External microstep driver

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kilfoy
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Joined: Fri Mar 11, 2016 7:51 am

External microstep driver

Post by kilfoy » Fri Mar 11, 2016 8:15 am

I have been able to get the proteneer hat to work w/ the pi and run 3 channels successfully. Since the populu drivers gets blazing hot, I figured I would try a different approach and utilize an external stepper driver . I purchased an external microstep driver from ebay http://www.ebay.com/itm/4A-CNC-Single-A ... SwJcZWf-mx

Based on the board layout, it looks like I should be able to utilize an external step driver from the 2x8 pin layout. I changed my x-axis to use the external stepper driver. I removed the populu chip from the X- axis (I tried it w/ and w/o). Per the post on protoneer: http://wiki.protoneer.co.nz/Raspberry_Pi_CNC in the section on External Drivers, it looks like I should be able to wire in the x axis step & drive as well as the enabler and run a 5v hot to the other side. I tried this out and no luck. I am curious if anyone has tried something like this and has gotten it to work.

If so, any guidance on wiring this up would be very gratefully appreciated..

Thanks, Leo

Bertus Kruger
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Re: External microstep driver

Post by Bertus Kruger » Fri Mar 11, 2016 6:27 pm

First item on the check list is to check that the external driver works.

How does the external drivers enable pin work is next on the list.

GRBL pulls the enable pin down if I remember correctly.

kilfoy
Posts: 2
Joined: Fri Mar 11, 2016 7:51 am

Re: External microstep driver

Post by kilfoy » Sun Mar 13, 2016 8:37 pm

Bertus - First - Thanks for the reply

I was able to get it to work. The motors and controllers worked fine - they were new for this project and I tried the motors out w/ the DRV8825 controllers. As I figured out, the issue was more on the wiring. This is my first CNC project and I have been doing this a lot w/ guidance/videos on YouTube and Forums. I did not find one in this category (its probably out there, but I did not find it).

In summary what i did

CNC Board Pins
Off the cnc board, you have a step and direction for each axis (which are positive) and an enabler + and enabler -, which is your 5 volt positive/ground.
X dir (positive)
X step (positive)
Y dir (positive)
Y step (positive)
Z dir (positive)
Z step (positive)
A dir (positive)
Z step (positive)
+ enable
- enable

External Stepper Controller Pins
The External Stepper controller is divided into 2 sides:

5 volt side
+ dir
- dir
+ step/pul
- step/pul
+ enable
- enable

The higher voltage side
4 stepper motor outputs
higher voltage input positive and negative

Wiring
From the CNC board,
- Each axis (X, Y, Z, A) Dir goes to the (+ dir) of each controller
- Each axis (X, Y, Z, A) Step goes to the (+ step or +pul) of each controller
- The (+ enable) goes to each stepper (+ enable) of each controller. Thus 1 board output goes to 4 controllers
- The (- enable) goes to each stepper (- enable) of each controller AND to (- dir) of each controller AND to (- step or - pul) of each controller. It is the shared ground. Thus, 1 board output goes to 4 controllers in 3 spots and the ground is shared. I just used jumper across the grounds on the negative side.

This seems obvious now, but as my first CNC project, I was scratching my head a bit. Thought I'd share.

Results
More importantly, the results are pretty great. My original concern were the DRV8825's ran hot, very hot.The motors I am running are NEMA 24's - 425 in/oz. In test runs, I measured the DRV8825's at +180 def F. Previously, I played with different heatsinks for the DRV8825 (copper, etc) to shed the heat, but they were running very hot. Additionally, the board/controllers should run at lower amperage. The motors are bigger than something you would use for a RIP RAP, but my end goal is a bigger table.

The external stepper controllers I have, cost $10 USD each, take up to 3 Amps continuous and 4 Amps peak and have a huge heatsink on the back side. There were a bunch of other External Stepper Controllers out there w/ more amperage, but this should do the trick for what I need now. The external drives run A LOT cooler. I ran some tests w/ no fan on the controllers and did not see any significant heating (less than 100 deg F with no load on the motors).

Leo

Bertus Kruger
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Re: External microstep driver

Post by Bertus Kruger » Mon Mar 14, 2016 6:15 am

Thanks for the detailed feedback. That is going to be very useful... Do you maybe have a few pictures of your setup? :)

hootie
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Joined: Tue Apr 26, 2016 4:25 pm

Re: External microstep driver

Post by hootie » Tue Apr 26, 2016 4:29 pm

So... if you wanted to run two steppers at around 4 amps, you'd go with two 4A CNC Single Axis 4A TB6600 2/4 Phase Hybrid Stepper Motor Drivers Controllers? It says each run just 1 4 amp stepper.

Do you know what the Protoneer board is rated in amps for each motor?

Bertus Kruger
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Re: External microstep driver

Post by Bertus Kruger » Tue Apr 26, 2016 10:42 pm

hootie wrote:So... if you wanted to run two steppers at around 4 amps, you'd go with two 4A CNC Single Axis 4A TB6600 2/4 Phase Hybrid Stepper Motor Drivers Controllers? It says each run just 1 4 amp stepper.

Do you know what the Protoneer board is rated in amps for each motor?
Yes. Two external drivers will do.

The RPi CNC board uses Pololu drivers and most of them max out at 2Amps.

David Taylor
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Re: External microstep driver

Post by David Taylor » Sun May 27, 2018 1:03 pm

A Question about Pi hat 2.58.
A look at the posts have much good information about the wiring, but also a little confusing for me.
Kilfoy's post
"Wiring
From the CNC board,
- Each axis (X, Y, Z, A) Dir goes to the (+ dir) of each controller...... OK with this
- Each axis (X, Y, Z, A) Step goes to the (+ step or +pul) of each controller ......OK with this

But here is a little confusing. The hat only has one enable pin, I would expect it to enable +, But, there is no enable - at the hat side.

- The (+ enable) goes to each stepper (+ enable) of each controller. Thus 1 board output goes to 4 controllers
- The (- enable) goes to each stepper (- enable) of each controller AND to (- dir) of each controller AND to (- step or - pul) of each controller. It is the shared ground. Thus, 1 board output goes to 4 controllers in 3 spots and the ground is shared. I just used jumper across the grounds on the negative side."
Does he mean, on the driver module, enable -, dir -, and pul/step- are connected together, and then to GND?

Also, at the hat end, the ground. Is this the "common" ground. So, I would connect all of the grounds together? There is only one GND on my stepper driver. Is this a common ground (it is from my 24V PSU)
many thanks, and regards, David

Ernesto2
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Joined: Sun May 06, 2018 7:17 am

Re: External microstep driver

Post by Ernesto2 » Sun May 27, 2018 6:19 pm

The board can be setup to either put out high(+5v) signals, or low(5v ground) signals using the grbl settings $2, $3, and $4. If you have the enable pin set to high, and your step and dir pins set to high, you'd run a ground from your 5v power supply to en- step- and dir- on your external drivers. If they are all set to low, you'd run +5v to en+ step+ and dir+.

The 24v plug on your stepper driver is the power supply that it taps into to supply the stepper coils. The input section of the external stepper driver runs on 5v provided by the protoneer board, either as a steady +5v in and pulsed ground(low) output signals, or a steady ground and pulsed +5v. Flipping the dir outputs in grbl settings will change the direction that the stepper drives. Flipping the pulse/step setting doesn't matter on some external drivers because they're just looking for a state change but some things, like my torch height controller, can only "see" low inputs so I had to change $2 to 4 to flip the output of my z axis.

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