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Wich stepper motor is the right for my project?

Former Member

I'm a film maker and I love to shoot with jib arms or small cranes.

Most of the optics I have are made for filming and thats why they are totally manual but for that really smooth and quiet. And the optics have teeth so I can use a gear-wheel to turn the focus and the iris.

But when using a jib arm I cannot reach the optic to change the focus, zoom or iris.

I actually built a rig for a stepper motor to turn the focus or whatever I need to turn on the optic.

I got it all to work but I'm facing two problems:

1.) speed

2.) the motor are to weak

 

I'm using the 28BYJ-48 by ROHS (5VDC) http://robocraft.ru/files/datasheet/28BYJ-48.pdf


To control the motor I'm using an encoder, wich is really nice because it is closest to the feeling of turning the actual focus.

With this stepper I can shrink down the delay in between the steps to make it faster or I can switch between half and full step.

The fastest speed is still way to slow. I could use a motor with less steps but that would mess up the accuracy.

On top of that the motor is to weak to turn the focus. I switched to a smaller gear wheel to increase the force and it was barely enough to turn it.

 

 

- It needs to be as small as possible.

- Needs to be controllable by an arduino.

- Should run on 5V DC

- Must be at least twice as powerful as the current motor i'm using on fastest speed

- Should have gears to change speed

- Should not be very noisy

- Since I need two (focus and iris) and I'm building it myself to save money, it should not be toooo pricy

 

Can somebody help me picking the right motor for my needs?


Thanks a lot!

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  • 0

    Hi Christoph

     

    I know very well your problems image and in my opinion there are some details and aspects of the problem that you should consider.

     

    • Stepper motors you are using, not to mode the entire camera but to slide the optics to me sounds fine. They have a torque of about 1.2 Kg / cm that hopefully are sufficient. TO manage the optics, of different sizes and diameters you need to make something less rigid like the image you attach, a motor support that can be moved until touching the optic ring. In my opinion the solution your have proposed can be optimised in some parts. I suggest to take a look on how works the manual focus rings helper to have some better inspiration.
    • The Stepper motor works at a low voltage (there are bigger ones that moves with 3.5 V only) but you can't think to power them with the same power line you are using for the Arduino. The voltage you are using (5V) is the same but the power supply that an Arduino can provide to external devices is not higher than 500mA, maybe lower and it is not sufficient and anyway risky.
    • In the motor schematics you have linked in the post, you see 5 wires: 4 are for the stepper control phases while the 5th (the red one, common to both phases
    • Most of the stuff related to the stepper motors power depends on the way you are controlling them, so it is important to know this detail. I have not in-home none of these motors, that I see in Spain are sold by electan.es for about 5 Euros but I think that controlling them with a ULN2003 or 2004 is more than sufficient with a motor supply of 1- 1,5 A
    • Unfortunately the datasheet you provided does not show the power consumption of these motors, but as I wrote above I think that something between 1000 - 1500 mA maybe sufficient.
    • Just as an example: for some educational purposes I have controlled a NEMA 17 stepper motor (3.5 V 2 A) with a CodeBug, a world smaller and simpler and less powerful than an Arduino and it worked fine. You can see the entire post here: Teaching electronics with CodeBug: Driving a stepper motor

     

    In the following images you see how the rotating ring of manual lenses can be easily converted for few cents to a reliable geared unit that I regularly use.

     

    Hope this can help. Looking forward for some more details and your progress image BTW: Better for the readability if in the post you add the images inside the test instead of attaching them.

     

    Enrico

     

    imageimageimage

  • 0 in reply to balearicdynamics

    Check the actual current requirements per winding  ,multiply X4 to get the current req for the volt you are running,sounds like my old friend current fadeout where the power supply cannot supply the necessary current ,I use steppers on my cnc and my pen plotter all homemade and my power supplys are old computer power supplies XT and AXT units,I am looking at an NEMA 17 motor and it requires 0.3 amps at 9.6 VDC,and if you check the data sheet it may say 0.3 amps per coil.......WCH

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  • 0 in reply to balearicdynamics

    Check the actual current requirements per winding  ,multiply X4 to get the current req for the volt you are running,sounds like my old friend current fadeout where the power supply cannot supply the necessary current ,I use steppers on my cnc and my pen plotter all homemade and my power supplys are old computer power supplies XT and AXT units,I am looking at an NEMA 17 motor and it requires 0.3 amps at 9.6 VDC,and if you check the data sheet it may say 0.3 amps per coil.......WCH

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