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MetalHead Mon 15 January 2018 05:07

Acorn and Clearpath
2 Attachment(s)
I have been reviewing this setup.

I think this is a good next step combination for the MechMate.

I still think our current systems are very reliable, cost effective and available, this is just another solid option.

philpods Tue 16 January 2018 02:13

Good one, I just ordered the acorn setup. Shall see how we go.

jhiggins7 Tue 16 January 2018 04:58

Wonderful. Are you using the Clearpath servos? If you don't mind sharing, which specific products are you going with?

philpods Wed 17 January 2018 03:34

Not going with the clearpath servos just going with motionking 34H2A9840 steppers. I like the idea of a supported software/controller system. I shall post something when I get my electronics and start playing.

ayetti Thu 12 July 2018 09:00

I’m gonna build with the acorn and clear path. Still trying to determine which motors to buy from techniq though. I’m open to input, and I’m re reading William t’s thread to get a better ide. I’m pretty sure they will need to be the Nema 23’s with the 1-4 gear, but again, I’m open to suggestions.

MetalHead Wed 18 July 2018 04:59

I think you are on the right path. I hope William can give us some photos of his motor drive and belt reduction setup. I would like to be able to build up a new set of electrical control box schematics around the Teknic/Acorn combination.

Richards Thu 27 September 2018 19:16

(This is a late post. I just ran across interest on the forum for Teknic ClearPath servos and Centroid Acorn two days ago while Googling).

About a month ago, I ordered a TinyG CNC board (because of a YouTube video by NYCCNC about an engraver he was building). After adding Molex connectors so that I could use Geckodrive stepper drivers, that $130 board did an amazing job. It seemed to be a cheap, but adequate, substitute for Mach3.

About then, I saw some Teknic/ClearPath videos on YouTube (NYCCNC, Neo4CNC and many others). After several texts to Teknic, I ordered an SDSK-3411P-RLN servo, an SDSK-2311S-RLN motor, an IPC-5 power supply, a POWER4-HUB and all of the necessary cabling. I ordered motor couplers from Oriental Motor, additonal Molex connectors and pins from Mouser, power supplies for auxiliary equipment from JAMECO, a set of 16mm linear rails with blocks (1500mm, $97) and a 30mm ballscrew with end mounts encluded ($40) on eBay. I thought that would be enough parts and pieces to test the Teknic ClearPath motors. THEN, I saw several videos about the Centroid Acorn. Unfortunately, because I had only skimmed their web page, I totally missed the fact that it only cost $299 to get an Acorn (assuming you already have Windows 10 and a monitor that can display 1920 x 1080 - I didn't, so I had to buy a copy of Windows 10 ($150 for 64-pro), an SSD ($57 from BestBuy) and a monitor ($124 from BestBuy).

The Centroid Acorn arrived this morning. By following their videos carefully, the basic setup functioned within minutes of powering up the Acorn.

I reasoned that if spending $279 for an SDSK-2311S-RLN to replace a Geckodrive G203v and Oriental Motor PK299-F4.5 at $275 would work, that having servos instead of steppers would cost the same as steppers (servo motors can create a large voltage increase when decelerating. Teknic advises against using any switching type power supply that is not specifically designed for servo motors. They approved a linear power supply with a toroidal transformer if it puts out 75VDC and has large capacitors to absord the voltage spike. To make sure that I could isolate any potential problems, I bought a power supply, hub and all connecting cables from Teknic, which added substantially to the price. I also ordered anSDSK-3411P-RLN servo on the recomendation of Eric at Teknic after he reviewed some data that I sent him. He said that the SDSK-2311S-RLN servo would probably handle the job, but by spending $50 more, the larger motor would certainly do the job. So, I bought both so that I would know first hand.

