Previous in Forum: Please Don't Feed the Animals   Next in Forum: Organically Grown Foods Cause Hepatitis Outbreak
Close
Close
Close
24 comments
Associate

Join Date: Nov 2012
Posts: 37

Measuring Rotating Shaft Torque

06/01/2013 2:13 PM

Anyone know of an inexpensive way to measure the torque of a rotating shaft. If I simply stalled it with a big torque wrench would the reading be correct? The shaft is being turned by a water wheel. Gerry D.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20964
Good Answers: 780
#1

Re: Measuring rotating shaft torque.

06/01/2013 2:19 PM

In this case, your method should work. (But don't try it with positive displacement devices!)

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply Score 1 for Good Answer
Guru
Hobbies - DIY Welding - New Member

Join Date: Apr 2008
Location: Bristol, Tennessee
Posts: 1176
Good Answers: 57
#2

Re: Measuring rotating shaft torque.

06/01/2013 5:47 PM

The standard torque wrench will tell you static torque only, not momentum. Look up 'pony brake' and see if you can use that.

__________________
mike k
Register to Reply Score 1 for Good Answer
Guru

Join Date: Feb 2011
Posts: 7045
Good Answers: 206
#3

Re: Measuring rotating shaft torque.

06/01/2013 6:02 PM

you might want to make sure your health insurance is up to speed before you take any more measurments

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30314
Good Answers: 817
#15
In reply to #3

Re: Measuring rotating shaft torque.

06/03/2013 3:56 AM

...and life assurance too.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Engineering Fields - Instrumentation Engineering - New Member Hobbies - Automotive Performance - New Member Technical Fields - Education - New Member Fans of Old Computers - TRS-80 - New Member Hobbies - Musician - New Member

Join Date: Jan 2008
Location: Tucson, AZ
Posts: 1331
Good Answers: 30
#4

Re: Measuring rotating shaft torque.

06/01/2013 6:34 PM

IF there is sufficient length to that shaft that you want to measure, you can install two strain-gauges, one on each end of the shaft at a precisely measured distance apart and each connected to small micro RF transmitter.

Assuming the strain-gauges are properly "calibrated" before and during their respective installations, you can receive the RF-transmitted data from each gauge and calculate the amount of shaft torque.

The mathematics might be daunting, but it can be done using the two "micro-strain" readings, knowledge of the shaft material, and a LOT of non-trivial mathematics.

__________________
...and the Devil said: "...yes, but it's a DRY heat..!"
Register to Reply Score 1 for Good Answer
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3945
Good Answers: 182
#11
In reply to #4

Re: Measuring rotating shaft torque.

06/02/2013 2:12 PM

I am sorry to say that you have not a very good experience with strain gauge usage.

In fact it is ONLY enough to bond on the shaft a shear bridge strain gauge from Vishay or Omega and in ONLY one section to obtain the signal and transmit it as you suggest (which is a good suggestion even quite expensive). The mathematics are not as complex as you claim since the shear stress is T/Wp where Wp= pi/16*d^3. The strain gauges measure tension/compression strains which will be equal to shear stress/ Young modulus in both directions and with contrary signs if the strain gauges are at 45° degrees with respect to axial direction. The distance between gauges is only required as known when one wants to measure BENDING forces since the difference is proportional to the bending force. In your suggestion you mixed principles used in bending with requirements for torsion. If you do not believe take the technical leaflets from any representative supplier of strain gauges and you will find where was your error.

Further more strain gauges cannot be calibrated. Only the after their bonding and connection with the conditioner/transmitter the equipped shaft can be calibrated as a torque sensor by applying a known torque at one end with other fixed and recording the obtained signal.

If the available shaft length is important the torque can be measured by deflection of a light ray using a mirror placed between two rings on a bending beam. In the middle the beam angle is proportional to the torque. Calibration can be done statically as above and the reading in the rotating situation by following the light reflected spot on a piece of paper.

Register to Reply Score 1 for Good Answer
2
Commentator
Canada - Member - I am from Canada Eh' Engineering Fields - Mechanical Engineering - Condition Monitoring, Advanced Diagnostics and Engineering Services Engineering Fields - Aerospace Engineering - Aviation Aftermarket Services for Honeywell Aerospace

Join Date: Oct 2008
Location: Saint John New Brunswick, Canada
Posts: 67
Good Answers: 1
#5

Re: Measuring rotating shaft torque.

06/01/2013 10:54 PM

I use these all the time. http://www.binsfeld.com/torquetrak/torquetrak-10k/ This is the most reliable and cost effective way IMHO. (And safer)

__________________
Better to have loved and lost than spend the rest of your life with a psycho.
Register to Reply Good Answer (Score 2)
Guru

Join Date: Feb 2011
Posts: 7045
Good Answers: 206
#9
In reply to #5

Re: Measuring rotating shaft torque.

