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10-06-2010, 02:29 PM   #1
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Pentax unveiled definition of new DC motor

It means "Direct Current motor"

http://www.pentaximaging.com/product.aspx?id=smc%20PENTAX-DA%2018-135mm%20F3...=camera-lenses

10-06-2010, 02:35 PM   #2
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Yeah, this was known from the day of the lens's announcement...
10-06-2010, 03:33 PM   #3
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That's what my car's starter motor is. I hope Pentax's is smaller and quieter!

Mike
10-06-2010, 08:34 PM   #4
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I would have to be direct current running from a battery. I don't think there are any alternating current batteries (at least until we recharge them). Please correct me if I'm wrong.

10-06-2010, 09:13 PM   #5
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QuoteOriginally posted by opiet70 Quote
I would have to be direct current running from a battery. I don't think there are any alternating current batteries (at least until we recharge them). Please correct me if I'm wrong.
Apparently, some DeLoreans use a Flux Capacitor.
10-07-2010, 01:05 AM   #6
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QuoteOriginally posted by Blue Quote
Apparently, some DeLoreans use a Flux Capacitor.
and a Mr. Fusion....an orange peel and some coffee grinds and you can take pictures for a 1000 years....just don't drop the camera ..
10-07-2010, 02:41 AM   #7
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QuoteOriginally posted by opiet70 Quote
I would have to be direct current running from a battery. I don't think there are any alternating current batteries (at least until we recharge them). Please correct me if I'm wrong.
With a few electronic components they can create as many alternating phases as they want. Look at the RC world which is ruled by tiny highly efficient 3phase motors.
10-07-2010, 12:00 PM   #8
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QuoteOriginally posted by Gimbal Quote
With a few electronic components they can create as many alternating phases as they want. Look at the RC world which is ruled by tiny highly efficient 3phase motors.
Good point. I hadn't thought of that

10-07-2010, 01:24 PM   #9
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I suspect any USM/SDM motor requires a rather high frequency AC supply for stable controlled speed. That's "high frequency" power-wise, not EMF-spectrum-wise, where HF is between 3-30 MHz. I can't find specifications for USM/SDM motor speeds, but I'm guessing they might be around 30k RPM, which would put them in the LF radio band.

Anyway, AC motor speeds are easily controlled by the frequency of the power feed, whilst DC motor speeds are entirely dependent on voltage levels. Frequency is simply crystal-controlled; voltage regulation would require a tachometer with feedback to the VR chip. Or so I recall my my youth misspent in electronics.
10-07-2010, 02:37 PM   #10
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With high torque applications requiring gear boxes, DC motors make more sense. I can't imagine my DA* 300 or my 17-70 spinning at 3K rpm much less 30k.
10-07-2010, 03:36 PM   #11
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Anyone have a clue as to whether there are objective advantages to this DC technology over SDM in camera lenses? 30k rpm is unheard of...
10-07-2010, 03:41 PM   #12
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QuoteOriginally posted by RioRico Quote
nyway, AC motor speeds are easily controlled by the frequency of the power feed, whilst DC motor speeds are entirely dependent on voltage levels. Frequency is simply crystal-controlled; voltage regulation would require a tachometer with feedback to the VR chip. Or so I recall my my youth misspent in electronics.
You can have a high torque DC motor with variable speed by using PWM (pulse width modulation).
Full voltage, just control duty-cycle.
10-07-2010, 04:30 PM   #13
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QuoteOriginally posted by Ex Finn. Quote
You can have a high torque DC motor with variable speed by using PWM (pulse width modulation).
Full voltage, just control duty-cycle.
Ooops, yeah, I forgot about PWM. Hey, I started on vacuum tubes, gimmee a break! There still needs to be feedback to hold any specific speed, whereas with an AC motor the speed is a function of the frequency, easily controlled.
10-07-2010, 05:08 PM   #14
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QuoteOriginally posted by RioRico Quote
Ooops, yeah, I forgot about PWM. Hey, I started on vacuum tubes, gimmee a break! There still needs to be feedback to hold any specific speed, whereas with an AC motor the speed is a function of the frequency, easily controlled.
I started on tubes, some call them "electron valves", also. .
Agree, there must be a feedback telling the drive circuit where the driven is. Be a pulse counter or resistive or some hybrid combo.
DC motor is lot easier to control as far as direction is concerned.

Cheers, Mike.

Last edited by Ex Finn.; 10-07-2010 at 05:25 PM.
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