Stepper motor suggetsions

Hi

I'm looking for advice on choosing the correct stepper motor and driver for an arduino project.

I would like to use the stepper motor to turn an object precisely 30 degrees, around 12 times a second, with a delay between each turn.

The delay needs to be at least (preferably more than) the same amount of time it takes for the motor to turn the object 30 degrees.

So around 1/24 second to turn 30 degrees and then 1/24 second delay, but ideally more like 1/48 to turn and 3/48 delay

The object's maximum weight will be approximately 1kg but probably less.

I'm assuming the basic 5V motor (28byj-48) that comes with the starter kit below wouldn't have the speed?

http://www.ebay.co.uk/itm/Ultimate-UNO-R3-Starter-Kit-for-Arduino-1602-LCD-Servo-Motor-Relay-RTC-LED-/272317374211?_trksid=p2385738.m2548.l4275

In addition, what driver would people recommend to fit the requirement?

Any suggestions?

You need to select a motor that provides the required torque, power and mechanical support required by the mysterious object, then choose an appropriate driver.

Forum members can only guess, in the absence of information.

Wow! What a friendly and welcoming response. It's great to see my first ever post so quickly and efficiently dismissed.

Does anyone else have any useful suggestions or advice?

Well I don't see how we are supposed to guess the load on the motor - and that is an essential piece of information.

There is some advice about motor selection in Stepper Motor Basics

...R

I am sure that I will use the wrong units of measure to try to describe this, but here it goes.
1/48 second is about 20 milliseconds.
You want to rotate an object 30 degrees in that time. That involves a lot of acceleration up to speed and deceleration back to zero, landing precisely at 30 degrees rotation, in a short time.
You give a weight of the object. Calculating the moment of inertia would require more information about the object. Size. Density distribution.
A 1kg frisbee with most of the mass in the rim will have a greater moment of inertial than a solid sphere of the same mass.

It would help a lot if you described your goal in greater detail. You gave a lot of good info. We need more.
Plus, I am curious what you are really trying to do.

I can't help but think that there are mechanisms that perform this action. Where a constant rotation is turned into a periodic rotation with a fixed period of rest. But my google-foo failed me in finding an example.

edit: ahh found one. Google Geneva Wheel

Thanks vinceherman. Being a total beginner to electronics I have no idea about what information is needed - I just have a specific goal in mind!

I was originally using a geneva wheel for my project but I found that the precision needed to create the wheel was beyond my skill - I figured a stepper motor would be a simpler approach.

It's tricky to try to explain what I'm trying to do but here is something similar:

My version will be made of small paper models mounted on a disc about 200mm diameter, and at some point I may decide to go down the route of making plasticine models or 3d printing (which is why I put 1kg max as a weight).

I did some research on stepper motors and it appears that the voltage/torque determines its max speed? I've read the 5V motor 28byj-48, mentioned in my original post, has been geared down to improve torque but I'm assuming this will mean it wouldn't be able to run at the speed i'm looking at?

So do you think the 28byj-48 will meet my requirements or I should be looking at a 12v motor?

Here is a link to the kind of paper model I will be making to give you an idea of density and mass distribution:

Wow! What a friendly and welcoming response. It's great to see my first ever post so quickly and efficiently dismissed.

Welcome!

I enjoyed watching the videos. Never seen stuff like that before.

After watching the videos, I thought a geneva movement would be more appropriate.
Then I read your reply, and I see you already thought of that.

IMO, this is not really an application for a stepper motor. You can't get that kind of explosive acceleration/deceleration. And I suspect your model would shake apart.

I would run the model at a constant speed, then hit it with a strobe light. :o

For a stepper, you want to rotate a 1 kg object? Best bet is to start big. Search through the NEMA range.

But..... steppers can make whining noises. So may need to consider that.

stepperman:
Here is a link to the kind of paper model I will be making to give you an idea of density and mass distribution:

I don’t see any role for a stepper motor in the demo in the video. It seems to me a simple DC motor with speed control is all that is needed so that the motion coincides with the strobe light frequency or the shutter speed of the movie camera.

If you want to do stop-motion photography then there is no need for speed or smoothness and a stepper motor might be convenient.

