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View Full Version : OT: Why would anybody need a stepper this slow???



Scatterplot
03-31-2007, 03:26 AM
http://cgi.ebay.com/Crouzet-Synchronous-Motor-Gearmotor-Stepper-New-230V_W0QQitemZ290098859183QQcategoryZ78206QQrdZ1QQ cmdZViewItem

21 revolution per YEAR stepper motor!!!:confused:

mark61
03-31-2007, 07:34 AM
So that the house you build can ALWAYS be syncronized/ and oriented with Jupiter and the planat Urainus!

mark61

Swarf&Sparks
03-31-2007, 07:37 AM
They're not steppers, they're synchronous motors.
Hey, you could build an orrery :D

Evan
03-31-2007, 09:48 AM
The stepper drive on my scope only runs about 15 steps per second.

http://vts.bc.ca/pics/scopedrive1.jpg

DR
03-31-2007, 11:03 AM
"The stepper drive on my scope only runs about 15 steps per second."



Hmmm....this brings up a question. I'm working on a very slowly rotating device driven 1:1 with a 200 steps/rev motor. At how slow a stepping rate do you suppose the motor ceases to have smooth motion, but more of noticeable ratcheting motion?

Weston Bye
03-31-2007, 11:47 AM
My article, The Quartz Movement, in the Digital Machinist was about this:
http://img.photobucket.com/albums/0803/Weston/Photo22.jpg
Electronics and mechanics to produce 1 RPM. Perfect for driving a second hand on a clock. The rest of the clock will appear in the next issue of the Digital Machinist.

The rotor moves in distinct 1 second steps.

Todd Tolhurst
03-31-2007, 11:56 AM
Smooth motion to the naked eye? Probably right about 15 steps/second. Film or video (or flip books!) frame rates slower than this are perceived as jerky.

Optics Curmudgeon
03-31-2007, 12:28 PM
Film is 24 frames per second, video is 30 (in the US).

Joe

Weston Bye
03-31-2007, 12:43 PM
The 8mm film format was available in 24 fps for professional work, but far more popular was the 18 fps for amateur/home movies.

ptjw7uk
03-31-2007, 06:00 PM
These motors were used in process control before the integrated circuit solid state timer became more widely available.
I used to use a 1 rev per 24hrs to control a liquid nitrogen supply for amass spectrometer. I believe there were 14 day per rev motors used in heating controllers in public buildings again now superceeded by solid state.
The Crouzet were a simple cheap solution and would last several years before needing replacement.
Peter

Paul Alciatore
04-01-2007, 03:30 AM
Film is 24 frames per second, video is 30 (in the US).

Joe

But that is not the whole story. 24 or 30 frames per second will show flicker.

Film projectors, at least the professional ones, will indeed run at 24 frames per second, but the projectors will chop the light several times during each of those frames so the flicker rate is actually much higher, perhaps 96 or even 120 actual flashes of light per second.

Video (standard NTSC video as transmitted by all TV stations for over 50 years) does have 30 frames per second but that is composed of 60 fields, due to interlace. Even at that, some people say they can see flicker so it perhaps is not enough.

I would guess that the flicker rate needs to be at least 75 and perhaps 90 or 100 images per second before the majority of viewers would not see the flicker.

Evan
04-01-2007, 09:20 AM
For a telescope drive it isn't the flicker or "jerk" rate that matters. The step rate is calculated so that the size of one step moves the scope at least 50% less than the theoretical maximum resolution of the scope in arc seconds. That is determined by the aperture of the scope. The larger the aperture the higher the required step rate since the rotation of the Earth is relatively constant.