About

Avayan is an avid electronics enthusiast. It may be his full time job, but that is not enough; instead he spends a great deal of his spare time working at home on his electronics lab, designing and assembling motor drives, as well as some robotic contraptions. Always learning from other roboticists, still Avayan has some information to offer to the robot hobbyist. Take advantage of this humble pool of information on how to get into robotics and enjoy from such an exciting field!!!

EBLDC is about Brushless Motors and the cool projects you can build with them. For the most part, BLDC stands for Brushless DC motor, with the three phase BLDC being the most popular version as of this writing. A stepper, on the other hand, is hardly ever known for being a brushless motor. As it turns out, though, it is! But if you open any stepper – bipolar or unipolar; two phase, three phase, four phase, or five phase –ย only to find brushes inside, be certain to let us know and we will change our stand ๐Ÿ˜‰

9 comments for “About

  1. Mladen Radolovic
    September 6, 2014 at 10:26 pm

    Hi Avayan!

    I need your help to make my final decision..
    Here you can see how my new project looks roughly (please download the file first and then open it):

    https://dl.dropboxusercontent.com/u/70391886/box.mp4

    The basic idea is to replace the deck with one another deck with rotational mechanism. It would be a magic robotic box.

    Please see the attached this picture. This is the side view of my design.
    R1 = Distance from the center point to the edge of Cradle
    R2 = Distance from the center point to the edge of Platform
    Center point of R1 and R2 should be same.
    Thickness of gap = R2-R1

    https://dl.dropboxusercontent.com/u/70391886/finale3.jpg

    I have to use a timing pulley on the motor and one on the deck shaft, connect these two with matching timing belt.
    I can hide the timing pulley from the deck shaft in the side of the box.

    Requirements for the motor:

    constant speed
    really accurate (200 steps/rev or 400 steps/rev)
    very quiet
    powerful enough (Holding Torque)

    People on the forum recommend me this stepper motor:
    https://www.sparkfun.com/products/10846
    and
    Adafruit Motor Shield V2 or Pololu DRV8825

    The “cradle” with decks of cards will most likely be made ??of wood or metal..

    What is your opinion about it?

    Best,
    Mladen

    • avayan
      September 8, 2014 at 11:44 pm

      Hi Mladen,

      This should be pretty easy for any stepper. The load is so tiny, you do not need anything tremendously complex to make it work.

      The holding torque on most steppers should be more than sufficient for this application, as the load is quite small.

      Controlling the speed to be continuous is piece of cake. Often you would want to have an acceleration profile, but chances are you do not need one here.

      The accuracy is also not a problem. Because the load is so small, chances are you will never lose steps. In this case, once you know how many steps you need to reach a position, all you need to do is count the steps on both directions and the deck will always land on the position it is supposed to.

      From all of these requirements, the one that worries me the most is the noise issue. Steppers are by definition quite noisy. You will need huge amounts of microstepping to make this completely noiseless. I once did a design with 1024 degrees of microstepping and this thing was completely silent. I couldn’t even see it moving! I would still give it a try in case your box could work as a noise shield of some kind. But the only way to know is by trying.

      Like I said, from the 4 requirements the only one that worries me is the sound related one. The other 3 are piece of cake!

      Good luck on this cool project!

      Unfortunately, the DRV8825 will be everything but silent. You may be able to trick older folks, but any teenager will immediately sense the high pitch squeal which characterizes the DRV8825.

  2. Aidan Phillips
    August 3, 2015 at 1:38 am

    Hello, love the projects on your website! I’m starting a new project, perhaps you’ve seen then on the web. It’s a vertical draw/plotting bot that uses two steppers, gravity and a pen chasis.

    In building the driver electronics i don’t want to buy an all-in-one chip. I’d like to learn as much as possible throughout the project, while keeping on a reasonable time line. For this reason I want to attack the stepper motor driver on a modular chip level. I thought about using lower level components even, but it would throw me way off my intended finish date. But segregating different functions to different chips will make it fun to design my own software architecture and probe around with a scope.

    I’d like to microstep to 1/8 on a constant current chopper drive.

    my load will require be about 16-25 ozin of torque. Since microstepping will quickly bring down my torque to overcome load friction, i’ve chosen a bipolar stepper rated for 51ozin. I took into account my low speed and microstep size to get that hold torque rating. Might be a bit overkill, but if i do plan to microstep down to 1/8th it’ll be on the money. I chose a .9 deg/step res, because in my application, the higher res the better. It’s rated for 9A/phase. I won’t need to run at more than 60rpm.

