On 3/27/13 3:20 PM, Bob Camp wrote: > Eight ohms at 28 volts would be just a bit under 4 amps. It's also > right at 100 watts. I'd be very surprised it you need anywhere near > that much current. You probably want a pure sine wave to keep > everything happy. A lot of the simple inverters are "sort of" sine > waves. I think I'd vote for something like an cheap audio amp driven > by a nice clean / stable 400 Hz tone. So, if I take my nice clean 10 MHz, rig up a counter that counts to 25,000, and a suitable PROM and DAC... (or run a DDS chip)... I think that would be a "clean and stable" 400 Hz. Of course, for the more mechanically inclined.. what about a big flywheel driving an alternator. You might be able to rejigger a car alternator. I don't recall how many poles they have..you might have to spin it pretty fast.

On Mar 27, 2013, at 22:54, Jim Lux <jimlux@earthlink.net> wrote: > On 3/27/13 3:20 PM, Bob Camp wrote: > > > Of course, for the more mechanically inclined.. what about a big flywheel driving an alternator. You might be able to rejigger a car alternator. I don't recall how many poles they have.. A motor driving a flywheel driving an alternator/generator is called a motor generator set. Some implementations are called a diesel electric locomotive. We used to use them as power conditioners for Cray class supercomputers. Also used by many home machinists to generate 3 phase from single phase power. Car alternators are generally 3 phase internally. Don't know if you could get 28vac out tho.

If you need good 3 phase 400 Hz you can get a VFD which goes up that high and program it to just sit there making 400 Hz. On 3/27/2013 11:16 PM, bownes wrote: > > On Mar 27, 2013, at 22:54, Jim Lux <jimlux@earthlink.net> wrote: > >> On 3/27/13 3:20 PM, Bob Camp wrote: >> >> >> Of course, for the more mechanically inclined.. what about a big flywheel driving an alternator. You might be able to rejigger a car alternator. I don't recall how many poles they have.. > A motor driving a flywheel driving an alternator/generator is called a motor generator set. Some implementations are called a diesel electric locomotive. We used to use them as power conditioners for Cray class supercomputers. Also used by many home machinists to generate 3 phase from single phase power. > > Car alternators are generally 3 phase internally. Don't know if you could get 28vac out tho. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1430 / Virus Database: 2641/5707 - Release Date: 03/27/13 > >

Crikey - an alternator? Automotive alternators typically have 6 poles, which delivers 60 Hz at 1200 RPM. You would need to go to 8000 RPM to get 400 Hz, or a bit more than 133 revs per second. That's really humming along. When I was younger, and found a tank gyro about 3" in diameter, it needed 115 VAC 3 phase. I found an electronic 28 VDC to 115 VAC 400 Hz that was single phase. A capacitor to the third phase wire would spin it up after you started it by hand. The motor doesn't care if the excitation is sine or square. There is a bit more heat dissipation from the harmonics in the square wave, but nothing to worry about in a small motor. If you are a purist, as many list members are, you could build a six step inverter to cut down on the harmonics. To be practical, divide 10 MHz from a GPS disciplined oscillator (which is necessary to be talking about this in this group), use a transistor to switch any available DC into a suitable audio transformer, and resonate it to 400 Hz with some caps. There was a time when I'd have killed for that kind of souvenir from a Northwest aircraft, but now I just sit back and read about it with fading interest. Bill Hawkins

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4404126&tag=1

  GPS & oscillator -> GPSDO

  GPS & 3x gyro + 3x accel   ->  GPS stabilised inertial navigation

 Björn

Hi Bill, > Well, I can come up with something topical, read on. :) [snip] > Topical in a more abstract way, strapdown systems really are very > interesting. They require precise integration of the rate output over > time to derive velocity and position, and really weren't practical until > the 70's when small enough computers existed to do the requisite > calculations. (I worked on the nav system for the Trident missile back > in my Draper Labs days). Well, for the analysis of your gyro performance, time-nuts are already equiped with one of the tools used - the Allan Variance. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4404126&tag=1 There is also the relation GPS & oscillator -> GPSDO where in the navigation field GPS & 3x gyro + 3x accel -> GPS stabilised inertial navigation system -- Björn

 http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4404126&tag=1

   GPS & oscillator -> GPSDO

   GPS & 3x gyro + 3x accel   ->  GPS stabilised inertial 

  Björn

Just an idea -- if 440 Hz would work, there are a lot of electronic tuning fork circuits out there. Here is one: http://www.spaennare.se/tfork.html You could choose another crystal frequency or divide-by ratio if it needs to be 400.00 Add a phase-shift circuit to get the other two phases (if needed), amplifiers and you are good to go. Dave > -----Original Message----- > From: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] On Behalf Of bg@lysator.liu.se > Sent: Thursday, March 28, 2013 05:48 > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] OT - DC-10 gyros > > Hi Bill, > > > Well, I can come up with something topical, read on. :) > > [snip] > > > Topical in a more abstract way, strapdown systems really are very > > interesting. They require precise integration of the rate > output over > > time to derive velocity and position, and really weren't > practical until > > the 70's when small enough computers existed to do the requisite > > calculations. (I worked on the nav system for the Trident > missile back > > in my Draper Labs days). > > Well, for the analysis of your gyro performance, time-nuts are already > equiped with one of the tools used - the Allan Variance. > > http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4404126&tag=1 > > There is also the relation > > GPS & oscillator -> GPSDO > > where in the navigation field > > GPS & 3x gyro + 3x accel -> GPS stabilised inertial > navigation > system > > > -- > > Björn > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.