Low cost / high speed / high torque stepper solution

[richards]

--- For Do-It-Yourselfers only ---

This morning while I was looking at an Oriental Motor PK299-02AA stepper motor and wondering whether I'd ever find a use for it, I FINALLY noticed that it is rated at 6mH Inductance and 3A. The proverbial light bulb turned on and I realized that I (possibly) had found the ideal motor/stepper driver combination if I paired it with a Geckodrive G540. It was one of those "golly-gee" moments. (That's what we say in Utah when we get really, really excited.)

Geckodrive sells a G540 combination unit that has four stepper drivers attached to a circuit board. The problem with that unit is that it is limited to 50VDC and 3.5A per motor. I've tested it extensively with PK296A2A-SG3.6 motors and with the (too small) PK268-02AA stepper motors (left over from the process control computers that I once designed). Although the "maximum" voltage for the PK299-02AA motor is 78VDC, it can be run at 50VDC with good results. Because it is rated at 3A, it seemed like a possible match with the G540. So I set up the test bench.

Power Supply = 48VDC (2 X 24V switching PS in series)
Current limit resistor = 3K 1/4W
Steps per inch = 1697.7928
Jog speed = 15 inch per second
Cut speed = 6 inch per second
Acceleration = 0.99G !!! (The acceleration was set that high to give me an indication of how the motor would handle on a CNC machine, i.e. would it miss steps - it didn't.)

The steps per inch is the number that would be required if a 4:1 belt-drive were attached to the motor and if a 30-tooth pinion were used (0.000589 inch per step = 1697.7928 steps per inch)

After running a test for two hours with a PK299-02AA motor on the X-axis and a PK268-02AA motor on the Y-axis, the 299 motor is at 46C which is warm but not hot enough to burn. The 268 motor is 58C, which is too hot to hold. The motors are rated at 100C with a maximum 80C temperature rise, so they are both well within their ratings. The G540's case temperature (bottom of case directly below the X-axis G250 stepper driver was 50C with the G540 just sitting on a piece of MDF. The G540 is rated with a maximum case temperature of 85C. The top of the G540 is 32C. Normally the G540 would be mounted to an aluminum case and a computer case fan would recirculate air inside the aluminum case. But the PK299-02A motor is not causing the G540 any grief.

The reason that this combination has got me all excited is that the PK299-02AA motor generates 620 oz*in of holding torque when wired half-coil. With a 4:1 belt-drive transmission, that is 2480 oz*in of torque or 155 lb*in, which is about 2X more torque than the 7.2:1 motors on my (upgraded) PRT-Alpha! The price of the PK299-02AA motor paying full retail from Oriental Motor is $205 each. The G540 sells for $299. A 48VDC toroidal based power supply (AnTek) is $95. A build-it-yourself belt-drive is about $150 per motor. If you bought Shopbot's V201 (or newer model) controller, you could build a complete control box, including the motors for about $2,000 that would have 2X the torque of my PRT-Alpha and all of the speed (jog speed possibly limited by the Shopbot controller's maximum pulse rate - I'm running the tests at 45,000 pulses per second maximum).

The smaller PK296-02AA motor ($137 each) is rated at 310 oz*in holding torque, which, with a 4:1 belt-drive, would give it 77 lb*in of torque, which is about the same as the 7.2:1 Alpha motor. That smaller motor has 3.5mH inductance, so it is a better match for a 50VDC power supply, but could be used with a 30-38VDC power supply to keep the heat down.

The beauty of the Geckodrive G540 is that it not only has four (replaceable) stepper drivers built in, but it also has four general-purpose opto-isolated inputs and two general purpose opto-isolated outputs. It also has a 0-10V opto-isolated output which can be used as a speed controller with the VFD of a spindle. Interfacing the G540 to a Shopbot controller would take some expertise (the G540 was designed to be plug-compatible with Mach3 - which would require us 'botters to totally rewrite all of our tool path files), but it would make a killer small system for those that only need the equivalent of the PRS-Standard features with the speed and torque of the PRS-Alpha.

[richards]

I've received several emails asking how the G540 can be connected to a Shopbot. A better solution might be to buy the G251 modules that have a screw terminal block and a heat sink attached to the module, then, wiring the Geckodrive G251 would be as simple as connecting a G203v.

It's hard to imagine that a little stepper driver 1.675" X 1.560" could drive a large stepper motor, but it can and it works very, very well. Although I don't have a G251, it and the G250 modules are exactly the same except for the connection options. The G250 is one of the four modules used in the G540 unit. The G251 sells for $69 each, compared to $147 for the G203v. The G251 will drive a PK299-02AA motor just as fast and with just as much torque as the G203v at on 46% of the cost.

