Stepper motors -> how to power them properly?

[Shaare]

Presumably you are aware that you can't just replace the servos with steppers?, either electrically or mechanically - servos are absolute devices (you tell it to go to point A, and it goes there and stays there). Steppers are 'relative', you tell it to go so many steps from where it currently is, and in what direction, and it will attempt to do so - but you've no idea if it actually made it or not. A servo will get there, or at least keep trying to do so - a stepper will simply make an attempt, and has no idea if it succeeded or not.

I'm presuming you're just wanting to use the steppers on their own, with no additional gearing?, and no kind of external positioning feedback - it's likely to considerably inferior to servos in that case.

Hi Nigel,

Thank you for your input.
My son and I have learned a lot just reading the comments here!

One thing I learned is the need to have the stepper go through a reset mechanism so it knows where's the start. That is for a later google. My son wants to build a precision robotic arm, he is learning openCV right now. So that means he'll likely use his raspberryPi for that and feed the arduino what to move if the pi can't handle all the sensors. My role is more as a debugger, I have programming experience so I help him out when he's really stuck and introduce him to what I learn on what he's interested in. I started my vacation and this year its a staycation so I'll be reading up a lot on steppers so as to maximize his learning experience.

Since we couldn't get the steppers off to a start right away, I bought him servos so he can at least make it and keep his interest alive.

For the steppers I'll need to get him to think of ways to create that gate to reset the stepper or tell it where's 0 so to speak (and I'll look into this myself!) then the power so what I have is 0.4 amps so with 4 coils this means 1.6 amps so he can use a normal driver referenced above. to power them maybe a laptop power supply with some resistances? What would you think?

Thank you all for your time!!

Antoine and Alex

 

[MaxHeadRoom78]

Just as a heads up, in the robotic world, generally (closed loop-PID) servo's are used, the machine knows where it is when powered up, with steppers, which are basically open loop servo's, they need to be referenced, or 'homed' first to calibrate the initial position.
The small RC servo's your son is playing with have a potentiometer that tells the motor controller the current position.
An example, the Segways and similar non industrial applications use PID servo's.
A resistance to maintain the rated current with increase in rpm for steppers is a little old hat now, sophisticated drives use PWM for precise current control.
Max.

 

[shortbus=]

I'm thinking currently using a laptop brick

Aren't laptop bricks a form of switch mode power supply(SMPS)? Steppers normally don't pay well with a SMPS, they are supposed to be powered with a "linear" power supply meaning a transformer, bridge rectifier and filter capacitor.

 

[MaxHeadRoom78]

I don't think the steppers care, it is the SMPS that usually doesn't take to the scenario!
Although many of the DIY CNC crowd use them, mainly due to the price.
Max.

 

[gophert]

For the obvious reasons - for 3D printers steppers are the right choice, and servos would be an incredibly poor one.

.
So you are saying that servos are the best motors to learn about both servo motors AND stepper motors? Or do you think he should actually use a stepper motor to learn about stepper motors?

However, bear in mind we're talking to the father (not the son), who might like to know that it may not go well.

I'm sure there are enough people here to help them work through it. And, for the record, it appears that this father is actually engaged with the son's activities so I'm not concerned.

 

[JimB]

Although many of the DIY CNC crowd use them, mainly due to the price.

My CNC milling machine uses a switchmode PSU to power the X,Y,Z stepper motors, and there are no problems.
I guess one just needs a PSU which is "beefy" enough.

JimB

 

[Pommie]

Note that steppers can have both coils powered at the same time so your maximum current is 3.2A.

The steppers that you linked to have a holding torque of 2.6kg.cm and weigh 0.22kg. Therefore your maximum arm length is about 11cm. Trying to cascade them (elbow and wrist) won't be possible as the holding torque is too low.

Mike.

 

[Nigel Goodwin]

.
So you are saying that servos are the best motors to learn about both servo motors AND stepper motors? Or do you think he should actually use a stepper motor to learn about stepper motors?

I don't quite see how you came to that conclusion, I was simply saying use the right type for the right job, a servo is an excellent choice for a small robot arm (as it does exactly what you need - 'out of the box'). A stepper motor system needs a lot more mechanics and electronics to approach a similar performance.

 

[Pommie]

As I have a few NEMA17 steppers and most of the parts required so, out of curiosity, I printed an arm that's 100mm between centers. A stepper was on the end of the arm and this was the result.

It manages 17 steps before the holding torque gives up - 50 step would be 90 degrees.

Mike.

 

[Nigel Goodwin]

As I have a few NEMA17 steppers and most of the parts required so, out of curiosity, I printed an arm that's 100mm between centers.

I'm mega impressed you printed an arm out to test it!

Nice video - and I jumped at the large THUMP at the end

 

[rjenkinsgb]

So you are saying that servos are the best motors to learn about both servo motors AND stepper motors? Or do you think he should actually use a stepper motor to learn about stepper motors?

"Servo control" relates to precision remote position or speed control of a device or system, regardless of the motor technology in use!

Stepper motors are convenient in some applications as the load position can be determined by counting motor steps, rather than having a separate feedback system for measurement. That keeps cost and complexity down, in situations where stepper motors are practical.

They are however limited in torque and speed. For higher loads and (generally) faster and more precise movement with high torque, DC (or brushless DC) motors with gearboxes and a separate position feedback system give better results.

"Radio control" type ready built servos are a small example of that approach.

It's also near universal for industrial machines and robotics, where fast positioning and high acceleration & holding forces are normal. I don't know of any machine tools or robotic systems above hobby/toy scale that use stepper motors as a primary drive.


It's "horses for courses" - anyone seriously interested in learning about position control for robot arms or just about anything, should really be learning the overall concepts rather than any specific type of motor, as different ones are appropriate in different applications.

 

[gophert]

"Servo control" relates to precision remote position or speed control of a device or system, regardless of the motor technology in use!

True, that's is exactly what "servo control" means. Even though the OPs question is about connecting stepper motors to an arduino.