stepper motors and spinning objects with controlled rpms

Hi Steve,

I would design this application around a bipolar stepper motor as there are more drivers to choose from and they will give you the performance you require. Plus you can most of the time wire a unipolar stepper as bipolar motor anyway.

A good driver for this application would be the DRV8825 as it has 32 degrees of microstepping which will translate into better motion quality; something you definitely want your rotating artwork to enjoy from.

I am thinking any NEMA 23 stepper will do the job. Chances are you will gear their speed down by using pulleys, so their available torque will be much more than enough. For example, a PK266 has a 166 oz-in torque capability. This is as much as 10 pounds at an inch of distance from the shaft if no pulleys are used. I assume the art piece (AKA the mass center)  will be at the center of the shaft, so even then you are set. If you step it down with pulleys, however, you can multiply the available torque by the speed reducing factor and you will gain more torque at reduced speeds, which is what I am assuming you will need anyway. For example, if you drive the motor at 100 RPM and the speed reducing factor is 10, you will have a torque of 100 pounds per inch and the art work will rotate at 10 RPM.

A NEMA23 motor can be found at very low cost on places such as eBay or many online surplus stores. I would look for a stepper with 200 steps per revolution to make sure the motion quality is as soft as possible. If NEMA23 is too much power (and if you use belt based speed reduction it might) you can always consider a NEMA 17 stepper. I have seen these sold for $4.00 on surplus stores.

To control the DRV8825 you can use either a microcontroller or simple logic. I think a microcontroller would work best if you want to control it all with your laptop. How to do this is documented on the web. I recently saw a tutorial on this topic at www.ebldc.com. They document the hardware and the software side, so I am thinking all the steps are covered.

Hope the info helps to get you started on this exciting project.

Best regards,

Jose Quinones

Will that spin the heavier art work?  How big is this motor, or how big of a motor do I need? 

Thanks for all the info.  :)

Steve

Okay.

So I just purchased 3 NEMA 23 motors on Ebay.  Now do I need three separate controllers for all three motors.  I've decided to use 3 motors for this project.  I can get 2 phase driver boards for 16 bucks each.  What else do I need in order to turn all three motors in different directions at different speeds via my laptop?  An interface of some kind and software and what else? 

What do you think so far?

Steve Lucas

Hi Steve,

I believe the NEMA 23 motor should be able to spin the 10 pound art but at the end it will all depend on where the center of mass lies and whether speed reduction will be used.

If direct driven (no speed reduction is used), then the center of mass cannot be further apart than 1 inch from the center of the shaft. I am assuming a 10 pound/inch motor but depending on what you bought, this could be more or less.

If you use speed reduction, then the torque will be multiplied by the same factor for which the speed is reduced. In this case, the mass center can be farther from the shaft center.

Hope the info helps,

Jose Quinones

Hi Steve,

Each motor will require its own driver. Can you share with us which driver have you selected?

There are many ways in which you can tackle this from your laptop. I have done this a few dozen times using MSP430's and an USB chip. I use VB NET to code the Windows application that talks to the MSP430 which then send pulses to the driver chip. I think a Launchpad board would be an excellent starting point. It has all that you need to communicate from the laptop. You will need to code it, though.

Best regards,

Jose Quinones

http://www.ebay.com/itm/3-Axis-CNC-Stepper-Driver-Board-Digital-Display-Tools-Kit-0-5A-2-5A-Version-/170756124087?pt=LH_DefaultDomain_0&hash=item27c1dbadb7

So I am thinking about buying this package, plus this for the power supply :  

http://www.ebay.com/itm/Lambda-Model-LUS-10A-24-DC-Power-Supply-Max-DC2-1A-/310357267786?pt=LH_DefaultDomain_0&hash=item4842bc154a

Let me know if I'm on the right track. 

Steve

Hi Steve,

Feel free to post your email and I will contact you directly. We can then discuss this matter further. Thanks!

Best regards,

Jose Quinones

eyeofanavrin@yahoo.com