Stepper motor circuit for a "stepped operation"?

Thread Starter

Vaghul_Venkatagiri

Joined Oct 27, 2021
5
Hello! I'm building a mechanical system which needs a lever to move periodically, there's a lever that needs to balance, and I've placed contact switches on either sides so when it tilts a little, a stepper motor pulls it back.

I've seen most stepper drivers giving continuous operation, can I get a circuit idea for a literal "stepped" operation? For example, if the lever tilts, it makes contact with the switch on that side, and the stepper motor pulls it back in steps until it reaches the center again. It would be great I can control the number of steps and the time interval between them, so that the lever can be brought back in a periodic manner. Hope that makes sense.
The best I could think of was to use a regular stepper driver, and pass it through a 555 timer pulse generator that makes and breaks the signal. Can someone suggest any ideas?:) I'm using a unipolar 6 wire stepper, a simple circuit without a microcontroller would be helpful

Thank you!
 

Papabravo

Joined Feb 24, 2006
17,245
A simple microcontroller will do a fine job with this. I highly recommend this approach if you are not extraordinarily familiar with analog electronics.
A drawing of the mechanical arrangement would be helpful.
 

LowQCab

Joined Nov 6, 2012
1,317
Does the Stepper-Motor need to exert a "holding-force" when not
actively moving the device ?

Is some "drag" or "notching", or "cogging",
going to cause a problem for your design ?

I'm not an expert on Stepper-Motors,
but every Control-Chip that I've seen has "Direction", and a "Step", Inputs.
It would appear that You simply want the Motor to move very slowly,
so the "Step" Input would simply be a very slow Pulse.
.
.
.
 

Thread Starter

Vaghul_Venkatagiri

Joined Oct 27, 2021
5
Does the Stepper-Motor need to exert a "holding-force" when not
actively moving the device ?

Is some "drag" or "notching", or "cogging",
going to cause a problem for your design ?

I'm not an expert on Stepper-Motors,
but every Control-Chip that I've seen has "Direction", and a "Step", Inputs.
It would appear that You simply want the Motor to move very slowly,
so the "Step" Input would simply be a very slow Pulse.
.
.
.
Ah yes I should have specified that too. No holding force while there is no movement. Just "pull and release" - "pull and release" while contact is made :)
 

Thread Starter

Vaghul_Venkatagiri

Joined Oct 27, 2021
5
Have you thought about using a RC servo instead of a stepper? Just one place selling them - https://www.pololu.com/category/23/rc-servos
Actually yes, but a servo has some resistance because of the gear reduction and it will be hard for the lever to push the servo. I was hoping for free play until the actuator makes a movement. Thanks for the suggestion!! I'll see if I can make any arrangement using a servo as well :)
 

dendad

Joined Feb 20, 2016
3,939
As mentioned, diagram showing the mechanical setup would help.
Using electromagnets may be better as with a stepper, there will be mechanical drag on the setup even when not powered.
There are plenty Arduino stepper projects around. And a cheap 3D printer control board may be a very good way to start with the controller if you don't want to build your own version.
 

MisterBill2

Joined Jan 23, 2018
9,797
The stepper is driven by a sequence of energizing the different windings . For a standard six wire stepper that means that the different windings are activated in a specific sequence. (perhaps you already knew that). The simple way to do that is with an up/down counter ring with four positions. It is also possible to operate in a half-step mode that alternates one winding on and two windings on. That would require either an 8 step counter or three flipflops and some decoding logic. I suggest an 8 step up/down counter and some logic to decode which windings are on for each step. Then as the balance was lost in one direction or the other the motor could be powered and stepped in the needed direction until balance was recovered.
 

Papabravo

Joined Feb 24, 2006
17,245
The stepper is driven by a sequence of energizing the different windings . For a standard six wire stepper that means that the different windings are activated in a specific sequence. (perhaps you already knew that). The simple way to do that is with an up/down counter ring with four positions. It is also possible to operate in a half-step mode that alternates one winding on and two windings on. That would require either an 8 step counter or three flipflops and some decoding logic. I suggest an 8 step up/down counter and some logic to decode which windings are on for each step. Then as the balance was lost in one direction or the other the motor could be powered and stepped in the needed direction until balance was recovered.
You can also use an 8-bit Parallel-In Serial-Out Bi-directional Shift Register with no decoding to do half steps on a unipolar 4 pole stepper.
 

