Stepper motor speeds

Thread Starter

fader700

Joined Jan 27, 2014
7
Hello
I am a novice when it comes to using stepper motors. I am familiar with servos and inverters but not stepper motors.
I have a project that needs to rotate an item 180° and then return to the start position by rotating backwards.
I built this using a basic 12vdc motor from RS, two proximity switches and a bunch of relays. This setup worked well but over time has damaged the gearbox because it needs to stop quickly in both directions, hard stops were fitted and the sensors adjusted to remove power to the motor and short the terminals to prevent further movement just prior to it hitting the end stops.
There is now a need to add a delay before it returns to the start position. There is simply no room left to add a timer relay and since it has broken the gearbox I need another solution.
I am considering using a stepper motor to control the motion but my experiments using an Arduino kit results in very slow movement. The half rotation needs to be around 500ms with as little acceleration and deceleration as possible. I am assuming this a limitation of the arduino kit I have.

This is the controller I am considering because of its in-built stepper motor controller, size and cost.
https://barth-elektronik.com/en/lococube-mini-PLCs/lococube-mini-PLC-STG-700.html

And possibly a stepper motor like this one
https://uk.rs-online.com/web/p/stepper-motors/8929328

Here is the criteria:
Rotate a load of approx 500g 180° in 500ms(approx)
Wait for a configurable time delay
Return to start position the same speed as the initial rotation.
System is currently 12vdc but can be upgraded to 24vdc
All the control gear has to fit in a 6" x 5" x 8" space.

What I need help with is the hardware to achieve the above. What criteria should I be looking at to know I will get the speed and control required and durability? Should I be considering stepper motors at all?

Thanks
 

Irving

Joined Jan 30, 2016
2,769
Can you give more detail of the load.... how is the 500g distributed relative to the motor spindle?

Stepper motors will do this as will DC motors - if properly configured - otherwise you will either have poor performance or failed/burnt-out hardware.

I don't understand your comment about acceleration/deceleration - you can't change the laws of physics - the lowest acceleration is where you accelerate for 90° and then decelerate for the remaining 90°, with no constant speed period in the middle... or did you mean you want a short acc/dec period and mainly constant speed running (but then acc/dec going to be high!).
 
Last edited:

djsfantasi

Joined Apr 11, 2010
8,390
…And can you post the sketch that you are running on the Arduino? Copy the code. Click on the three dots, select “Code” and paste your sketch where the cursor is located.

The stepper motor can run fairly fast.
 

Thread Starter

fader700

Joined Jan 27, 2014
7
Can you give more detail of the load.... how is the 500g distributed relative to the motor spindle?

Stepper motors will do this as will DC motors - if properly configured - otherwise you will either have poor performance or failed/burnt-out hardware.

I don't understand your comment about acceleration/deceleration - you can't change the laws of physics - the lowest acceleration is where you accelerate for 90° and then decelerate for the remaining 90°, with no constant speed period in the middle... or did you mean you want a short acc/dec period and mainly constant speed running (but then acc/dec going to be high!).
The load is central to the motor spindle so it is balanced. There will be some fluid inside the load that will slosh around but it is a small amount relative to the weight. I don't expect it to have a significant effect on the load.

The accel/decel idealy would be zero but that probably is defying the laws of physics! I just need this thing to spin 180° without any significant cushioning at the end of rotation. Driving it into a hard stop would provide the best result but would also destroy it eventualy.

I am trying to find out if using a stepper motor is the right way to go. I can probably work out the details if I know it will work effectively.
 

Thread Starter

fader700

Joined Jan 27, 2014
7
…And can you post the sketch that you are running on the Arduino? Copy the code. Click on the three dots, select “Code” and paste your sketch where the cursor is located.

The stepper motor can run fairly fast.
I tried this at home over the weekend so I don't have it with me. But, the sketch came with the kit and it states the max speed setting in the code. I know stepper motors can run faster than I observed but I have no information about the stepper motor in the kit. It is probably a high gear ratio hiding the true speed.

As I put in my reply to Irving I am really just looking for someone to say it is the right way to go, I have only my experience with the arduino kit when it comes to stepper motors. If people tell me it will work I will start looking at power, torque, inertia etc.
I should mention the project can not be Arduino based.
 

Thread Starter

fader700

Joined Jan 27, 2014
7
7.5 deg step angle is pretty coarse, can you live with that?
The rotation is 180° ish. Not looking for precision.
I haven't really got into the details, the motor I have linked to is probably not ideal, seems to have a small holding force so probably not powerful enough to do the work.
 

Thread Starter

fader700

Joined Jan 27, 2014
7
Just to clarify.