    Here’s the motor i want to use”
    http://www.omc-stepperonline.com/9deg-nema-17-bipolar-stepper-motor-09a-36ncm51ozin-17hm150904s-p-267.html

    and here’s my current driver plan
    disclaimer, The picture of my eagle schematic is a very rough draft, mainly a block diagram, chips will change, and values haven’t really been put inn yet.

    https://www.flickr.com/photos/99469359@N03/20210392046/in/dateposted-public/

    I want to put about 8 times the voltage that will get me .9A/phase through the chopper driver for good ramp times. This means about 45 volts.

    The driver starts with a dual DAC that will get signals for an arduino. It will follow the sin/cosin drive patterns, and my lookup tables will be in the code for me to switch resolutions. Then that stage moves to a voltage comparator that compares the DAC value with the current sense value of my *classic* L298n dual full bridges. The diodes on the phases will be fast switching schottkys.

    I wanted to know what you thought about this design. Do you see any foreseeable issues with my attack strat. on the driver?

    Will the L298n handle the the high switching times that microstepping requires? (I know it’s dependent on my speed and resolution, but just to gain a note of feasibility. A lot of people say the L298 is so ancient and all, but I can’t find anything in the data sheet that says it wont stand up to microstepping.

    What kind of power supply do i need to handle the inductive load that get pushed through those flyback diodes?

    Thanks for any time you give to my questions.

    Aidan

    • avayan
      August 4, 2015 at 7:49 pm

      Hi Aidan,

      Thanks for checking my blog! Looks like your project will be an excellent way to get into knowing steppers from a deeper standpoint. I have seen these printers and it is just amazing how awesome their output is!

      As others have pointed out, L298 is rather dated. I would have used some other dual H Bridge with N Channel FETs, but for learning L298 should do. Now, let me bring a few items into the light and then you can determine whether you want to continue with the L298 or try something else.

      1. After reading your very detailed description (thank you for that!), my main concern is the operating voltage and the selected power stage. You plan on using 45V but that is going to be quite deadly for the L298, which has an Abs Max of 50V. The problem is that when you use a power supply voltage of X volts, you should use a power stage capable of handling at least 2X volts. Why? Well, because voltage transients caused by speed changes and current recirculation, will most likely increase the application’s rail voltage. If your power stage can take 2X, then you have enough head room to survive most transients. Do note, that to be able to call an application reliable and robust, 3X is often used! It may seem like overkill, but if your motor is going very fast and all of a sudden something stops it (for whatever reason!), all the energy inside of the winding (e.g. the motor’s BEMF) will go into the power supply, rising the application’s rail voltage and killing the power stage, in this case the L298.

      2. On the other hand, I don’t see why you would need to use 45V. In fact, I am positive you will not need to. You are right on stating that the higher the voltage, the faster you can charge the winding. However, what this gives you is the ability to go faster and it seems to me your maximum speed is rather low. At 60 RPM, you will dealing with 1 Rev per second. Since this is a 0.9 degree per step stepper, you will need 400 full steps to do 1 revolution. Hence, your step rate is 400 full steps per second. It would be nice to get a torque/speed curve to see what kind of torque you get at this speed, but I feel pretty confident that at 24V and 0.9A, you should be able to easily reach this speed without too much torque loss. Increasing the voltage would slightly increase the available torque at this speed, but then you would be too close to the device’s Abs Max.

      As a result, I think it would be a very good compromise to run this application at 24V, 400 SPS (Full Steps Per Second) and 0.9A. If you were trying to approach 1000 SPS, then I would be worried as this is the point where most steppers start to crap out madly. Do note, however, that I am basing these claims on 99% of my experience which is 200 Steps/Rev steppers (1.8 degrees). It is always possible the 400 Steps/Rev steppers can’t go as fast as the 200 counterparts. Usually, the more steps per revolution, the slower they go. This is just the name of the game, I am afraid. But each motor is unique, so this is not necessarily a law. And just because they have two times the number of poles does not mean they can only move at half the speed.

      3. Another concern that I would have, which I didn’t read you mentioning, would be the switching frequency. You talk about “high switching times that microstepping requires”, so I am going to assume you meant high switching frequencies. In essence, you want a switching frequency which is higher than 20 KHz, but not too high as to increase switching losses. I understand these implications very well for FETs but not so much for BJT’s. But since the L298 can go to as much as 40 KHz, I am thinking you should be fine. Do keep this topic in mind for when the time comes, because switching frequencies become problematic if they are too large. And you will not want anything less than 20 KHz because then you start hearing high pitch noises which are quite annoying.

      4. The fact that we need to add diodes is one of the reasons why I would try to stay away from the L298. There is a bunch of devices out there which have the diodes internal so this is something you would not need to worry about. But, since you want to learn and this is a good area to experiment, make sure the diodes switch as fast as possible! I do not know how much dead time the L298 has, but basically during dead time, the diode will take the current. If the diode is not fast enough, voltage may spike to dangerous levels. If the diodes are not there, chances are the device will go Bye Bye! Like I said, this would be a good area to play with and see different voltage responses at the outputs.

