PRIME MOTIONConnecting to a machine
Prime Motion talks to your controller over a USB cable from the tablet, the same serial link a computer would use. Everything about that link lives in Settings → Connection.
What it can connect to
The controller's USB port must present one of the common USB-serial chips or a native USB serial port:
| Seen on | USB device |
|---|---|
| Many Grbl boards | FTDI FT232R, FT232H, FT-X |
| Low-cost boards | CH340, CH341A |
| Some boards | CP2102, CP2104 |
| ESP32-based controllers | the ESP32's own USB serial port |
| STM32-based controllers | the STM32 virtual COM port |
The firmware behind it must be Grbl 1.1, grblHAL or FluidNC; see Supported controllers.
How the connection opens
There is no Connect button. When a supported controller is plugged in and switched on:
- The first time, Android asks whether Prime Motion may use the USB device. Allow it. If you refuse, the link stays down until you plug the controller in again and allow it.
- With Auto-Connect on Startup on, Prime Motion opens the link to the active machine profile.
- It reads the controller's identity and settings, and the position readout comes alive.
If the cable is knocked out mid-session, the link drops and Prime Motion reconnects on its own when the controller reappears, provided Auto-Connect on Startup is on.
Reading the state of the link
| Where | What it tells you |
|---|---|
| Settings → Connection → Live connection | CONNECTED in green, or DOWN in red |
| Settings → Connection → Firmware | The same family, version and source as Settings → Firmware; Live from controller identifies this connection's answer, while Last read from or Catalog seed identifies a reference |
| The state tag on Control | Offline with no link; otherwise the controller's own state: Idle, Run, Hold, Jog, Alarm, Door, Check, Home, Sleep or Tool |
| The Notes card on Control | Machine not connected — Connect in Settings → Connection while the link is down |
A connected machine is not yet a ready machine. Homing is still required before anything that moves it becomes available; see the homing gate.
Serial settings
Baud Rate is the speed of the link: 9600 up to 921600, default 115200, which most Grbl controllers use. A new value applies the next time the link opens.
Status Polling is how often Prime Motion asks the controller where it is: 100ms, 200ms (the default), 500ms or 1000ms. More often gives a smoother position readout and a little more traffic on the link.
Firmware Family is the starting assumption for a controller that does not announce itself. Most do, and Prime Motion corrects the assumption from the controller's answer.
Switching machines
Choosing another machine in Active Profile closes the link to the current one. Reconnecting uses the newly active profile.
When it will not connect
Work through these in order. Most failures are the first one.
- Cable and power. Is the controller switched on? Is the cable a data cable, not a charge-only one? Try another cable.
- Permission. Unplug and replug the controller. If Android asks for permission, allow it.
- Auto-Connect on Startup. It must be on in Settings → Connection.
- Active Profile. Is the profile for the machine you have plugged in active?
- Baud Rate. Check it against what your controller expects. 115200 is right for most.
- Restart the controller. If the link was up and the controller stopped answering, power it off and on again rather than assuming a fault. The Notes card says Controller is refusing G-code — every line rejected when the controller answers but refuses everything; disconnect and reconnect, or restart the app.
If none of that works, contact support@primemotioncnc.com with the controller's make and model, the USB chip if you know it, and what Live connection and Firmware show.