Pendulum- How to Calculate HP and Torqe?

[Trever]

I have a design idea cooked up in my head. I have a pendulum with a big mass at the end. How would I calculate the HP and Torqe at the pivot point? I'm frying my brain over this.

 

[Cockroach]

Horsepower is simply an expression of power, as in the expenditure of work over time. I would apply the work-energy theorem and obtain power as the quotient of energy (Joules) with pendulum period (sec). This would be dimensionally consistent with power, that is, watts.

Similarily, torsion is simply an expression of a moment. The torque at the pivot point for a pendulum is the moment arm. That expression depends on your exact pendulum design, i.e. conical, simple or compound, torsional.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Speedy]

Trever,

I don't know your exact application but I imagine it is some sort of mechanical energy storage device. Correct?

If so then the pendulum is effectively not doing any work or dissipating poweras it swings. ( This is not entirely true as there are some frictional losses. )

To answer your question there is no power and torque available unless you actually decide to take energy from the pendulum. If so then there will be a drop in the swing angle of the pendulum.

 

[FrenchCAD]

I agree with Speedy on this one. The only work creation I can imagine with a pendulum is if you let it go with gravity until it stops...

Cyril Guichard
Mechanical Engineer

 

[jbknudsen]

Trever, check out this thread
thread404-54598
There is some good info on pendulum calcs here, maybe this will help.


Good luck,

Jay

 

[Cockroach]

I'm not too sure of the point "Speedy" and "FrenchCAD" are trying to make. Work is performed against gravity, which acts as a restoring force, hence vibratory motion of the pendulum.

Infact, "jbknudsen" correctly points to the algebaic set of equations governed by the energy method. Note "g" for the acceleration due to gravity, acceleration of the pendulum mass, hence force which is performed only in the vertical direction, i.e. against gravity. Much like ballistic motion, neglecting air resistance implies no horizontal force, work is strictly vertical since the mass rises and falls against gravity.

I prefer the differential equations in the derivation since they correctly lead into Elliptic Integrals of the Second Kind, our situation if angle of depression is greater than, say ten (10) degrees. The energy method discussed considers only linear approximations to the sine wave in the degenerative case. This may be well beyond the scope of discussion however.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[FrenchCAD]

"Infact, "jbknudsen" correctly points to the algebaic set of equations governed by the energy method. Note "g" for the acceleration due to gravity, acceleration of the pendulum mass, hence force which is performed only in the vertical direction, i.e. against gravity. Much like ballistic motion, neglecting air resistance implies no horizontal force, work is strictly vertical since the mass rises and falls against gravity."

Yeah, that's why I say, only gravity can give energy to the pendulum so that it can transform it into a force.

Cyril Guichard
Mechanical Engineer

 

[guyguy]

in your question you describe a simple pivot point. around such a pivot, theoretically, there's no tourqe! (and therefore no power) ofcourse the system has it's potential/kinetic energy and momentum...

 

[FrenchCAD]

Then we all agree on that point, we just don't say it the same way ;-)

Cyril Guichard
Mechanical Engineer