Here is a list of all the postings Joseph Noci 1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: capacitance in long cables|
Not really fair, or very nice, that answer, Andrew...
Duncan's question was :
Now one for the electronic gurus............................... There must be some capacitance between the cores, so what happens when I switch on? If the message cable wasn't connected to anything else I'd expect it to go to half of 12v, which would be embarrassing as it would exceed the 5v limit on the electronics. If I had a battery scope I'd just measure it, but I haven't, and we have no mains power. We do have a generator, but would that be good enough for my expensive scope?
Duncan did not ask why it is not working now, after being OK for two years...
No problem suggesting alternatives to Duncan's signalling solution and implementation, but that's not what was asked, no?
A reasonable answer to his question does not monkeys of us make..
Either zeners or caps - don't need both. If you had lightening in the area, zeners would be better, but then the ground is probably questionable with lightning around..
Caps are all that is needed - 10nf for 20m, 47nf for 100m good enough.. The simulation is a 'perfect' one - the voltages you get with a scope will most likely be a fair bit less, as I have not modeled the inductance of a 100meter length in the setup, nor taken any dielectric ( cable insulation) losses into the model - but that is becoming esoteric.. and offers little to the solution here.
Just one point on Joe's test, shouldn't there be a capacitor from the nominal 2.5v point to ground?
Uhmm, there is one....?? 10nf...3rd solution image..
lets assume a 8mm OD 3core cable of 1mm sq Cu - this has typically around 97pf/meter tween cores.
take 20 meters - thats 1940pf, with a R of 1k to gnd and one to 5v.
A +12v pulse on an adjacent wire will spike the signal wire up to approx 10v, and down to approx -5v when the +12v turns off.
Add a 10n cap tween signal line and ground, and the spike reduces to +4.1v and +0.9v when the 12v is turned on then off.
Here's reasonable proof..
2x1k load, no cap to gnd
2x500ohm load, no cap
2x1k load, 10n cap
|Thread: Unusual Project|
Everyone keeps mentioning 'wings'. Well, if we accept that whatever it is is a wing, then I see only one wing and one wing engine - which seems MUCH bigger than the tail engine,and if the 'wing' can tilt, then all this thing can do is the most spectacular sub-warp donut...
And this is a spacecraft, no atmosphere involved - the fans pulverise small asteroids to feed the Positron Warp Drive.
Have you been banned from the workshop Neil?
|Thread: Scaling back forum activity|
|Thread: DIY Rotary Quadrature Encoder|
Neil, I think it is actually very good - If for example you were to use it for a spindle encoder for an ELS, it would be more than adequate at 0.5degree non-linearity. If used however as a 1:1 axial sensor on a rotary table, 0.5 degree error may not be acceptable..
What do you mean by absolute In terms of this device? It can give absolute angle in degrees from a calibrated zero point, give quadrature with a calibrated reference signal, and provide a 24bit PWM output related to angular position.
Regarding placing the IC in the center - I did make a automatic vacuum pencil that fits on my PCB engraver. The engraver also has a centering camera with cross hair, the idea being that I can engrave the PCB, and since the centre is then known, use the camera cross hair to center the pickup of the device and place it on the PCb with the vacuum pickup...If I were going to make a half a dozen...
Makes nice VFO tuning knob on my radio...
That's why I stuck to a circular construction - center is controlled to small enough tolerances quite easily. The placement of the chip on the board is not to difficult - I did it by centering the device pins on the PCB tracks, under a microscope. Final measurements on the microscope stage show that the IC body ended up centered within 0.06 mm of the pcb disc center. The datasheet indicates a 0.25degree non-linearity for a 0.25mm displacement, 1.5 degree for 1mm displacement, so not to difficult to get it fairly good.
If the PCB were assembled on a pick and place machine then the result is easier to control...
As to the accuracy of the actual magnetic field..best to buy a specified magnet from a reputable supplier!
|Thread: Arduino Pendulum Clock Design - Comments Welcome|
Not trying to do that at ALL! I Nowhere mentioned trying to lock the pendulum to GPS...I locked a reference oscillator to the pendulum...