My intention with this thread is to hear somebody say either 'yes, stepper motors are a good solution for this' or 'What are you thinking? Why don't you...?

I know the best solution to achieve this is to go pneumatic but that I am being told to avoid it if possible. It is going into a lab so I don't think they want the noise.
 

BobTPH

Joined Jun 5, 2013
5,227
I think what you mean about acceleration is the opposite of what you are saying. You want it to accelerate quickly to a speed, go through the 180 and then decelerate quickly. This is high acceleration, not zero. If the acceleration is zero, it never moves!

Bob
 

Irving

Joined Jan 30, 2016
2,769
Assuming the load is a disc - what diameter and what material? Or give a better description - its important.

As already said - slowest acceleration = lowest torque, fastest acceleration = shortest time accelerating = largest torque = expensive!
 

panic mode

Joined Oct 10, 2011
2,167
steppers can do that if properly sized even though they are not speed demons. in fact they are rather slow and quite noisy but they are good when it comes to torque. noise level goes down with microstepping but so does the speed too. when designing an actuator you need to get the math right. as suggested get the mass and more importantly inertia of the system, define desired motion profile. short acceleration interval means high acceleration value. low acceleration means it takes long to reach some speed. the lowest acceleration in your case is when unit accelerates for 90deg and decelerate for 90deg. with high acceleration rate you may be able to reach peak speed after moving 10deg for example, travel 160deg at that speed then decelerate over last 10deg. but that would require a lot of power and be more expensive. you would probably do well using hobby servo and a microcontroller. they are using DC motor like you originally did with relays but have gearbox and speed/position control. you say you already tried Arduino so to see if your setup was optimized we need to see your code. you can also get everything inside one unit - quicksilver for example packages servo motor, servo controller and PLC into one compact unit. it is not inexpensive but it is very nice and can work with 12 or 24V directly.
 

shortbus

Joined Sep 30, 2009
9,441
This could also be done more mechanically. Some type of linear actuator(there are more than one type) the actuator would have a gear rack attached. This rack would then engage a pinion gear mounted to the shaft of he disc that needs to move. When the linear actuator is engaged in one direction it would rotate the disc in one direction. When the actuator is retracted the disc would rotate the opposite direction.

By removing some teeth from the rack gear you could/would get a pretty precise rotation degree and not have to stop the actuator in an exact position.
 

Thread Starter

fader700

Joined Jan 27, 2014
7
I think what you mean about acceleration is the opposite of what you are saying. You want it to accelerate quickly to a speed, go through the 180 and then decelerate quickly. This is high acceleration, not zero. If the acceleration is zero, it never moves!

Bob
Yes absolutely right. Pls excuse my english, i'm a yorkshireman!
 

Thread Starter

fader700

Joined Jan 27, 2014
7
I thank everybody for the advice. I am going to use pneumatics after all. After looking into the finer detail I would need a motor with enough beef to deal with the accel and decel and provide the speed required to get the whole thing done in 500ms. The cost has escalated considerably from the equipment I started to look at.

From my experience with servos I know the power required for high accel and decel, especially with high inertial loads can really ramp up the servo and motor requirement. The power required can be reduced by gear ratios but this impacts speed. I usually get the suppliers rep to spec this equipment, usually means its a free upgrade if they get it wrong :)

If I ever get enough time I am going to make a point of learning more, although my initial look at working out rotational inertia was a bit daunting. Thank god for online calculators :)
 

Irving

Joined Jan 30, 2016
2,769
I still would like to know something about the load - approximate size/shape/weight distribution - it may not be as bad as you think...
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
I am a novice when it comes to using stepper motors. I am familiar with servos and inverters but not stepper motors.
I have a project that needs to rotate an item 180° and then return to the start position by rotating backwards.
I built this using a basic 12vdc motor from RS,
Have you looked at motor mechanisms that are already doing similar things, such as 12v wiper motor/mechanisms?
They can usually be had cheap from wreckers etc, the mechanism maybe could be modified to suit your application, they have quite a bit of torque and fast accel/decel.
Generally they do not even reverse the motor.
 
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MisterBill2

Joined Jan 23, 2018
12,399
A stepper motor is speed-torque limited because the inductance limits how fast the current that provides the torque can increase. There are work-around schemes but they are not efficient. A pneumatic system is limited by the time it takes for the pressure to rise enough to make the motion happen. But that time can be short . If a lever is used to make the translation from linear to rotary the torque will vary a lot. A rack//pinion can be better but it costs more. a cylinder/chain/sprocket can work but it is really hokey. Two cylinders can be better but keeping the chain on the sprocket can be a challenge. And it uses a lot of air.
 
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