Merging modern software development with electrons and metal
Random header image... Refresh for more!

Stepper Vs Servo Motor Torque Curves Part IV

NEMA17 Torque CurvesNEMA17 Torque Curves

My final look is at NEMA17 motors.  Today’s contestants are:

  • In yellow, the IMS (now Schneider) MDI1PRL17C4x triple stack NEMA stepper motor with integrated driver and controller.  I’ve used these cute little motors before; they are a great fit for the right application.  As normal, the programming language sucks, but a CANOpen version is available.
  • In red and blue, a Panasonic MUMS011A1 NEMA 17 servo motor.  These motors have unfortunately been out of production for years; I loved their performance, encoder (10000 cpr), good looks, and price (about $250).
  • In green, a Quicksilver Controls QCI-A17H3 stepper motor with encoder that’s driven like a servo.  I’m including it to show how much improvement you can get from closed loop stepper control.


  1. The MDI1PRL17C4 shows typical stepper characteristics, with torque rapidly dropping off; it can’t even reach 2500 RPM.
  2. The MUMS011A1 shows typical servo performance, with a pretty flat torque curve, 3:1 peak to continuous torque, and compared to the steppers:  higher speeds, less continuous torque at low speeds, more continuous torque at high speeds, and much higher maximum torque.
  3. The QCI-A17H3 doesn’t turn the stepper into a servo, but compared to an open loop stepper, it has substantially higher maximum speed (4000 RPM – the highest of any stepper I’ve looked at), and offers significantly higher torque at higher speeds — in exchange for a higher price, of course.

Some General Stepper & Servo Notes

  1. Steppers are much simpler to drive: you can easily build a low cost drive using an integrated chip (e.g. from Allegro Microsystems, ST, or TI) or buy a commercial driver for $100-$150 (from Automation Direct, Gecko Drive, etc).  Many low cost PLC’s such as Panasonic’s FP0/FPG have built-in step/direction outputs.
  2. But open loop steppers are very annoying, because you have to figure out your needs before start: you have to specify fixed currents for holding and running torque.  If your current is too low, the motor will miss steps.  If your current and duty cycle are too high, the motor will get hot – and if a bit of extra torque is needed to overcome something unexpected, you’re out of luck.
  3. Closed loop steppers still aren’t servo motors.  However, I’m looking forward to affordable sensorless closed loop control (available or coming from Trinamic, TI, and probably others), which will improve stepper performance and minimize stepper heat generation.
  4. I think servo motors’ torque curve fits well with many applications: a lot of time you just need maximum torque for a short time period.  Servo motor system prices are also coming down (OK, not the basic motor, but there are affordable encoder, drive, and controller choices).


April 26, 2013   No Comments

Make a Panasonic FP0 Power Cable (AFP0581 Replacement)

PLC Power Cable Parts

PLC Power Cable Parts

I recently bought a FP0-A21 analog I/O unit and since it didn’t come with a power cable, I decided to make one.  Because Panasonic does not provide any part numbers, I had to do a little detective work and searching on Digikey to figure out what to use: Molex 51067 series connectors with Molex 50217 series contacts.

The Panasonic part number for the cable assembly is AFP0581; it is used on the FP0 PLC’s, FP0-A21 analog I/O units, FP Sigma PLC’s, and possibly more.

My parts list is simple:

  • 1 Molex 51067-0300 housing
  • 4 Molex 50217-8000 18-24 AWG tin crimp sockets (I like to get at least one extra just in case I screw up).
  • Brown, Blue, and Green 22 AWG wire.

I found an appropriate crimper, and matched the same order as my existing power cable (see below).

PLC Power Cable Wires

PLC Power Cable Wires

Note that like most crimp connectors, the crimp socket can only fit in one way; hopefully the picture below will help.

Connector Closeup

Connector Closeup

October 14, 2012   No Comments

Best Industrial Equipment For The Garage: 2011 Update

Overall my original post on buying surplus industrial automation equipment is still on the mark.  I won’t repeat it again this year; instead, here are some comments based on 3 years of monitoring eBay and adding to my collection.

In Silicon Valley there are only two decent electronic surplus stores: Excess Solutions and Advanced Component Electronics.  There hasn’t been a good local source for mechanical surplus since Triangle Research closed its doors.

On the web, PLCCenter has a great selection, is great for getting an idea of what stuff costs new, but has premium pricing (except for some on-sale items).

eBay is still the best source, but you need to be patient and know what equipment is worth.  In general, I’m willing to pay 10-20% of the original cost, but many eBay sellers try to get 50%, and a few even ask for more than 100%.  In general, “Buy It Now” means “I think my junk is worth a lot”.  Availability is very spotty; some months there’s a lot of interesting stuff, some months there is nothing.

Also, be sure to check condition and return policies.  Many eBay sellers do not have the ability, equipment, or inclination to test industrial equipment, so if it says “as-is”, don’t pay a lot.  Most of the industrial equipment I’ve bought has worked, but I’ve bought a number of AMC and Elmo drives that don’t want to communicate (since the lights blink, I haven’t given up yet; I haven’t had time for extensive troubleshooting).