One possible problem is the limited pulse rate generated by some of the Shopbot controllers. The Geckodrive modules, G201, G202, G203v, G250 and G251 all generate 2,000 steps per revolution. That gives excellent resolution (2X better than the Alpha driver - as it is normally configured), but it also requires a lot of pulses to move an axis. If you built a belt-drive transmission with 4:1 reduction, and if you used a 30-tooth pinion gear, each pulse would move the axis 0.000589". Moving an axis 10 inches per second would require a pulse rate of almost 17,000 pulses per second. Moving an axis 15 inches per second would require a pulse rate of about 25,500 pulses per second. I don't know how fast the various Shopbot controllers can generate pulses. (I can't find my notes on the V201 that I'm using on my PRT-Alpha, but I think that I tested it up to 30,000 pulses per second - but that may just be the faulty memory of any old man.)

So, if you're looking at a possible do-it-yourself update for an older Shopbot, use the following prices to give you an idea of what to expect:

Stepper drivers, G251 X 4 X $69 = $276
Stepper motors, PK299-02AA X 4 X $205 = $820
Power supply, Antek 1 X $95 = $95
Self-built transmissions, 4 X $150 = $600
Total = $1,791
Add about $100 - $200 for misc. wire, connectors, etc. and you've got an electronic package with 2X the torque of the Alpha and jog speeds of 10-ips to 15-ips, depending on your controller's pulse generating capacity.

If you use the smaller PK296-02AA motor, that cost $138 each, you would save $67 per motor, or $268. The smaller motor, when geared 4:1, gives 77 lb*in of torque, or almost exactly the same as the Alpha 7.2:1 motor. In addition, the 4:1 belt-drive would give better resolution (4 X 2000 compared to 7.2 X 1000) and there would be no possibility of backlash, although my 7.2:1 gearboxes don't have any apparent backlash.

[robert_cheal]

Hi, Mike
I would very much like to do something like that as soon as I am able to so.

I have been looking forward to seeing you at Magna.

Robert

[jon]

I recently upgraded to the 7.2 gearheads, and have noticed some slop in my cuts that I think might be attributed to backlash. The reason I say this is because the slop disappears when the old ASM911AA-2.65V steppers are subbed back out. Has anyone else noticed this? Or is this the trade off for increased resolution? The test part I use to cut is a square with slots cut into the flats. I'm seeing a slight curve or vector 'slop' occuring after 90 degree corners. All the axis' are tight, and I have a spindle.

[richards]

The SG (Spur Gear) gearboxes are advertised as having 1-degree to 2-degrees of backlash. In comparison, the TH (Tapered Hob) gearboxes are advertised to have as much as 43-arc minutes of backlash. A minute of arc is 1/60 of one degree. So 43 arc min = 0.71 degrees. So, worse case, an SG gearbox that has 2-degrees of backlash would have 2.7X more backlash than a TH gearbox.

Of the four SG 3.6 motors that I have, only one gearbox has any discernable backlash.

The Oriental Motor document that describes their gearboxes and the backlash for each type of gearbox is found at:

www.orientalmotor.com/products/ac-dc-step-motors/geared-step-motors.html (http://www.orientalmotor.com/products/ac-dc-step-motors/geared-step-motors.html)

The PK296A2A-SGxx motors are compact and relatively inexpensive (about $260 each). Another alternative would be to buy the PK296-03A or PK296-F4.5A motor and add a belt drive (4:1 if you use an 18-tooth pulley on the motor and a 72-tooth pulley on the drive shaft). Building a belt-drive transmission will cost about $100 to $200 per motor, depending on the materials you use and whether you do the work yourself. I've just bought the parts to make four belt-drive transmissions out of aluminum. The total price of parts, without the motors is $484. The motors cost about $140 each, so my cost, per motor will be about $261. The belt-drives have no backlash. They have 4X the tourque of the motor (4 X 300 = 1,200 oz*in = 75 lb*in = Alpha torque) and with a 30-tooth pinion drive gear, they will have a resolution of 0.000589" per step (compared to 0.0006545" per step for the Alpha 7.2:1 motors - the Alpha motors have 1,000 steps per revolution, the Gecko stepper driver has 2,000 steps per revolution). Even driving those motors with a modest 20,000 steps per second pulse stream will jog an axis 11.78" per second.

