ShopBot Alpha Control Replacement

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Gary Campbell
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ShopBot Alpha Control Replacement

Post by Gary Campbell »

An ongoing project for me is to make as easy as possible the changeover from ShopBot's quirky controller to Centroid's Acorn. SB has done some strange things over the years and the connection to the OM Vexta driver is no exception. The OEM version uses an unshielded ribbon cable between the drive and their control board that terminates in an IDC header connector. I've made up some shielded replacement cables with flying leads to allow making connections to an Acorn system much easier.

As you can see in the video linked to below, the motor is capable of much smoother slower movement than with the OEM controller. .5ips (30ipm) is the minimum feedrate unless some specialized trickery is done. I have run feedrates as low as 5/100ths of an inch per second smoothly on ballscrew machines with Acorn Control. Another benefit is that the SB OEM controller has very limited pulse rate. So limited that on the alpha, their flagship machine, they use "electronic trickery" that sets the drive to output 5 step pulses for every one it receives from the controller. Depending on the software version this has been problematic as the "gearshift" would sometimes stick in one mode or another, making a mess out of whatever is on the table.

That gearshift has one other consequence. Resolution is reduced by a factor of 5 when rapids are active. Net result is less than 500 steps per inch resolution, way below even most entry level machines. Doesn't sound like much of a problem at a casual look, but since all positioning moves are rapids, and executed at the much lower resolution count accuracy can suffer. And don't get me started on the rounding errors!

The drive that was tested is an "off the shelf" unit. It does not have SB's weird programming and I have surely not used the "resolution multiplier" for the rapids. Resolution multiplier... sounds like something better is happening, right? Not so much. Resolution multiplier is like most cigarette boats.... someone is compensating for a small something. Pulse stream I would guess.


Anyway, here is the video:
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Gary Campbell
Posts: 2164
Joined: Sat Nov 18, 2017 2:32 pm
Acorn CNC Controller: Yes
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CNC Control System Serial Number: Acorn 238
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Marquette, MI
Contact:

Re: ShopBot Alpha Control Replacement

Post by Gary Campbell »

Here is a decade old SB control box. Of course it has some user wires added and that anonymous user may not have used my cable routing methods, but I wanted to show those "rainbow ribbon cables"

Disclaimer: the current models have a control board that mounts directly to the drives (different model) and has eliminated the ribbon cables.

IMG_20181228_112515.jpg
GCnC Control
CNC Control & Retrofits
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gerald martin
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Re: ShopBot Alpha Control Replacement

Post by gerald martin »

Looking great Gary! Looks like the Alpha motors will run better on Centroid control than ever before!

Gerald
Gary Campbell
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Re: ShopBot Alpha Control Replacement

Post by Gary Campbell »

Gerald...
They will run better than on the old controller, but they will never run like your ClearPaths :lol:
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Sword
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Re: ShopBot Alpha Control Replacement

Post by Sword »

That anonymous user probably opened the door, took one look and said, "There's no use in bucking the system" and went with the flow and then quickly shut the door. ;)

Do you have the ability to reprogram those drives or is that only able to be done at the mother-ship? Or is it unnecessary?
Scott
Gary Campbell
Posts: 2164
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Re: ShopBot Alpha Control Replacement

Post by Gary Campbell »

Scott...
Yes, No, depends on what you want/need out of the machine. The reality is that if a few users were to look it over, we would NEVER toss in the numbers that the factory did!.

I am going to test this one today at 5000 st/rev vs. the 1000 setting and see how it performs.
GCnC Control
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Gary Campbell
Posts: 2164
Joined: Sat Nov 18, 2017 2:32 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: Acorn 238
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Marquette, MI
Contact:

Re: ShopBot Alpha Control Replacement

Post by Gary Campbell »

Last bit of testing done on these drives and motors.

Resolution tested at 5000 steps/rev (required increasing step pulse rate to 200khtz) works fine for those that may need a higher resolution solution

Alarm operation tested, as the ability to stop machine if a position loss is detected (especially on a slaved axis) is the most important aspect of a closed loop stepper system. See below the "knuckledraggers" alarm tester
Alarm Test2.jpg
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Sword
Posts: 652
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Re: ShopBot Alpha Control Replacement

Post by Sword »

:o Let me step behind you before you hit the button! :lol:

More rez is good. Any downside to that other than being able to meet the 200hktz requirement? Torque, speed loss?
Scott
Gary Campbell
Posts: 2164
Joined: Sat Nov 18, 2017 2:32 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: Acorn 238
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Marquette, MI
Contact:

Re: ShopBot Alpha Control Replacement

Post by Gary Campbell »

Scott...
You'll have to test that. I'm going to download the OEM program from this drive in case anyone wants it
GCnC Control
CNC Control & Retrofits
https://www.youtube.com/user/Islaww1/videos
Gary Campbell
Posts: 2164
Joined: Sat Nov 18, 2017 2:32 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: Acorn 238
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Marquette, MI
Contact:

Re: ShopBot Alpha Control Replacement

Post by Gary Campbell »

The parts required to change a SB alpha (ASM-98AA motors) over to Centroid control are available in kit form here: viewtopic.php?f=62&t=2630
GCnC Control
CNC Control & Retrofits
https://www.youtube.com/user/Islaww1/videos
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