
  • Then down arrow (Y-) (watch)
  • Then up arrow (Y+) again
  • Then down arrow (Y-) again

Do the same for X: right arrow (X+) and left arrow (X-).

Why? The first movement after the change can sometimes seem the same. Alternating helps you immediately understand the new direction.

Alternating test: up arrow (Y+) and down arrow (Y-)
Method 2 — USB

Via cable with Serial Terminal

If you don't have WiFi, use the USB cable and SerialTerminal.com.

1 Connect via USB

USB cable connected to machine

2 Open SerialTerminal.com

SerialTerminal.com screenshot

3 Find the port

  • Windows: Device Manager → Ports → COM3, COM4...
  • Baud rate: 115200
Device Manager with COM port

4 Type the same commands

$3 to read, $3=1 (or 2 or 3) to change.

Terminal with $3 commands
Common errors

❌ "I typed 3=1 instead of $3=1"

The correct command is $3=1 — with the dollar sign in front.

❌ "On first test it seems the same"

Alternate up arrow (Y+) and down arrow (Y-) several times. The first movement can be deceiving.

❌ "Up arrow (Y+) goes up, I thought it was wrong"

On CostyCNC up arrow (Y+) must go down. If it goes up, you need to change $3.