The belt-drive transmission that I've described requires high-performance motors and high-performance motors require high-performance stepper drivers. I use the Geckodrive G203v (mounted on a slab of 3/8" thick aluminum for a heatsink), a 35VDC power supply and 100k 1/4w current limit resistors. The motors are wired half-coil, although the PK296-F4.5A could be wired bipolar parallel for even more torque but at a cost of substantial heat. When wired half-coil and driven hard for long periods of time, the motors will reach about 60C, which is well within their intended temperature range. The PK296-F4.5A motor, when wired bipolar parallel and run at 6A will hit 80C to 85C, which is still within its intended temperature range, but 80C is hot enough to cause blistering - too hot for me.

[rb99]

Are there any plans for the belt drives available?

Thanks,

RIB

[richards]

Richard,

I've built several different models for my PRT-Alpha, including models using acrylic, Delrin and aluminum for the side plates. Today I built a 'quick and dirty' 6:1 unit using the smaller PK268-02AA motor. That model was built using aluminum. Until now, I've always thought that the size 23 motors would be too small, but it looks like I may have been wrong. That little unit jogs at 16-ips. After running it on the test bench for two hours, it was barely warm. Normally I run my tests using a Geckodrive G203v, but this one was attached to a G540 module.

I'll show that unit, plus some other electronics tomorrow at the Magna Camp (Salt Lake).

I can send you some generic drawings that you could adapt to your needs. I use AutoCAD LT, which creates DXF files. If you're interested, send me an email.

[rickwoody]

"Stepper drivers, G251 X 4 X $69 = $276
Stepper motors, PK299-02AA X 4 X $205 = $820
Power supply, Antek 1 X $95 = $95
Self-built transmissions, 4 X $150 = $600
Total = $1,791
Add about $100 - $200 for misc. wire, connectors, etc. and you've got an electronic package with 2X the torque of the Alpha and jog speeds of 10-ips to 15-ips, depending on your controller's pulse generating capacity."

Can these components be connected to the V3 controller?

Rick

[Gary Campbell]

Not to pi$$ on anyones parade here, but for Rick to say that his combo has twice the torque of the Alpha means that he hasnt seen my machine cut full depth thru 3/4" plywood as fast as his listed jog speeds. BTW, my machine is a stock PRSa (circa 2010)

It takes torque to gain speed. It takes torque to overcom inertia. It takes torque to push a bit hard thru thicker material. I will not argue that the earlier machines needed both speed and torque. Starting with a smaller motor and installing a gearbox adds lots of torque, but sacrifices speed.

Please sir, dont quote theoretical numbers or comparisons without real world data. As they say: "In theory, there is no difference between theory and real world. In the real world, no evidence has been found to support the theory"

[ken_rychlik]

Actually Rick didn't say it. He was quoting Mike.

To answer Rick's question, yes it is possible to hook this up to a shopbot control card. It is not a plug and play kind of thing though. It would take someone with some electrical knowldedge and some research on their part as well.

[Brady Watson]

It is not a plug and play kind of thing though. It would take someone with some electrical knowldedge and some research on their part as well.

VERY good point, and readers should understand this.

All theories aside, and not to minimize Mike's research, but it is very hard to beat the performance and value of a PRS Alpha drive system. Yes, it is not "cheap"...but what is "cheap" at the end of the day, on a tool that is used to make a living?

Forget that Alphas have positional feedback and can go into 'Alpha Mode' or self-correct. The tool will run all day long (and day & night) without missing a beat, if you aren't running a beat computer, and cut with 150 pounds of cutting force, reliably, up to 12 inches per second. It will rapid position at 30 inches per second as well, although the gearboxes are really only rated for around 22 IPS. It was carefully researched and engineered to run all day, every day - production duty.

300 pounds of cutting force???? 2X that of an Alpha? Who wants that? I've only put my tool into 'Alpha mode' exactly two times since 2006. Both times were induced by parts moving and wedging the machine on one side of the gantry, forcing the tool to adjust for this & eventually stop with a safety alarm. 300# of force on a slow moving metal mill is fine. On a fast moving router - no way, Jose. Think about safety. 300#s on ANY part of your anatomy ain't pretty.

If you are tinkering around, no doubt you can get impressive numbers with off the shelf parts...but what kind of warranty and support are you going to get?

-B

[Gary Campbell]

Kenneth...
Thanks for the clarification. Mike is a dear friend of mine and we have spoken about this issue. I am sure after those conversations he would be the first to agree that he is NOT talking about the current PRSalpha motor/driver combo.

