Slider Crank Mechanism Torque Question

[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.

Thanks in advance for your help.

 

[jrmichler]

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.

 

[bugdry]

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.

 

[BvU]

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 ...

 

[bugdry]

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.

 

[BvU]

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

 

[bugdry]

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

 

[BvU]

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 !

 

[bugdry]

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.

 

[bugdry]

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.

 

[anorlunda]

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

 

[BvU]

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 !

 

[bugdry]

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.

 

[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.

Fabricate that slot and make it work properly may be difficult.

An additional idea:
http://507movements.com/mm_419.html