Our big challenge for coming weekend...

diycnc-discuss
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(Paul de Groot) #1

Our big challenge for coming weekend…
https://wp.me/p8oeKV-1ad

(Paul Frederick) #2

@brian_alley GRBL is CNC lite. Which is as far as a lot of folks are willing to go.

(Paul de Groot) #3

@brian_alley in a nutshell, arduino only does 3 axis, 30kHz stepping, 8 bits pwm @ 1kHz and is limited by 32kb size. SG does 5 axis, 100kHz stepping, 16 bits pwm up to 80kHz and has a soft spindle start and tool change ports. 96kb room so it can be extended with more gcode commands :wink:

(Paul de Groot) #4

And of course has all the hardware on board…just wire it up.

(Paul de Groot) #5

No need for internet :grin:

(James Rivera) #6

Just curious: What advantages are there over a Smoothieboard, if any?

(Paul de Groot) #7

@James_Rivera I’m thinking of at least two points: hardware (swap-able drivers, led indicators, isolated ports, mosfet output ports) and firmware (you can add G-code features). I implemented a few features like frequency configurable pwm, soft start of the spindle and tool change but you can add anything yourself to it e.g. canned cycles etc.

(Paul Frederick) #8

@James_Rivera GRBL is about as cheap and simple as it gets. You can buy all the electronics to get GRBL going for just what a cheap Smoothieboard costs. But that comes at a price. Still, having gone another route myself I can see the appeal for some.

(Paul Frederick) #9

@Paul_de_Groot those little Allegro drives are jokes. People like them that don’t understand power. They see 2 Amps and 32V then think it’ll do the job. When power is actually expressed in Watts. No one says a little driver can do 2 amps at 32V. That would be 64 Watts. Try pushing that much power through one of them little SMT chips and it’d go blowing clear off the board. I think they’re good for more like 2.4W? Which isn’t even the power of a night light. So complete dim bulb material. GRBL setups seem pretty susceptible to noise from what I’ve seen too. Sometimes less is less.

(Paul de Groot) #10

@Paul_Frederick the drivers are in sockets so you can swap them for different parts. Also the step, dir and enable pins have been broken out for external drivers which I will demo this weekend. Indeed it’s all about bringing a viable alternative to hobbyists.

(Paul de Groot) #11

Btw the photo of the post is of the original grbl shield which might confuse you. So here is the actual board.missing/deleted image from Google+

(James Rivera) #12

Lots of Mosfets!

(Paul Frederick) #13

@Paul_de_Groot if electronics don’t have a hole for accepting hardware then it is just not a power part. Gluing heat sinks on top of SMT chips don’t cut it. Plus those chip carrier boards are not really full stepper motor drives. Which is why they’re not really marketed as drives. They are lacking control signal isolation. Frankly I’m amazed they work at all. Beyond that with the low digital storage capacity of an Arduino there’s only so much that can be done as far as motion controller software goes. Once I was chatting with a developer and they remarked that trajectory planning was nonexistent on GRBL. It is just a feature there’s no room to include. I don’t know what it compiles to but the source of the planner for LinuxCNC is 89.5 KB