In this post I describe three further upgrades: 24V power, moving the electronics under the bed, and the Robotdigg aluminium effector.
In my last post I described how I upgraded to 0.9 degree/step motors to improve the resolution of the printer. I hadn’t allowed for the higher back EMF of these motors when running at the speeds (up to 333mm/sec) that I used with the original motors, so I had to reduce the maximum speed to 150mm/sec. The obvious solution was to change from 12V to 24V power.
This change was easily accomplished. I replaced the 12V 100W LED power supply by a 24V 120W one. The reason for increasing power to 120W was to ensure that I have enough for a future dual extrusion upgrade. The 12V heater cartridge in my E3Dv6 hot end had to be replaced by a 24V one, so I purchased these 24V 30W cartridge heaters. I ordered one of these 24V 40 x 10mm fans to replace my hot end fan, and another to serve as a electronics cooling fan. The Duet electronics can already handle 24V input, the SSR was rated for up to 32V input, and the heated bed uses AC mains power; so those components did not need to be changed.
Controller electronics under the bed
I wanted to move the Duet controller board under the bed in order to make the machine tidier and more portable. The Duet has the Ethernet socket, USB socket and SD card slot on one edge of the board, so only that edge needs to be accessible from outside. As only one side of the base triangle is made from two separate extrusions with a gap between them, the Duet has to go on that side next to the mains inlet components. Fortunately, there is room to do this with a sufficient gap between the Duet and the mains components.
The new Duet 0.8.5 revision from Think3DPrint3D improves on the revision 0.6 board in several ways. In particular, it supports a fifth stepper motor driver, third heater channel and second PWM fan driver. This makes it capable of driving dual extruders without needing an expansion board. In a single extruder system, you could use the additional heater channel to control a chamber heater.
Other improvements include the use of side-facing push buttons for the Erase and Reset functions, and moving most of the LEDs to the edge of the board with the connectors. This makes it especially suitable for under-the bed-mounting. The Duet 0.8.5 also provides dedicated connectors for two always-on fans, the Z probe, and a PanelDue.
You don’t need a version 0.8.5 Duet to move the electronics under the bed unless you want dual extrusion. The main issue with using a 0.6 Duet is access to the Reset and Erase buttons. The Reset button on the 0.6 Duet is at the edge of the board but facing upwards; nevertheless you could make accessible via an angled hole in the panel, and print a plastic prodder to activate it. The Erase button is more difficult because it is further from the edge. But if you are careful, you can avoid the need to use it. Once you have loaded my fork of RepRapFirmware, you can send the command M999 PERASE to put the board into programming mode. If Bossac then reports “Flash page is locked”, use bossac -u to unlock it. The only time you should need to press Erase again is if you upload completely dud firmware, or firmware that does not support the M999 PERASE command. Alternatively, you could fit a normally-open push button to the rear panel and wire it in parallel with the Erase button.
New printed mains inlet panel and tray
As well as the original cutouts for the mains components, the new mains inlet panel includes a finger guard at the end bearing the mains voltage components, a slot for holding the front edge of the Duet, and holes to access the Ethernet and USB connectors and the SD card slot. I also added holes for the Reset and Erase buttons of the Duet 0.8.5, and a thinner section for the LEDs on the 0.8.5 to shine through. You can find the design here.
Mounting the Duet horizontally in a confined space is not ideal from a cooling perspective, especially with other components such as the power supply, stepper motors and SSR also generating heat – and of course there is some heat from the bed heater despite the cork insulation. So the rear Duet mount has a 40 x 10mm cooling fan to blow air over both sides of the board in the region of the stepper driver chips.
I made a new tray to fit on the bottom of the printer, this time using 300 x 300 x 2.5mm aluminium sheet. The mains terminal block, power supply and SSR are mounted as before but moved to make way for the Duet. The printed rear Duet mount is attached to the tray using two M4 screws.
The mains wiring is as before, but you should keep it all well-separated from the low voltage wiring. I ran the 24V power cable and the X stepper motors cable in the slots of the extrusion behind the power supply, so that they do not have to pass the mains terminals. The AC mains heated bed cable passes under the Duet, but it is secured to the tray by two cable ties, one at each end of the run. All nuts inside the tray are Nyloc ones – you don’t want loose nuts shorting out the wiring. As before, remember to add a grounding wire to the upper 20mm extrusion, and check with a multimeter that the tray is grounded through the power supply.
Caution: the heated bed positive and negative terminals are the opposite way round on the Duet 0.8.5 compared to the Duet 0.6. On the 0.6 board the +ve terminal is nearest the power input terminal block, but on the 0.8.5 board this is the -ve terminal. The polarity doesn’t usually matter if you connect a heated bed to it, but it does matter when using the Duet to drive a SSR.
The PanelDue connector is on the corner of the board and so is underneath the top 20mm extrusion. Even with a right angle Molex connector fitted there, the cable for it would pass uncomfortable close to the mains wiring. So I connected the PanelDue to the expansion connector as before.
Robotdigg aluminium effector
In my previous round of upgrades I replaced the printed carriages by Robotdigg aluminium ones. On a delta printer it is important that the spacing between bearings is that same at both ends of each pair of parallel rods, and this should be easier to achieve with machined metal parts than with printed ones. Robotdigg makes an aluminium effector to go with their aluminium carriages, and I hoped that by using this I would achieve equal spacing between bearings to a greater precision.
Before fitting the new effector, I measured the bearing spacings on the metal carriages, the printed effector, and the aluminium effector:
Carriage bearing support spacings: 40.14,40.13, 40.14mm
Printed effector bearing support spacings: 40.48, 40.50, 40.50mm
Aluminum effector bearing support spacings: 39.70, 39.70, 39.70mm
The original printed effector was giving me a difference in bearing spacings of about 0.35mm. The aluminium one would give me a difference of 0.45mm. To reduce this, when attaching the Traxxas joints to the effector, I included a 0.50mm thick M3 washer under one joint in each pair to reduce the difference to 0.05mm.
The primary purpose of the upgrade to 24V was to increase the travel speed, which I had to reduce to 150mm/sec when I upgraded to 0.9deg/step motors. With the 24V supply, I found that travel speed of 200mm/sec was achievable for all types of moves. I have since done some more firmware optimization and I now achieve more than 300mm/sec.
I had hoped that using the aluminium effector and the attention I paid to getting equal bearing spacings at either end of the diagonal rods would reduce the tilting of the effector as it translates in the XY plane, and thereby allow me to reduce or remove the Z probe trigger height correction factors in the G30 commands in the bed.g file. Unfortunately, this has not been the case. There must be other inaccuracies in my build that are causing a small amount of variable effector tilt.
Moving the electronics under the bed has made the printer neater and more portable. I had been reluctant to do this earlier because of my plans for dual extrusion, but the Duet 0.8.5 has made this possible.
Acknowledgement: My thanks to Think3DPrint3D for providing the Duet 0.8.5 controller board.