So, before I start, yes, I know there are plenty of really great pre-made boards that will work. If I wanted simple and easy I would just get one of those.
Here is my idea. GrblHal will run on an RP2040 (Pi Pico) based board. The Arduino CNC shield would be easy to wire up to it. I have 2 BTT TMC5160 Plus external drives. I also have extra 48V and 36V power supplies.
Due to the power capabilities of the TMC5160 (up to 10 amps) I should have no problems driving 2 steppers off each drive. This way I only need 3 axis with the Z running off the TMC2209/8 on the shield. The steppers are 48mm OMC’s.
In my head, this is all working out great, I already have GrblHal working on an RP2040 and talking to UGS.
So, my reasons to do this: I have the parts on hand, I love a challenge, and I think I can get more power (Force) from the motors at the higher voltage.
Am I missing anything? (Other than being limited to 1 end stop per axis)
I think you’ll run out of machine rigidity long before you run out of stepper power with the steppers we already use with 2209s…
Too big and you’ll turn the failure case being to rip your machine apart, rather than just skipping steps
I agree, I do not have to run them at full tilt, I can run them both off 24V and even dial them back if needed. Adding + and - end stops as well as “soft Limits” in the software should help also. I will have to dig into the drives a bit more and see if StallGuard or other settings will reduce the possibility of problems.
I also have a regular set of 3 TMC5160T that are a lot less wild, they may be the better option. They are standard step stick style.
@stevempotter built a machine along these lines. He used TB6600 drivers, was running GrblHal on some board and running at 40V. His big claim is significantly improved speed. Here is one topic where he writes about the speed of his machine, and I know there are others topics where he outlines more of his build. Note, he paired the machine with a water-cooled spindle, which is more powerful than a Makita router. Steve built his machine to be portable, and took it to Maker Faires.
Thanks for the good summary of my Portable Primo, Robert! I am still in the “skip steps rather than rip the machine apart” design space at 40V with the stock steppers. I should also note some rigidity improvements:
- recess the legs 70mm into the torsion box base in tight holes;
- Use 2mm thick stainless steel tubing rather than galvanized conduit.
- Make all plastic parts out of carbon fiber-reinforced ABS filament.
I think the idea of end stop switches at both ends of each axis is a good one to reduce the chance of damage to the machine. (I use Hall effect magnetic switches)
Don’t forget to keep Hardware Endstops enabled in the settings.
I note that the Teensy 4.1 mcu I use with my grblHAL machine is MUCH more powerful in almost every way than a pico2040 mcu. Also better than an ESP32 in most ways (except no wifi).
With only having 3-axis control, you must gang two stepper motors on each (x & y) axis. This eliminates the possibility of software squaring. I would not do without that. But others do fine with hardware squaring, “boot up machine with axes shoved against well-adjusted hard stops.”
Also, you may want an extra axis for rotary carving, etc.
This comparison makes it clear:
https://www.perplexity.ai/search/teensy-4-1-vs-rp2040-IiuyHY6QRmaKDIBSUMs.lA
You might want to look at the BTT SKR Pico 3D printer controller board. It uses a RP2040 and a klipper SBC host (raspberry pi usually). It may give you some inspiration for your controller.
On the 5160s, You’ll need to make your controller with the ability to use SPI mode which is more difficult to tune than drivers in UART mode.
Driving anything more than 2 amps on NEMA 17 motors is going to be hard since most of them are rated for 2.8 A or less and you aren’t supposed to run them more than 0.707x the rated power (PeakA x 0.707=RMS). This is to prevent surges on current from burning the drivers/traces out.
I think it’s a workable idea, but the cost of the drivers at $10-20 each for no more improvement than using 0.3-0.5 more amps (until you burn out the motors/traces) with NEMA 17 motors, is probably not as cost effective as you think.
I recommend looking at other drivers if you want to use higher voltage. The TMC2240 is a good choice that can use up to 36V 2.1A and UART by soldering a jumper on the driver, but there’s quite a few other options too.