difference between "industrial" servo motors and RC servo motors ?

Wikipedia isn't a bad place to start.

Note the mention of positional control. This applies to RC servos AND servos used for motion control and other industrial applications. The position may span only a few degrees for RC, and thousands of degrees for motion control. Obviously 10,000 degrees means multiple rotations of the shaft, but the idea is the same.

-- Gordon

pogo wrote:

There are different ways to build/design/tune motors. The cheapest way to build a high efficiency motor will result in a fast spinning, low torque motor. This is not suitable for positioning tasks, which generally require low speeds and high torques. Thus, industrial servo motors use expensive magnets and such to achieve high torques at low speeds, in contrast with general industrial motors which are better tuned for continuous rotation.

Hobby servo motors are a whole different beast. They use relatively cheap, high-speed motors; but they compensate for low motor torque with a high gear ratio at the cost of low speeds and high friction. This tradeoff is fine in most hobby equipment, but isn't acceptable for many industrial tasks. For example, the productivity of a pick&place robot arm is directly related to how fast it can move, and high friction may lead to heat problems.

For a wow factor, these are the most expensive motors I know of:

I found these for a walking robot project, but we selected different motors after we got a price quote: over $30k each for a mid-range model! Somebody must have a good use for them. We didn't get a quote, but the last motor on the datasheet weighs 1400 pounds and draws over 6 kilowatts. I've heard similar motors are used to drive tank turrets.

Back on topic, a servo motor is just a motor with a position-feedback controller attached.

Later, Daniel

Hmmm. Good info as usual guys - thanks !

So do Industrial servos still use the same PWM that hobby servos use ? Could something like a Scott Edwards SSC be used to control a big industrial servo motor (with appropriate power connections, of course).

Evolution Robotic's high priced Scopion robot uses servo motors instead of the steppers the ER1 came with. Why would they choose that over lower priced straight DC motors + speed controller ?

Thanks !

No; not without adding significant sensor and amplifier circuitry. Hobby servos use PWM to specify the target position of the motor. The servo motor has a built-in sensor (potentiometer) and controller (analog timer circuit) to move the motor to the desired position. An industrial servo motor is just a motor - no sensor or controller.

Industrial servo controllers generally have embedded processors and use digital position commands. Totally different than hobby servos. Here are some links to industrial controllers (I have no experience with these products).

No idea. Maybe they wanted higher torque and more precise position control?

Daniel

No, the Scott Edwards SSC is not a motor controller. It's a format converter between RS-232 and the pulse width modulated signal used for R/C servo control.

A real DC servomotor controller designed for hobbyists is this one, from Active Robots:

A more powerful controller is this one, from Roboteq:

Motor controllers usually require an encoder for feedback. Encoders are simple, overpriced devices; every mechanical mouse has two, but the industrial ones cost more than ten mice. For somewhat silly historical reasons, encoders aren't usually integrated into the motor housing; they're usually an extra box on the shaft.

It's possible to control a DC servomotor with nothing but a pot as feedback. This is rarely done, but I've done it using a Galil motor controller and a 24VDC screw-jack type actuator. This isn't for precise positioning, but it's how we shifted the gearbox on the Overbot.

John Nagle

Hmmm ... I plan on using a couple of Globe IM-15 motors with HEDS encoders, and controlled by Devantech MD22 or 2 MD03s. Could these motors be considered as "servo motors" then ?

See:

Thanks again. I'm learning a lot from this group!

You've got 3/4s of a servo motor there. With motor and encoder and H-bridge (sometimes called amplifier) you have 3 out of 4 necessary components. You need something to close the loop to make the "servo" complete. That will usually be some electronics that responds to the error in desired/commanded position and applies a signal to the amplipher (or H-bridge) to minimize the error. But until then, you've just got an open loop encoded motor.

So, when I (appropriately) hook up the encoders to my processor of choice, and then have that drive the H-bridge, I have a servo ! Right ?

Yes.

Infact an RC Servo is a Servo because it has a position pot for feedback, a motor, a driving bridge, and electronics that close the loop. The key thing is the closed loop, that makes it a servo.

Thanks! I think I got it now ... I was getting too hung up on symantecs, I think. Thanks again.