Like Brady says, there may be hundreds of lurkers out there, there is no reason to have them think that a few $200 motors, $69 drivers and some homemade gearboxes will double the performance of the alphas currently being built.

Mike's posts here, and on other forums, has always been spot on. He has offered up a great solution for those wanting a DIY budget upgrade for one of the earlier SB models or a very cost effective solution for a DIY machine build.

There has to be some common sense applied here. All the motors are coming from the same place. When could we expect to get, from the same vendor an under $300 package that outperforms an over $1000 package? Even nitrous cant do that!

The current alphas are very expensive. And worth every penny if your living depends on them.

[bleeth]

If any of you "lurkers" haven't noticed there is a current batch of SB owners in the process of adding the PK299 F4.5A's to their machines with gearboxes. See the subject (Gear Boxes) under modifications to Shopbots. Some have the early Alpha's with 1:1 motors that need the gearboxes to get improved resolution, and some have earlier PRT's or PRS's Standards and need to step up resolution and/or speed with motors and gearboxes. The program is designed for those who already have Gecko drive controllers (Either independantly built or SB 4G types). No one who has checked into it thinks that doing so will equal the current PRS Alpha. Or if they do they are fooling themselves.
Not all of us can afford to or wish to possibly overextend ourselves and upgrade to the latest and greatest. Therefore the above conversion is a way to vastly improve our current setup without as high an investment. I can tell you, since I am in the middle of it, that the complete process of identifying ALL of the specific parts and engineering is not a "123-I'm done" deal and takes a definite time and research investment. I have also pointed out in previous posts that if I had my druthers I would just buy a new Alpha.
The defense of the new Alpha against "hotrodding" an older PRT or PRS standard is akin to an owner of a new Northstar Cadillac braggin that his car is technically superior to a Studillac. (If you don't know what it is look it up). By the same token claiming that it is the same or superior to do those conversions to an older machine and have the equivalent of a new one is also patently absurd.
Not pointing any fingers here or flaming anyone-we ARE all friend here-just wishing to keep the conversation to the point.

[fozzyber]

Thanks to all here. I am watching this post as well as the gear box thread,
I have a early prt circa 2001, with non g4 , I don't need an alpha but would like to increase speed and res, I am watching these postings with great interest. I think my upgrade path will be controller, gear box, motors.
in that order. thank you to all the creative minds out there.
Now hopefully after I give Obama his cut for last year (:mad:#*&%@*&%$:mad:) I can toss some jack at the shopbot,,,,


Jerry

[robtown]

Must we... really? Don't we get enough "political discourse" in our faces on a daily basis from EVERYWHERE else?

[richards]

Talking about stepper motors and drivers is a lot like talking about religion or politics, i.e. without a great deal of study and experience everything is superficial.

There's no magic in one type of stepper motor over another or one kind of driver over another. A stepper motor that is properly selected for the job will do the job properly all day long. A stepper motor that is too small for the job or mismatched to the driver will cause problems.

Rule Number 1: Determine how much torque you need to do the job.

Rule Number 2: Determine how fast you need to move and axis.

Most people would think that the answer to Rule Number 1 is "how much torque is available?" That's not a good answer. The material you're cutting might limit the torque required. The cutter you're using might limit the torque required. The ability of the CNC's frame to push a cutter without having the frame flex might limit the torque required.

What's a safe answer? 80 lb*in. Why is that a safe answer? It's safe because that's the torque provided by the Alpha 7.2:1 motor/gearbox, so we can assume that the PRS machine can handle 80 lb*in of torque without too much flexing.

Rule Number 2 is dependent on Rule Number 1. As soon as you know how much torque you need, the next step is to open a spreadsheet and run the numbers, using factory specs from good companies. (I use Oriental Motor. Shopbot uses Oriental Motor. Oriental Motor is a great company.)

As you 'run the numbers', you'll find a lot of motors can produce the torque required when they're used with a belt-drive gearbox, so which motor do you choose? My answer is to choose a size 34 motor that has eight wires or leads that has the lowest inductance. A size 34 motor has more surface area to dissipate heat. (Stepper motors can and do get hot - really, really hot.) Oriental Motor has two popular motors that meet those requirements: The PK296-F4.5 and the PK299-F4.5. Both of those motors can be wired bipolar series, half-coil or bipolar parallel. Bipolar parallel gives the most torque at high speeds, but at the cost of high temperatures. Bipolar series gives the most torque at low speed, but but at the cost of VERY poor high speed performance.