06/02/2013 1:36 PM

cool link, I had never seen one of those before

Register to Reply
2
Power-User

Join Date: Aug 2010
Posts: 209
Good Answers: 8
#6

Re: Measuring rotating shaft torque.

06/02/2013 3:09 AM

If the torque you want is the transmitted torque under running conditions, the answer is no. There are many ways of reading the torque cheaply. So many that it would waste your and my time to go thru them all. The basic idea is to interpose something between the driving and the driven shaft. Or, to replace either the driving or the driven shaft with a measurable device, then reproduce the running conditions (speed, etc). If you give more info on the problem, the options can be greatly reduced. such as approximate shaft speed and power , size and nature of connectors, desired accuracy of reading, etc. (the etc. includes factors such as ambient lighting and sound level, visibility and access to the area). Examples: interpose a rubber mount that shortens or twists under load, then when stopped, reproduce the amount of distortion with the torque wrench; add an adjustable pressure shaft connector (like a rubber tube attached with hose clamps), tighten until it just catches, or just slips. then read the stopped torque; adjustable v-belt,etc.

The less information you give, the more options need to be considered when answering, and the usual option is to guess what the conditions are (including how much you want to spend to get the data), and to throw out the first thing that comes to mind. How often do you want to measure the torque? A spiral spring connector with appropriate calibrations can be made cheaply (as in make your own torque indicator). You can read this either directly or with an electronic camera for stop action. A photo of the shaft, connectors, etc. is also an excellent help in getting useful information. The more you give, the more you get.

Register to Reply Good Answer (Score 2)
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3945
Good Answers: 182
#12
In reply to #6

Re: Measuring rotating shaft torque.

06/02/2013 2:21 PM

The usage of the torque wrench can be the method to calibrate the shaft with the measurement equipment. Since I doubt a very high dynamic loading the static calibration can be good for rotating measurements.

As I mentioned above any elastic element fixed between 2 shaft sections will deform as the shaft under load. This can be a cut rubber hose on which axial lines have been drawn. Their angle under load is proportional to the shaft deformation thus with the applied torque. One can make some pictures during calibration and from same position with same camera a series of pictures during loading in rotation using the calibration pictures a quite correct measurement can be done.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9046
Good Answers: 1031
#7

Re: Measuring rotating shaft torque.

06/02/2013 8:22 AM

Stop the wheel and wind a rope around the perimeter of the water wheel. Add weights to the rope until the wheel will not start. Multiply the weight in pounds by the radius in feet to get foot-pounds of torque. This would be the starting torque, but for a water wheel, I wouldn't expect it to be much different from the running torque.

Register to Reply Score 1 for Good Answer
2
Guru
Hobbies - DIY Welding - New Member

Join Date: Apr 2008
Location: Bristol, Tennessee
Posts: 1176
Good Answers: 57
#8
In reply to #7

Re: Measuring rotating shaft torque.

06/02/2013 1:33 PM

Starting torque is the weight of the water only. Running torque includes the weight of the wheel, quite different. Think flywheel. Consider momentum. You can hold a water wheel or a wind turbine back with your hand, until it gets moving.

__________________
mike k
Register to Reply Good Answer (Score 2)
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9046
Good Answers: 1031
#10
In reply to #8

Re: Measuring rotating shaft torque.

06/02/2013 2:06 PM

I think the moment of inertia of the wheel would be a consideration only if the speed of the wheel is changed, thus changing its angular momentum. If you slow it down, it would supply more torque to the shaft for a short time. To speed back up, it would have to deliver less torque to the shaft. The total torque would be the algebraic sum of the torque delivered to the shaft plus that needed to accelerate (or decelerate) the wheel. In other words, any torque from slowing the wheel is just borrowed from its angular momentum and has to be repaid to return the wheel to its original state.

Register to Reply Score 1 for Good Answer
Associate

Join Date: Nov 2012
Posts: 37
#13
In reply to #10

Re: Measuring rotating shaft torque.

06/02/2013 6:20 PM

Hello engineers. Thanks for all the constructive comments. They kind of confirm that there is no safe, easy, inexpensive way to do it ! I'll just have to rig up a belt-driven generator and dump load and get the v x a = watt ouput. I need to know the torque when rotating. I was hoping that some genius would have a cunning plan. Thanks again though your comments have mostly been helpful, Gerry D.

Register to Reply
Guru
Hobbies - DIY Welding - New Member

Join Date: Apr 2008
Location: Bristol, Tennessee
Posts: 1176
Good Answers: 57
#14
In reply to #13

Re: Measuring rotating shaft torque.

