Measuring RPM From Video

[Chris-PA]

......more difficult to read log if you are searching for the can res freq.?

my interest is in other areas at the moment.

I figure you have something in mind, but I'm not sure what it is. If you are interested in resonance tuning of the can muffler, I don't think there is evidence supporting the effectiveness of that here.

1. Changing the outlet will surely change both the external and internal frequency plot, but as this is recorded externally you won't know what is happening inside the can (which is what matters).
2. The presence of harmonics is not evidence of useful resonance that can be used in the can. There are harmonics in the driving signal too, so their presence does not mean the can is resonating.
   
3. Tuned pipes work on the fundamental, not the harmonics, and I'm skeptical one can tune on the harmonics that way.

Here are plots from Brad's recent thread showing the plot from the dual outlet 661 ( http://www.arboristsite.com/community/threads/ms661c-muffler-mod-testing.281169/ ) - it's running from 9800-10,000rpm:

Log:

Linear:

I can confirm Audacity runs just fine on Windoze too

Cool! It's a nice program.

This is a graph out of Nero WaveEditor featuring the frequency levels of my PS-7900 cookie cutting pear (video featured HERE) , but I can't figure out where to read the hertz from:

View attachment 429198

Audacity won't run on my desktop PC (and I know why) , so I'll just stick to what my tach claims!

I don't know that program - is there any kind of spectrum analyzer under Tools or Effects?

 

[malk315]

The spectrum analyzer for left and right at the bottom is too simple to be useful... Looks like a peak at around 3500 but clearly that isn't right. Would need at least a full screen w/ more granularity for frequency and dB.

 

[Chris-PA]

Oh - the depth gauges on the chain on The 46cc were considerably too high. Too many stump sharpenings I guess. That's consistent with what I saw - slow cutting but not much load on the saw.

 

[NWCoaster]

I figure you have something in mind, but I'm not sure what it is. If you are interested in resonance tuning of the can muffler, I don't think there is evidence supporting the effectiveness of that here.

1. Changing the outlet will surely change both the external and internal frequency plot, but as this is recorded externally you won't know what is happening inside the can (which is what matters).
2. The presence of harmonics is not evidence of useful resonance that can be used in the can. There are harmonics in the driving signal too, so their presence does not mean the can is resonating.
   
3. Tuned pipes work on the fundamental, not the harmonics, and I'm skeptical one can tune on the harmonics that way.

Here are plots from Brad's recent thread showing the plot from the dual outlet 661 ( http://www.arboristsite.com/community/threads/ms661c-muffler-mod-testing.281169/ ) - it's running from 9800-10,000rpm:

Log:
View attachment 429200
Linear:
View attachment 429201


Cool! It's a nice program.


I don't know that program - is there any kind of spectrum analyzer under Tools or Effects?

Cool discovery of this program and congratulations for figuring out how to use it. I am a Vibration Institute certified level 3 vibration analyst.... that's what I do for a living every day, so it is cool to see someone utilizing time waveforms and spectrum plots to find the fundamental running frequency of their saw- good job!! We always use Linear scaling in each axis since it is more intuitive for your brain to look at, and also switch from Hertz to Cycles per minute (CPM) since you are also used to looking at things in relation to (RPM) running speed. Also if you can bring up a harmonic cursor and place the primary on the top of the suspected 1x peak , the rest of the cursor boxes will jump up to the tops of the harmonics to help confirm you have found the right peak that is actually the 1x (Running speed). ( The repeating pattern shows up). If anybody has any vibration system related questions.... fire away, this is my bag babay......Lol. So far as the harmonics, think about a pebble being dropped in a pond with the wavelets being produced as they radiate outward from the point of impact. There are multiple waves even though there is only one original impacting event.( All radiating outward with the same frequency but reducing amplitudes) Every object has its own natural primary frequency ( or multiple frequencies, there are only three elements to any vibration system in the world: Force, stiffness and dampening.

