Mini torque gage
Mini torque gage
(OP)
I need to find or make a mini torque meter or gage. This will be used to measure the reaction torque of tiny motors driving propellers and ducted fans. Say 10-20 watts output at 10000-20000 rpm.
Very little space is available. About one inch diameter by one inch long to fir inside the fan tailcone. Smaller is better so as to avoid restricting cooling air flow past the motor.
Very little space is available. About one inch diameter by one inch long to fir inside the fan tailcone. Smaller is better so as to avoid restricting cooling air flow past the motor.





RE: Mini torque gage
RE: Mini torque gage
But thanks for the suggestion.
RE: Mini torque gage
or else you can say that with a smaller fan (less electrical power input) you're accomplishing the same cooling effect (and so are more efficient).
RE: Mini torque gage
http://www.interfaceforce.com/
Regards,
Cory
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RE: Mini torque gage
Probably not enough room to mount any sort of standard torque/load cell. Strain gaging the shaft isn't too hard but getting the signal out into the stationary world is tough. Any room for a rotary transformer or telemetry unit?
Something I've wondered about is using two encoders mounted some distance apart on the shaft. The torque would twist the shaft and change the relative phase between the two encoders. Again, probably a custom unit.
RE: Mini torque gage
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RE: Mini torque gage
RE: Mini torque gage
1) Mount the fan on a couple of thin wires -- My first guess would be about half the size of a coat hanger. These will be your torque reaction springs.
2) Make sure that both ends of the wires are FIRMLY ATTACHED, i.e., one end is firmly attached to the motor and one end is firmly attached to the base.
3) Securely mount a very small mirror on the side of the motor.
4) Securely mount a laser pointer at some point off of the motor and aim the laser at the mirror.
5) Mark the point on the wall where the laser reflects at rest.
This can potentially be EXTREMELY accurate, but your problem may be calibrating it.
Good luck.
Historical side note: This is one of the ways that the gravitational constant was originally verified to exist between all objects. A barbell-shaped mass hanging off of a long string in a vacuum chamber had a small mirror affixed to the bar. A change in movement of the reflected point of light of a few millimeters at a distance of a hundred feet away was enough to measure the gravitational pull of an orange on a marble.
-T
Engineering is not the science behind building. It is the science behind not building.
RE: Mini torque gage
For a small motor, instead of wire 'leaf springs', I'd try a piece of surgical tubing slipped over the motor and a fixed stub of similar diameter, say a diameter or two away. Make the tubing longer to get a lower spring rate. Secure with wrapped wire or ty-raps.
Mike Halloran
Pembroke Pines, FL, USA
RE: Mini torque gage
Cory Pad: All way too huge!
BobM3: I cannot measure torque of a rotating shaft. I nust use reaction torque. Shaft is .094 inch diameter.
sreid: These strain gags offer some hope. I will study further.
Engineer Tex: The difficulty is that the mirror is inside the motor shroud AND the fan duct AND the wund tunnel wall. All this should destroy any pretense of accuracy.
Mike Halloran: Surgical tubing slipped over the motor would totally block cooling air.
RE: Mini torque gage
RE: Mini torque gage
You can eliminate half the windows by placing the mirror on the back of the motor at 45 deg to its axis, and the laser in the tailcone, right on the motor axis.
Mike Halloran
Pembroke Pines, FL, USA
RE: Mini torque gage
CoryPad: I looked at the smallest one. Still too big.
MikeHalloran: Why does multiple windows not distort? I would need to contrive transparent parts of a 1.12 inch diameter motor shroud, a 2.50 fan shroud. The wind tunnel wall will be transparent anyway.
Laser being read from straight aft would be read through the rotating wind tunnel fan. Not good.
I have looked at a conceptually simple unit using a hairspring to restrain motor rotation and a simple pointer mounted on it reading against a scale on the housing. This can be read looking past te front edge of the fan housing through the wind tunnel duct window about 45 degrees forward. Might work.
RE: Mini torque gage
If so, the latter can be accounted for. I think mechanical losses probably could be too. If you know the motor's absorbed power at speed/no load, then doesn't that equal electrical + mechanical losses, and won't mechanical losses remain the same regardless of load?
I dunno, but I'd look into calibrating the motor.
RE: Mini torque gage
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Ted
RE: Mini torque gage
Mike Halloran
Pembroke Pines, FL, USA
RE: Mini torque gage
Cheers
Greg Locock
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RE: Mini torque gage
RE: Mini torque gage
RE: Mini torque gage
http://www.kineoptics.com/WTB.html
RE: Mini torque gage