      5. You ask what kind of power supply you will need. Pretty much any power supply should do. I have heard there are power supplies that do not like to sink current. I am not certain which PS topology would these be, but if you have good electrolytic capacitance at the input, chances are you will not have to worry about this as the caps will take the hit. I will try to see which PS topology is the one you do not want to use, although I don’t think there are too many of these left out there.

      Hope the info helps!

      • Aidan Phillips
        August 4, 2015 at 11:44 pm

        First of all, I’m genuinely touched that you’d take the time to help me out with some of your knowledge. It really feels good, and i really do appreciate it. And i do have some questions in response!

        First of all, I am totally open to changing to a better full bridge system with CMOS and in-bedded diodes; I’m all in favor of maximum efficiency(except no all in one chips!) . I’d love to hear your recommendation. However, I’d still like to perform the current sensing outside of the bridge chip (with the comparator).

        Secondly, I’m under the impression that my switching frequency would be mainly controlled by the physical properties of the coil (inductance and resistance) as well as my applied voltage. The comparator would disable the fullbridge as soon as the phase current goes over the stepped sinwave current level, thereby chopping the current. So in my mind it’s these waves that are setting the frequency, and it would only change with a different applied voltage/current ramp time.

        Thirdly, I just wanted to know if you think this modular chip system can get me to 1/8 microstepping ability. Does the the comparator/DAC system make sense to you? I’m sure i could try analog reads from a microcontroller and compare the current to the stepped sin/cos wave values in the code before turning on and off my full bridge, but it seems like it would be nice to have the functionality on an external chip level. I mainly followed the block diagram on the webpage below.

        http://motion.schneider-electric.com/technology-blog/bipolar-chopper-drive-circuit/

        What other concerns would i have starting at a low level like this? People are very up in arms about me trying to do this when i ask questions about it. For my application, approaching it with multiple chips seems pritty doable.

        I look forward to hearing from you, thanks so much!!!! If this is the wrong place to ask questions, and you prefer email, just let me know.

  3. Geo
    January 7, 2016 at 5:35 pm

    Hai,
    I have one application. I need to use the stepper motor. I need to make laser show using stepper motor. Notmally galvomotor will work for that. If you have any idea about these. Please let me know. How it is possible… I need circle

    • avayan
      January 8, 2016 at 12:38 am

      Hi,

      Thanks for checking my blog! I like your project, but I must admit I find it hard to accomplish. Is it impossible? Of course not! But the problem is that steppers can’t move very fast, which I think is a crucial aspect of motion controlled laser shows. Let me tell you how it works with a Galvo and you will see which are the challenges which need to be overcome.

      A galvo is in essence very similar to that electric motor which is used on analog multimeters (AKA the d’Arsonval movement), except that this actuator is made to oscillate at pretty darn fast speeds. In other words, it goes back and forth (left to right and then right to left) many times per second. In order to make this work without the system blowing into pieces, the system must operate on a closed loop endeavor. I could be mistaken on this assessment, but the idea is that the system always knows where the mirror is pointing to and then a “video” signal, which is nothing other than whether the LASER is ON or OFF, bounces of the mirror and the image is drawn.

      I can’t think of how to do this with a stepper on open loop because steppers are just too slow. That is what they are good at, moving slow! Albeit not too slow…

      The only shred of inspiration which I can summon would be to transform the stepper into a servo but if you dare to look into that no doubt you will end up trying the galvo. Steppers as servo are doable but rest assured they are not easy at all. To make matters worse, it may not work because they have too many poles! But if you want to try it, I would go for a low step count unipolar stepper as opposed to a high step count bipolar stepper.

      Another way would be to use a BLDC motor but this too would need to be done on a Servo fashion. You would need to know where the motor is at all times and then apply your video signal accordingly. Now, a circle is quite forgiving so you may not need the ultimate in closed loops. You may be able to just swing it and even if it is out of sync it will simply rotate but who can possibly see that? It’s a circle!

      I wish you luck on your endeavors! This is definitely quite the exciting project!

  4. Effy
    January 19, 2016 at 12:11 pm

    Hey, I just found your site for the first time, looking for the difference between slow and fast decay in stepper motors.

    I have an unsolicited design tip for you: make the sidebar on the right narrower. It looks like your site is split now 50/50. There’s very little on the right side, and all the main content is stuffed onto the left. I would reallocate the space to something like 75/25. Take it or leave it ๐Ÿ™‚

    • avayan
      January 19, 2016 at 3:05 pm

      Well, first of all thanks for visiting this web site and second, mega-thanks for pointing me into this ridiculous blunder on my behalf. I think it looks way better now, so again, thanks for the heads up!

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