Gear Design 1

[delimashare]

Hi Everybody,

I have to design 3 gear assemblies which run a switchgear inside an enclosure. Here I attach a drawing for one gear only(for a similar project). I have to do my calculations and select the diameter, length, cross section, material...etc. for the linkages, shafts, axles, chains, ball joints and frames. Dimensions shown on drawings have to stay the same because they are related to the enclosure dimensions.
I was provided with the following information:

The linkage is tested at 5000 Lbs (1100N).
For this Torsion bar manual operator, the force is 250 N min and 450 N max.
Any information will be helpful.I need to start somewhere.

Thanks in advance.
Delimashare

 

[desertfox]

Hi delimashare

I can't view the autocad file can you reload it as a pdf file.

regards

desertfox

 

[DesignerGuy16]

FYI.

http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=6703438

Get AutoCAD TrueView. Lets you open ANY release dwg/dxf files and resave to a previous release.

James Spisich
Design Engineer, CSWP

 

[delimashare]

Thank you .Here I attach the drawing as pdf file.
Hope this will work.
Regards,
Delimashare

 

[desertfox]

Hi delimashare

You need to apply your operators force to the handle with which he will operate the switchgear then using a static analysis work through using leverage ratio's for each link and gear etc and see if the gear switches, if the force the operator applys through the operating handle is not enough to operate the switchgear you need to increase the length of the handle and work through the process again untill the operator can switch the gear on or off using the handle within the specified operating forces.

desertfox

 

[delimashare]

Thank you desertfox.
I'm not sure if I understand you.Which part is the handle? I assume it is the bar that the operating man uses manually to operate the switchgear. So we have to apply 250N-450N on this bar? How do we measure the force applied?And how do we estimate the force on the gears then?
I thought that the final force on the GEAR should be 250N-450N in order to rotate the gears.
Please advise, if possible in figures or equations.
Regards,
delimashare

 

[desertfox]

Delimashare,

Yes, the handle is the bar that the operator uses. Also, yes, you have to apply 250N-450N on that bar.

You do not measure the force applied, you have to assume the lower figure for example. Then calculate using simple levers through your mechanism to ensure that the gear can be operated. I assumed from your first post that the 1100N was the force to turn the gear.

I was thinking that the operator has to apply 250 or 450N and through a lever system that force is increased to 1100N in order to operate the gear.

You have to work through your mechanism calculating the force at each lever point in order to establish whether you can get 1100N at the gear.

desertfox

 

[delimashare]

Hi everybody,
thanks desertfox,
Here I continue,
In order to operate the gear,an L shape handle of 20"x6"is used. The short side is inserted inside a nozzle at the gear closure door in order to operate the gear,and the 250N force is applied on the long side. Now, Can we calculate the force on the 6" part by the equation: 250Nx20"=6"xF which gives F=833.3N ,then continue estimating force on linkage L2 by the same equatuion:833.3Nx6''(length of handle short side)= Fx7"(length of linkage L2) which gives
F=714.25..if this is correct how do we find the force on shaft,knowing that there will be an angle..and what is the worst case sinario to work on for angles, provided that the gear should turn 1/4turn to open/close the switch.??????
Please help,
Delimashare

 

[desertfox]

Delimashare,

Yes you're on the right track doing what you are doing, ie equating forces and moments. Now the torque on any shaft is whatever the force is multiplied by the perpendicular distance of that force to the centre of rotation. For your switchgear I would start at the gear end of the switch ie the force required at the gear to turn it a quarter turn, in addition I would take the maximum load at that point and add 10-15% for friction in the mechanism. Then work backwards from the gear to see what force the operator needs to apply to the handle.

desertfox

 

[delimashare]

Thank you desertfox,
I worked backwards and did my calculations to find the operator force needed.I assumed that the force on the G1 (horizontally in the direction of chain)is equal to the force on G2 in the same direction.Is that correct?My estimated force was less than 250N in the worst linkage angle position,which is fine .What is the next step ?Is it to calculate the cross sectional area of the shaft?and what is the material recommended for this shaft? and it has to be a hollow shaft?please advise.
Regards
delimashare

 

[desertfox]

Hi delimashore
If G1 and G2 are the same size the torque at each gear would be the same which means the force would be too.
Well for indoor switchgear I think ordinary mild steel will do.
Look up torsion on a circular bar for your stress calculation I think off the top of my head the formula for shear stress is


shear stress = torque * r/(J)

torque is torque on shaft

r = radius of shaft

J = polar moment of inertia

Your shaft can be hollow or solid, it depends if you want to save handle weight.

desertfox

 

[delimashare]

Hi,
I'm calculating the diameter of the shaft using the formula:
Tmax=(pi/16)x sheer stress x ((D4-d4)/D)
T is torque
sheer stress varies acc. to material used
D is outside diameter of shaft
d is inside diameter of shaft
I don't know where to apply polar moment of inertia here?
Regarding my previous question on forces on gears,I wanted to be sure that the chain length doesn't have any effect on forces or torques on gears.
Also,I did force analysis ONLY, taking angles into consideration to calculate OPERATING FORCE needed.I didn't analyse torques. Is that right?
Thanks,
delimashare

 

[desertfox]

Hi delimashare

The polar moment is already in your formula that your using so thats fine.
Your post on the 23/07/09 deals with torques ie:-

your quote:-
In order to operate the gear,an L shape handle of 20"x6"is used. The short side is inserted inside a nozzle at the gear closure door in order to operate the gear,and the 250N force is applied on the long side. Now, Can we calculate the force on the 6" part by the equation: 250Nx20"=6"xF which gives F=833.3N ,then continue estimating force on linkage L2 by the same equatuion:833.3Nx6''(length of handle short side)= Fx7"(length of linkage L2) which gives
F=714.25."

Force times length is torque therefore in order to work out the forces you needed to work through the leverages, so as far as I can tell your doing the right thing.

 

[delimashare]

Hi all,
and thank you so much desertfox.
I still need some help in analysing the forces and torques.Please see attached a pdf dwg. on which I show how I worked on this.I also put my question on the same drawing,to make it easier to follow up.

Regards,
delimashare

 

[MechEng2005]

The .pdf isn't working for me at least...

 

[desertfox]

Hi delimashare

Your files not working for me either, please upload it again

desertfox

 

[delimashare]

Hi desertfox,,
Sorry for that .I don't know what the problem is.Here is the file again.
Thanks
delimashare

 

[delimashare]

Hi desertfox,
It seems that the file is not working for me either.Here I attach it again in Autocad 2004.Hope it will work this time.
Thanks
delimashare

 

[delimashare]

Hi All,

MechEng2005 ,
Sorry I have just noticed that the files are not working for you too.
Anybody knows the reason? I'm uploading the files in the same way I used to do it before.But it is not working.!

Regards
delimashare

 

[delimashare]

Another Try
delimashare