Here are some observations:

I chose the RLN version of the servos because it the RLN customarily used at 800 counts per revolution although you can set it higher - both the RLN and the ELN have the same encoder but the software inside the motor differs, according to Teknic. The ELN is typically used at 6,400 counts per revolution. The 1605 ball screw moves 5mm per revolution, so 5mm / 800 = 0.000246 inches per pulse, which is about 5X finer resolution than is needed on a typical CNC router. I chose the S version of the 2311 motor ($279) because it has the highest torque and can run at 4,000 RPM. I chose the P version for the 3411 motor ($328) because it can also run at 4,000 RPM. I wanted 4,000 RPM just in case I had to add a 2:1 timing belt to the ball screw to increase torque. That would still produce 6.5 inches per minute jog speed. Eric at Teknic said that if the ball screw had bearing blocks at both ends, then even a 1,500mm screw would not whip excessively.

Bench testing the SDSK-2311S shows excellent torque when compared to the much larger PK299 stepper motor, i.e., no lost steps.

Now to the Centroid Acorn board and software. It has more features than a CNC router will ever need (because wood is affected by moisture). You can map the ball screw. You can map any backlash. You can build offsets for tool lengths and diameters. You can design thingsright in the software without needing VCarve or other CAD/CAM software. I've probably spent 40 hours watching Acorn videos and I'm just beginning to see the potential of that little $300 system. Of course some of the capability requires a "Pro" license for $140 extra. Compare that to Mach3 and an ESS board. I'd go with the Acorn any day.

Are there things that I don't like about ClearPath motors? Yes. I would rather have encoder counts available instead of choosing one of the four status signals that are available from each motor; but, my old PRT-Alpha didn't send any messages; it just stopped when it's internal encoder detected a problem. Using the extremely easy-to-use setup software provided by Teknic with its built-in oscilloscope, a properly setup system will never fault out.

Are there things that I don't like about the Acorn. It's too soon to give a bench test report, but I prefer to have one wire per connection. The excellent schematics provided by Centroid show multiple connections to some port pins. That can be fixed by using terminal blocks. Also, the inputs and outputs are ACTIVE LOW, meaning that if you connect 12VDC to the common terminal, your input device must SINK current (NPN) and your output device must also expect a 0 volt signal (NPN, i.e., SINKING instead of PNP-SOURCING). If you use Geckodrive G203v stepper drivers, pay particular attention to the schematic provided by Centroid. It shows the need to add 220 ohm resistors to each DIR and STEP signal. The less expensive G201x driver can have its COMMON line tied to +3.3, +5 or to GND. If tied to +5, then no resistors would be necessary.

A note about the TinyG board:
It's a good value for the money. It connects easily to G203v stepper drivers if 4-pin molex connectors are added to the board. However, using the TinyG with ClearPath servos is another story. The TinyG only outputs 3V signals and can only accept 3V inputs. Also, it puts out a 0V enable signal. ClearPath servos can be used with 5VDC, 12VDC or 24VDC signals and they REQUIRE a valid ENABLE signal. That requires additional off-board circuitry. I'm in the middle of testing some designs, but it appears than using a single NPN 2N2222 type transistor per signal will work. The polarity of the DIRECTION signal can be easily changed in software.

Sorry about the extremely long post and for hijacking the thread, but there seems to be interest in the ClearPath servos and the Centroid Acorn. On first impression, they look really good together.

Tom Ayres Fri 28 September 2018 03:47

Mike, there's a great bit of info here to consume, very informative and thank you for sharing this. It explains things more clearly for those who are on the fence. Please continue to share your experience of this combination with the rest of us. Too long? I don't think so, good info!

chopper Wed 03 October 2018 19:02

hey guys haven't been here for a while I have been running the acorn for almost a year, ( I am using stepper motors not servos )
it is great and inexpensive, plus it works way better than mach,a least for me
no more jerky arches etc. very easy to set up, no more smooth stepper, has touch screen and a nice wireless pendant, they are coming out with a new version geared towards the routers I think it will be out soon don't be afraid
it works great!!


Richards Fri 05 October 2018 12:16

So far, in my limited testing, I can say only good things about the Acorn board. Centroid has excellent wiring diagrams on their website that show how to connect popular stepper drivers as well as Teknic ClearPath servo motors to the Acorn board. They have an "Acorn User Guide" that explains the inputs and outputs. They have a very comprehensive CNC users manual that clearly shows how to use G-Code.

