Measuring RPM From Video

[malk315]

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.

What you say has been debated for years. Many argue the opposite of what you say -- this article and many like it describe what I'm saying, point #5 in the article really sends home why it's really difficult to get malicious code into opensource:

http://www.pcworld.com/article/202452/why_linux_is_more_secure_than_windows.html

Realize that all of the source of a complete linux OS comes from pure source code -- in the case of embedded even the compiler that builds the source is typically first built as a cross compiler from it's source to create the target. In this case it makes what you say "back doors embedded into the machine language" impossible. Are you saying people who write malicious code write it only in the target's native assembly language? Your statement just makes no sense...

Irony to what you say also -- most firewalls and other security appliances run linux for it's superior ability at networking and security! Chances are if you are at home with a router fronting your internet connection it's running linux.

From the SANS internet storm center from only a few years ago:

"Here’s how poisonous the Internet environment is these days: According to the SANS Internet Storm Center, just connecting an unpatched Windows XP system to the Internet can result in a malware infection in an average time of four minutes."

I'm not here to start a war with whether linux is secure or not -- it can be argued both ways, but not due to "back doors being embedded into the machine language".
Sorry to de-rail the thread... Although it's got some good tech going but still not chainsaw related here...

 

[Chris-PA]

Sorry to de-rail the thread...

It wasn't you - clearly "Ponzi" is another Brush Ape alias, and derailing the thread was his intent like it always is.

 

[malk315]

I've been reading enough threads to learn about this legendary "brush ape" and his habits of starting new users on weekends and derailing threads etc.
I went on the off chance it might not have been... but did read earlier on this thread someone saying they "smelled something" ... LOL.
Avatar seems to be a bit of a giveaway too...

Either way -- interesting stuff. Thanks for your response and thanks for doing the thread.

 

[malk315]

By the way since this thread is all about sound -- a good portion of my addiction to running saws is the sound. They just sound bad a$$ period. I don't think that will get old any time soon.

 

[cgraham1]

I have no idea what the hell any of you guys are talking about.

 

[bikemike]

wish I was a computer nerd then id try it my 46cc pro cuts great at 9k under load and pulls hard too with the 3/8 carlton full chisel on it. No load 13k rev limited found that out at the Brainerd gtg on tack I have a hard time to believe the 42cc strato is gunna take on the 46cc

Recently I finished a squish reduced 42cc Poulan/Craftsman that I've been very happy with. I also have a 46cc Poulan 2775 that was the first saw I ported, and I have usually been quite impressed with it. They are two different designs, although both clamshell homeowner saws. The 46cc runs a 20" bar with 0.325" Oregon 20BPX, while the 42cc has a 19" GB bar running 3/8 lo pro Oregon 91VXL (so it has a narrower kerf). I wondered how they compared, and so I tried cutting cookies off a white oak log.

This tree has varied a lot, with some of it being quite soft and some quite hard - and this chunk was hard. The 46cc saw has had a difficult time in the past on very hard wood, and here it was no exception - it got crushed by the 42cc saw (14sec vs. 24sec). It didn't feel like it was struggling, and so in an attempt to figure out what's going on I decided to try to measure the rpm from the video (audio really).

First, here are the two videos:




I run Linux, so I'm using an application called Audacity - there may be Windows programs that can do similar things. I selected a portion of the track where the rpm and amplitude seemed fairly constant, and then selected Plot Spectrum from the Analyze menu:

View attachment 429059
The plot can be full screened, and the cursor will tell you what the frequency is at the cursor (this is the 46cc):
View attachment 429060
The first big spike is the fundamental frequency of the engine, in this case 161Hz. Multiply by 60 and you get 9660rpm. Now for the 42cc:
View attachment 429061
It shows basically the same thing, which tells me the issue here is probably mostly the chain (which was sharp). Anyway, this can be done for most any of the saw recordings we show on AS, although of course the result does depend on what part of the recording you select.

Wish I was a compu

 

[bikemike]

By the way since this thread is all about sound -- a good portion of my addiction to running saws is the sound. They just sound bad a$$ period. I don't think that will get old any time soon.

I with you there bro.

 

[Chris-PA]

wish I was a computer nerd then id try it my 46cc pro cuts great at 9k under load and pulls hard too with the 3/8 carlton full chisel on it. No load 13k rev limited found that out at the Brainerd gtg on tack I have a hard time to believe the 42cc strato is gunna take on the 46cc

The 46cc was the first saw I ported. I used to be very impressed with it, and with the 20BPX chain, but not as much now. It may be that my standards have changed, but there's a strong possibility that the chain is not up to par, as it's been rocked a few times and fixed up. I have not had time to really look into it carefully enough, and I have a new loop that I may use instead after hand filing it. The saw feels more like it's not being worked, or it may have lost too much low end power for that chain.