And By Martin Kyte
The pendulum triggers the arduino timer which fires the impulse some fixed TIME later (Arduini timing). The impulse only occurs at the same POINT if the pendulum is travelling at the same speed.
Yes, of course, I get the picture, but against WHAT do you measure it???
My suggestion was not to lock to the GPS(DO), but to use the GPSDO as a reference to see how accurate and consistent the pendulum swing is. The second 'GPSDO', which IS locked to the pendulum, ie, converted to a PENDULUM LOCKED OSCILLATOR ( NOT the pendulum to it, if you read carefully..) is just so that you can easily compare two hi-frequency PHASE LOCKED clocks to measure accurately the delta and therefore the pendulum timing and jitter. The first clock is phase locked to GPS 1PPS, the second to PENDULUM 1PPx
If you are chasing the sort of accuracy implied in Dave's intent, just observing the pendulum opto- sense pulses on a 'scope is not going to cut it..
If your measurement tools are of lower accuracy or resolution than what is being measured, you ARE blowing smoke..
Dave, would the frequency locking concept used in many GPSDO's not work here ?- where they lock to the GPS 1Hz time clock -
The GPSDO I built uses the 1Hz time stamp from the GPS, which has a lot of jitter and short term inaccuracies, and the rising edge of that is clocked by the reference oscillator we are trying to stabilize, and then into a phase detector whose output is filtered in software - often a 32 to 64 tap IIR filter, easy on an Arduinio at 1Hz...This then locks the reference oscillator.
So, if you get two of those medium class GPSDO's , available relatively cheaply, and use one as your reference - then use the second one as the clock lock - instead of the 1PPS GPS time stamp feeding the phase detector, feed it from the pendulum opto detector. Then lock THAT GPSDO's reference oscillator to the pendulum period, and compare the reference GPSDO oscillator clock to the pendulum locked clock by means of another phase detector. That way there is no chance of locking to any obscure reference.
Maybe I'm just blowing smoke..
WRT magnetic excitation of a pendulum - and not being familiar with the field at all - I can accept that the 'sharp' impulse can perturb the pendulum in modes additional to the desired one - what about this -
Place the electromagnet at the one end of the pendulum swing and use an optical sensor to detect the pendulum position as it approaches the magnet. Have the magnet ALWAYS energised, the level of to be determined while tuning the setup. Then as the opto is triggered, linearly reduce the magnetic field ( current through the coil) to zero, with the zero achieved at some adjustable distance before the pendulum turns around in its swing.
To try have a 'sufficient' magnetic field lying in wait for the pendulum's approach, and as it enters the (now very gentle) tug of the field reduce the field to zero as the pendulum approaches end of swing.
I believe this would impart very little undesired perturbation to the pendulum, and any second order effect should terminate before the pendulum turns around.
edit: - remove an errant 'n'...
Edited By Joseph Noci 1 on 08/09/2020 15:38:53
|Thread: DIY Rotary Quadrature Encoder|
Michael, perhaps this explanation is of some use? AS5147 operation - the pdf is oriented more toward the choice of magnet, but reasonably describes how the device works.
I guess it depends on where you are and how easy it is to procure these things! Fedex/DHL 10 day shipping to me in Namibia varies between US$100 and US$150 from the USA, and about 70 to 80% of that from the UK. From China it is about 1/2 that, but this year I have had poor luck from that part of the world - shipments taking 2 to 3 MONTHS...and some shipments still outstanding since January...
In my world, I sometimes feel that, while most of the rest of you can go out and buy a balanced mixer at the local component store, I have to go out into my back yard, among the granite and quartz mountains, and dig out some Galena while keeping an eye open for a willing cat...
100 of those PCB's can be had for US$40.00. The chips are $7.00 ea for qty 100. I suppose I could do 50 of the housings and shafts in a day maybe?...
The concept is just neat and can easily be adapted to motor shaft ends, etc, without belts and the like.
Michael, exactly as was said - the 4 analogue outputs of the hall sensors are read and a fancy algorithm looks at the relative amplitudes/phase angles and computes the actual angular position of the shaft ( rather, the magnet..) From that it follows that the quadrature outputs are actual just an extension of the position determination. Some very smart design engineers out there, integrating all that into a $10 little chip!
