# Slider Crank Mechanism Torque Question

• bugdry
In summary: It may be difficult to fabricate a slot that works properly, but an idea on the website 517movements.com may be easier to implement.
bugdry
I hope that it is okay for me to ask this here. It has been a long time since i did mechanism analysis.

I have what I hope is a quick question. I calculate the torque required to rotate crank AB and therefore lift up the link BC to be 88lb-in. I assumed that link AB has no weight, no friction at the joints and i kept the length of BC at 10.5". I am trying to determine the minimum motor size i need to lift link BC, with link AB moving at a maximum of 60rpm.

I know i am also missing the inertia load to start the rotation. But i am just going for a ball park torque figure for now.

#### Attachments

• TEST MECHANISM 1 - Sheet1.jpg
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• sample data.xlsx
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You can start by looking at the values in your "Torque at theta" row, and ask if they make sense. Then look into how your spreadsheet calculates trig functions.

Hint: Consider the difference between degrees and radians.

Thanks. I have updated the equations to using radians, but it didn't change the torque at all. It would make more sense to me for the torque required to be 89lb-ft, not 89lb-in.

I am trying to solve this with trig. But my problem is that it doesn't seem like the usual slider crank mechanism, with the slider able to pivot. But in my design, I need the long link to pivot.

Hi,
May I ask: what is the purpose of this device ? It seems to me BC just wiggles and points A and C are fixed in position ...

BvU said:
Hi,
May I ask: what is the purpose of this device ? It seems to me BC just wiggles and points A and C are fixed in position ...

It is to gently rock a keg after it has been filled. With the CO2 feeding into the keg, you gently rock them and it can force carbonate a keg in about 30minutes. Instead of rolling them across my legs while I sit on a chair, I wanted to be able to strap the keg into this and run it for 30minutes while I work on other things. Mainly i thought it would be cool to design and make it.

#### Attachments

• keg shaker.JPG
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• keg shaker 2.JPG
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Ah !
So why not counterbalance the crank mechanism purplish wheel ? Less energy loss, less wear, etc ...

I don't remember how. Its been 15 or so years since i dealt with anything but static designs. lol

bugdry said:
updated the equations to using radians, but it didn't change the torque at all
Strange ! It did make a big change for me: from

to

or one period of a sine when plotted. Makes a whole lot more sense.

But this is the static torque at 0 rpm !

BvU said:
Strange ! It did make a big change for me: from

View attachment 274062

to

View attachment 274064

or one period of a sine when plotted. Makes a whole lot more sense.

But this is the static torque at 0 rpm !
Ah ok, yes sorry. I meant that the max torque didn't really change.

ok, well I thought this would be a pretty straight forward project. I guess not. I will keep shaking them by hand. Thanks for the help guys.

Wouldn't it be simpler to scale up this Weebles toy big enough to hold a keg?

Is it necessary to move the keg up and down ?

Why not use a crank and shaft to just swing the bottom end ?
(or the top )

Forces required are a small fraction of what's needed to lift the things !

Lnewqban
I was just thinking that last night. I was like there has to be an easier way to do this. I am going to work on that idea today. The mechanism just needs to slosh the liquid around in the keg to facilitate the absorption of CO2 into the liquid.

bugdry said:
I was just thinking that last night. I was like there has to be an easier way to do this. I am going to work on that idea today. The mechanism just needs to slosh the liquid around in the keg to facilitate the absorption of CO2 into the liquid.
Fabricate that slot and make it work properly may be difficult.

http://507movements.com/mm_419.html

## 1. What is a slider crank mechanism?

A slider crank mechanism is a mechanical linkage that converts rotary motion into linear motion or vice versa. It consists of a rotating crank connected to a sliding piston or rod, which moves back and forth in a straight line.

## 2. How does a slider crank mechanism work?

The crank rotates, causing the connecting rod to move the slider back and forth. This converts the rotary motion of the crank into linear motion of the slider. The slider can then be used to power other mechanisms or perform a specific task.

## 3. What is the purpose of a slider crank mechanism?

A slider crank mechanism is commonly used in engines, pumps, and other machines to convert rotary motion into linear motion. It is also used in devices such as bicycles, where the pedal motion is converted into rotational motion of the wheels.

## 4. How is torque calculated in a slider crank mechanism?

The torque in a slider crank mechanism can be calculated by multiplying the force applied to the crank by the length of the crank arm. This is known as the torque arm. The torque arm is the perpendicular distance from the axis of rotation to the point where the force is applied.

## 5. What factors affect the torque in a slider crank mechanism?

The torque in a slider crank mechanism is affected by the length of the crank arm, the force applied to the crank, and the angle at which the force is applied. The angle between the crank and connecting rod also affects the torque, as well as the friction between the moving parts.

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