The Acorn uses Open Collector Inputs and Outputs. That means that all output signals (Step/Direction and Relay controls for vacuum or other devices) are HIGH when OFF (24VDC if connected to the screw terminals, 5VDC if connected to the DB-25 header) and LOW when ON. The outputs SINK current and the INPUTS expect any device attached to the board to SINK current. In my case, the Gecko G203v drives require a different circuit - with is clearly explained on one of the Acorn schematics.

They include a "Wizard" program that enables you to quickly setup your motors and I/O devices. Ramping is extremely simple - you just enter a time into the wizard. The ClearPath servo motors that I have attached to the Acorn are automatically set by the Wizard to 0.5 seconds for ramping. I tested other times with excellent results.

They also have a "tuner" program that tests your settings after you install motors on your CNC machine. I have not run that program yet, but it seems to be similar to ClearPath's tuner program that exercises each servo motor after the motor has been installed.

I've always recommended high-end stepper motors and drivers, i.e., Geckodrive drivers and Oriental Motor stepper motors. The G201x or G203v drivers are in the $125 range. The PKP299 motors are in the $140 range. So a stepper solution would cost me about $265 per motor/driver. That motor/driver puts out about 600 oz/in at 500 RPM and about 124 oz-in at 2000 RPM. The ClearPath servos cost more, $319 for the SDSK-2331S-RLN which puts out 500 oz/in at 500 RPM and 125 oz/in at 2000 RPM or $329 for the SDSK-3411S-RLN that puts out 500 oz/in at 500 RPM and 150 oz/in at 2000 RPM. The important thing about the ClearPath servo motors is that their "error" signal can be daisy-chained through the motors so that the Acorn board is notified of any missed step condition. When wired as their wiring diagram suggests, the motors will turn off automatically. For those of you who are familiar with the Shopbot Alpha system, the ClearPath servo motors do the same thing at a much lower price.

For those of you who use Geckodrive drivers, you know that those drivers require 2000 pulses per revolution (10:1 when compared to 200 steps per revolution of Oriental Motor drivers). The RLN model ClearPath servos are advertised as 800 encoder pulses per revolution; however, you can change that number in the Acorn wizard to be at least as high as 6400 encoder counts per revolution. With a 25 tooth pinion gear and a 4:1 belt reduction, 800 counts per revolution gives you 0.0012 inches of travel per encoder pulse. Changing 800 to 1600 in the wizard gives you 0.0006 inches of travel per encoder pulse. (I just tested that with the Acorn board and the two ClearPath servos, and it works as advertised.)

Now, just a comment on 2000 RPM. The ClearPath motors will absolutely deliver that speed (the ClearPath motors that I use are rated at 4000 RPM because I'll use a ballscrew instead of a belt drive); but I can't think why anyone would use that speed in a CNC machine. At 800 encoder counts per revolution, that means the axis would be flying at 32 inches per second. Bad things can happen fast at that speed. With my Shopbot PRT-Alpha, I kept jog speeds to 15 inches per second or lower so that I had time enough to hit the Emergency Stop button.

If you're thinking about a new controller, think seriously about the Centroid Acorn. If you're thinking about replacing your stepper motors, think seriously about the Teknic ClearPath servo motors. I'm designing a small 4-foot x 4-foot machine with linear rails and ballscrews for maximum accuracy. It will use the Acorn controller and ClearPath servos.

chopper Sun 07 October 2018 20:42

I was reading your posts, I am running the acorn board and I love it, the support is great so is the info for initial setup.
and thank you for sharing the info, my question to you is about the servo's
I am currently running kellining 450 ozin steppers with 4 to 1 belt drives but I am also using 30 tooth pinions which puts me closer to 3 to 1, I haven't had an
issue with missed steps etc. all seems to be working well, but I am curious and I do not know much about servos and I am trying to understand what is the gain with the servos, are they more accurate? are they smoother cutting? it seems they have a bit more power,
thank you,
Charlie // chopper

TheDave Mon 08 October 2018 13:54

I remember this same discussion long ago about servo vs. stepper. I found the thread and actually Mike and Gerald were discussing it:

The thread has a lot of good discussion, remember this was back in 2006. I think at that time this was Gerald's reasoning for going with stepper motors:
Originally Posted by Gerald_D View Post
Manjeet, some of the things about servo's that it make it difficult for a DIY builder:

1. They have low torque and therefore there must be fitted with "torque-multipliers" (gearboxes/belts/screws).

2. They are expensive if you want to buy ready-packaged NEMA-34 solutions - otherwise you need to find individual cheap solutions on E-bay and in scrapyards.

