GRBL breakout shield questions

Hey all!

Firstly, electronics are not my forte…

I’m making a new machine using c-beam and lead screws. I am hoping to use the grbl breakout shield kit and drivers purchased here:

Under ‘compatible steppers’ there is a link to the larger 262oz motors which are listed. I’m going to try out my older 140oz motors but i’m hoping to get pretty aggressive with this machine.

I don’t have a whole bunch of info on the specifics of either so was hoping someone could help me clarify.

Also, is it possible to use a z-touch plate with that board?, i haven’t seen any info on this either.

Excuse me if i’ve simply overlooked this (which is admittedly, fairly likely). FWIW I have asked the same question on the forum of the seller, they aren’t known for being very reliable with responses.

Both the 140 oz/in and the 262 oz/in motors on that web site are rated at 2.8 amps/phase. The 8825 drivers are rated at 2.2 amps with “appropriate cooling”, but are more realistically rated at about 1.5 amps/phase.

This would give you roughly half of the torque that the motors can produce.

As Larry states, the shield is technically compatible with either stepper motor - but you wont be able to extract the maximum torque the steppers are rated for. I am running Nema23/260oz of a similar shield with the DRV8825 drivers and it work just fine for what it is - but I am not cutting aggressive.

If you want maximum torque choose bigger drivers so you can go all the way up to 2.8A/coil and for maximum speed go as high on voltage your setup allows :wink: Make sure the rest of the system can handle it mechanically :wink:

I am running the 8825’s at 2.2A with cooling fins and a fan without problems on NEMA17 motors rated 2.5A The X-Gantry motor produces the most heat but not at dangerous levels on a 45min job.

I would spend a bit more money and get a better controller.

Thanks for the replies guys. Did anyone have a suggestion for a better controller? Ideally where I don’t have to buy 4 separate drivers. That’s the main appeal of that board, having it all in one. Open to suggestions, preferably that won’t break the bank! I’m running a mac.

I will be replacing the stock components with an Ethernet Smooth Stepper and a Gecko G540. I will also be replacing easel with Mach3. This will be around a $700 upgrade.

Upgraded stepper motors and other improvements will follow behind these upgrades.

I went with the Ethernet Smoothstepper and Gecko G540 as well as a G251 to add a 5th motor driver. It was a great upgrade…it allowed me to add a rotary axis and split the 2 y-axis motors to their own drivers. It is a great combination.

Yeah that is where it can get tricky. The smaller singe chip stepper drivers max out at 2.2 amps. So all of your cheaper controllers with the drivers “on board” (GShiled, TinyG, etc.) will have this limitation. Limiting you to the lower torque Nema 23’s.
(Plus having the chips all on the same board means that when you fry one you have to swap out the whole thing, or wire in a bypass to an external driver.)

This is why there is such a big price jump to the “pro” drivers like the gecko.

I have been looking into the same thing. As my tinyG controller has been developing problems (something, static maybe? Fried 2 of the pins, killing z-probing and micro stepping on the Z axis)
And on both the Z shiled and the TinyG it seemed like my standard nema 23’s were just a bit underpowered.
For now I am sticking with a modified gshiled (the stepper chips are on removable sub boards, for ease of repair) because it was $27. :wink:

But it looks like a leadshine or gecko controler is the “best” option, but after you factor in the controller the eathernet interface board and Mach3 (or 4) it winds up costing almost as much as the XC did. :confused:

The X Controller looks like a good mid-priced compromise with the higher current capacity and other features. (It is just out of my current tool budget).

So a lot of this depends on your budget.

So, in a number of discussions I’ve read on Inventables about power output, I’ve wanted to ask if just a simple power amplifier (x4) could be added in between the controller and motors?

So, I just stumbled on these guys:

Lower current means I could use the default board, however I’ve read the trade off with lower current steppers is a greater voltage requirement. These say 24-48 is recommended. I imagine that if that is per stepper, the original shield i linked would be useless anyways? Again, hopeless with electronics so apologies in advance…

Someone just tell me it won’t work so I can bite the bullet and get a new electronics setup.

The higher voltage is needed because of the (relatively) high inductance of these motors. This relates to the speed of the motor. Torque is a function of the current.
i.e. with 24V and the 8825 driver, the motor will achieve it’s maximum torque but will be slow.

I run a Gecko G540 on my x-Carve. Not the cheapest option but solid and reliable and supports motors of up to 3.5A and 50V.

Yes and no. The real reason to use a higher voltage is to overcome the back emf of the motor winding. This results in a faster current rise which gets you better starting torque for the motor.