 

[one.man.band]

thx for posting the linear graph.

on either side of a spike, on the linear graph, freq below and freq above get together in sync to form a peak in the center. basic wave harm motion. doe not matter to them if its the fundamental freq or not. so applies to all. everything has a natural harmonic, and after all the vibes, will resort to that. evidence of this visually is seen in all the empire state building style peaks.

tuned pipes don't rely on sound waves, but finite waves which are a 1000 time stronger. sound waves are the mechanism for the sonic wave timing.......and only used for design.

the freq. thing is interesting because dB are a measure of pressure. no pipe design equations out there include pressure as a variable, and are lacking in that regard.

while tuned pipe calcs remain useful, today's motor sports use pressure transducers to dial in everything.

brads graph shows that the muff is more in sync with the fundamental than yours. the amplitude of the latter peaks approaches the strength of the fundamental.

 

[one.man.band]

Cool discovery of this program and congratulations for figuring out how to use it. I am a Vibration Institute certified level 3 vibration analyst.... that's what I do for a living every day, so it is cool to see someone utilizing time waveforms and spectrum plots to find the fundamental running frequency of their saw- good job!! We always use Linear scaling in each axis since it is more intuitive for your brain to look at, and also switch from Hertz to Cycles per minute (CPM) since you are also used to looking at things in relation to (RPM) running speed. Also if you can bring up a harmonic cursor and place the primary on the top of the suspected 1x peak , the rest of the cursor boxes will jump up to the tops of the harmonics to help confirm you have found the right peak that is actually the 1x (Running speed). ( The repeating pattern shows up). If anybody has any vibration system related questions.... fire away, this is my bag babay......Lol. So far as the harmonics, think about a pebble being dropped in a pond with the wavelets being produced as they radiate outward from the point of impact. There are multiple waves even though there is only one original impacting event.( All radiating outward with the same frequency but reducing amplitudes) Every object has its own natural primary frequency ( or multiple frequencies, there are only three elements to any vibration system in the world: Force, stiffness and dampening.

thanks NW, now that you mentioned that feature........ have to load it up again.

 

[one.man.band]

the point where the can itself attenuates the fundamental piston frequency and comes into its own natural resonance is debatable. but, i think there is enough evidence shown in the different graphs that it could be a strong possibility.

 

[wde_1978]

I don't know that program - is there any kind of spectrum analyzer under Tools or Effects?

Couldn't find any such option , so I pulled out my laptop and installed Audacity and loaded the same file.

I don't really understand which spike of the graphs I am supposed to look for , but this is what I came up with.
This graph claims about 8940 rpm though I know it was more as the saw got a tach mounted.


Interesting non the less , this way one can try figure out approximate rpm's out of a video or audio file.

 

[Chris-PA]

We always use Linear scaling in each axis since it is more intuitive for your brain to look at, and also switch from Hertz to Cycles per minute (CPM) since you are also used to looking at things in relation to (RPM) running speed.

Interesting that different disciplines have different practices - in electronics we typically use log for both, perhaps because the range of the amplitude and frequency can be so much higher.

Also if you can bring up a harmonic cursor and place the primary on the top of the suspected 1x peak , the rest of the cursor boxes will jump up to the tops of the harmonics to help confirm you have found the right peak that is actually the 1x (Running speed).

I was not able to do this in Audacity. I'll have to play more later, as I'm just tanking a quick break from outdoor projects.

 

[Chris-PA]

Couldn't find any such option , so I pulled out my laptop and installed Audacity and loaded the same file.

I don't really understand which spike of the graphs I am supposed to look for , but this is what I came up with.
This graph claims about 8940 rpm though I know it was more as the saw got a tach mounted.
View attachment 429218 View attachment 429219

Interesting non the less , this way one can try figure out approximate rpm's out of a video or audio file.

