Terry pretty much nailed the reason I suggested the DataQ system. Yup, no doubt
you can use Arduino and if that’s your thing, then absolutely, go for it.
There’s probably a few resources and libraries around for data acquisition. Any
microprocessor with analogue inputs will work as a hardware interface to either
an amped sensor or to the external instrument amp of a straight bridged sensor.
There are also other acquisition systems that are cheaper and/or faster and/or
offer higher resolution than the DataQ options, but many don’t have the
software front end that sells the DataQ.
Regarding the sensors: there are 2 main types. Those with only strain gauges
and those that include an instrument amp or stable operational amplifier(s).
You ideally want the latter as you can interface it directly with your micro or
acquisition module – unless your module accepts things like millivolt
thermocouple inputs, but even then, I’d personally prefer something like a 0-5V
or 0.5-4.5V output from my sensor.
As for the hole: yes, you will need a hole somewhere in your chamber –
preferably in the forward end with perhaps a small length of tube/pipe between
the sensor and the chamber which can also be filled with grease as Ken
suggested. This is to protect the sensor’s diaphragm from direct exposure to
the hot chamber gases.
Depending on the accuracy required, you can possibly mount a strain gauge
directly to the outside of the casing if you *really* wanted to avoid holes
(that’s what I did with my pyroless deployment chamber
www.propulsionlabs.com.au/Pyroless_Release/Stress_
<http://www.propulsionlabs.com.au/Pyroless_Release/Stress_&_Stretch2.xls>
&_Stretch2.xls ) , but if you’re testing more than 1 motor, then you’ll find
that screwing and unscrewing a pressure sensor is much more convenient. Also,
you’ll have to allow for & protect against high temperatures for the strain
gauge option.
The other option if you really wanted to avoid holes is you acquire your
pressure from a load cell ie. measure the thrust on a load cell and subtract
your theoretical thrust coefficient OR use a straight orifice as nozzle ie. no
convergent or divergent section; only a straight short throat. This should
provide thrust with no thrust coefficient ie. Pc x At, so simply divide by At
to get your Pc.
Again, it’s not much work to put a tapped hole into a forward bulkhead in the
vast majority of cases.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
Ramizcan Umut Seckin
Sent: Thursday, February 23, 2023 3:40 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Subject: Re: S-26.500 KNSB Sugar Shot test tomorrow
Troy,
Isn’t it easier using an Arduino laying around (also cheaper) instead of the
DataQ module?
I never tried transducers before, do you need to make a hole in the bulk head
or can it be done without (used load cells till now)?
Last question is it possible to just use a transducer in order to make a
impulse graph?
Raum
On 21 Feb 2023, at 22:47, Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx
<mailto:troy@xxxxxxxxxxxxxxxxxxxxx> > wrote:
John,
Seriously, you can pick up a cheap Chinese transducer up for not very much at
all these days eg:
https://www.aliexpress.com/item/4000704177712.html?spm=a2g0o.productlist.main.37.36306a5c49iiuO&algo_pvid=8e31b2f2-0268-4b88-aa52-48ab4ca50125&aem_p4p_detail=202302211321284979106786310800001783306&algo_exp_id=8e31b2f2-0268-4b88-aa52-48ab4ca50125-18&pdp_ext_f=%7B%22sku_id%22%3A%2210000006206659883%22%7D&pdp_npi=3%40dis%21AUD%2124.09%2122.89%21%21%21%21%21%40211be59e16770144882715524d06f7%2110000006206659883%21sea%21AU%21100784320&curPageLogUid=jwiSi6bY02xM&ad_pvid=202302211321284979106786310800001783306_19&ad_pvid=202302211321284979106786310800001783306_19
and a basic DataQ module for $50 which you shouldn’t lose in a mishap
https://www.dataq.com/products/di-188/
Not much investment provided you have a PC to run it with or even some flight
electronics have the capability to log additional data channels. Craig
Strudwicke’s old flight computer was one example of that. In fact, my
multimeter does data logging.
I mean, for *candy* motors, you generally don’t worry, but for something this
size – as you would know, there’s a fair bit of work in producing something on
this scale irrespective.