…R

stepperman:
Hi

I'm looking for advice on choosing the correct stepper motor and driver for an arduino project.

I would like to use the stepper motor to turn an object precisely 30 degrees, around 12 times a second, with a delay between each turn.

The delay needs to be at least (preferably more than) the same amount of time it takes for the motor to turn the object 30 degrees.

So around 1/24 second to turn 30 degrees and then 1/24 second delay, but ideally more like 1/48 to turn and 3/48 delay

The object's maximum weight will be approximately 1kg but probably less.

I'm assuming the basic 5V motor (28byj-48) that comes with the starter kit below wouldn't have the speed?

http://www.ebay.co.uk/itm/Ultimate-UNO-R3-Starter-Kit-for-Arduino-1602-LCD-Servo-Motor-Relay-RTC-LED-/272317374211?_trksid=p2385738.m2548.l4275

In addition, what driver would people recommend to fit the requirement?

Any suggestions?

You have to do the math (this looks totally infeasible at first glance, the angular accerations are extremely large
with large inertial mass as load).

The weight of the object is irrelevant, however, all that matters for rotation is the moment of inertia (MoI) which
is strongly dependent on the object size and geometry, not just the mass.

To accelerate and decelerate from 0 to 30 degrees in 41.7ms means acceralating to 15 degrees in 20.8ms,
which takes 1210 rad/s/s angular acceleration, with a top speed of 25 rad/s (250rpm)

A 1kg mass with effective inertial radius of only 2cm has 4.0e-4 kg m^2 MoI

The torque to accelerate that at 1210 rad/s/s is 1210 x 4e-4 ~ 0.5Nm

Note the peak power is 0.5Nm x 25 rad/s = 12.5W mechanical. Not going to happen for a NEMA17 I don't think.

For 1/48th second the accelerations/torques are 4 times larger and the peak power 8 times larger...

I agree that this is not an application for stepper motors.
@stepperman, are you intending to use strobe light to provide the ‘stop’ in the rotation?
When I read your description it sounded like you wanted it to snap to the next position and then remain there motionless for a brief period, then repeat.
Here is another video. Look at 4:18 in this video

The ‘intertrope drive unit’ appears to produce exactly the effect you describe.
I am not sure this is any less difficult to make that the geneva wheel though.

Thanks all, the video vinceherman posted was where I originally got the idea to use a stepper. I thought using a stepper motor would be a 'quick fix' to the issue but if the amount of torque needed isn't straight forward and cost efficient I'll revert back to the geneva wheel.

For those who are interested the zoetropes in the video do not use a strobe or sync with the camera shutter. Instead they create the illusion of animation from 'jerking' from one position to the next (a bit like the gears and second hand of a clock).

I've tried this with a geneva wheel but the speed and impact of the driver pin causes a lot of vibration and noise. And the parts have to be small, sturdy and precisely engineered in order to work well. Have a look at the video around 4:30 and you can see the kind of forces involved.

Still, I have had a few ideas recently that may solve some of these issues...

stepperman:
Instead they create the illusion of animation from 'jerking' from one position to the next (a bit like the gears and second hand of a clock).

Or like the motion of a film projector in which each frame jumps from one position to the next very quickly and is then stationary for a bit.

I wonder if it would be easier to think of it as a system to prevent rotation (for the viewing period) rather than to create rotation for a very brief moving period. For example a DC motor running continuously with a "soft" coupling (probably a spring) that would allow the motor to continue while a ratchet stops the motion. Energy will build up in the spring so when the ratchet releases the device it will move quickly until stopped by the next ratchet. The escapement of a mechanical clock would probably provide ideas for the ratchet.

And have you seen one of these things with your own eyes rather than through a camera? I'm suspicious of snake-oil :slight_smile:

...R

Yep....... a good example of a bulky thing like a merry-go-round..... an extreme case. It will have a fair bit of inertia. So after if it would be accelerated up to speed. It will then need to be decelerated.... in order to get to the held position at the right time. It won't be straight forward due to the torque, forces etc involved.

Another thought that crossed my mind overnight is driving a large gear attached to the roundabout with a small gear with most of the teeth removed. The big gear will only move forward a little bit for each revolution of the small gear and for most of the revolution of the small gear the big gear won't move at all.

...R