Eva Robotics' EvoDrive ST-23 hands-on

[Nefastor]

Hi everyone,

I'm the happy owner of three EvoDrive ST-23 servomotors. In case you don't know these motors and Google has gone bankrupt, here's a link to the manufacturer :

EvoDrive ST-23 Integrated Stepper Servo

I'm starting this thread to talk about my experience with these very interesting motors. To give you some context, I'm an embedded systems expert with an emphasis on electronics and motion control. I also built two milling machines so far, both operational, of which you'll see photos very soon.

Also, I'm a frenchy, so please forgive any poor english and if you have doubts about something I said, don't hesitate to ask me to rephrase

Jean

[Nefastor]

When I designed my first machine tools, I used pretty much what was handy. That meant the stepper motors came from "ye olde electronics shoppe" and with little information beyond amperage, max torque and stator inductance.

Very soon I became a speed demon : I live in an appartment building, so if I'm going to make noise with a machine tool the faster the cutting is done, the less likely the neighbors will come banging at the door. I also like the idea of cutting fast and without any coolant or lubricant, because it's a lot cleaner. And it just looks damn cool

Eventually I reached the limits of what my machines could do. One important problem was midband resonance. I installed viscous dampers but it didn't help where I thought it would. And Gecko stepper drivers aren't sold in France. So I had to invest in a better solution.

Brushless AC servos were my first choice. They are known to have no midband resonance and are very fast. They are also very expensive. After some Googling, I found out about the EvoDrive solution : a stepper motor driven like a brushless AC servo, complete with encoder and integrated closed-loop driver.

At the moment, the largest unit is based on a NEMA-23 frame motor (the ST-23), and plans are being drawn for a NEMA-34 unit.

Jean

[Nefastor]

Matt Alder, Eva Robotics' Managing Director, immediately took interest in why I was ordering EvoDrives and offered very useful advice.

This is the sort of behavior I'm used to at work, when I order a few hundred servo motors costing several thousand dollars each. This is what separates "ye olde electronics shoppe", where stepper motors come with loose wires tied into a knot and scratched bodies, from people like Harmonic Drive : deep knowledge of the product they sell and a drive to ensure their products won't end-up shelved in a dark corner of their clients' warehouses.

Also, this is what explains the price difference between your typical servo and your typical stepper motor.

Speaking of getting what you pay for, Eva Robotics ships its motors in very nice boxes with foam in every direction : even though they ship from Australia, rest assured the motors will get to you in one piece. Opening the box feels more like opening the box of your new iPad than opening a scotch-tape covered cardbox filled with packing peanuts and loose equipment. The ST-23's even had "that new smell" we're all addicted to. Or perhaps that was a wiff of Australian air stuck into the box ? I live in Paris after all, it's a miracle I don't have to wear a gas mask. Most days.

Servos are notoriously harder to use than steppers by one or two orders of magnitude and the ST-23 is no exception... but at least you can test them out of the box in minutes. All it takes is a USB cable, a power supply and a little Windows application that comes with your motors. This will allow you to toy with gauges for speed, torque, position, acceleration and you can start tweaking the PID and parameters to your heart's content.

First thing that will strike you is the noise. What little noise the ST-23 makes is entirely different from anything you've ever heard a stepper sing. Don't worry, it's not broken.

Jean

[Nefastor]

Like I said, using servos is harder than using steppers. Do it wrong and you'll wonder why you've spent so much to end-up with a machine-tool that can't even cut in a straight line. Do it right, and you'll undestand why all the serious machine-tool manufacturers, the Mori Seiki of this world, don't know what a stepper motor is.

The ST-23 is both easier and harder to use than a regular servo : it's easier because it's well-integrated and full of features and it's harder because it's a unique technology (a vector drive stepper motor) which means any experience you have using servos may need revising.

Since I've been playing with a set of ST-23's since last July, I thought I'd share my experience with you and also answer any questions you might have. There aren't many posts on the EvoDrive on CNC Zone and I think they deserve more attention.

I'm a very busy guy, however I'll do my best over the coming weeks (and months) to grow this thread. Setting up the EvoDrive takes many parameters, almost none of which can be understood intuitively in terms of their impact on machine-tool cutting performance. So my plan is to equip a small DIY milling machine with three ST-23's, write a small machining program, and cut it many times over while changing one parameter at a time. This will be shot on video and posted on your favorite viral video website. It should give you a good idea of what to expect and how to fix your servo setup if you encounter an unexpected bump in the road. It might help you even if your servos aren't from the land of kangaroos and koala bears

I won't spend a lot of time on how to integrate the ST-23 in your machine tool because it's dead easy. They are NEMA-23 motors with electronics at the back, and you can wire them directly to your CNC controller, such as a parallel port break-out board. They even have programmable I/O (a typical servo feature) that you can use for emergency stops and error outputs, and even to wire limit and zero switches. It's way easier than using stepper motors. If you can't figure out how to do it, chances are you're on the wrong forum and you should leave before you hurt yourself

One thing of note, though : the ST-23 is configured through a serial port (RS232 or RS485) or USB. The default application provided by Eva Robotics requires a recent operating system and software packages that you might not want to run on the PC which also runs your machine tool. In fact, I've tried it and it didn't work. Until a lighter application is released (something I submitted to Eva Robotics) I'm afraid you'll need to use two different PC's to setup your machine-tool. You can also program your own, it's easier than it sounds. However there are good news : once your servos are setup to your satisfaction, this second PC is no longer necessary.

