Any servo system will display that behaviour; the limiting factor is how much torque you can get out of the motor to correct the disturbance, and by what degree. The motor is what it is - no amount of electronics is going to make it more powerful.
This is only a drawing - not a real oscillograph, but it makes me think I should see sine waves in real life.
Attachments
We can't let you get away so easily.
Even if you give up on construction - keep posting your ideas!
That circuit fragment I copied up last post... it has two electrolytic capacitors C16 and C17. These are well known for drying up and becoming leaky, even in a handful of years. That may be a common fault in all SP10s after such a long time in service.
re: C for PICS.
Are there any free compilers that produce *good* hex code though? My limited experience so far was that the free compilers generate poor code - inefficient use of memory, many redundant op-codes, and slow or unpredicable timing. The code optimiser costs big money.
I kinda like ASM, because I like to know I have complete control over exactly what is going on... it can be so tedious to create though - and madening to modify a few weeks later when you (I) have forgotten how it was suppossed to work!
I can ask about this. My suspicion is that currently memory space is less of a constraint than it was, say, 10 years ago. Even when I was writing in C, I found it useful to check the generated code (the assembler version), especially when the timing yielded unexpected results. I believe that the secret is to keep the interrupt routines simple.
Then you have been naughty!!!
Did you neglect to document your code properly? ....adding comments and making flow charts? .... I think most of us are guilty of that....
Memory space is a bit of an irrational thing for me - something the young people of today know nothing about.
I suppose it's like people who grew up in 'The War' cannot waste food; I still think it's a sin to waste RAM, remembering a time when you had to get your whole program and OS into 16kB.
Am I showng my age? Bah that's nothing.. my first 'record player' had to be cranked every two sides, and the needle replaced just as often.
I suppose it's like people who grew up in 'The War' cannot waste food; I still think it's a sin to waste RAM, remembering a time when you had to get your whole program and OS into 16kB.
Am I showng my age? Bah that's nothing.. my first 'record player' had to be cranked every two sides, and the needle replaced just as often.
Things are progressing...
I've decided on a Wein bridge for the phase excitation oscillator, since it requires no inductors, and it gives a low distortion sinus. Don't be confused though - this sine wave is not the one that actually drives the motor, so low distortion maybe is not all that important.
Anyhoo.. it's an easy oscillator to make work, with everyday parts (like an NE5534, as I used here - a good use for the noisier ones that have no place in pre-amps!)
With that done, and an active full-wave peak detector to recover the signal from the phase pickup coils, this is the waveform that I get: oscillograph.
(now that's one of the three 6Hz or so signals that will actually drive the motor)
There is some distortion, which does NOT come from the detector circuit - it's a very linear detector topology. So I went searching for the source....
It turns out to be in the construction of the motor itself:
[It seems I can't put two picture in one post, so see next post for this picture]
take a close look at the copper-coloured reluctance ring: the 'top' and 'bottom' of the diamond shaped holes are flattened off, which puts a plateau on the lower limit of the magnetic coupling between the exciter coil and the phase pickup coil.
After AM demodulation, that shows up at a slight flattening off of the lower peak of the sine wave.
I suppose purist might even want to remove this ring and file it to a better shape???
I don't believe it will have any notable effect on the final system; the motor/platter inertia will damp most of it, and the negative feedback servo will reduce any residual non-linearity to imperceptible levels.
Next step, get 3 L165V power op amps. These will become the motor drive circuits. WAY simpler than actually building a discrete transitor power driver, if slightly more expensive (the L165V is us$3.50 at my supplier).
I've decided on a Wein bridge for the phase excitation oscillator, since it requires no inductors, and it gives a low distortion sinus. Don't be confused though - this sine wave is not the one that actually drives the motor, so low distortion maybe is not all that important.
Anyhoo.. it's an easy oscillator to make work, with everyday parts (like an NE5534, as I used here - a good use for the noisier ones that have no place in pre-amps!)