That looks like it's working, however it is giving you the spectrum for the entire file. If you go over to the amplitude plot and select a section where the amplitude appears constant, and then click on Replot on the spectrum graph it will show you just the section you've selected. This should give you a more accurate reading in that section.

I'm going to have to try installing it under Windoze on my work laptop.

 

[Cj genever]

Great idea! I'm sure I could if I had to... glad I have a digital timing gun!

 

[Ponzi]

Get yourself a, "Tachometer."

 

[malk315]

Get yourself a, "Tachometer."

Right but then how do we tach Brad's and others' videos after the fact with the tach that we buy? A little innovation there! I have a fast tach that can't do what YouTube and a little free software can!


Sent from my XT1080 using Tapatalk

 

[Cj genever]

Get yourself a, "Tachometer."

Any good digital timing light doubles as a "tachometer". They can even do the math if you have a redundant spark in a four stroke (because apparently dividing by two is hard, lol)

 

[Cj genever]

Right but then how do we tach Brad's and others' videos after the fact with the tach that we buy? A little innovation there! I have a fast tach that can't do what YouTube and a little free software can!


Sent from my XT1080 using Tapatalk

Ok, now the need for this software makes more sense. I wonder of you ran the audio through a background noise filter and then clamped the tach onto a speaker cable it would read correctly? It may need to be passed through a transformer first to increase the voltage to that of an ignition coil? Of course, I also ponder how much info is being lost in digital compression and transfer of these audio files.

 

[angelo c]

I am a Vibration Institute certified level 3 vibration analyst.... that's what I do for a living every day,


Ok heck !!! There goes the neighborhood....everything was fine in my last neighborhood until the family of "acoustic vibration analysts " moved in.....

 

[NWCoaster]

I am a Vibration Institute certified level 3 vibration analyst.... that's what I do for a living every day,


Ok heck !!! There goes the neighborhood....everything was fine in my last neighborhood until the family of "acoustic vibration analysts " moved in.....

Lol..... too funny....

 

[LegDeLimber]

There are several interesting programs on this site.
http://www.techmind.org/audio/index.html#intro

The frequency counter/musical tuner is a nice simple interface. But also gives a wave shape with the display.
i've been wanting to grab a some cassette deck heads and use them as probes around a rev limited ignition.
A four channel (or more) sound card and some (appropriately attenuated ) probes could be intersting to watch as you run through the revs.

Most of these programs could be used with magnetic pickups and acoustic too.
Think you guys would be surprised to see a visual of what a slight rich or lean tune does to the exhaust noise signature.
I reckon a fair number of us can already tell it by ear.

ignition timing changes will show in the mechanical noise.
So will carb tune .... probably oil ratios too...just depends on out test rigs
acoustic pickups and IF memory servs me, I think people were using a small ceramic disc capacitors ( on a stick) to make knock sensors.

i've got a handful of these utilities ( looking for some O-scope utils also)
that i want to try some things with.
I'll post up a listing later, got a computer monitor that's going wonky.
and all the freeze spray/keyboard cleaner has that phukin bitterant in it nowdays ( thank to the huffers)
so i ve got nothing to hit the board with to hunt for the hot part.

somehoe I'm Not too crazy about trying propane for electrical troubleshooting, ya know?

 

[Ponzi]

Right but then how do we tach Brad's and others' videos after the fact with the tach that we buy?

In Brad we trust.

lol One thing is for sure, don't put anything on a Linux box you'd like to keep secure. The back door is embedded directly into the machine language of such systems. That's always the tradeoff for free software. It's called, "copyleft," in the trade and the joke is on you. Open source software is just that.

Chris has a very original idea here, though. Gotta give him that. Actually he has the occasional stroke of mastery.

The tail doesn't wag the dog though. Tune the saw then run it.

 

[Chris-PA]

Here's a bunch of plots of Brad's 661: http://www.arboristsite.com/community/threads/ms661c-muffler-mod-testing.281169/page-3#post-5398190