Pentax unveiled definition of new DC motor

arm_jstp · 10-06-2010, 02:29 PM

It means "Direct Current motor"

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

deadwolfbones · 10-06-2010, 02:35 PM

Yeah, this was known from the day of the lens's announcement...

Stringmike · 10-06-2010, 03:33 PM

That's what my car's starter motor is. I hope Pentax's is smaller and quieter!

Mike

opiet70 · 10-06-2010, 08:34 PM

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.

Blue · 10-06-2010, 09:13 PM

Originally posted by opiet70

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.

SteveM · 10-07-2010, 01:05 AM

Originally posted by Blue

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 ..

Gimbal · 10-07-2010, 02:41 AM

Originally posted by opiet70

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.

opiet70 · 10-07-2010, 12:00 PM

Originally posted by Gimbal

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

RioRico · 10-07-2010, 01:24 PM

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.

Blue · 10-07-2010, 02:37 PM

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.

**Ash** · 10-07-2010, 03:36 PM

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...

**Ex Finn.** · 10-07-2010, 03:41 PM

Originally posted by RioRico

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.

RioRico · 10-07-2010, 04:30 PM

Originally posted by Ex Finn.

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.

**Ex Finn.** · 10-07-2010, 05:08 PM

Originally posted by RioRico

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.

10-06-2010, 02:29 PM	#1
arm_jstp Veteran Member Join Date: Apr 2009 Location: Blacksburg, VA Posts: 485	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

10-07-2010, 05:08 PM	#14
Ex Finn. Site Supporter Join Date: Nov 2007 Location: Southern Maryland. Espoo. Kouvola. Photos: Gallery \| Albums Posts: 7,975	Originally posted by RioRico 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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10-06-2010, 02:35 PM	#2
deadwolfbones Veteran Member Join Date: Sep 2007 Location: La Crescenta, CA Posts: 7,450	Yeah, this was known from the day of the lens's announcement...

10-06-2010, 03:33 PM	#3
Stringmike Senior Member Join Date: Jul 2008 Location: Arizona Posts: 283	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
opiet70 Veteran Member Join Date: Apr 2009 Location: Dallas, TX Photos: Gallery \| Albums Posts: 499	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
Blue Moderator Site Supporter Join Date: Jun 2008 Location: Florida Hill Country Photos: Gallery \| Albums Posts: 17,377	Originally posted by opiet70 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
SteveM Veteran Member Join Date: Jan 2009 Location: Vancouver Island, BC, Canada Photos: Gallery Posts: 3,294	Originally posted by Blue 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
Gimbal Pentaxian Join Date: Apr 2007 Location: Sweden Posts: 2,106	Originally posted by opiet70 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
opiet70 Veteran Member Join Date: Apr 2009 Location: Dallas, TX Photos: Gallery \| Albums Posts: 499	Originally posted by Gimbal 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
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	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
Blue Moderator Site Supporter Join Date: Jun 2008 Location: Florida Hill Country Photos: Gallery \| Albums Posts: 17,377	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
Ash Loyal Site Supporter Join Date: Mar 2007 Location: Toowoomba, Queensland Photos: Gallery \| Albums Posts: 23,920	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
Ex Finn. Site Supporter Join Date: Nov 2007 Location: Southern Maryland. Espoo. Kouvola. Photos: Gallery \| Albums Posts: 7,975	Originally posted by RioRico 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
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	Originally posted by Ex Finn. 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.