Troy
From: <mailto:arocket-bounce@xxxxxxxxxxxxx> arocket-bounce@xxxxxxxxxxxxx <
<mailto:arocket-bounce@xxxxxxxxxxxxx> arocket-bounce@xxxxxxxxxxxxx> On Behalf
Of John DeMar
Sent: Wednesday, February 22, 2023 6:29 AM
To: <mailto:arocket@xxxxxxxxxxxxx> arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Subject: Re: S-26.500 KNSB Sugar Shot test tomorrow
Ken,
The one thing it may tell us with some certainty is that the cause wasn't
the hardware. Even with an aluminum case, it should have held 1500 psi. But, it
would be helpful to see the retaining ring, to see if it's intact or sheared or
rolled.
Regarding the instrumentation, burn time plus success is good enough for the
relatively low cost of this motor. The loss of any sensors and related
equipment could exceed the investment in the test article.
-John DeMar
Las Cruces, NM
https://www.linkedin.com/in/jsdemar/
On Tue, Feb 21, 2023 at 12:02 PM roxanna Mason <rocketmaster.ken@xxxxxxxxx
<mailto:rocketmaster.ken@xxxxxxxxx> > wrote:
Other than the test video, without any instrumentation, post test hardware
inspection (and speculation) will be all you can do to conduct your analysis.
One channel minimum of Pc, chamber pressure, trace would be helpful. Even an
analog pressure gauge on video would give
at least a low frequency reading and maybe give the failure pressure...
Posting some pics of the post test hardware would give more eyes on the subject
and more chances of zeroing in on the overpressure mechanism.
Ken.
On Tue, Feb 21, 2023 at 8:25 AM John DeMar <jsdemar@xxxxxxxxx
<mailto:jsdemar@xxxxxxxxx> > wrote:
Rick,
From those specs on the case and screws, I get about 2800 PSI to shear the
screws (derate grade 8 tensile strength by 50%). Assuming 1/4" wall
standard-grade oil pipeline steel, the case should have deformed the holes at
2000 PSI and sheared at 2400 PSI. High grade pipeline steel would shear at 3000
PSI. I didn't derate for temperature based on the short time to heat soak.
So, plenty of margin on the hardware for a normal operating pressure in the
1000 to 1500 PSI range.
-John DeMar
Las Cruces, NM
https://www.linkedin.com/in/jsdemar/
On Mon, Feb 20, 2023 at 7:18 PM Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx
<mailto:dmarc-noreply@xxxxxxxxxxxxx> > wrote:
The case was approximately 12 inch by 9 feet long, quarter inch wall oil
pipeline steel pipe.
24 grade 8 half inch bolts in two rows holding the quarter inch wall steel
retaining ring.
The forward bulkhead was a steel plate welded in the motor case.
5 grains of KNSB propellant 20 inch long with the cores varying from 2.5 inches
at the bulkhead to 4 inches at the nozzle
We used aluminum motor cases as our mandrels covered in silicon sheet and
greased for release.
The nozzle grain weighed in at 124 pounds with the others slightly heavier
because of smaller cores.
The nozzle had a 94% ideal density, normal density for me is 96-98%
I was up all night Thursday and much of Friday night helping student teams so I
left soon after our 12 inch test.
Not sure what caused the anomaly, lots of speculation and guessing. I'm still
investigating the cause.
We had two previous successful 12 inch KNSB sugar tests, one with 2 grains and
one with 3 grains.
This test had five grains and was designed to be progressive to test our three
piece safety nozzle.
Design pressure at start up was higher than the two previous 12 inch tests.
Flew a 4 inch KNSB motor just a couple hours before the 12" test
<https://www.youtube.com/watch?v=jWspWbTCXbM> UCLA Rocket Project Avionics &
Recovery test
<~WRD0000.jpg>
UCLA Rocket Project Avionics & Recovery test
<https://www.youtube.com/watch?v=jWspWbTCXbM>
https://www.youtube.com/watch?v=jWspWbTCXbM ;
Rick