Prunt Board 3 is a 3D printer control board with six TMC2240 stepper drivers, two 15A heater outputs, four fan outputs, four thermistor inputs, and four endstop inputs that is designed to offer smoother and quieter operation.
The hardware is said to offer better ESD protection than boards such as the Duet 3 Mini 5+ or BTT SKR 3 EZ and supports hardware-accelerated step generation, but the magic happens with the Prunt firmware and associated server, which enable a 31-phase velocity profile for smoother operation and higher-quality prints compared to boards running Klipper or Marlin firmware. Let’s have a look at the hardware first.
Prunt Board 3 specifications:
- 6x TMC2240 stepper drivers, all capable of running at 3A with minimal airflow
- 2x 15A heater outputs with short circuit protection (1.3 µs response time)
- Fan outputs
- 4x fan outputs supporting 2, 3, and 4-pin fans, all up to 2A with short circuit protection
- Individual current limit per output
- Hardware counters for high-speed fan tachometers
- 4x thermistor inputs
- Buffered to reduce noise and increase the maximum ADC sample rate
- Support PT1000 and most common NTC thermistors with protection against shorts to other wires on both pins, including heaters
- 4x endstop inputs
- Input OVP – Fully protected
- Power OVP – Diode protection
- Dedicated power rail
- Software or hardware-powered step generation for precise timings and step rates
- Host interface – Fully isolated USB Type-B port for connection to host
- Power Supply – TBD
- Dimensions – 144 x 117 mm
Prunt firmware and software relies on G4 motion profiles as opposed to G1 profiles, as explained by the developer:
Most popular 3D printer motion controllers (Klipper, Marlin, RepRapFirmware) top out at 3-phase G¹ tangential motion profiles: a trapezoidal velocity curve where acceleration is always either zero or the maximum allowed value. The problem is that real-world objects simply cannot change acceleration instantaneously. Forcing 3D printer motors to try results in vibrations, ringing artifacts in prints, and accelerated wear on components.
Some commercial and niche open-source controllers step things up with a trapezoidal acceleration curve, a 7-phase “s-curve,” which is meaningfully better but still describes motion that isn’t physically possible.
Prunt Board 3 goes two steps further. By making the 4th derivative of acceleration a rectangular wave, we arrive at a 31-phase velocity profile with significantly smoother motion. To make this concrete, we’ve plotted velocity and its first 4 derivatives for both 3-phase and 31-phase profiles. Every plot was generated in Prunt motion controller itself, because Prunt lets you set tangential limits for each derivative individually, meaning you can emulate other controllers by tweaking a few parameters in the GUI.
The Prunt motion controller also supports advanced corner blending using a degree-15 Bézier curve instead of relying on a brief period of infinite axial acceleration at every corner. Improved motion profiles and corner blending benefit not only print quality and speed, but also enable somewhat quieter printing, as demonstrated in the short video below.
You’ll find hardware and software documentation on the project’s website, where I also learned that the board can be switched into Klipper/Kalico mode by installing a jumper, so you can easily compare Prunt and Klipper on the same hardware. The STM32 firmware and server source code, both written with the Ada programming language, can be found on GitHub, along with binary releases. The server requires a Linux machine, and while Raspberry Pi 4/5 can be used, we’re told that they “may not be powerful enough to run the current version of the server software under all circumstances”, and they plan to tune the software in a future release to improve that part. I also found a version of the software for laser engravers, but it’s only intended to be used by professionals for safety reasons.
Prunt 3D has just launched the Prunt Board 3 on Crowd Supply with a $9,500 funding target. A $180 pledge is requested for the board, including free shipping to the US, but a $1 shipping fee is added for the rest of the world. Deliveries are scheduled to start by September 9, 2026.
Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.
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Sorry for my noob question.
Did I understand correctly, that this board is just the real-time driver board and all the complicated calculations are out sourced to an on prem server?
I was under the opinion that the heavy lifting was done by the gcode generator, but maybe things have changed?
Prunt provides both firmware and server, so I understand it’s a combination of the two. If it were just the Prunt server handling everything, then wouldn’t it be possible to feed the Prunt G-Code to machines running Klipper or Marlin firmware directly?
Maybe its an extended g code? As I think to understand it offers smoother movement, maybe more sub-steps, more axes operating in parallel?
It seems the board itself has no special extra computing power, as you mention an STM32 of some kind…
Only the stepper drivers seem to be somewhat exotic with 256 uSteps etc. https://www.analog.com/en/products/tmc2240.html
The MCU is a bit special in that it has enough timers for ever single step/dir output to be hardware driver. However, most of the magic happens on the host which transforms g-code into low level commands. There’s more details in this section on our website and the section following it: https://prunt3d.com/docs/features/#g-motion-profiles
Thanks for your explanation that makes alot of sense.
The clever thing is that it is split between computation power on server and a reasonably dimensioned real time mcu.
So finally, after an eternity — it’s now 13 years, a fast and at least theoretically good Motion Controller… The last one was TinyG. Anyone still remembers this video 😅? https://youtu.be/Om0wTqFA-Dw