06/02/2013 11:23 PM

The generator plan is good, it may be easier to hook up than to find scales and construct a band brake for a pony brake. Afterwards, you still have a generator setup for future use.

__________________
mike k
Register to Reply Score 1 for Good Answer
Associate

Join Date: Nov 2012
Posts: 37
#16
In reply to #14

Re: Measuring rotating shaft torque.

06/03/2013 10:31 AM

OK Mike, The Pony site is interesting. I was considering it but I have a spare generator and control box for charging the batteries of our trawler. I also have divers V-belts and pulleys. A rheostat and dump load is what I need now. I have no experience of dump loads but I have a rheostat if I can find it our gear shed. Thanks for the help. Gerry D.

Register to Reply
Guru
Hobbies - DIY Welding - New Member

Join Date: Apr 2008
Location: Bristol, Tennessee
Posts: 1176
Good Answers: 57
#18
In reply to #16

Re: Measuring rotating shaft torque.

06/03/2013 1:42 PM

A tank of water, maybe with some electrolyte (salt) in it, and a couple of metal plates will make a dump load. That's what I saw in use to test big gens on a minesweeper. You will need an amprobe capable of reading the amps, if you don't have one, you may be able to rent one for the test.

You should be able to get your reading before the water gets to hot.

__________________
mike k
Register to Reply
Associate

Join Date: Nov 2012
Posts: 37
#19
In reply to #18

Re: Measuring rotating shaft torque.

06/03/2013 7:11 PM

Thanks for the useful info Mike. I have amp-meters and volt-meters and was intend to get expert advice on the dump load. The water turning the wheel will be seawater. Would it do as a dump? wouldn't overheat anyway! Gerry D.

Register to Reply
Guru
Hobbies - DIY Welding - New Member

Join Date: Apr 2008
Location: Bristol, Tennessee
Posts: 1176
Good Answers: 57
#20
In reply to #19

Re: Measuring rotating shaft torque.

06/03/2013 10:51 PM

The unit I saw was using a tank. For safety, I would recommend that. Electricity has such a habit of getting into mischief, I would want to keep it contained in an insulated tub. You only need a quick measurement. For releasing electricity into a body of water, you need more experienced advice.

__________________
mike k
Register to Reply
Associate

Join Date: Nov 2012
Posts: 37
#22
In reply to #20

Re: Measuring rotating shaft torque.

06/04/2013 6:28 PM

OK Mike k, sound advice,surely. Gerry D

Register to Reply
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3945
Good Answers: 182
#21
In reply to #19

Re: Measuring rotating shaft torque.

06/04/2013 3:43 AM

The problem with seawater is that its resistivity depends on its salinity.

Before making your electrodes it would be good to make a measurement in order to obtain an information about it. The best would be to use 2 identical rectangular or circular plates totally in water at a known distance and measure at a reduced scale what you want to do: supply a voltage difference and measure the passing current at different distances between the plates. This will give an indication about what dimensions you should use for final load.

The electrolysis will generate gaz bubbles on the electrodes and thus modify their active surface.

Register to Reply Score 1 for Good Answer
Associate

Join Date: Nov 2012
Posts: 37
#23
In reply to #21

Re: Measuring rotating shaft torque.

06/04/2013 6:39 PM

Thanks nick name, You seem to know what you'e talking about but measuring passing current sounds like I'd need a special instrument to work under-water. _ I think I'll take mike m's advice get a little expert help in that part of it. Thanks for your advice though, it is spot on topic.Gerry D.

Register to Reply
Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3945
Good Answers: 182
#24
In reply to #23

Re: Measuring rotating shaft torque.

06/05/2013 12:40 PM

NOOOOO! To the 2 electrodes you weld/braze wires isolated and measure everything in the free air. The wires are connected to a source (battery) and with the voltmeter you measure the voltage difference + ampermeter in series for the current.

You may as well measure ONLY the resistance in Ohm but you must be aware that the measured value is valid only if there is no chemical interaction between "water" and electrode.

I know what I am speaking about because I used the principle for the simulation of hydraulic resistance of narrow gaps.

Register to Reply
Associate

Join Date: Nov 2012
Posts: 37
#17
In reply to #7

Re: Measuring rotating shaft torque.

06/03/2013 10:40 AM

Hi Rixter, I've already done that with a one meter radious arm and a spring balance but I would like a cross check. It gave me Kilo / metre figures in stall. Useful but not enough. Thanks for your useful suggestion though. Gerry D.

Register to Reply
Register to Reply 24 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

70AARCuda (1); Fredski (2); Gerry D (6); mike k (5); nick name (4); PWSlack (1); Rixter (2); The Green Bastard (1); Tornado (1); woodpower (1)

Previous in Forum: Please Don't Feed the Animals   Next in Forum: Organically Grown Foods Cause Hepatitis Outbreak

Advertisement