The 42cc is not strato, it's this saw: http://www.arboristsite.com/community/threads/reducing-squish-on-a-poulan-clamshell.273087/ It is more highly modified than the 46cc, and the numbers and port shapes are more carefully selected. But it's also got that 19" GB bar with 68DL Oregon 91VXL lo pro on it. The kerf is considerably narrower, and there's just no getting around that it has less wood to move. I will be looking into that in the near future, and will probably try the lo pro bar on the 46cc saw for better comparison.

Still, that 42cc Craftsman has become a real favorite. I still like my ported GZ4000 clones, but when I need the slightly larger bar this thing pulls it well.

 

[one.man.band]

/

edit: 1x is too much

 

[one.man.band]

eh?

 

[heyduke]

The 46cc was the first saw I ported. I used to be very impressed with it, and with the 20BPX chain, but not as much now. It may be that my standards have changed, but there's a strong possibility that the chain is not up to par, as it's been rocked a few times and fixed up. I have not had time to really look into it carefully enough, and I have a new loop that I may use instead after hand filing it. The saw feels more like it's not being worked, or it may have lost too much low end power for that chain.

The 42cc is not strato, it's this saw: http://www.arboristsite.com/community/threads/reducing-squish-on-a-poulan-clamshell.273087/ It is more highly modified than the 46cc, and the numbers and port shapes are more carefully selected. But it's also got that 19" GB bar with 68DL Oregon 91VXL lo pro on it. The kerf is considerably narrower, and there's just no getting around that it has less wood to move. I will be looking into that in the near future, and will probably try the lo pro bar on the 46cc saw for better comparison.

Still, that 42cc Craftsman has become a real favorite. I still like my ported GZ4000 clones, but when I need the slightly larger bar this thing pulls it well.

it would be interesting to vid a comparison of the two saws, 42cc & 46cc, running the same bar and chain. also, great idea to use audacity as a remote tach.

 

[heyduke]

chris-

yes, i had to try. i used a vid of my trusty but ancient husqvarna l65. i cant fully explain the results.



there is an initial spike at 100hz, 6000 rpm, but at 560hz there's a 12db greater spike that translates to 33600 rpm. so it appears that the harmonics (6th?) are greater than the primary freq. my guess is that i have the old saw set to spin 10,000 unloaded wfo. in this vid it is cutting a ten inch cookies. any ideas? think i'll try a receent vid of three top handles.

 

[Chris-PA]

eh?

Well, that's interesting Joe, but I don't really see that much of a correlation once the main spikes are superimposed. And I can't come up with any rationalization for relating the ratio of pressures vs angle of rotation angle through one cycle with external sound pressure vs rpm. What would the mechanism be?

chris-

yes, i had to try. i used a vid of my trusty but ancient husqvarna l65. i cant fully explain the results.

View attachment 430401

there is an initial spike at 100hz, 6000 rpm, but at 560hz there's a 12db greater spike that translates to 33600 rpm. so it appears that the harmonics (6th?) are greater than the primary freq. my guess is that i have the old saw set to spin 10,000 unloaded wfo. in this vid it is cutting a ten inch cookies. any ideas? think i'll try a receent vid of three top handles.

I would pick the center of the spike, which would be a bit higher. It looks like the spectrum of a larger section of the file, or the whole thing. Try selecting just a portion where the saw is running steady and re-plot. You should get a better defined plot.

At higher frequencies you see the harmonics on top of the generally high background levels from all the cacophony a saw makes. This makes those harmonics look bigger that they are.

 

[heyduke]

Well, that's interesting Joe, but I don't really see that much of a correlation once the main spikes are superimposed. And I can't come up with any rationalization for relating the ratio of pressures vs angle of rotation angle through one cycle with external sound pressure vs rpm. What would the mechanism be?

I would pick the center of the spike, which would be a bit higher. It looks like the spectrum of a larger section of the file, or the whole thing. Try selecting just a portion where the saw is running steady and re-plot. You should get a better defined plot.

At higher frequencies you see the harmonics on top of the generally high background levels from all the cacophony a saw makes. This makes those harmonics look bigger that they are.

i did try limiting the amount that i sampled. in the end i just used the sound in the middle of one cookie, just a few seconds. the spikes are at harmonic intervals, multiples of 100hz. the old L65 isn't particularly noisy. the vid was recorded with a canon g9 and it's possible that the microphone isn't senstive to freqs low as 100hz and attenuated that portion of the spectrum. anyway, i did the same thing with audio from three top handles, two echos and an 020t and they looked much more like the spectra from your poulans. the primary freq, around 115hz had the greatest amplitude, then only small spikes until the fifth or sixth harmonic which was only a few db less than the primary, and subsequent harmonics that stepped down. pretty cool. that vid was recorded with a newer nikon that i got for hd video and it's mic may have better response at the bottom. now i'll just have to run nuclear magnetic resonance spectra for my mix and bar oil, oh yeah, my cerveza too.