A common component to many of my machine computerisations has been a quadrature encoder. I have always used optical encoders, all with A/B outputs, some also with index output, for applications that require position timing, such as the lathe ELS.
I also use these encoders extensively as MMI input sensors for display data entry, frequency tuning on radios, etc. So, I end up using lots of the darn things, and the costs become a little silly.. I tried making units, with slotted discs, etc, especially for the low pulse count applications, such as data entry, but it is just to finicky.
So, I decided to try a magnetic encoder - chips implementing this function abound these days, with some being really complex - a neat, simple device is the AS5147P datasheet here with a programmable output interface that can do all one would need - I use the ABI ( chan A, B and index) outputs, and these can be programmed to output from 256PPR to 1024PPR ( 4096 edges).
It can also output angles with 14bit resolution.
The device will easily cope with up to 28K rpm, is US$10.00 for one.
It uses a diametrically magnetized neo magnet, 8mm diameter, 3mm thick.
Programming is via SPI , easily done from any Arduino, and the device can be permanently programmed with your desired setup, so that it remains simply an encoder when you power it, with the SPI interface no longer needed.
It works very well indeed.
I knocked up a prototype to test, just used some PVC rod, with an Aluminium shaft holding the magnet
If higher performance ( speed..) is needed, bore out the ends of the PVC body shaft hole to take 2 x 6mm ID bearings..
26mm diameter PCB for the device:
PVC Body, the magnet in the shaft and the pcb assembled
edit - fix syntax...
Edited By Joseph Noci 1 on 06/09/2020 15:12:19
|Thread: My Morgan SCARA coming together|
Wiring and Coax cable to the induction heated hot-end, the fans, thermister, extruder stepper, etc.
Everything moves, drawing squares and circles with a pen in the hotend position looks very very good, hotend induction heating works fantastically well, extruder is a butchered Bondtech unit from a big creality printer.
Next step to fit the bed heater, bed leveling sensor, and a Nextion based control panel so the PC is not needed.
The leveling sensor to use the Texas LDC1101 - a very neat induction measuring device which will use a sliding ferrite rod ( 1mm diameter) that contacts the table and moves into the sense coil. The change in inductance ( a 24bit value) is easily converted to a distance measurement with 20um accuracy, with 5um resolution, from 40degC to 120degC
Just another over-done sensor excercise...
well, therein lies the rub..the 'increase' in resolution is true to a very limited extent, and depends on many things. The proportional increase of resolution with increased microstepping exists only in the magnetic field vector, and in the math..This is not necessarily where the rotor actually moves to! With no load on the motor, the field vector may want the rotor to position itself say 20% away from the current full step position, toward the next, but the strong static magnetic field from the closer stator magnet pole is stronger than that dynamic field vector, so the rotor moves less than it should , sometimes not at all.Bearing stiction makes it worse. As the tween full step position torque is compromised, the rotor lags the field vector and at some point the forward vector is stronger than the lagging static field and stiction, and the rotor moves and catches up ( or almost does..or overshoots). Add to this a load, a leadscrew and the driven table stiction and inertia, and the delta worsens. The electromagnetic field vector is following the improved resolution almost perfectly, but the rotor not...
Microstepping is not the best way to achieve small feeds per stepper pulse...As I said, it does wonders in overcoming rough stepping at low speeds, ie, smoother running, but that can generally be achieved with 1/2 or at most, 1/4 stepping. In most cases where it is found that the 'system' runs more smoothly at some specific microstep value, it is because the system resonance and motor resonance are happiest at that rate - NOT because things are better at that 'resolution'. At 1/2 or 1/4 step, motor resolution does in fact quite closely follow the field vector, depending on the applied static loads.
Microstepping is also advantageous when the applied load dynamic profile is that of an undamped spring - a stepper driving a carriage via a toothed belt, with the carriage slides being low friction ball glides without slide wipers, etc. The mass is easily and quickly accelerated,but bounces and overshoots, etc. At full step, when accelerating thru the MOTOR resonance point(s), the inertial, undamped ' bounce', quickly makes the motor loose steps.