Don’t forget new equipment; many vendors (including Siemens and Panasonic) have offered somewhat-affordable starter packages including equipment and software (e.g. PLC and programming software).  Some new PLCs are so inexpensive you don’t even need a starter kit: for example, Automation Direct’s Click PLC starts at $69 and the software is free.

Comments on specific equipment:

  • Last time I checked, it appears the Cognex Insight smart camera software is now a free download (after registration).  But I recommend verifying this before buying an Insight camera (which will probably cost >$100).
  • DVT smart cameras are still often available on eBay, with pricing ranging from $50 (Legend 510 bought at the right time) to $500 or more (color model such as the 542C).
  • Galil motion controllers availability is good, with a wide range of pricing (there are many unrealistic sellers).  USB and Ethernet models are more expensive, although if you’re lucky you can buy one for under $250.
  • CANOpen interfaces from Kvaser and Ixxat are frequently available for $50-$150.  I’d recommend getting a used Kvaser or Ixxat instead of a new interface from someone else (which will be at least $100 anyway) because they have the best software support.
  • Copley CANOpen servo drives are available fairly often; a reasonable price for an Accelnet is $50-$120; the Xenus is more expensive (>$150).  The Accelnets are my favorite servo drive.  I avoid the older models (800-xxxx)  because I can’t find any documentation for them.
  • Elmo CANOpen servo drives are frequently available.
  • Ethernet Powerlink drives and EtherCAT drives are occasionally available , but the prices typically aren’t reasonable.
  • MEI controllers are often available, at a wide price range, but I’ve never seen the software included.  If you don’t have MEI software, don’t buy the board.
  • Panasonic PLC’s are frequently available, but in general I think the asking prices are too high.  At least Panasonic now provides a code-sized limited (but still quite useful) free version of FPWin Pro 6.
  • Opto 22 I/O controllers, such as the B3000 and LCSX, are frequently available, often at reasonable prices ($50 and up).  Opto 22 PACs are rare and expensive, especially the current models.  Opto 22 I/O module availability is good.
  • Wago 750 and Beckhoff K-bus availability is good, and, if you’re patient, you can get them at a reasonable price.
    • The most popular couplers are for DeviceNet, CANOpen ($25-$75), Profibus, and Ethernet (>$100 for 750-842); I’ve also seen Interbus, serial, and EtherCAT.
    • Digital input and output modules are the most common, and cheapest.
    • Analog modules are less common, and more expensive, but if you’re patient, you can get one for <$50.
    • Specialty modules, such as encoder interfaces and stepper drivers, are the least common and most expensive.

June 20, 2011   5 Comments

Panasonic FP0-R PLC Surprises

Recently, I used my first Panasonic FP0-R PLC in a machine (as a drop in replacement for a FP0). Even though I’ve read the FP0-R specifications, I did have a couple surprises along my journey to a working machine.

The not so good surprises:

  • You need the FPWin Pro V6.0 or newer development software to initially download to the FP0-R.  Pretty frustrating, since I only had FPWinPro V5.3.
  • OK, Panasonic also offers FPWinGR, but I’ll never consider it, because FPWinPro implements the IEC-61131 programming standard (yeah, structured text! ) and when I first tried FPWinGR, about a decade ago, it was, to put it nicely, a putrid steaming pile of crap (OK, I’ve seen worse, but it wasn’t very good then).
  • Of course, getting a new, full versions of these (FPWinPro or FPWinGR) costs money.
  • The free program loader program I was using, PLC UpDown V2.55, doesn’t work with the FP0-R, and I can’t find a newer version.  FP UpDown let me upload the memory of the PLC into a NSU file and then download that NSU file into another PLC.
  • Panasonic does have a free loader program, FPLoader, that does work with the FP0-R, but it only downaloads FPWinGR programs (not FPWinPro), and can’t upload.

But I was pleasantly surprised, because:

  • Panasonic has a free FPWinPro version, FPWinPro 6.2 basic, that is only limited by the maximum program size, which varies depending on the PLC model; it’s 2.7K/300 steps for the FP0/FP0-R and 12K/500 steps for the FP Sigma.  My current programs are all smaller than that, so thank you, Panasonic!
  • The FP0-R has compatibility modes that let it mimic FP0 PLCs such as the FP0-C32 and FP0-T32.  When the FP0-R is in compatibility mode, you can use FPWinPro 5 (or FP UpDown).  I found trying to switch between native and compatibility modes a little unpredictable.
  • So you can still download a large FP0 program without upgrading to FPWinPro V6 by first using V6.2 basic to set compatibility mode, and then using the older software to download the big program.
  • The second serial port is now much faster, with a maximum speed of 115200 bps, while the FP0’s topped out at 19200 bps.
  • The USB tool port worked smoothly.