3. They need a lot of wiring (many connections) - a mistake in the wiring normally makes the motor run out of control. A mistake with a stepper causes no motion.
I think the bottom line from back then was that under the right circumstances servo motors ran smoother than steppers, but the cost was too prohibitive.
At this point it looks like you can get a good servo setup for only a little more than a good stepper setup. If you need that extra smoothness it's not going to cost you too much more.

chopper Mon 08 October 2018 19:15

thanks Dave for the reply....
I just trying to see the differences in the two technologies,
I know the servos have progress alot since 2006.
I have contacted clearpath to see what they have to say.

thank you,

chopper Tue 09 October 2018 21:00

this is what clear path said when I asked what the advantage would be to switch to servos over steppers:

You might see smoother cuts with a servo motor (vs your stepper) but it depends on your machine design. Many steppers will vibrate at low speed and if the CNC machine is not stiff enough, you might have cut quality problems. A servo motor doesn’t suffer from this vibration behavior so in this case, the servo would produce smoother cuts.

The main differences between stepper and servo are that servos are:

* more efficient (not hot to the touch while sitting still)

* quieter

* have 2-13 times the power of a stepper (faster rapids and faster cut speed)

* won’t lose steps

so it seems to me there isn't enough gain to switch to servos unless you have a motor or motors go bad,or a motor drive(s) / power supply go bad, or are building new and use servos instead of steppers, or are having issues that would warrant the change (need more power etc).

thank you,

MetalHead Wed 10 October 2018 07:32

I do agree with Charlie. No need to convert a great running machine. But consider this newer design if building a new machine or overhauling a well used one.

Richards Wed 10 October 2018 21:23

A lot has changed since I wrote those early posts. (I still have that original servo motor sitting on the shelf with the Geckodrive servo driver.) The ClearPath servos changed my mind.

Price: I use only Oriental Motor steppers and Geckodrive stepper drivers. The motors cost $150 - $210 (PK296 or PK299), G203v costs $125. Total = $275 - $335. A SDSK3411 costs $330 plus $40 for factory built cables (or you can build your own cables for less than $10 if you have access to a Molex crimper). Both motors require about the same size (watts) power supply and both can be used with a toroidal based power supply, so power supply price would be the same.

Setup: ClearPath has a setup program that shows you exactly how your motor is working. Then, after you've installed the motor on your machine, the software completely tests everything so that you know exactly what the motor can and cannot do.

Speed: The ClearPath has speeds up to 4,000 RPM, depending on the model (D, P, or S). A 3:1 belt drive moves an axis 21 inches per second at 1,000 RPM with a 25-tooth pinion gear. With prices of eBay ball screws at less than $100 for a 1550mm 1605 ball screw and two 1500mm long rails (15mm wide) with four trucks also costing less than $100, a 48x48 machine with ClearPath motors would move that axis 13 inches per minute with accuracy that I only dreamed about with my PRT-Alpha but be aware that linear rails and ball screws for an eight-foot axis are SUBSTANIALLY higher.

Centroid Acorn has made connection easy with accurate and detailed schematics for many devices. The Acorn directly connects to the ClearPath motors without the need for any accessory board (compare that to Mach 3, break-out-board, and ESS - which would be the functional equivalent, making the Acorn's $299 price a bargain in comparison).

In short, if you're happy with what you already have, then keep it, but if you're planning a new build or if you're ready for a major upgrade, do yourself a favor and at least consider Acorn and ClearPath. I was so impressed that I bought an Acorn board, two ClearPath motors, a ball screw and a set of rails for testing. I 'm bread boarding a controller right now. It looks like I'll be building a 2x4 or 4x4 machine this winter. That also means that I'll still have seven PK29x motors and five G203v drivers that will continue to collect dust on the shelf. If those stepper motors and stepper drives and Mach 3 were as good as the ClearPath motors and Acorn, then I wouldn't be writing these posts.