Reloadron

Joined Jan 15, 2015
6,204
Using a stepper motor if you don't have one already I would think about one which has a shaft extending out both sides. I would think about attaching a rotary position encoder on one side so you always know where the zero is. Then consider your rotation per step or half step. A typical stepper motor is 1.8 degrees per step so figure 360 degrees / 1.8 degrees = 200 steps per revolution. A motor which can do half steps would be 400 steps per revolution. Next, as mentioned, consider the required torque. Next you have a stepper motor controller to drive the stepper motor. They offer very accurate position control and function in CW and CCW operation.

Next you can consider a servo motor which could also work fine assuming you have one, like a stepper motor, which will handle and hold the load.

Either can be controlled using a uC (micro-controller) along with some coding and in either case a uC is a good way to go. So figure depending on your needs a stepper motor is well suited for applications requiring low speed, slow acceleration and low accuracy where the rotational step change meets your needs and a servo motor will give you high speed, high acceleration and likely higher accuracy. The cost of either will depend on you needed rotational torque and holding torque. Knowing your requirements you decide the best fit. :)

A servo motor also is easier to control is something else to consider.

Ron
 
Last edited:

MisterBill2

Joined Jan 23, 2018
9,797
In post #1 the TS gave us a fairly adequate description of what the hardware was and what the stepper motor was desired to do. The nice hing about steppers is that it is easy to stop them, and they tend to stay stoped. And for this application a stepper is the best choice. A model servo, intended for RC devices, is not easy to drive with a switch. A servo motor is vastly over-kill, and a regular reversible motor will coast way too much.In addition, for position detection we already know that there are two limit switches that tell when it has to run , when to stop, and which way to go.So no encoder needed. Certainly a shift register can do it but that would tend to demand a micro to run it, and the TS mentioned they would rather use hardware. Decoding a three stage 4-bit binary counter for the winding states is not that complex, steppers have done it with 74 series TTL for many years. CMOS is better becaause of needing vastly less power.
 

Thread Starter

Vaghul_Venkatagiri

Joined Oct 27, 2021
5
As mentioned, diagram showing the mechanical setup would help.
Using electromagnets may be better as with a stepper, there will be mechanical drag on the setup even when not powered.
There are plenty Arduino stepper projects around. And a cheap 3D printer control board may be a very good way to start with the controller if you don't want to build your own version.
Of course, here's a diagram
1635410899528.png
So the lever has a heavy load that makes it swing slowly. The project is actually a gyroscopic monorail, so the gyroscope is attached to the lever and as it experiences precession, the stepper gently pulls it in periodic tugs. It doesn't hold the lever in place since it has to move freely after each tug. More specifically, the gyroscope can bring itself back to balance, so the aim of the stepper would just be to give it the initial push. Hope this makes it clear :)
 

Thread Starter

Vaghul_Venkatagiri

Joined Oct 27, 2021
5
And thank you everyone for your replies! I'll explore the encoder idea and the logic suggested, and possibilities of using a servo (without much resistance while it is being rotated by the load when its not operating)
Thank you once again :)
 

LowQCab

Joined Nov 6, 2012
1,317
You can't fight a Gyroscope with a Stepper-Motor.

The Control-Model You need is exactly what is contained in every Hobby-Quad-Copter.

"" High-performance / low-noise / high sensitivity MPU-6000 with
6-Axis-Gyro and Accelerometer. ""


They can maintain "Square-with-the-World" positioning with 4- Motor-Outputs,
and have built-in PID-Feedback-Controls.

Costs about ~45.oo for the Flight Controller, Motors and ESCs are extra.
The Flight-Controller can also directly control Model-Servo-Gear-Motors.
It can also act as a Suspension-Control for a smoother ride.
.
.
.
 

MaxHeadRoom

Joined Jul 18, 2013
23,908
On stepper motors, they can be kept energized at zero RPM at the rated current to obtain maximum (rated) holding torque.
Also the term 'Servo Motor' often used here refers to the RC style servo which is quite a bit different from the DC/BLDC servo motor used in industrial motion control.
The version meant by the poster often has to be deducted by decifering the wording.
 

MisterBill2

Joined Jan 23, 2018
9,797
On stepper motors, they can be kept energized at zero RPM at the rated current to obtain maximum (rated) holding torque.
Also the term 'Servo Motor' often used here refers to the RC style servo which is quite a bit different from the DC/BLDC servo motor used in industrial motion control.
The version meant by the poster often has to be deducted by decifering the wording.
I am sure that in this instance the reference was to a small RC "servo" not at all like a servo-motor.
And I believe that some reference was made to gearing,
 
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