With that done, and an active full-wave peak detector to recover the signal from the phase pickup coils, this is the waveform that I get: oscillograph.
(now that's one of the three 6Hz or so signals that will actually drive the motor)
There is some distortion, which does NOT come from the detector circuit - it's a very linear detector topology. So I went searching for the source....
It turns out to be in the construction of the motor itself:
[It seems I can't put two picture in one post, so see next post for this picture]
take a close look at the copper-coloured reluctance ring: the 'top' and 'bottom' of the diamond shaped holes are flattened off, which puts a plateau on the lower limit of the magnetic coupling between the exciter coil and the phase pickup coil.
After AM demodulation, that shows up at a slight flattening off of the lower peak of the sine wave.
I suppose purist might even want to remove this ring and file it to a better shape???
I don't believe it will have any notable effect on the final system; the motor/platter inertia will damp most of it, and the negative feedback servo will reduce any residual non-linearity to imperceptible levels.
Next step, get 3 L165V power op amps. These will become the motor drive circuits. WAY simpler than actually building a discrete transitor power driver, if slightly more expensive (the L165V is us$3.50 at my supplier).
Attachments
The SP10 motor reluctance ring, referred to in the previous message.
While staring at it I had another thought.... for the masochistic purists (puritans???) it would be possible to laser-print a more sinusoidally accurate black/white image, much like this string of diamonds (or even cut it out of paper, like those party festoons of figures holding hands!), and stick this printout/cutout on the outter periphery of the motor - where the brake band is normally. Then read it with three photo-diodes.
While staring at it I had another thought.... for the masochistic purists (puritans???) it would be possible to laser-print a more sinusoidally accurate black/white image, much like this string of diamonds (or even cut it out of paper, like those party festoons of figures holding hands!), and stick this printout/cutout on the outter periphery of the motor - where the brake band is normally. Then read it with three photo-diodes.
Attachments
.
I'm back!
I would just stop the bottom edge clipping, perfection and all that!.
Under near stall, but locked condition, the voltage stays the same but the drive current goes from about 100mA to nearly 1A.
The voltage is actually 28 volts. If I have managed to do this, here is a image of the drive waveform under load. How to put a thumbnail in would be good?
Regards
Dave
.
I'm back!
I would just stop the bottom edge clipping, perfection and all that!.
Under near stall, but locked condition, the voltage stays the same but the drive current goes from about 100mA to nearly 1A.
The voltage is actually 28 volts. If I have managed to do this, here is a image of the drive waveform under load. How to put a thumbnail in would be good?
Regards
Dave
.
>>I would just stop the bottom edge clipping, perfection and all that!.
It isn't clipping - well not in the sence that amplifiers clip, due to transistor saturation, or running out of headroom.
You have a way to 'peak' the bottom of the wave?
What I'm getting does look rather cleaner than the 'real' SP10 signal you're measuring.
The broadening of the trace at the peaks is because the waveform fluctuates very slowly, and the pic is a very slow exposure.
28V ? Ok.. we can do that.
{Thanks for the number 28!}
It isn't clipping - well not in the sence that amplifiers clip, due to transistor saturation, or running out of headroom.
You have a way to 'peak' the bottom of the wave?
What I'm getting does look rather cleaner than the 'real' SP10 signal you're measuring.
The broadening of the trace at the peaks is because the waveform fluctuates very slowly, and the pic is a very slow exposure.
28V ? Ok.. we can do that.
{Thanks for the number 28!}
The motor drive voltage can't be 28v, must be 2.8v:
12.6R coil resistance (each phase), and I measure the back emf at around 0.7v rms at 33rpm.
If the current consumption is 100mA (lets knock off a few mA for ancillary circuitry) and say it's 30mA per phase, that gives an mmf of 12.6 * 0.03 = 0.36v. Plus the back emf of 0.7 = 1.06 v rms.
1.06 v rms = 2.99v p-p --- very close to the 2.8v I thought was printed on my circuit.