Richards Wed 10 October 2018 22:06

One thing that I neglected to mention is that a 7.2:1 rack and pinion drive with a 25-tooth pinion moves the axis 0.5454 inches per stepper motor shaft revolution. A 1605 ball screw moves the axis 0.1968 inches per revolution. That means that a 300 oz-in motor driving a gearbox, such as the PK296 motor used by Oriental Motor in their popular 7.2:1 gear motor, could be replaced by a 108 oz-in motor driving a ball screw (but keep in mind that using ball screws and linear rails on machines larger than 48x48 get expensive in a hurry).

vustasmith Sat 20 October 2018 10:03

Hello Mike,
I am planning to build a MechMate with dimensions 3.0m x 1.8m, is it going to be of any advantage using clear path + alcorn or should I go with the traditional route of Stepper motor. If clear path + alcorn is the choice what will be the ideal configuration for the transmission and drive system

Richards Sat 20 October 2018 11:34

Because of the size of the table you listed, ball screws and linear rails would be very costly. In that case, I would resort to using a belt-drive transmission, probably with a 4:1 gear reduction if I were set on servo motors or use either a belt-drive or gearbox stepper motor solution. The Oriental Motor PK296 with a 7.2:1 gearbox is limited to 40 in-lbs of torque by the gearbox (640 oz-in). The PKP296 motor rated at 6.3A gives about 450 oz-in without reduction, so a 4:1 belt would give you 900 oz-in holding torque (Geckdrives cut the current in half after a slight delay to keep the drives from overheating, so the rated 1,800 oz-in is really no more than 900 oz at 4:1.) A PKP296 and G203v costs about $225-$250 per motor/driver. A ClearPath SDSK-3411S-RLN motor at $330 per motor would give you a minimum of 600 oz-in holding/running torque with the same 4:1 belt-drive. That motor tops out at about 2,350 RPM, so a 4:1 drive would give you about 590 RPM and a 1.25 pitch diameter pinion could still move that axis at 35+ inches per second - at least 3X too fast for my tastes. The slightly more expensive SDSK-3421S-RLN at $350 per motor would give you 1,200 oz-in maintained torque at 4:1 but is limited to 1,410 RPM, so it has a jog speed of over 20 inches per second - still too fast for my tastes. Because I'm using the normal torque spec, that motor also has a cut speed of over 20 inches per second - if your spindle and cutter can plow through the material that fast.

We're looking at about $125 difference per motor between a traditional high quality stepper/driver and the clearpath servo. If you worked your machine so hard that you wore out the motors in two years (very unlikely), the difference is 17-cents per day per motor to have full holding torque, a smooth start/stop without jerkiness, and total control over all motor parameters, including auto shutdown if the motor detects lost steps. The power supply would cost about the same ($125-$150 from AntecInc for a 70VDC supply for the servos or for a 35-40 volt supply for the steppers). Cabling from Teknic is about $50 per motor or about $2.00 per connector w/pins if you make your own. Teknic suggests you buy the Molex crimper at about $300 from Digi-Key to crimp the pins, but I use the very excellent Engineer PA-21 tool at $50 that fits the Molex 39-00-0047 terminals perfectly (two crimps, one for the wire and one for the insulation). I bought the PA-21 tool after reading the Molex warning that their tool has only a 3-month warranty and that it was meant for occassional field use only. For $300, I expected a heavier duty design.

Either the Oriental Motor or the ClearPath would be an excellent, top quality choice. Before I received my ClearPath motors, cables and Power Supplies, I was very satisfied with the Oriental Motor/Gecko solution. Now that I know that a much better solution exists at a very realistic price difference, I could work a little harder to make the extra money to buy the better solution.

vustasmith Mon 26 November 2018 06:21

Thanks Mike for the excellent analysis.
It was most helpful

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