Now look at the numbers again. 80 lb*in of torque is the same as 1,280 oz*in of torque. BUT 80*in at what speed? Holding torque (motor stopped) or jogging torque (motor moving at maximum velocity)? Stepper motors trade torque for speed. Look at the manufacturer's torque curves and you'll see what I mean. The faster the motor spins, the lower the torque the motor produces. If you look carefully at the torque curve, you've probably see a 'shoulder' or 'knee' point where torque quickly drops off. The secret is to keep the speed on the high torque side of that 'shoulder' or 'knee' point.

Look at the AS98AA motor and compare it to the PK9x motors. It's very similar to the PK296-F4.5 motor. For all three motors, that point is about 1,250 RPM. The AS98AA motor has about 225 oz*in of torque at that speed, the PK296 motor has about 200 oz*in of torque and the PK299 motor still has about 300 oz*in of torque. So, we're still comparing apples to apples.

At this point, we know that with the proper power supply and the proper stepper driver all three motors will cut at the same speed. If we give the AS98 motor a 3.6:1 belt-drive, it would have the same usable torque as the PK296 motor with a 3.6:1 belt-drive.

BUT, we have a problem. The maximum belt-drive ratio that we can get without going to a multi-stage design is 4:1. AT JOG SPEED, with a 4:1 ratio, the PK296-F4.5 motor will give us about 800 oz*in of torque or about 50 lb*in which is less than the 80 lb*in that we're looking for; however, the PK299-F4.5 motor can handle the problem. It has just over 300 oz*in X 4:1 = just over 1,200 oz*in which is just over 75 lb*in or just under 80 lb*in, depending on how you look at the chart.

Now that we know the PK299-F4.5 motor can match the AS98 motor for torque and that a 4:1 belt-drive can give matching high-speed torque, it's time to see if the pulse rate to drive that motor/belt-drive at 22 IPS (remember, that's the recommended maximum speed for the Alpha 7.2:1 motor).

Using a 1.5" diameter pinion gear (30-tooth) would move an axis 4.7124 inches per revolution. So, 22 IPS would require 22 / 4.7.124 X 4 = 18.6741 revolutions per second (remember, we have to compensate for the 4:1 belt-drive). 18.6741 revolutions per second equates to 1,120 RPM. We're still within the good torque range of the motor.

The other fly in the ointment is the pulses per second. A Geckdrive requires 2,000 pulses per revolution. The Alpha driver normally requires 1,000 pulses per revolution. So, 18.6741 revolutions per second with a Geckodrive requires 2000 X 18.6741 pulses per second. That's pretty fast. The Mach controller can easily handle that speed. Some of the Shopbot controllers might have a hard time keeping up.

So, depending on the controller that you have, jog speed might suffer when comparing an Alpha motor to a PK motor.

Cutting speed would not be affected, at least speeds up to 12 IPS.

Now it's time to address the 600 lb gorilla that's been sitting in the corner. What about 'Alpha Mode'? The AS98 motor can recover when it momentarily slows down. What I'm going to say will not make me popular around the water cooler. In my opinion and from my experience, Alpha Mode is not what it's cracked up to be. In my early days with my PRT-Alpha when I tried to push the envelope as far as possible, I often forced the machine into Alpha Mode. What it bought me was a divot in the cut that usually ruined the piece. Think what happens when the machine enters Alpha Mode: an axis can try to recover for up to 1/2 second before the driver sends a fault signal. (The actual time depends on a 'pot' setting on the stepper controller.) If you're cutting at even a lowly 5-IPS, that 1/2 second delay means that one axis is up to 2-1/2 inches behind its expected position. The three axes are not coordinated to all slow down proportionately. Result = ruined part.

I quickly learned to slow things down so that the machine NEVER entered Alpha Mode. Result = NO ruined parts.

Stay within the capabilities of the motor and the driver and the power supply and the transmission and the cutter and the flex of the machine and you'll have a good experience. Push any one of those things too far and you'll be pulling out your hair.

------

If you're really into electronics, you can always add an encoder to a stepper motor that would display any missed steps and, with the proper programming, send a fault signal to the controller to stop the cut if a motor missed too many steps during a pre-determined time period. (One missed step would be 0.00059 inches. Depending on the type of cut, a few missed steps might be acceptable with no visual indications that a problem had occurred.) The encoder and microprocessor (not counting design time, programming time, or the cost of the initial prototype circuit board) is about $50 per motor.

