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Topic: rotary torque sensor (Read 2058 times) previous topic - next topic

wiillii

Hi!

I want to measure torque on rotating shaft. After hours of searching i could not find any option which doesnt cost a fortune. Existing sensors with data loggers, as a complete solution, are expensive.

My calculations shows following measurements:

max. torque: 75 Nm
max. rotary speed: 100 rpm
max. power: 300

i want to build my own system for these requirements and i want to use arduino as a data logger. But the problem is, i have no idea about what i should be doing. Here are my questions:

1-The output voltage is linear to torque input. And the output voltage of sensor is +/- 5 V DC. But how am i going to know, which torque value gives which output voltage?

2-Sensor has inner resistance and some other specifications. How do they affect my end results?

3-Did you have any other idea instead of using a rotary shaft to shaft torque sensor?

Thanks a lot, every feedback and every idea means so much to me!

flyboy

I've considered such a problem recently, but have not researched.  One of my college classmates used this problem for his senior design project, but that was 15 years ago.  He had the same problem, the only commercially available solution was very expensive.  I don't remember what he used in his final solution.

My thoughts: Use a strain gauge on the shaft.  Circuit to measure the strain gauge is also on the shaft--both rotate with the shaft.  Power the circuit using a wireless charger.  Communicate the measurement with a bluetooth module or some other wireless device.  All of this should be sufficiently small so it does not create a balancing problem and to prevent damage to the torque measurement hardware.

This is all hypothesis and I have done absolutely NO testing or prototyping of any kind.

Maybe this will help jumpstart some ideas for you.

Paul_KD7HB

If this is anywhere near correct: http://planetcalc.com/1908/#, you are way off on the power value.

My solution would be to couple a DC electric motor to the shaft. Apply power to the DC motor to rotate in the opposite direction to your shaft. Adjust the current to the electric motor until it is able to slow your test shaft. Measure the motor's current and voltage at that point and then compute the power and then the torque needed to slow your shaft.

Heat generation will be a problem, so the test needs to be done rather quickly.

Paul

dwightthinker

You didn't say if it was rotating or stationary torque reading?
Also, what kind of torque are you talking about?
A car engine puts out torque as does a servo.
One would use completely different methods.
If it is a static torque, you could use the part they use in a
cheap bathroom scale.
Rotating torque can be measured by having two pickups at the
ends of a shaft that has some spring. If there is torque one end
rotates such that there is an increase in phase angle between the
to pickups. Magnets and hall effects make sense here.
Calibration is easy, torque is measure as some weigh at some
distance. Put an arm on your measuring setup and hang a
weight on it.
If measuring inch-pounds, say 10 inch-pounds, use a 5 inch
arm and 2 pound weight.
Dwight

wiillii

#4
Oct 05, 2015, 09:07 am Last Edit: Oct 05, 2015, 11:17 am by wiillii
@flyboy:

i have found something similar. It is called DMS - "Dehnmessstreifen" and they use usually 1 or 2 channel telemetry for that. But the application seems a bit difficult. I will look into it. I have doubts. If it is really cheap and still accurate, why dont we see DMS applications everywhere? Are you familiar with DMS applications? What is best for my case? whats the difference between half bridge and full bridge strain gauges? And still, calibration is a main problem.

@Paul_KD7HB:

Actually i have thought about it, but i am still not sure how i measure it correctly. I mean DC electric motor doesnt have equal input and output. I could measure the rotation speed and do some calculations instead of adding another motor to do same calculations. Do you have any idea how i eliminate the deviation and possible measuring errors? I have seen some DC eletric bike motors with integrated torque sensor but i have no idea how do they work. What do you think, are they usuable for this task?

By the way, only one shaft has that rotational speed value. Most of the sensors have limited rotational speed values. For this reason i wrote only maximum values of different shafts which i want to test.

@dwightthinker:

i am talking about rotating torque readings. Your idea sounds interesting. But i have several possible problems about this one. All these shafts are rotating on water. It is kinda hydro electric generator which floats on water. It isnt stable because of that. I cant imagine if i can eliminate it. But i will look into that too, maybe i can find a way. Otherwise i can use it while i test it in my garage.

I haven't found a solution yet, but i am thankfull for all these ideas. I will look into these. But i can use every new perspectives. Don't hesitate to write or ask.

dwightthinker

If you are using a generator, measure the voltage and current
output. You'll be able to back calculate the torque.
Dwight

MarkT

Quote
I want to measure torque on rotating shaft. After hours of searching i could not find any option which doesnt cost a fortune. Existing sensors with data loggers, as a complete solution, are expensive.
That doesn't surprise me - its hard measuring the force on something you cannot connect to.
You can get fairly cheap wireless modules, but you'll have to do the design yourself and probably
need strain guage(s), amps, battery and wireless TX all in miniature packages...

Quote
My calculations shows following measurements:

max. torque: 75 Nm
max. rotary speed: 100 rpm
max. power: 300
75Nm x 10.5 rad/s = 705W, not 300W
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

dwightthinker

If it has a shaft of some length, two magnets and two hall zero crossing sensors
could be calibrated to measure running torque.
The twist of the mounting can be used to measure torque.
Dwight

emmanuelbabu

hi wiilii

im working on a similar project, to calculate torsion, you might find the following links useful:

https://www.google.com/patents/US5001937

http://www.amazon.com/Seeedstudio-Grove-Ir-Distance-Interrupter/dp/B00VB2ELQU

Have a look...which arduino board are you using??

Emmanuel

TomGeorge

Hi,
I know its a while since any posts, but has anybody thought of load sensors in the motor mounts.

Four mounting points, four load-cells, motor torque will cause differential loads due to reaction torque of motor casing against its rotor.

Just a thought.

Tom..... :)
Everything runs on smoke, let the smoke out, it stops running....

MarkT

The magnets idea is interesting, but I doubt very sensitive.

Perhaps having a reasonably high resolution encoder on each end of the shaft would
be much more sensitive to small torsional strains (a large torsional strain might be
a bit risky, allowing for shaft failure, unwanted torsion oscillations).

You would then read from both encoders and record the difference in counts, which would
provide a discrete indication of torsion angle and hence torque.

The down side is that any shaft capable of 75 Nm is probably too fat for any cheap encoder
(5mm and 6.35mm are common sizes for cheap encoders).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

stefa24

https://sites.google.com/site/agritronica/
https://sites.google.com/site/t3chconcrete/
https://www.youtube.com/channel/UCnY1DNrSywgadjyqqtbvyew
arduino UNO rev 3
ide 1.6.0

X3msnake

The down side is that any shaft capable of 75 Nm is probably too fat for any cheap encoder
(5mm and 6.35mm are common sizes for cheap encoders).
For that you can always use a gear and do a indirectamente reading with the encoder attached to the smaller shaft

MarkT

Backlash and rigidity considerations would make that problematic I think.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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