First Build: Shopbot Upgrade

All things related to the Centroid Acorn CNC Controller

Moderator: cnckeith

cvmakerspace
Posts: 5
Joined: Mon Sep 20, 2021 4:34 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

First Build: Shopbot Upgrade

Post by cvmakerspace »

My finger is hovering over the order button for an Acorn and a Gecko G540 drive. We just purchased a shopbot that has the PK296A1A-SG3.6 motors for x and y. I need to double-check on the z-axis motor as my pictures don't show it clearly.

I am trying to come up to speed stepper motor drives as quickly as possible, but it would be nice to get some hardware on the way.

I am pretty sure these motors and the Acorn have been used before, and I believe I saw some guys using the G540 drive as well.

My couple of simple questions are:

- will the PK296A1A-SG3.6 motors work with the G540?
- what power supply would you use? (a switching supply or a simple transformer/bridge/cap supply)?
- what power supply specs would I need to have (voltage and current for 3 motors of the PK296A1A-SG3.6 type, driven by the G540).

If this is too big of an ask, please send me off to the proper threads and/or documents. At this point, I am looking for some guidance and not necessarily a fully engineered system. But, hey, the more details, the better!

Thanks in advance,
Brian
Columbia Valley Maker Space
BC, Canada
Richards
Posts: 692
Joined: Sun Sep 16, 2018 9:01 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: South Jordan, UT

Re: First Build: Shopbot Upgrade

Post by Richards »

The Oriental Motor steppers that shipped with the Shopbot have high inductance. That means that they need high voltage to operate efficiently. Shopbot ordered the six-lead motors to be shipped with only four leads. They also specified that the leads should be series (high inductance). That makes the G540 a poor choice of stepper driver for those motors. You'll get better performance with those motors by using a Leadshine driver that is rated for 80VDC.

You can find motors better suited for 50VDC from AutomationTechnologiesinc.com. The KL34H260-42-8A draws 4.2A if wired unipolar and 6A if wired parallel. The Leadshine DM860E from AutomationDirect.com can handle current up to 7.2A. That motor has 1.65mH inductance, so a 35VDC linear power supply would work great. The motor has about 300 oz-in torque when wired unipolar and about 500 oz-in torque when wired parallel. Y ou'll be fine If you build a simple 3:1 belt-drive transmission using a 20-tooth XL timing pulley and a 60-tooth timing pulley (AutomationDirect has them), along with the appropriate belt. Your design will dictate the length of the belt. I used 170XL-037 belts when I made transmissions for my PRT-Alpha router. I Also used 25-tooth pinion gears (1.25" pitch diameter) on my PRT-Alpha.

There are a lot of other good open-loop motors that are inexpensive. Look for inductance (mH) less than 2mH for use with a lower voltage power supply. (GeckoDrive recommends using the formula: SQRT(inductance) X 32 to determine the MAXIMUM voltage to use with a motor. Keep in mind that stepper motors get VERY hot when run at maximum voltage. You can use a motor that has inductance up to 5mH if you use a 70VDC power supply.

If you decide to replace your motors and drivers, why not look at the closed-loop steppers or Teknic's ClearPath servo motors? Those motors/drivers will generate a fault if they miss steps.
-Mike Richards
ShawnM
Posts: 2190
Joined: Fri May 24, 2019 8:34 am
Acorn CNC Controller: Yes
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: 7804734C6498-0401191832
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Clearwater, FL

Re: First Build: Shopbot Upgrade

Post by ShawnM »

cvmakerspace wrote: Mon Sep 20, 2021 11:05 pm I am trying to come up to speed stepper motor drives as quickly as possible, but it would be nice to get some hardware on the way.
Here's some great info if you are trying to wrap your head around this and it's on the Gecko website. Maybe you've read it......

https://www.geckodrive.com/support/step ... asics.html

While the G540 does it's job there are far better options out there that will yield far better results.
martyscncgarage
Posts: 9912
Joined: Tue Mar 28, 2017 12:01 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: Yes
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: Yes
CPU10 or CPU7: Yes
Location: Mesa, AZ

Re: First Build: Shopbot Upgrade

Post by martyscncgarage »

ShawnM wrote: Tue Sep 21, 2021 8:49 am
cvmakerspace wrote: Mon Sep 20, 2021 11:05 pm I am trying to come up to speed stepper motor drives as quickly as possible, but it would be nice to get some hardware on the way.
Here's some great info if you are trying to wrap your head around this and it's on the Gecko website. Maybe you've read it......

https://www.geckodrive.com/support/step ... asics.html

While the G540 does it's job there are far better options out there that will yield far better results.
+1 on Geckodrive's document.
Once I read it years ago it was a game changer for me when I was using open loop steppers. Matching components is key....
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
cvmakerspace
Posts: 5
Joined: Mon Sep 20, 2021 4:34 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

Re: First Build: Shopbot Upgrade

Post by cvmakerspace »

I agree with the Gecko Drive Stepper Motor Basics documentation suggestion. I am sure I will be going over that a number of times.