January 15, 2011   No Comments

New Micro PLCs Go In Different Directions

It’s interesting to compare and contrast new micro PLCs from Siemens (S7-1200) and Panasonic (FP0-R).  Both are compelling upgrades from the previous series (Siemens S7-200, Panasonic FP0), but while Siemens adds Ethernet connectivity, Panasonic adds a USB port.

The FP0-R series looks like a direct replacement for the FP0, but with more: more memory, faster instructions, faster counters, and faster pulse outputs.  The biggest upgrade is a USB port, which is very nice: no custom programming cable required!  Or save some money: I like to use PLCs with two comm ports, one for communicating with the PC, and one for debug.  With the added USB port, I can use a PLC with one serial port, saving about $30, and use the USB port for debug.

I hope Panasonic has improved the USB port speed; I’ve heard that the FPX series uses an internal serial/USB bridge, so the USB port is limited to a wimpy 115,200 bps.

The FP0-R still isn’t as capable as the FPG (FP Sigma) series, but since it’s the same price as the FP0, I’m already looking at changing over from the FP0 to the FP0-R.

The Siemens S7-1200 models appear similar to the previous S7-200 models, but with more: more memory, more analog (even the base models have analog inputs), faster instructions, faster counters, more expansion (using signal boards) and faster pulse outputs.

What’s wonderful?  Siemens added an Ethernet port with Profinet and standard TCP/IP capabilities.  Networked devices are so much more convenient and useful than PC-connected USB devices.  For example, Profinet should make it simple and inexpensive to create a peer to peer PLC network, in addition to high speed communications to HMIs.  You have to add expensive networking modules to create a Panasonic PLC network.

The S7-1200 CPUs include other goodies, such as room for extra boards on the base CPU (for extra comm ports or wimpy (2DI/2DO or 1AO) I/O boards), 1M flash memory for extra (non-program) storage, and a proprietary memory slot.

Unfortunately, Siemen’s STEP7 Basic software currently only includes Relay Ladder Logic and Function Block programming; Panasonic’s FPWinPro supports all five IEC61131 languages, including my favorite: Structured Text.

Like the previous S7-200 series, base models have limited expansion: no signal modules for the 1211, 2 for the 1212, and 7 for the 1214.

The Panasonic FP0-R PLCs are much smaller; the transistor output models use high density box header connectors , while Siemens provides screw terminals.  I much prefer the box headers, since I can easily make a cable to a custom PCB breakout board.  It’s hard to wire directly with screw terminals without additional terminal blocks (for extra power and ground, etc).

The Panasonic FPX series are more like the S7-1200, since they also use screw terminals and provide room for plug in modules.

Excluding communications (USB vs Ethernet), the S7-1200, FP0-R, and FP-X are all similar in capabilities and price (IIRC, S7-1214 DC/DC/DC, FP0R-C32CT, and FPX-C30TD are all about $280, while the FP0R-C32T is about $245).

Which will I use?  I’d love to try out the S7-1200, but for my current projects the FP0-R and FPG are a better fit, since they support Structured Text and use box header connectors.

The S7-1200 is pretty close to a no-brainer if you need Ethernet:  Panasonic’s Ethernet module (FPWeb2; ~$430) alone costs more than a S7-1214 CPU; Automation Direct’s Ethernet modules start at $175, and you still have to add the PLC CPU.

I plan to write about this in more detail: I think micro PLCs are a great alternative to PC I/O options such as PCI boards from Advantech or USB modules from Measurement Computing.  The PLC’s cost the same or less for 24V I/Os, and have the advantage of being programmable — it’s nice to have the PLC handle some I/O, while the PC handles the rest via serial, USB, or Ethernet communications to the PLC.

Final notes:

  • Panasonic has gone backwards by not listing prices and requiring registration to download PDFs.
  • If you’re interested in the S7-1200, talk to your local distributor to see if they have a package deal.  For example, in Silicon Valley, E&M periodically offers 1 day introductions with a nice deal on the S7-1211.

October 29, 2009   2 Comments

Making a Panasonic PLC Programming Cable

I’ve added a section on my wiki describing how to make a serial cable to connect to the Panasonic FP0 or FP Sigma Programming Port. Later I hope to update it with more pictures.


FPG Programming Cable

July 16, 2008   6 Comments

Kudos to Panasonic

Update 5/14/2008 – Bad Panasonic! It looks like they’ve removed the list prices.  You can still get online pricing (from OnlineComponents and Allied Electronics), but it’s still stupid to remove the price list.  It was handy as a quick guide to what’s available and what it roughly costs (online searches aren’t as convenient).  By the way, local distributor pricing is often better than national catalog pricing.

I was looking at Panasonic Electric Works America’s website recently, and noticed that they now have links for suggested list price for most of their products; for example, FP Sigma PLC pricing. Note that actual prices through a distributor will typical be at least 10-20% less.

I like to have list prices, because I need to have an idea of what stuff will cost. I’m not concerned about every dollar, but it makes a big difference if a PLC is $500 or $3,000.


July 20, 2007   2 Comments