Jean

[Nefastor]

For the upcoming ST-23 demonstrations I'll be using my very first DIY CNC mill. The photos will come soon but here's what's better said than shown :

The "ultralight" mill was built using DIY shop aluminum extrusion. Essentially, it's square aluminum tubing 23.5mm by 23.5mm, with about 1mm wall thickness. I chose this material for three reasons : it was cheap and easy to come by in any amount I wanted, it is easy to cut using an angle grinder (which I do on my balcony) and it has nice patterns of pre-drilled holes in interesting shapes on all its sides.

The linear guides are generic metallic ball-bearing drawer slides, the kind your desk drawers might use. These are insanely cheap, very efficient and remarkably straight, however they tend to flex when pressed on from above. Given the fact I always intended to cut fast and shallow, I didn't feel it'd be a huge problem, and it wasn't.

Linear motion is achieved using ACME M8 threaded rods (stainless steel) and captive bolts. This means the screws have a 1.25mm lead.

Motor shaft couplers were made from rubber tubing, a solution that worked surprisingly well. Given the very light forces involved, no thrust bearings are used, only the motors' bearings. Don't try this at home

The spindle is a Bosch professional straight grinder capable of 30,000 RPM. Before the ST-23's were installed, this grinder was pretty much more expensive than the rest of the machine-tool.

The control PC is a 6 years old machine and uses a native parallel port and Mach 3 under Windows XP 32-bit. For the CPU geeks out there it's an Athlon XP 2500+ machine. Your average smartphone is more powerful than that.

This machine-tool is a proven design, it was used for over a year with NEMA 23 stepper motors and cut dozens of complex MDF parts that were used to help make its successor. It was also used for my first tests in dry-cutting aluminum. Then I mothballed it because its successor is massively better (we're talking 25mm ballscrews and Hiwin rails, brushless spindle, SmoothStepper and NEMA34 motors, and a top feed rate of 2.5 meters per minute. And I'm far from done improving it)

It made sense to use this very light machine for a number of reasons. First, it was sitting there collecting dust. Second, swapping the steppers with the ST-23 took about 5 minutes, 3 of which wasted searching for the right wrench.

Finally, it's such a nice machine design, that now that I have ST-23's I have every intention to build a new, identical machine based on this design, but with 10mm-lead ballscrews and every high-quality component I can fit in my budget. Assuming the results of initial testing on this mill satisfy me 100% of course.

And there you have it : this thread is actually self-serving sorry, I'm not the altruistic type

Jean

[luis.gm]

Hi Jean,

I actually found their website some minutes ago and I am impressed with some of the videos they show.

I have not had the opportunity to try them but they seem to perform formidable, and I am thinking on getting myself one of these to play a little bit.

What happened with your project, any nice news?, would love to hear more of your work with these motors.

Kind regards,

lg

[Nefastor]

Hi Luis,

I got the notification for your reply litteraly as I was going to bed so this will be a short answer... to tell you you're in luck.

To keep it short, I stopped posting in this thread due to the apparent lack of interest of the community, and intended to move my prose to a blog (that's going to happen this month)

As for the ST-23's, they ended up not being strong enough for the machine I bought them for (it did require NEMA 34 strength) but they found a home on a smaller machine where they are doing more than fine. Still, in terms of power, the ST-23 is better than your typical frame 23 motor, which is why I tried them.

I'm not only used to working with ST-23's and servos in general, I also like to share. If you're OK with it, we'll go through your intended application(s) and I'll tell you which kind of EvaRobotics product will work best (if any does : I'm not an EvaRobotics salesman :-)

I'll also show you a video of my own mill running ST-23's so you can hear them work. It's not online yet.

So, what kind of project do you have in mind ?

Jean

[luis.gm]

Hi Jean,

I want to tell you that I really enjoyed reading about your evoadventure so if you make a blog dont forget to let me know and I would really like to see the video you mentioned.

Well to be honest I don't have a specific project in mind but usually thats not really a problem, i love to think about something and just do it, so for me its very interesting to experiment, its kile a hobby hehe, and therefore I am interested in testing these drives.

Have you had the chance to try the dspDrive technology from nanotec? i have seen that steppert with them run also quiet and fast but no chance to get a comparison with the evodrive stepper.