Under load, I calculate it will go up to around 4.0v
This means that for the new design, the power supply doesn't need to be as high as the original 31v; I'm guessing something like -9/+9v, or maybe -12/+12v.
Another question: does the SP10(ii) use reverse motor drive to bring the platter to standstill ? From the schematic I have, it seems it puts the mechanical brake on the instant the stop button is activated.
12.6R coil resistance (each phase), and I measure the back emf at around 0.7v rms at 33rpm.
If the current consumption is 100mA (lets knock off a few mA for ancillary circuitry) and say it's 30mA per phase, that gives an mmf of 12.6 * 0.03 = 0.36v. Plus the back emf of 0.7 = 1.06 v rms.
1.06 v rms = 2.99v p-p --- very close to the 2.8v I thought was printed on my circuit.
Under load, I calculate it will go up to around 4.0v
This means that for the new design, the power supply doesn't need to be as high as the original 31v; I'm guessing something like -9/+9v, or maybe -12/+12v.
Another question: does the SP10(ii) use reverse motor drive to bring the platter to standstill ? From the schematic I have, it seems it puts the mechanical brake on the instant the stop button is activated.
Circuitry as far as it has develped, if anyone wants to see what I used to get the waveforms above.
I'll be buying power op amps tomorrow, so things might start to get uncontrollably thrilling quite soon!
http://web.eject.co.za/s8nspawn/electronics/sp10sch.gif
(97kB gif image)
I'll be buying power op amps tomorrow, so things might start to get uncontrollably thrilling quite soon!
http://web.eject.co.za/s8nspawn/electronics/sp10sch.gif
(97kB gif image)
Speak now or forever hold your piece
I'm about to start doing the PCB layout. If anyone has any practical hints on the SIZE of the board, please do tell.
Since I have no specific box in mind, I'm just going to make the boards arbitrarily square-ish, around 6"x5".
One board for power and driver, one board for control (smaller).
The control board is separate since I might well create several different designs, and if they are pluggable, it's easy to compare performance. The power board contains the expensive parts, so I don't want to duplicate it.
I'm about to start doing the PCB layout. If anyone has any practical hints on the SIZE of the board, please do tell.
Since I have no specific box in mind, I'm just going to make the boards arbitrarily square-ish, around 6"x5".
One board for power and driver, one board for control (smaller).
The control board is separate since I might well create several different designs, and if they are pluggable, it's easy to compare performance. The power board contains the expensive parts, so I don't want to duplicate it.
I haven't got them yet - out of stock; located a different source who has in stock, to be got tomorrow (R33.00 each).
These will be evaluation boards, but I'm very confident they'll work the way I want them to first time round. (The power amp and PSU part anyway).
This is why the controller is a separate board - it may need mods along the way.
These will be evaluation boards, but I'm very confident they'll work the way I want them to first time round. (The power amp and PSU part anyway).
This is why the controller is a separate board - it may need mods along the way.
This circuit is becoming slightly complex!
Was one of the original specifications "simple" ?
The 3-phase power stage:
http://web.eject.co.za/s8nspawn/electronics/sp10drv.gif
Oh, maybe its not SO compliated - it's not exactly performing a trivial function, like driving a DC motor.
I have the L165's ! Even cheaper than the price I originally thought.
Was one of the original specifications "simple" ?
The 3-phase power stage:
http://web.eject.co.za/s8nspawn/electronics/sp10drv.gif
Oh, maybe its not SO compliated - it's not exactly performing a trivial function, like driving a DC motor.
I have the L165's ! Even cheaper than the price I originally thought.
This is interesting to read as you guys are figuring out what to use for the power supply/controller.
I just wanted to voice some support, instead of just lurking ..
To me this is an exciting project... I'm looking foreward to one day upgrading my SP-10's and being able to just have the motor mounted to the plinth.
Again, great work!
Rick
I just wanted to voice some support, instead of just lurking ..
To me this is an exciting project... I'm looking foreward to one day upgrading my SP-10's and being able to just have the motor mounted to the plinth.
Again, great work!
Rick