Stepper Motor or Servo Motor, which one I need?

Using Arduino Motors, Mechanics, Power and CNC
1

Hi guys,
I'm trying to build a device that will have to turn a turntable for about 0.5 degrees at a time.

So far I tried the 5v 28BYJ-48 motor with ULN2003 controller, but it appears to be rather weak and inaccurate at taking small steps, especially with some load on top of it. It could turn by 0.5 degrees one time and for 1.5 another.

Second option is to get a 10v pancake motor like this one RC Dalys | Airsoft ginklai, radijo bangomis valdomi modeliai, dronai, jų dalys , but it is bigger and costs more.

Another option would be a servo motor, such as this one RC Dalys | Airsoft ginklai, radijo bangomis valdomi modeliai, dronai, jų dalys
Yet I'm quite new to servo's - any idea if I would be able to get to constantly turning for about 0.5-1 degrees?

Thanks. )

2

.5 deg is about the limit for discrete movements of a standard hobby type servo. I did a test and a standard hobby servo got ~426 discrete movements in ~190 deg of rotation. These types of servos usually have a ~5us dead band built in to keep them from hunting.

3

The steppermotor has a step of 1.8°. You would need a reduction gear to get to 0.5°.

Some People use brushless DC Motors to stabilize their camera hanging under a multicopter drone. It it supposed to be more accurate than servos.
Check out: brushless gimbal Controller at hobbyking.com to get an idea.

4

The steppermotor has a step of 1.8°. You would need a reduction gear to get to 0.5°.

Not really, I can use microsteps, which would supposedly reduce the minimal turning at least by half, to 0.9 degrees, which is fairly acceptable.

5

Doesn't that device have a 64-1 gear reduction output? - Scotty

6

Artem85:

The steppermotor has a step of 1.8°. You would need a reduction gear to get to 0.5°.

Not really, I can use microsteps, which would supposedly reduce the minimal turning at least by half, to 0.9 degrees, which is fairly acceptable.

Yes you can, and half steps are usually reliable. But be careful because torque drops with microstep size: Microstepping Myths and Realities | FAULHABER Tutorial You might want to look into 0.9 degree full step motors.

7

How fast does it need to turn? Perhaps a very low geared motor would work - like this for example Pololu Metal Gearmotors

...R

8

Some news ) bought a simple continuous rotation servo motor, played around with it and found it to be rather inaccurate when turning small angles.

 myservo.write(0);
  delay(10); 
 
 myservo.write(90);
  delay(1000);

Here it was supposed to turn for 10ms and then pause for a second. Sometimes it would turn for about 0.2 degrees, sometimes for about 2-3 degrees. So it's a write-off. (

How fast does it need to turn?

It needs to turn for a small fixed amount of degrees and then pause for a second.

You might want to look into 0.9 degree full step motors.

I already ordered the 1.8 deg. motor, but you're right. If it'll perform well, I'll get the 0.9 one.

Thanks. :slight_smile:

9

How big is this turntable? How much torque is needed to turn it/overcome friction?

10

MarkT:
How big is this turntable? How much torque is needed to turn it/overcome friction?

160mm in diameter, not sure about the friction, but should be able to turn 1-2 kg weight placed on the turntable.

11

How well this will work without gears will depend on the friction. You'll want design a system that keeps friction low. A lazy-susan-style arrangement should do you.

I've been doing some really fine positioning stuff recently and steppers certainly are capable of performing well at these tasks if the hardware is set up correctly. I've been driving a 0.9 degree stepper at 1/16th steps and there are certainly conditions when executes those motions correctly and reliably (I've measured it). Equally, if the load is too much then all bets are off. Getting this to work well is all about matching the stepper to the hardware and deciding in advance what speed and accuracy you need.

12

So far I tried the 5v 28BYJ-48 motor with ULN2003 controller, but it appears to be rather weak and inaccurate at taking small steps, especially with some load on top of it. It could turn by 0.5 degrees one time and for 1.5 anothe

I've never used one but that's surprising - are you sure it wasn't caused by the code or wrong wiring ? I expect them to be much more precise