A couple more questions:

1) Does anyone think it is worthwhile trying to reuse the old motor drive that came with the Shopbot (along with an Acorn)? I am going to look into the old PC cabinet just to get some familiarity with the old drive and how it is connected.

2) I saw in the Stepper Motor docs on the Gecko site that linear and switching power supplies are talked about. Does anyone have an opinion on which to use? I am leaning towards a transformer/bridge/caps solution, but may have to use an inexpensive switching supply initially. I just don't want to see strange stepper behavior that could be due to the power supply.

Thanks in advance, guys. Such a great wealth of knowledge on these boards!
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: First Build: Shopbot Upgrade

Post by Gary Campbell »

While you are doing your homework, ponder this: From the part number you have a 2 phase, 96 ozin, 1amp motor. You need to take that into consideration when you match components. You will never get any speed or power from them and the gearboxes may have excessive backlash, unless they were rarely used.

Another thing to consider is how antiquated those motors are. They are to today's motors as a beta max vcr is to a modern dvr. 3 generations obsolete.
GCnC Control
CNC Control & Retrofits
https://www.youtube.com/user/Islaww1/videos
cvmakerspace
Posts: 5
Joined: Mon Sep 20, 2021 4:34 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

Re: First Build: Shopbot Upgrade

Post by cvmakerspace »

Gary:

Thanks for the comment. The machine is pretty much an unknown at this point, and I don't know what shape the motors are in. As part of the learning process, I would like to get the motors moving and see what happens. I guess I should choose the motor drives and power supplies carefully so I can re-use them when (not 'if') the motors are replaced.

There seems to be a large combination of motors and drives to consider - and I have some homework to do!

Cheers,
Brian
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: First Build: Shopbot Upgrade

Post by Gary Campbell »

For Brian and others that may follow this thread....
I am attaching a PDF that shows how to determine how much backlash your gearmotors have. This will allow you to determine if you wish to proceed with a build with worn motors. You can spend $10K on a controller and if you connect to motors with >0.005 backlash you will never get a quality cut.

Please be certain that I wouldnt use them on a router if they had over 0.0015 to 0.002, but for wood you can relax your standards.

Tests are shown on a PRS model, but the PRT is similar.
Dial Indicator to Check Pinion Play.pdf
(317.75 KiB) Downloaded 72 times
GCnC Control
CNC Control & Retrofits
https://www.youtube.com/user/Islaww1/videos
martyscncgarage
Posts: 9912
Joined: Tue Mar 28, 2017 12:01 pm
Acorn CNC Controller: Yes
Allin1DC CNC Controller: Yes
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: Yes
CPU10 or CPU7: Yes
Location: Mesa, AZ

Re: First Build: Shopbot Upgrade

Post by martyscncgarage »

Gary is giving you good advice. He knows Shopbot well.
Time to upgrade motors and drives and make sure you match them up well.
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
Mesa, AZ
cvmakerspace
Posts: 5
Joined: Mon Sep 20, 2021 4:34 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: No
Oak CNC controller: No
CNC Control System Serial Number: none
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

Re: First Build: Shopbot Upgrade

Post by cvmakerspace »

For one of the old 2001 shop bots like we have, what motor/drive combo would you suggest (that won't break the bank)? I am sold on the acorn controller, just don't have the CNC chops to sift through the large selection of stepper motors out there.

I guess one big question is the torque rating for the motor. I presume that you need enough torque to move the gantry effectively, and the more torque, the quicker you can move?

Also, I have seen gear reduction motors (like the old one I have), I have heard of belt drives as well as seeing direct-drive motors. We are not initially looking for production-grade accuracy - this is for our local Maker Space and we can sacrifice speed/accuracy for price (initially, anyway)

Any suggestions would be great!
Post Reply