Mounting and cooling the Duet
Duet 3 Mainboard 6HC v0.6
click on the image for a larger version
All Duet variants have four 4mm clearance holes at the corners of the board. You can use M4 screws to attach the board to a panel or an enclosure. The hole patterns / mounting centres are 115mm x 92mm, full dimensions are shown in the diagrams:
Duet 2 Wifi Dimensions
Duet 2 Ethernet Dimensions
The diagrams show the mounting hole points in the format X,Y so the bottom left hole is at X=4mm, Y=4mm, the top left is at X=4mm, Y=119mm and so on. The board has 3 additional 2.54mm holes at: (53.1,9.1),(56.7,28.7),(81.5,22.) for mounting the Ethernet Module.
Adam Sweeting has created a 3D model of the Duet 3 Main Board 6HC hosted on GrabCAD at https://grabcad.com/library/duet-3d-duet...
Phil Maddox has created a 3d model of the Duet 2 Wifi hosted here:
Giuliano Moschini has created a model based on the Duet 2 WiFi model for the Duet 2 Ethernet:
The Duex CAD file is here, thanks to Morten Nielsen for making this version:
On Duet 0.6 and 0.8.5 boards, and pre-production Duet 2 Wifi boards, the mounting holes are plated-through and connected to the ground plane. On Duet 2 production boards, the holes are isolated and not plated through.
- If you mount the board on a metal surface, use standoffs to ensure that the back of the board cannot short against the plate. A minimum standoff length of 5mm is advised, however larger is preferred for better cooling.
- Do not use metal washers under the mounting screws, or screws with large heads (e.g. button head). Nylon washers are recommended. With a metal washer there is a risk of creating a short between the E1 LED and ground.
Duet Wifi and Duet Ethernet
The PCB is designed to transfer heat from the stepper drivers and power mosfets to the underside of the board. Therefore your mounting method should encourage good airflow underneath the board.
If you mount the board vertically, make sure that cool air can enter at the bottom of the board, flow upwards behind the board, and escape at the top. Convection cooling will usually be sufficient, but if you are using high stepper motor currents then you may wish to add a fan below the board to encourage the upward flow of air. Make the spacing between the back of the board and the panel or enclosure large enough to allow a good flow of air.
If you mount the board horizontally then a cooling fan is recommended, especially if there are other heat-generating components in the vicinity such as power supplies, SSRs or stepper motors. Position the fan to blow air underneath the board (preferably along the top as well), especially along the row of stepper driver chips and between the power input and bed heater terminal blocks.
Important! The higher the motor currents you set, the more important it is to cool the board. Always use a cooling fan if you run a Duet 2 Wifi or Duet 2 Ethernet above 2.0A motor current.
The drivers on the Maestro run hotter than those on the WiFi/Ethernet, so extra cooling may be required. Speculation is that if the currents are set to no more than 800mA then it may be OK without a fan.
Using MCU temp as proxy temp reading for driver temp
The MCU (AKA CPU) can generally be used as a good indicator of the driver temps. This has the benefit of giving a real time temperature reading to use for thermostatic control of a chassis fan.
M106 P2 T45:65 H100:101:102
Sets up an electronics cooling fan that starts to turn on when the MCU temperature (virtual heater 100) reaches 45C and reaches full speed when the MCU temperature reaches 65C or if any TMC2660 drivers (virtual heaters 101 and 102) report that they are over-temperature.
M308 S2 Y"drivers" A"DRIVERS" ; configure sensor 2 as temperature warning and overheat flags on the TMC2660 on Duet M308 S3 Y"mcu-temp" A"MCU" ; configure sensor 3 as thermistor on pin e1temp for left stepper M950 F2 C"fan2" Q100 ; create fan 2 on pin fan2 and set its frequency M106 P2 H2:3 L0.15 X1 B0.3 T40:70 ; set fan 2 value
Creates sensors for the driver overtemp flag and the MCU temp reading using M308 as S2 and S3. Creates a fan port for Fan2 with M950. Then creates a fan command to link those sensors to fan2 with a temp range of 40-70 using M106.
Note that the MCU temperature must be calibrated to get an accurate temperature reading. See here: Calibrating the CPU temperature
The Duet 2 Wifi has a built-in antenna. (It is unclear whether the board could be FCC certified if it had a connector for an outboard antenna.) This antenna cannot work from inside a metal box; it must protrude from an opening. Covering it with plastic should pose no problem. Exactly how much the antenna needs to protrude and/or be visible depends on the quality of your Wifi at the printer location. If this is an issue then there is an external antenna version of the board now available.