[richards]

The fact that a Geckodrive might require a faster pulse rate than the Shopbot controller can provide when fast jogging speeds are desired drove me to the Geckodrive site where I noticed that their NEW step multiplier board board for the G201x and the G203v has been released. (This is a new design that purportedly eliminates the 'jitter' that Brady discovered on the older design that was used with the G202 and G201 stepper drivers.)

A step multiplier board lets you use a slower pulse stream to drive the stepper motors. The documentation on the new board is a little fuzzy, but it looks like you have the choice of 1:1, 2:1, 5:1 and 10:1, so, using the 2:1 setting, the Shopbot controller would only have to furnish half as many pulses per second. The drawback is that resolution is also cut in half; however, at 2:1, the resolution would be 0.0012" per step. I doubt that you could get repeatable movements any better than that on the PRS doing production work. (That's less than 1/2 the thickness of a piece of copy paper.)

Now for the fun part.

If someone were doing step and repeat work where he needed the fastest possible jog speeds between parts but still needed the highest possible resolution when cutting the parts and he wanted to use the PK299-F4.5 motor and a Geckodrive stepper driver, it looks like he could use the new pulse multiplier board and an electronic switch to switch between 2,000 steps per rotation for the highest resolution and 200 steps per rotation for the fastest possible speeds. (A similar 'trick' is used by Shopbot to drive the Alpha motors. One resolution is used for cutting and another resolution is used when jogging. The Alpha stepper drive has a provision to allow on-the-fly speed/pulse changes.)

Ramping would be critical, but it is conceivable to also alter ramping withing the program so that the jogging routine used one set of VR parameters and cutting used another set of VR parameters.

As long as I'm just writing about potential and not about what I've been able to do at the test bench, let me point out the advantages of using a standard stepper motor with a Geckodrive stepper driver and a pulse multiplier board with electronic switching:

1. Better resolution with a 4:1 belt-drive than the Alpha motor gets with a 7.2:1 gearbox. (Remember that the Gecko uses 2,000 steps per rotation and the Alpha uses 1,000 steps per rotation. The Alpha would have to use an 8:1 gearbox to equal the resolution of the Gecko driven 4:1 belt-drive.)

2. Faster jog speeds. The Alpha is limited to 22 ips due to its gearbox. The belt-driven standard stepper is limited only by the ramping times and torque of the motor used.

3. Cost. The basic motors, drivers and power supply using a standard motor and Gecko for the entire system cost about as much as one Alpha motor/driver; however, to be perfectly fair, if you hire someone to design and build a system using standard motors and Gecko stepper drivers, it may actually cost more for the standard motors and Gecko stepper drivers.

And now back to that 600 lb. gorilla that I mentioned in my previous post. The standard motor and gecko system does NOT have a feedback/Alpha Mode.

[steve_g]

Mike:
I see your point regarding ruined parts even though the Alpha mode was entered… In defense of Alpha mode, I often cut small step and repeat parts, these jobs are likely to be unattended in that I’m in another part of the shop. In the few times that alpha mode was engaged, it resulted in one bad part while the balance were still indexed properly with previous cuts.

Thanks for the time you put into intelligent, researched postings!

Steve

[richards]

Steve,

You have a perfect application for Alpha Mode.

To be perfectly fair, almost always, my problems came when I was cutting panel parts from plywood, i.e., long multi-axis cuts at high speed. Plywood is notorious for being inconsistent. My practice cuts, where I determined feed speed, where likely on pieces that were more consistent than the production sheets.

Until I went to the first Maker Faire in San Mateo, I didn't know that the Alpha stepper controller's fault time was selectable. Ted Hall took the time to show me how it worked. His eyes lit up when he explained how it all worked. That's a sure sign that he really enjoys what he does. That's also when I gained a lot of respect for him and his products. After all, my ignorance on the proper procedures to use and the proper settings could have been cured by picking up the telephone years earlier and simply talking to someone about my problem. Had I set the delay time to a very short setting, I would probably have learned in a hurry that I was pushing the machine too hard for the kind of cut that I was making.

I never regretted having purchased the Alpha model.

If my health ever returns and if I ever buy another machine, I'll probably order a Shopbot without electronics and install my own controller - not because my design would be better but simply because I enjoy the electronic side more than the production side. To me, breathing sawdust is a necessary evil to get to see electronics at work. (In my former life as a process control computer designer, my last major project had options to use from six to twelve stepper motors to control a Kodak 5-S professional photo printer. Instead of using air cylinders and rotary solenoids, everything was controlled by stepper motors, filters flags, paper advance, mech plate, paper curtains, everything.)