need to measure the torque

[Florin777]

Part of a university project, I need to measure the torque on the propeller at various RPM.
Does anyone know how to build a simple torque meter rather than buying those expensive digital ones?

[fhhuber506771]

Long music wire in a brass sleeve. Bend each end 90 deg.

Mount the sleeve and one end to the fixed part of the motor mount assembly.

Affix the motor mount itself to the other end such that the motor shaft lines up with the long, sleeved part of the wire.

Right behind the motor mount you put a disc with refernce marks.
Affixed to the motor mount is a pointer.

From there its a matter of calibrating the thing (determining what mark means how much torque) You do that by hanging assorted weights from a known length arm affixed to the motor mount and adjusting the arm mount so it is level (parallel to the ground) with the weight hanging on it.

The size of the music wire used (length and diameter) will depend on what torque range you need...

Then you'll need a tachometer to measure the RPM at the same time as you take the torque reading.

[Florin777]

thanks for the reply
could you draw a quick sketch of this?

[fhhuber506771]

quickly?... no...

Rough of the parts...

[Florin777]

thanks for the sketch, looks nicer than expected hehe
i thought it would be challenging to measure the torque while the motor is running at const RPM, as most measurements i see on internet are made with the motor stopped

[fhhuber506771]

it needs constant load to give a steady reading... so you want to use it in a draft-free room. No fan... AC not blowing...

[Florin777]

Thank you for the ideas guys.
I have something in mind now, I will put in on paper then scan it here.

[fhhuber506771]

Also... you will want to test using at least 3 differnt props... because changing the prop will change the torque at any given rpm.

[bwalt822]

If you measure the power being fed to the ESC with a wattmeter you can then determine the efficiency of your motor/ESC system BTW.

Then if you put the whole thing in a wind tunnel (if your school has one big enough) you can figure out the efficiency of your prop but im guessing you wont have the time for that.

[Florin777]

Anything that could go wrong with these sketches?

[bwalt822]

You dont need a ball bearing plate, just put the motor mount on a hinge that is parallel to the shaft of the motor. Sum the moments about the hinge shaft, you will know the moment from the scale so you can solve for the moment about the motor. Just make sure the motor wants to turn the apparatus to put force on the scale and not lift it.

Then rotate the motor 90 degrees to face the scale, use the same procedure to determine thrust. The only issues will be to build the motor stand as small as possible to eliminate the effects of the propwash hitting the stand itself.

[Harpye]

Do you need the torque of the motor shaft or the torque on the load ? / Prop
for the motor torque you could mount a thin imbalanced Aluminum disk on the shaft and a static imbalanced steel disk with several neodymium magnets directly in front. then you could load the static disk with some excenter mass and use it as a pendulum... now the eddy current retarder you just built forces the pendulum to deflex.. if you put a scale to the static disk and a pointer on the rest of the disk you could put different load on the motor by variation of the distance between the disks... and if you measure the speed of the motor vs the torque you are able to get the motors characteristic ... with or without prop .

hope that this was able to be understood..

Hansjoerg