How do I measure resistance to rotation

[tudorsailor]

I have acquired a towed generator. I have now read the maintenance instructions (as suggested to me on a propr thread!) It says......

If the cogging or breakout torque has been correctly minimised, the resistance to revolution should be no more than 2kg-cm (30oz-inch).

Is it too simplistic to try and attached a rod to the spindle and apply less than the max torque and see if it turns. 2kg at one cm is difficult as the distance is so small. If i make a 10cm rod, am I right that it should turn with a weight of less than 200gms?

TudorSailor

 

[kolster]

No not too simplistic, that's exactly the way to measure torque which is force X distance.

 

[AngusMcDoon]

Killograms used as a measure of force. Blurrrgh! I can feel a pedant induced bout of queasiness coming on. Someone will mention A/h next!

 

[tudorsailor]

Killograms used as a measure of force. Blurrrgh! I can feel a pedant induced bout of queasiness coming on. Someone will mention A/h next!

Edited now! Mea Culpa. I am a bone fixer and not an engineer

TudorSailor

 

[AngusMcDoon]

Edited now! Mea Culpa. I am a bone fixer and not an engineer.

It's not you (you're a bone fixer), it's the manual you copied the quote from. That should have been approved by an engineer. I'll rephrase what they meant...

If the cogging or breakout torque has been correctly minimised, the resistance to revolution should be no more than 0.02 Nm...

 

[awol]

Someone will mention A/h next!

..... so what units would you use for the rate of change of charge flow, then?

:ambivalence:

 

[AngusMcDoon]

..... so what units would you use for the rate of change of charge flow, then?

Coulombs Newtons per kilogram metre second of course.

 

[awol]

Coulombs Newtons per kilogram metre second of course.

Hmmm - surely that should be CN/kgm or my preferred unit Watts per volt second? layful:

 

[AngusMcDoon]

Hmmm - surely that should be CN/kgm or my preferred unit Watts per volt second? layful:

Oh alright then.

I was just putting another /second in, as is the standard way for this forum.

 

[tudorsailor]

It's not you (you're a bone fixer), it's the manual you copied the quote from. That should have been approved by an engineer. I'll rephrase what they meant...

Well the good thing is that by using the incorrect terminology, it allowed an ignoramus like me to work out how to test the resistance is not excessive. Now ! need to actually rig up something to put this in practice. Need a piece of wood with a hole in the centre (or should that be the mid point) so that the weight of the wood is eliminated.

Maybe I am a bone engineer as I do have a vague understanding of bio-mechanics............

Thanks for the support!!

TudorSailor

 

[AngusMcDoon]

Maybe I am a bone engineer as I do have a vague understanding of bio-mechanics...

Think spiral fractures. A large force acting at a short distance has the same effect as a small force acting at a long distance : crack...ouch...another job for TudorSailor.

 

[JumbleDuck]

Someone will mention A/h next!

If you try to increase the current in a superconducting magnet too fast it will "quench" - ie go normal and boil off all the liquid helium round it as the magnetic field collapses and dumps its energy as resistive heat. As a result, all superconducting magnets have a maximum safe sweep rate for current, in A/h.

As for kg-m ... meh. Just change it to kgf-m and you're good to go.

 

[AngusMcDoon]

If you try to increase the current in a superconducting magnet too fast it will "quench"...

I expect they weigh a few kN.

 

[tudorsailor]

Think spiral fractures. A large force acting at a short distance has the same effect as a small force acting at a long distance : crack...ouch...another job for TudorSailor.

Is there a mechanical equation for failure relating to the speed at which torque is applied? You are more likely to get a fracture if the force/torque is applied quickly and without build up - take arm wrestling causing spiral fracture of the humerus for example......

TudorSurgeonSailor

 

[AngusMcDoon]

Is there a mechanical equation for failure relating to the speed at which torque is applied? You are more likely to get a fracture if the force/torque is applied quickly and without build up - take arm wrestling causing spiral fracture of the humerus for example.

That depends on how brittle the material is and gets deep into material science. No simple equation. A lack of understanding of brittle failure has caused many tragedies - Liberty ships are a well known example.