I am trying to verify how well my optical tachometer project is working. I noticed that the RPM varies when measuring the RPM of my Dremel tool.

I recorded 10 readings 1 second apart and this is what I got

5640
5760
5460
5460
5940
5460
5820
5700
5700
5820

Has anyone ever measured the rpm of their Dremel and noticed a similar behavior?

Dremel is not exactly known for their high precision so, if I had to guess I would say this is typical behavior but wanted to see what others thought.

 

The sound the Dremel makes is based off its RPM any you can hear an 8% change.

 

The sound the Dremel makes is based off its RPM any you can hear an 8% change.

What?

If you are saying can I detect an audible change in rpm then yes but only over a long period of time. I cannot detect changes within the 10 seconds or so that I took the sample. And that is what I am really most concerned about. I am wondering there might be improvements I can make to my target to make the reading more stable or if these fast changes are just the nature of the tool.

 

I am trying to verify how well my optical tachometer project is working.

Those values average 5,676 ± 3%. Sounds good to me. Would you expect anything better?

There's a slight upward trend that might be significant. If you factor that in, the standard deviation is even smaller.

 

Those values average 5,676 ± 3%. Sounds good to me. Would you expect anything better?

There's a slight upward trend that might be significant. If you factor that in, the standard deviation is even smaller.

Just want to verify that this is normal behavior and not something I am doing wrong with may hardware setup.

But perhaps I should do a standard deviation on my data set to balance things out and get a less sporadic display ?

 

The fact that a universal motor operates in a runaway basically, I would not consider that an odd variation?
I can check mine tomorrow and see what transpires.
Max.

 

I typically just set mine for 100% power and let the RPM's go wherever the load takes them.

If they seem too low for what I am doing I just stop pushing on it so hard.

 

You might want to repeat the experiment while monitoring the AC line voltage.

 

Instead of measuring a, "run-away" motor, measure something synchronous like a 3450 RPM induction motor.

 

You might want to repeat the experiment while monitoring the AC line voltage.

If I had such a monitor.

 

DVMs work very well for that purpose, but you would have to note the reading manually.

 

I am trying to verify how well my optical tachometer project is working. I noticed that the RPM varies when measuring the RPM of my Dremel tool.

I recorded 10 readings 1 second apart and this is what I got

5640
5760
5460
5460
5940
5460
5820
5700
5700
5820

Has anyone ever measured the rpm of their Dremel and noticed a similar behavior?

Dremel is not exactly known for their high precision so, if I had to guess I would say this is typical behavior but wanted to see what others thought.

Add a few drops of silicone oil to the drumel and it should be even better than 3%. The little warbling would is the speed change and mine has a fast warble (sub second) Overplayed on a slow 5 to 15 second warble.

 

DVMs work very well for that purpose, but you would have to note the reading manually.

I could give that a try. Thought you meant like a logger which I have used back in the day.

 

Clocked my Dremel tool and the lowest range was way higher at around 12,000 rpm, about the same amount of variation.
5 ranges with 27krpm for maximum.
You most likely have the high performance model.
Max.

 

An important distinction here is where the observed variation is coming from. Some fraction is real variation in the Dremel rpm and some fraction is from the imprecision of the measurement. That includes both the device's internal precision and whatever the detection method is. I mean, it may miss a revolution or two, or see two when there was only one, that sort of thing. When you're talking about a combined standard deviation of less than 3%, it gets difficult to identify the sources.