The OpenServo Project

When it comes to using servos in projects, there is a definite distinction between the cheap ones and the expensive high power and precision models. The OpenServo project gives you a couple options for enhancing your servo experience. By replacing the control board with a new one based on a familiar microcontroller, a whole new set of features can be attained. For those of you out there with a need for servos like these, you can buy the pre-built replacement board (unfortunately sold out right now), or build your own from the provided schematic, BOM, and source code.

Comments

  1. Spork says:

    Cool hack. Very useful.

    I’ve been working on a stepper motor controller of my own, I like them better than servos. =]

  2. Scott says:

    This reminds me of the Commodore 64’s 1541 disk drive that had a 6502 chip in it – some programs would run using that processor’s capacity as well. There might be the potential for “distributed” operation here – servo acting not only as physical actuator but part of a networked system.

  3. rallen71366 says:

    @Spork – Ah, but servos drive CNC machines so nicely! Their smooth action, and high torque, impart such electromechanical sweetness, it makes my heart leap with joy! :)

    It’s the defining difference between a hobby class machine, and a professional piece of manufacturing equipment.

  4. Willrandship says:

    Stepper motors don’t twitch when you power them. that matters in CNC.

    I love both personally!

  5. zippy says:

    Stepper motors are sloooooooow and have no feedback, which is obviously important if your not taking girlyman cuts with your machine. Thats at least my preference

  6. Spork says:

    @rallen71366
    As Willrandship said the initial twitch is an issue for sub thousandth accuracy. I also find steppers to be far more accurate. That — and the Bridgeport mill that I have uses steppers not servos. Which is the de facto professional mill.

    Servos do have their place. Don’t get me wrong, I just use steppers more often.

  7. Andy Lippitt says:

    No power-on twitch with these guys. They boot with the H-bridges powered down and you can sample position without powering a position.

  8. svofski says:

    I really wish I could just buy a few of these, fully assembled or at least only the assembled boards. One of the reasons why my delta bot project has stalled indefinitely was, and still is, horrible servos. Powerful, but twitchy and lacking feedback.

    On a second note, I really wish RC servos would just die as a standard already.

  9. ken says:

    Spork: I agree completely – I had to check my mill to verify the power on twitch, which simply moves the machine to its power off position. Also, you have to spend big $$$ on servos to get high accuracy. Even then some drift is inevitable. The problem with steppers on production mills is lack of speed (also poor efficiency generates a lot of heat as they get bigger).

    I have a shelf full of second rate stepper controllers, and have switched to GeckoDrives for my CNC needs. My latest project, on the other hand, is very much in the hack-a-day spirit – a stepper motor and ULN2003 scavenged from an old printer driven by an MSP430. Trapezoidal micro stepping is working perfectly for this low speed, low power, but high accuracy design.

  10. Ive got one of these waiting for me to play with.
    What impressed me was the idea of having them on one bus and the feedback from the controller by sending a command and receiving the result over the bus.

    Its a pity its not small enough to fit in a micro servo.

  11. MRE says:

    I dont know what you guys are talking about. Most, if not all industrial grade servos (plus three inches in size) are actually stepper motors. They use quadrature feedback using disk tech much like a tiny cd. With good drives, microstepping is simple. They have incredible torque per motor weight and size. Ive worked on built machines that could sling 300 pounds of weight straight vertical at half a meter per second and land not on a dime, but on the wings of a fly.
    The stepper servo in that machine was about five pounds, 3x3x6 inches attached to a 3/4 inch ball bearing leadscrew, with two threads per inch.

    I dont know your idea of what classifies industrial grade, but certainly not the same as mine.

    Those were mitsubishi drives by the way… couple hundred usd.
    Futaba hobby servos and oversized printer steppers are not even in the same league.

  12. mosheen says:

    The only difference between a industrial stepper and servo is the rotary encoder on the servo.

  13. ken says:

    mosheen: Steppers and servers are very different beasts, though they can serve the same purpose. Steppers operate synchronously, generally at maximum torque. Servos constantly seek their position using feedback instead of synchronous signals. Servos often use DC motors, which can’t be controlled synchronously, even if you wanted to. Brushless servos are also common – these use three phase DC brushless motors. Steppers are typically 2 phase.

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