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Looking for a stepper motor driver for a spherical stepper motor.

Jonathan Navor
Expert 7815 points

Hi Team,

Good day! 

The stepper motor drivers are for bipolar stepper motors. It means that they are able to control 2 coils. For example these stepper motor drivers here.  Stepper motor driver products (ti.com)

However, the spherical stepper motor will have a minimum of 22 coils. Do you think I could use the drivers in series? Using the same microcontroller is enough? Would you recommend any specific microcontroller that can control the 11 drivers I need?

Kindly please help us with these customers' needs. Thank you in advance. 

Best regards,

Jonathan

  • 0
    TI__Mastermind 37683 points

    Hi Jonathan,

    Can you send us the datasheet of the spherical stepper motor. I personally have not seen a 22 coil stepper motor.

    Also, what is the voltage and current requirements of the motor?

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    TI__Expert 7815 points

    Hi Pablo,

    Customers need a high stepping. All the other parameters are flexible. They are building this spherical motor as part of the Ph.D. project so there is no datasheet

    Voltage 10-30V
    Current 0,5-3A
    My spherical stepper motor will look similar to the spherical stepper motor of the paper I attached, which has 30 coils.

    Simulation_of_rotation_behavior_of_a_14-12_spherical_motor.pdf

    Thank you.

    Best regards,

    Jonathan

  • 0 in reply to Jonathan Navor
    TI__Mastermind 37683 points

    Hi Jonathan,

    Thank you for providing the information.

    This is my first time seeing this type of motor. It is indeed very interesting. Another question I have which is not very clear in the paper is the timing requirements for each coil. In a standard two phase stepper motor, there is a 90 electrical degree phase shift between each winding current. How does this translate to a 30 coil motor? Will more than 2 coils be energized at the same time?

    Sorry for multiple questions but I want to understand how this motor operates and its requirements. It is indeed possible to use multiple motor drivers for controlling multiple coils at the same time but the main issue will be synchronization between the different motor drivers.

    Regards,

    Pablo Armet

  • 0 in reply to Pablo Armet
    Prodigy 60 points

    Hi Pablo,

    I appreciate your willingness to help me find the right driver.

    I've seen different approaches in papers. For example, some motors with PM-based rotors have alternating N and S polarities, and the rotor is spherical. So the current changes by 90 electrical degrees for the next step. In this case, all coils are energized (paper attached 1, fig 24). 

    Another approach I've seen is for reluctance-based rotors. In these cases, the rotor is a disc shape, and only a pair of coils are energized (paper attached 2). 

    There are a bunch of other configurations. Paper attached 3 shows a little comparison in fig 1. 

    But I am planning to have 2 pairs of coils energized each time. My rotor will have a disc shape (similar to the paper attached 2, fig 1. But it will be thinner). And the arrangement of the coils will be as shown in the paper attached 4, fig 3. 

    I need high precision for this spherical motor. I don't know if I will do it by increasing the number of coils or if micro-stepping is enough.

    Happy to know your opinion about using multiple drivers. Would you suggest a driver for it? And a microcontroller able to perform this synchronization between the multiple drivers?

    Regards,
    Thaisa

  • 0 in reply to Thaisa Kannen
    TI__Genius 17318 points

    Hey Thaisa,

    This seems like a very cool project.  

    I read through the 30-coil paper you posted and skimmed a few of the others.  It seems like no matter how you do it you will need a way to control which sets of stators / coils of wire have current going through them.  Unless you already have a proposed circuit diagram, I can think of two ways to achieve this: 

    1. A single stepper motor driver along with a MOSFET array that would allow you to control which stator(s) were connected to each motor phase.  You might only ever need 1-2 coils activated at a time just like a standard stepper motor, so you could just use 1 motor driver.  The FETs would allow you to select coil 20 and 21 to get current from motor driver output A, and leave all the other coils disconnected.  

    2. Multiple motor drivers, 1 phase per coil pair or 1 phase per coil.  This would give you the most control, as you could turn on as many coils as you wanted at one time, but I doubt the control sequence needs more than 2-4 coils at a time otherwise the motor would probably lock up.  

    3. Even though I know this is called a stepper motor, it's possible that it will be easier to accomplish this by using a half-bridge from a brushed DC motor driver for each phase.  This would be the equivalent of using a stepper motor driver in Full-Step mode (no microstepping).  This might be easier because instead of having to keep track of the % output of each driver or not-sending a step signal if you don't want to change, and instead you just control whether the half-bridge is forward, off, or reverse at the time.  You would need to have 1 full-bridge per coil, so you could use 30 drivers with 1 full bridge each, or 15 drivers with 2 full-bridges each, etc. 

    Like Pablo said, I think if you can give us a table like Table 7-4. Relative Current and Step Directions that would be very useful, without that we are just guessing on its operation.  

    On the microcontroller side of things I think your biggest concern either way will be the number of GPIOs.  You'll need to count up the number of control wires needed based on the control method you go with (SPI might help decrease this requirement) and then pick a microcontroller that can support that, or pick an external multiplexer or other slave device that can accomplish it.  

    Here are the links as IEEE, seems like your links above aren't working for some reason:

    Simulation and analysis of a novel PM spherical 3-DOF actuator with E-shaped stator and blade-shaped rotor structure

    Design and Analysis of a Novel Spherical Motor Based on the Principle of Reluctance

    Geometrical Equivalence Principle Based Modeling and Analysis for Monolayer Halbach Array Spherical Motor With Cubic Permanent Magnets

    Permanent magnet eddy current loss analysis of the permanent magnet spherical motor

  • 0 in reply to Jacob Thompson
    Prodigy 60 points

    Hey Jacob,

    Many thanks for your thoughts! It is very useful.

    About the table like the 7-4 you mentioned, I don't have this table. I understand it is the current for coils A and B for micro-stepping. My plan is to start with a full step, and then increase to micro-stepping. As I will be using 2 pairs of coils ON at a time, I guess I could use this table as a reference. Does it change your IC suggestion?

    Thanks,

    Thaisa

  • 0 in reply to Thaisa Kannen
    TI__Genius 17318 points

    Hey Thaisa,

    If you're only using 2 pairs of coils ON at a time I agree with using the table as a reference.  Doing that then it would probably be easiest to use 1 stepper motor driver that supports microstepping and then use an array of FETS/relays to choose which coil to control.  For flexibility I would pick a driver with fairly high current capabilities, such as the DRV8434A.  That seems more economical than buying and wiring a dozen stepper motor drivers in my opinion.  

    Edit:  You might want the DRV8434E instead.  The 8434A has an indexer for the stepping that might get in your way for such an experimental project.  The 8434E doesn't have the indexer and might work better when doing your initial testing.  

    Regards,

    Jacob Thompson

  • 0 in reply to Jacob Thompson
    Prodigy 60 points

    Hey Jacob,

    Thanks a lot for your suggestion!! This is very helpful.

    Regards, 

    Thaisa