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#1
10-04-2013, 09:21 AM
 AaronX Guest Join Date: Feb 2011 Location: 127.0.0.1 Posts: 3,469
How can I measure my blender's speed?

Blendtec says their blenders go up to 28,000 rpm. I want to know how my average blender stacks up.

But more than that, I'm interested in ways to measure high speeds using household objects. I'm not thaat interested in comparing blenders, so looking at wattage or just saying, "Most blenders spin at 10,000..." aren't enough. Could I use a guitar pickup to detect the blades? I think a laser, detector and counter would work.
#2
10-04-2013, 09:43 AM
 JerrySTL Guest Join Date: Jan 2013 Posts: 2,166
On bicycles we use a small magnet attached to one of the spokes and a pickup attached to the frame to measure how many times the wheel spins around. That way you can tell how fast the bike is going once you input the wheel/tire diameter.

However I don't think a bicycle-specific computer would work. Even though the magnet is 'small' it would probably would weigh enough to throw a blender out of balance. Also Lance Armstrong couldn't get a bike wheel to 10000 rpm no matter what drugs he was taking.

Still you'd think that the scientific community would have such a device.

Another thought would be using an adjustable strobe light. Paint one of the blades and when you get it to 'freeze' (like a timing light on a car) you'd know how many times per minute the blades are spinning.

Last edited by JerrySTL; 10-04-2013 at 09:43 AM.
#3
10-04-2013, 09:54 AM
 JerrySTL Guest Join Date: Jan 2013 Posts: 2,166
Found them! Go to amazon.com and search on "rpm meter". They have a bunch of non-contact models for under \$25 that go to 99,999 rpm.
#4
10-04-2013, 09:57 AM
 leahcim Member Join Date: Dec 2010 Location: Boulder, CO Posts: 3,484
Quote:
 Originally Posted by JerrySTL Another thought would be using an adjustable strobe light. Paint one of the blades and when you get it to 'freeze' (like a timing light on a car) you'd know how many times per minute the blades are spinning.
I think that strictly, you'd only know that the blades are rotating at a multiple of the speed of the strobe light, although you may be able to take multiple readings to infer a higher speed -- if it freezes at 500Hz and 700Hz, then it has to be going at least the least frequency that is a multiple of both: 3500Hz.

I think the simplest with consumer-level tech is a laser-pointer/photo-detector/oscilloscope setup, with the laser blocked by the blade at some point in its rotation. Then just watch the signal on the scope.
#5
10-04-2013, 10:14 AM
 AaronX Guest Join Date: Feb 2011 Location: 127.0.0.1 Posts: 3,469
Quote:
 Originally Posted by JerrySTL Found them! Go to amazon.com and search on "rpm meter". They have a bunch of non-contact models for under \$25 that go to 99,999 rpm.
Only \$25? Wow, that's even cheaper than most DIY solutions, unless you already have the parts. Still hoping for innovative solutions, though.
#6
10-04-2013, 10:15 AM
 Joey P Charter Member Join Date: Jun 1999 Location: Milwaukee, WI Posts: 26,586
It's not all about RPMs though, it's about torque. Who cares if it spins at 28,000 if it's going to jam the first time you drop a chunk of ice in it. OTOH, if your's spins at 15,000 but can grind up concrete...

Now, if it spins at 28,000 (and, say, regular ones spin at half that) it's certainly going to have some momentum behind it that'll help push it through some of the harder things, but that doesn't mean the motor is strong.
#7
10-04-2013, 12:07 PM
 Omar Little Guest Join Date: Apr 2000 Location: Within Posts: 11,673
We have a Blendtech blender. It will blend just about anything.

You tube has numerous videos of that thing grinding iPhones, iPads, soda cans, etc.
#8
10-04-2013, 12:11 PM
 aNewLeaf Guest Join Date: Dec 2012 Location: Colorado Posts: 2,602
Quote:
 Originally Posted by AaronX Only \$25? Wow, that's even cheaper than most DIY solutions, unless you already have the parts. Still hoping for innovative solutions, though.
I've got a LEGO rotation sensor. I'd have to gear down, but I could measure a blender's RPM with my RCX.

ETA- I also have a standalone LEGO rpm counter. But I'd use the RCX.

Last edited by aNewLeaf; 10-04-2013 at 12:13 PM.
#9
10-04-2013, 12:24 PM
 beowulff Member Join Date: May 2001 Location: Scottsdale, more-or-less Posts: 14,960
Frankly, this sounds like an excellent way to cut your fingers off.
#10
10-04-2013, 12:57 PM
 ducati Guest Join Date: Mar 2004 Location: Atlanta, GA Posts: 2,363
Non-contact tachometers are common.

Under 14 bucks and free shipping!
#11
10-04-2013, 12:59 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 73,120
My first though was to attach a mirror to it, bounce a laser off of it to a distant retroreflector, and see how much the returning beam was deflected. Basically, the same way that Michelson measured the speed of light, except in reverse.

I make no claims about the practicality of this method, of course. But it would in principle work.
#12
10-04-2013, 01:58 PM
 AaronX Guest Join Date: Feb 2011 Location: 127.0.0.1 Posts: 3,469
I wanted to tie 1 m of string to it and see how long it would take to wind it up.
#13
06-11-2014, 09:25 PM
 arcticsilo Guest Join Date: Jun 2014 Posts: 2
I know this is an old thread, but I just finished writing up a description of how to measure blender speeds with two relatively simple DIY methods. The first method uses a simple stroboscope (like JerrySTL suggested) rigged up with an Arduino. The second method is easier, and all you need is to record the sound and then use software like Audacity to look at the frequencies. Here is the writeup: How to Measure Blender Speed: Methods.

Both methods worked surprisingly well for the Vitamix blenders that I tested.
#14
06-12-2014, 04:38 AM
 AaronX Guest Join Date: Feb 2011 Location: 127.0.0.1 Posts: 3,469
Wow fascinating, if anything I didn't think Arduino and LEDs would make a decent strobe at 380Hz.

I think a guitar pickup might also work...
#15
06-12-2014, 02:23 PM
 arcticsilo Guest Join Date: Jun 2014 Posts: 2
The default Arduino clock speed is 16 MHz, and you can generally implement code with microsecond resolution, so I wasn't anywhere near the upper limits. The one thing that I found to be slow/limiting is the serial-USB connection that I used to display the frequency. It's not a problem as long as you don't try to do a data transfer on every cycle. (My solution was to only initiate a serial transfer upon a button press on the board.)
#16
06-12-2014, 04:24 PM
 TroutMan Guest Join Date: Sep 2008 Location: Portland, OR Posts: 3,672
Very interesting, arcticsilo. I hope you stick around the Board and continue to contribute.

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