I spent many hours testing and tuning these setups on various cnc machines I built and retrofitted, to try get the most out of them, and if you stick to those concepts ( exceptions abound..) life is a little less difficult! Adding rotary dampers to the motor also works wonders in smoothing out motion and eliminating lost steps.
EDIT - just to add - stepper drivers/controllers are many a culprit in poor motor performance. The shape of the integrated PWM current waveform in the motor windings plays a huge role in stepper smoothness, acceleration and general performance. A simple PWM signal that attempts to simulate a sinusoidal current profile in the motor winding does not cut it when looking for smooth motors, or higher performance. The better range controllers ( analogue type..) will have some pots that allow the user to adjust the current waveform, while running the motor at the first, 2nd and third resonance RPM. The motor is simply placed on a hard surface - table top - and spun up from 0 rpm, slowly, till it vibrates madly. The pot(s) are then adjusted till smooth, and the next rpm point found, etc. All this is doing is pre-distorting the applied currents , and the magnetic field vector to help smooth the rotor steps. And this setting works only for this motor! This process must not be done with the motor fitted as it is the motor rotor resonance that is being compensated. The rest of the system friction and damping mass will mask this.
The good old GECKO drive controller worked this way and were fantastic. There new ones are digital..have not tried them yet.
Digital stepper controllers do exactly the same, but the controller itself observes the back-EMF to find the resonance points, and adjusts the PWM to achieve the same. The benefit of a digital controller is that it will compensate over the full user required RPM range, not just over the lower end.
Edited By Joseph Noci 1 on 29/08/2020 14:00:41
Kevin is quite correct - The issue is HOLDING TORQUE - This is drastically reduced with microstepping - eg, to 0.6% of max when using 256 microsteps/step. When running, or using as a 'motor' - little torque is lost.
Microstepping also worsens motor position accuracy when loaded, and even when not, simply due to the torque required to overcome magnetic detent.
The major advantage of microstepping is to overcome step-losing low speed resonances.
|Thread: Emco FB2 Quirks and Additions|
To add to the variation of FB2's and clones -
I have a FB2 head assembly clone - purchased maybe 15 years ago, that I used as an 'add on' to a horizontal mill.
It looks like a real FB2, but with the switch assy on the motor - see pics. The quill is good, no measurable runout on the inside of the taper. However, the gearbox differs a lot - no fiber gears, and rather noisy. Also the gear mesh is not great. Compared to the FB2 gear set, the gears are all narrower - by about 20%, and the teeth do not mate to proper depth - as though the gear diameters are under size. It works fine, but the noise is quite irritating!
edit - correct syntax..
Edited By Joseph Noci 1 on 28/08/2020 20:40:58
|Thread: Change to the Code of Conduct|
I understand that concept Jason - no problem there. The holders were from China, the tips from Germany - The latter no doubt comply with your italic statement, the former? This is where it is a little grey for me..The Chinese supplier is well known, but then so are Banggood..
I won't become paranoid over this - If I think the knowledge is worth posting I'll give it a bash and let You be the judge!
As an aside, would we be permitted insight into the membership base - number of UK members versus rest of the world? Be interesting!
Edited By Joseph Noci 1 on 28/08/2020 10:03:45
I think whatever the rules and variations are, Moderators will always have an impossible task. Complaints about how the web site works, why is the method of attaching photo's is 'draconian', etc, abound, but no one is prepared to step up with the money, time and effort to fund it and try to do better...Life in general is making the best of a varied set of compromises. If you really feel you have been done by, with your post being 'unfairly' deleted, take it up in a PM with the moderators, but generally things work OK, no?
I do however think the guidelines leave the slightly finer points open to confused interpretation sometimes. I understand the issue of competitive advertising , and even non-competitive direct advertising, but does that not preclude many a useful set of information to modellers from being aired?
For example, in 2017 I posted my experiences in procuring a set of MULTIFIX tool holders, and associated KOMET cutting tips - I think that info would still be of good value to fellow modellers, but would that now be precluded under the present setup?
I am subsequently reluctant to add the reference to my postings ( you can find it if you dig yourself, I guess) but Jason maybe you could provide some guidance on this? Not moaning, just trying to calibrate my understanding of the rules!
Promise I wont post any more photographic dissertations ...
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