Member postings for Joseph Noci 1

It does not have the flex springiness of a carbon fibre rod, ie a matrix of fibres in resin. It's mass is nill and I would think would be superior to a 'solid' rod - unless the rod was of significant dimension and mass so that it's inherent resonance is far lower than the pendulum rate.

I think you need to read my post slowly...

I did not say 'use a carbon fiber rod' - I suggested a single fibre, pure fibre, no plastic matrix involved to absorb moisture( which would nominally not be present in a vacuum anyway) - no twanging possible, much less temp coef than your steel, in fact nominally negative when made hot...

I searched ( tediously) through all the pendulum threads and posts to find what was said about using carbon fibre as the pendulum rod - All I found was related to a carbon fibre in rod form, but not much help beyond that.

Since a single carbon fibre extracted from some high modulus Carbon Tow has a thermal expansion coefficient perhaps 6x less than aluminium, perhaps up to 3x less than steel, and that single fibre will easily support 10kg, is it not practical to use a fibre to support the bob - each end of the fibre fixed say 100mm apart at the top of the pendulum support structure and the bob fitted at the apex of the fibre down below. That would eliminate lateral swing, with a pure arc - along the lines of the dual support spring. I question the 2nd order effects of steel/brass springs - they will resist and assist the swing in their own way. . Perhaps this application of carbon fibre has been covered and rejected for good ( or bad?) reasons, but I could not find any reference.

If you really wanted to compensate the Carbon Fibre thermal performance with ambient temp, simply measuring the temp inside the tube would be sufficient - the fibre is so thin, it would hardly differ in temp from the sensor and surrounding low air pressure ( I assume not a high vacuum..). 

Edited By Joseph Noci 1 on 20/04/2023 12:53:41

What about fitting an ESP8266 WiFi uP ( or similar - there are many types) and asmall battery into the pendulum bob position(inside the bob?). Use a thin tube rather than a solid rod for the pendulum and run thin wires up midway with a thermistor at the end. Set the ESP to wake up and do a temp sense every 10min or so and collect that on WiFi. A CR2032 Li cell would last a year or more.

If a tube is a no-no, use the rod and superglue 34gauge ins wires neatly along its length to the thermistor.

Duncan, My comments were based on your initial statement re the dummy being outside the chamber...like me..

Edited By Joseph Noci 1 on 18/04/2023 11:26:54

Since Air temp is irrelevant ( no air in the column), surely only the temp of the pendulum rod inside the column is? It's temp is what makes it's length vary, and the lack of air means air density with temp has no meaning.

I had a similar issue with cross laminated Cedar planks - Eventually discovered that the resin in the raw wood was not fully dried when embedded in epoxy, and the heat frmm the epoxy exotherm during curing ( about 40 to 45deg C) caused the wood resin to exude and this inhibited the epoxy cure in a number of places. In direct sun the epoxy would soften more and dribble out in the wood grain.

There was no cure (sic)..

Subsequent laminations were preceded by long periods of drying in a wood curing oven - 3 weeks @ 40dec going down to 30degC in the last week.

I suspect in your case the 'small tree' sections were uncured and high in wood resins, maybe even wood sap.

I think the only way out is going to be to cut out the offending area completely, and redo it with cured wood..

And then stretch your pendulum that your are trying to insulate from the environment..

Nice to see the ELS is still working Duncan.

Thank you Moderator, for the 3D insert...!

Some may remember my Polar 3D printer - I have issues with drive motor to arm gear ratios and associated print nozzle travel resolution at the moment. I intend fitting a sub 3Arcsec gearbox between the motor and current drive train - my choices are 10:1 and 20:1 ratios ( the current train is 8.5:1, so end result is 85:1 or 170:1) . The 20:1 (170:1) is my choice for resolution, but that places limits on nozzle linear rate -servo max speed, etc.

However, I am not sure what sort or linear lay-down rates users are achieving with their printers , therefore not sure what to aim for. Obviously it is subject to many factors - filament type, print temperatures, nozzle size and filament feeder feedrate capability, etc.

Given a good, solid printer, with a good feed head and basic 'fast print' filament, with 'basic print quality' ( all good enough for rapid prototyping) what linear axis rates are being achieved?

(EDIT - I did not post a 3D print intro in the title, as I posted this in the 3D print forum section - thought it would add that for me!)

Edited By Joseph Noci 1 on 29/03/2023 14:46:05

Caps in parallel add, so final RC remains the same.

Not really - it depends on the duration of the pulse as well. A 1us pulse will be suppressed by that cap.

Even for a 1MHz rep rate, your do not need fancy resistors, etc...The Resistor is only 100 ohms, so any carbon film 1/2 watt will be just fine. Even a 1/2watt wirewound resistor of 100 ohms will do - it will have an inductance of around 150nh = 1ohm @ 1MHz , which is lost in the noise of the 100 ohms, and way above the pulse rate you might work at.

Make C1 a ceramic 1uf, nice and fast, and C2 can be electrolytic. Use 3 x 1000uf and that will reduce the ESR nicely. Ditch C3. That is a typo...U1 is essential.

However, running this circuit at 20Hz is nonsense. The RC time constant of R1-C2 is around 300millisec. 63% of the 5V supply is 3V, which is around the threshold voltage of a typical white led. So the voltage at R1/C2 junction will reduce and stabilise at the LED junction voltage and stay there as the pulse rate is increased. The current through the LED will then only be limited by R1, ie 50mA. Hi current pulse will only be evident below the RC time constant period...This will be modified by the period of pulse to some extent - a very short pulse - 10 of ns, won't discharge C2 completely, so the regulation point will be higher.