Best!
luis

[Nefastor]

Ah, a fellow tinkerer*! It seems we’re both alike, me I tend to «*freehand*» my projects until I get a good feeling, then I commit to an actual engineering process (usually the trusty old V cycle). It’s a tactile process, so I have tons of thingamabobs and doodads lying on shelves. I get to learn about their technology, let all the information percolate in my brain, and eventually everything finds its use.

For that way of working, you will love the ST-23's flexibility. I don’t know if you’ve used servos before but they aren’t simple motors : by virtue of their integrated processing power they let you customize their operation. I’m not just talking about drive parameters, but actual motion programming. It’s as if you have a small industrial PLC glued to your motor.

Let me give you a CNC-related example : the ST-23 can be programmed to stop moving in case of a fault. For instance if you hit the mechanical limit on an axis and the motor doesn’t have enough torque to break everything.

You can program the ST-23 so that, when this type of event occurs, it will set a discrete output to “0” and leave it to “1” when everything is fine. You can also program the ST-23 so that it will not move if one of its discrete inputs is at “0”.

What this allows you to do, is stop all your motors when any one motor has a problem, using little more than wires. And you also get a signal to feed back to your controller.

You can also use these programmable I/O lines to install limit switches, for example.

There’s also the serial ports : through them, you can control the motor but also retrieve information like speed, torque and position. And of course you can change every parameter you want. This can be done with a good old 8-bit microcontroller if you want. As a matter of fact there's something called the EvoDuino you might want to look at.

Whatever your application, I’m sure you’ll find a use for this kind of programmability.

Every servo on the market has similar features and as they go, the ST-23’s aren’t very advanced, but the point wasn’t to completely eliminate all the control logic from your machine. The way I see it, this just gives you some room to experiment, which is very welcome when you’re trying to add features to a machine or fix something you forgot.

And in terms of price / feature ratio, the ST-23 is a nice deal. Most features you'd find on high-end servos you'd never use anyway, just like no one uses more than 10% of Word or Excel's capabilities. So why pay for it ?

To answer your question, I do get the spam from Nanotec at work. I have never used their products, somehow I either need motors of several kilowatts or a few watts, but nothing in between. Perhaps someday there’ll be an opportunity. However I’m pretty sure their closed loop steppers will be more expensive than an ST-23, based solely on the fact that Nanotec is bound to have higher overhead costs than a small outfit like EvaRobotics. Same way an OrientalMotor stepper motor will cost three or four times as much as a similar motor from a DIY CNC shop. Doesn’t mean it’s going to be three or four times better.

At any rate, should I come across a comparable servo system, I'll make a comparative study.

Regarding my blog, it’s more than likely that once I’m ready I’ll insert the link in my CNC Zone signature. Keep reading, it’ll pop up eventually.

Can you tell me more about you ? On which side of the planet do you live ? I'm from Paris, France. When I'm not in my lab you can usually find me at a hackerspace.

Take care,

Jean

[luis.gm]

Hi Jean!

Wanted to reply you earlier but i found myself several times mega late at night, but here I am.

We are neighbors, im living in Germany, not that far uh? thinking about how big the world is.

Regarding the Evodrives well, for me, part of their simplicity to use and implement them is also their attractiveness. In my case i am looking for something that can be easily mounted, controlled, adapted to differend projects and kind of flexible to play with, and if it can be conected to a PC or PLC to interact in a simple way with it, its simply at the moment more than enough.

I know that servos are not easy, and also expensive, so i would also only go for them if an application really requires them, but at the moment i feel confortable with steppers, and it seems that Eva Robotics have an ace up the sleeve with the Evodrive, so im really curious to see how the they work, I made my order and should come in the next days so soon I will have a chance to try them. I am really excited about it.

Im also very interested on seeing your comparative with servos, that is gonna be a good one! of course when you have time to make it, and im also hoping to see your blog, whatever first happens.

Let me know if u have any updates!
All the best!

lg

[Nefastor]

Don't worry, I know how it is. We tinkerers always have too many things to do and not enough time to do it. I haven't had much time to work on my blog this week, it doesn't even have photos yet :-)

Glad to hear you've ordered the ST-23. They are nice toys and the more you tell me, the more I know you'll enjoy playing with them.

For instance, you were talking about adapting it to different projects : I'haven't had to do it yet but I believe the configuration software allows you to save your motor settings into a file.

Yes, the world is very small now thanks to the internet :-) Look at us, buying motors from Australia !

I'm a bit swamped with work right now but let's keep in touch, OK ? If you hit a snag with the servos, don't hesitate to ask me, chances are I found a solution.

I will be building a custom RepRap soon, it will probably use the ST-23. I'll keep you posted.

Take care !

Jean

[luis.gm]

Hi Jean,

Its been a while but we are still here, hows it going over there.

Here I have had lots of work soo.. did not have too much time to play with the evos, but I did try them and they feel reeaaally good, and smoothh.

What about you and your projects? did you finish your blog? i am really looking forward to have a look into it and of course to see your mill! that is a must!

Hope you are doing good!, keep me updated of the moves you make.

Kind regards,
lg