### Author Topic: Torque needed to twist off a bottle cap  (Read 14473 times)

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#### airman00

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##### Torque needed to twist off a bottle cap
« on: August 31, 2007, 05:09:21 PM »
I need to know the amount of torque needed to twist off a bottle cap from a soda bottle. Can anyone guess an approximate torque? Or where I can find that out from?
Thank you,
Eric
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#### ed1380

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##### Re: Torque needed to twist off a bottle cap
« Reply #1 on: August 31, 2007, 05:30:22 PM »
securly mount a 1ft long rod to teh cap. and lay the bottle down, with teh cap  hanging off of a table, and then start adding  weights at the end of the rod.
once it twists off, you know how many ft/lb you need
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#### Gertlex

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##### Re: Torque needed to twist off a bottle cap
« Reply #2 on: September 01, 2007, 07:36:58 AM »
securly mount a 1ft long rod to teh cap. and lay the bottle down, with teh cap  hanging off of a table, and then start adding  weights at the end of the rod.
once it twists off, you know how many ft/lb you need

Account for the torque provided by the rod too, of course.

Unless you mount the center of the rod to the cap, then it cancels itself out.
I

#### ed1380

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##### Re: Torque needed to twist off a bottle cap
« Reply #3 on: September 01, 2007, 03:46:30 PM »
securly mount a 1ft long rod to teh cap. and lay the bottle down, with teh cap  hanging off of a table, and then start adding  weights at the end of the rod.
once it twists off, you know how many ft/lb you need

Account for the torque provided by the rod too, of course.

Unless you mount the center of the rod to the cap, then it cancels itself out.
yeah didn't think of that.
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##### Re: Torque needed to twist off a bottle cap
« Reply #4 on: September 09, 2007, 02:42:49 PM »
Quote
Account for the torque provided by the rod too, of course.
FYI, its:

torque = .5 * (weight of rod) * (length of rod) + (weight of object) * (length of rod)

#### SomeSaba

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##### Re: Torque needed to twist off a bottle cap
« Reply #5 on: September 23, 2007, 11:39:22 PM »
Quote
Account for the torque provided by the rod too, of course.
FYI, its:

torque = .5 * (weight of rod) * (length of rod) + (weight of object) * (length of rod)

I *always* been confused on that:

Torque= rF (disntace * force)

Weight is a force, but to calc weight dont u have to say W = mg (mass and grav. acc. 9.8m/s^2)!?!?

So if u mass it on a scale thats the mass right?? so u have to multiply it dont u?

#### Ro-Bot-X

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##### Re: Torque needed to twist off a bottle cap
« Reply #6 on: September 23, 2007, 11:54:25 PM »
Wrong, you can scale only the weight, not the mass. Then you can calculate the mass using the formula you mentioned.
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##### Re: Torque needed to twist off a bottle cap
« Reply #7 on: September 24, 2007, 04:41:59 AM »
Weight is mass times gravity.

Weight is a force, while mass is not.

#### dcole07

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##### Re: Torque needed to twist off a bottle cap
« Reply #8 on: September 24, 2007, 12:32:29 PM »
securly mount a 1ft long rod to teh cap. and lay the bottle down, with teh cap  hanging off of a table, and then start adding  weights at the end of the rod.
once it twists off, you know how many ft/lb you need

Account for the torque provided by the rod too, of course.

Unless you mount the center of the rod to the cap, then it cancels itself out.

Unless he uses one of those mass-less rods!

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##### Re: Torque needed to twist off a bottle cap
« Reply #9 on: September 25, 2007, 06:04:13 AM »
Couldnt he just use a torque wrench,just find a way to fit the cap in there.

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##### Re: Torque needed to twist off a bottle cap
« Reply #10 on: September 26, 2007, 03:01:22 AM »
when calculating the torque the direction is also important.
T=rf is wrong

Correct
T=RxF (cross product)
=R*F*sin(angle) (absolute value)
=det [i     j     k ]
[Fx  Fy   Fz]
[Rx  Ry  Ry]
where det is the determinant of the matrix.
« Last Edit: September 27, 2007, 06:39:26 AM by Tsukubadaisei »
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#### ed1380

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##### Re: Torque needed to twist off a bottle cap
« Reply #11 on: September 26, 2007, 06:14:15 PM »
Couldnt he just use a torque wrench,just find a way to fit the cap in there.
AFAIK torgue wrenches are made for high amounts of toruqe
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#### Robotboy86

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##### Re: Torque needed to twist off a bottle cap
« Reply #12 on: September 27, 2007, 03:06:56 PM »
..not to be mean or anything..

BUT:

Just use a big servo and call it a day.  Its going to be less then friction that human skin can withtake..  as such, its not going to be a lot.

my guess is under 40ft/lbs.

Probaly far under.

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##### Re: Torque needed to twist off a bottle cap
« Reply #13 on: September 27, 2007, 04:37:03 PM »
Quote
my guess is under 40ft/lbs.
I think you meant 40lb*ft

btw, thats a lot!

Im guessing more like 5lbft . . .

#### Robotboy86

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