You said you want to increase the pulse rate - this will make it worse. For 50Hz rate, you need an RC constant of at least half that, 10ms or so, which would make R1 = 3ohms , making lower pulse rates instantly destructive...

What rate do you want to run at? This sort of circuit is remarkably non-linear - the LED current reduces fast with increase in pulse rate, and is highly dependant on source pulse width.

I think a short description of your final application might suggest a better circuit, or allow tailoring of this one to suite..(avalanche circuits are commonly used for this)

Edited By Joseph Noci 1 on 17/03/2023 06:11:00

I have overpainted powdercoated parts often - mostly to have multi-tone colours on a large powdercoated part - never sanded or roughened the surface prior to painting. Also never used a primer.. All I have done is wet the area profusely with lacquer thinners till the surface is notably tacky, and then paint on the new paint right away - I have used enamel ( turpentine base) and Lacquer or Thinners based brush-on, roll-on and even rattle can spray paints. I have examples that I did 8 or 9 years ago and there is no loss of adhesion at all..Quick, easy and no fuss.

Edited By Joseph Noci 1 on 13/03/2023 07:48:13

I use Boelube 70200 solid lube and 70104 handheld lubricator ( liquid lube) - both work very well for drilling and tapping Ali,brass, mild and stainless steel. The 3oz solid lube is half used over 4 years... Maybe an option to Trefolex?

Come now Mason....let's all play nicely here - its about 'time'...

Never found John's ego an impediment to sound discourse at all - he does like to chase the science and thats good...

This thread is great and has stimulated thought in many folk - lets keep it that way.

During the installation of a Solar PV system on the house roof, I had to drill many 12mm holes( 350 holes..) in 6mm Stainless steel sections ( 316 grade).

A Cobalt drill did approx 50 holes at which point the exit burr extended 2 to 3mm.

I used 3 Cobalt drills ( conventional conical point) for approx 150 holes and ran out of drills in the town...

The only drill I could find then was a RUWAG bit - RUWAG always struck me as a Weekend DIY store supplier, and I had no faith in the product 'quality' - based on no experience whatsoever. Anyway, purchased 4 of these drill bits:

https://ruwag.co.za/products/turbo-metal-drill-bit?variant=12690802606174

Even that name put me off!

The result after 74 holes, with the SAME drill bit!!

Coolant was used, - a squirt bottle with soluble oil/water mix, one liberal squirt at the start of drilling ( the conical bit required a second squirt halfway thru the hole..)

Slight crumbling of the corner edges

Nice cuttings..

Part drilled hole

74th Hole entry (top) and exit (bottom) burr

Who would have thought!

Edited By Joseph Noci 1 on 25/02/2023 06:51:21

I would'nt - 1 Hz error is within 0.1ppm for that OCXO - much better than your pendulum right now - MUCH better...

Let the OCXO run with the picpet thingy and log data for 24hours - use timelab or whatever and do the ADEV and see what you get.

mm, trying hard not to get drawn too deep down this tunnel..I suffered it during my two GPSDO's development...

However..Any time to digital convertor - picpet, etc, must be fed with a ref frequency superior in accuracy/stability to the measurand - Michael said it - what is the reference you are using? Is it the GPS? If so , what frequency have you set its pps clock to? Not 10MHz I hope...

Michael also mentioned :

Meanwhile, it seems to me that the most accurate thing you have available is the GPS … and the ability to divide its output by integer values.

The divide by integer is not quite correct - to be clear, the only low jitter values the GPS 1PPS output can be programmed to are 1,2,4,8,16 and 24MHZ - ie, divide by 2's. 8 is an integer, and div by 8 gives 6MHz with bad jitter...etc.

HOWEVER, Bbe careful of the Monkey here...you can spend most of your spare time chasing a stable and accurate ref clock...while the stability and accuracy of you desktop pendulum is orders poorer than even a basic 1PPM TCXO.

Before said TCXO's characteristics are challenged and begin to contaminate the pendulum performance, you may find a year or more of pendulum development in the way...

A 1PPM 10MHz osc is quite adequate for substantial stability and frequency accuracy measurements. Use a 1ppm or 0.5ppm TCXO ( 10USD) , pack it in a styrofoam brick, stabilised PSU, settle for two or three days and you will be hard pressed to do better , and will not need to, till your pendulum is REALLY good...This will manifest in ADEV where the pendulum rivals the refclock, ie when ADEV gets down to around 10 minus 6 or so...

Using 1sec ref clocks from internet time servers, via the Pi, etc, timestamped and shuttled around - You have to be very good at it to not add subtle shifts and jitter to the result, which you will believe is good and will lead you astray. You have little means of verifying the quality of result.

Re the Freq of your OCXO Dave - I suggest it most unlikely that the 10Hz error is correct. An OCXO with 2Hz adjustment (0.2ppm) is generally reserved for fairly decent OCXO's - of which the frequency accuracy will generally be within the adjustment range after a specified aging life time, generally specced at 5 years, some even 10 years. Banging the OCXO will mess it up a bit, but it takes quite a bang, some 10's of G's..

It is all too easy to blame the indeterminable when the test setup is not quantified, qualified, and well understood.

Edited By Joseph Noci 1 on 24/02/2023 20:01:48