 

[one.man.band]

Well, that's interesting Joe, but I don't really see that much of a correlation once the main spikes are superimposed. And I can't come up with any rationalization for relating the ratio of pressures vs angle of rotation angle through one cycle with external sound pressure vs rpm. What would the mechanism be?.

... just a few things.
- the middle pressure graph is of a tuned pipe @10000 rpm.
- actually an un-tuned pipe at this rpm
- pressure is not 1:1 related w/sound. whether it is a tuned or box exh.

correlation:
- pressure and the sound wave begin at the same time.
- the trans/exh open and close events in both happen after the initial event. thus superimposed at first spike.
- the grouping of spikes in the box happen way too early. the superimposed image is not spot on.
- the mass grouping is the muffler attenuating, or at least trying to tame the amplitude.
- imo, the muff volume/outlet is squashing the primary spike by trying to change the freq. basic muff attenuation.
- would consider your sample to be one cycle. rpm.

mechanism:
- if something can be induced into res, it will continue to res until the amp comes down.

..so far, only two tries........one saw (max. rpm 13500), would not rev past 9500 rpm w/a 5/8" opening and another had a noticeable gain.

-exh has more influence than anything else, would have to believe that every stone should be flipped over trying to find something that can compliment an adequately sized exit hole. or not.

 

[Chris-PA]

... just a few things.
- the middle pressure graph is of a tuned pipe @10000 rpm.
- actually an un-tuned pipe at this rpm
- pressure is not 1:1 related w/sound. whether it is a tuned or box exh.

correlation:
- pressure and the sound wave begin at the same time.
- the trans/exh open and close events in both happen after the initial event. thus superimposed at first spike.
- the grouping of spikes in the box happen way too early. the superimposed image is not spot on.
- the mass grouping is the muffler attenuating, or at least trying to tame the amplitude.
- imo, the muff volume/outlet is squashing the primary spike by trying to change the freq. basic muff attenuation.
- would consider your sample to be one cycle. rpm.

mechanism:
- if something can be induced into res, it will continue to res until the amp comes down.

..so far, only two tries........one saw (max. rpm 13500), would not rev past 9500 rpm w/a 5/8" opening and another had a noticeable gain.

-exh has more influence than anything else, would have to believe that every stone should be flipped over trying to find something that can compliment an adequately sized exit hole. or not.

I'm afraid I'm just not seeing the relationship between the two plots, but I will give it some more thought.

 

[Chris-PA]

i did try limiting the amount that i sampled. in the end i just used the sound in the middle of one cookie, just a few seconds. the spikes are at harmonic intervals, multiples of 100hz. the old L65 isn't particularly noisy. the vid was recorded with a canon g9 and it's possible that the microphone isn't senstive to freqs low as 100hz and attenuated that portion of the spectrum. anyway, i did the same thing with audio from three top handles, two echos and an 020t and they looked much more like the spectra from your poulans. the primary freq, around 115hz had the greatest amplitude, then only small spikes until the fifth or sixth harmonic which was only a few db less than the primary, and subsequent harmonics that stepped down. pretty cool. that vid was recorded with a newer nikon that i got for hd video and it's mic may have better response at the bottom. now i'll just have to run nuclear magnetic resonance spectra for my mix and bar oil, oh yeah, my cerveza too.

Maybe the L65 has an effective muffler! It certainly could be the recording microphone, or perhaps the location of the mic.

 

[Chris-PA]

Here are some plots from my cheap Chinese G621 clone off of this older video:

This is a 62cc saw with a 24" bar buried in white ash, running around 10,200rpm:


I'm pretty happy with that!

 

[heyduke]

Here are some plots from my cheap Chinese G621 clone off of this older video:

This is a 62cc saw with a 24" bar buried in white ash, running around 10,200rpm:
View attachment 430904
View attachment 430905
I'm pretty happy with that!

Maybe the L65 has an effective muffler! It certainly could be the recording microphone, or perhaps the location of the mic.

mostly, i think the L65 has soul. it was born before the epa or carb. i don't use it much. it just followed me home to get off a shelf in somone's garage and to get the schmutz emptied out of its fuel tank. it's an old vid. i should try again with my newer cameras. i really suspect the mic.

 

[Chris-PA]

I've been meaning to get around to measuring the rpm in this video of my 40cc GZ4000 clone cutting little white ash cookies with 0.043" chain:


I tried a couple of the cuts, but this was typical:

That's 12,700rpm.