×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Gear Design

Gear Design

Gear Design

(OP)
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
 

RE: Gear Design

Hi delimashare

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

regards

desertfox

RE: Gear Design

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

RE: Gear Design

(OP)
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

RE: Gear Design

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

RE: Gear Design

(OP)
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

RE: Gear Design

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

RE: Gear Design

(OP)
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

RE: Gear Design

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

RE: Gear Design

(OP)
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

RE: Gear Design

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.
 

RE: Gear Design

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

RE: Gear Design

Hi delimashare

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

desertfox

RE: Gear Design

(OP)
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

RE: Gear Design

hi delimashare

Yes I can see the file now.
I think your calculations are not correct, what I expected to see was 1280N X radius of gear wheel then to work the force out in S1 I was looking for

force S1= 1280N X radius of gear/(perpendicular distance
                                  between line of S1 force
                                  and pivot point of gear


Then work through the bottom half of the mechanism back to the handle again using the lever lengths of the mechanism.

desertfox

RE: Gear Design

(OP)
Hi All,
desertfox,Thank You so much for you time and help.

1)The Linkage is welded to the gear and rotated by applying the force on the linkage itself. That's why I considered the linkage length to estimate the torque on the gear?  If this is wrong what would be the force on the linkage(L1) on gear1?Don't we have to consider it?

2)and in your equation :
force S1= 1280N X radius of gear/(perpendicular distance
                                  between line of S1 force
                                  and pivot point of gear
I could'nt figure out the direction of (perpendicular distance).It makes an angle of how much with horizontal line or x axix????

3)And do we estimate torque on shaft S1 or not,I thought we don't,because it is only compression/tension forces on this shaft only???

delimashare

 

RE: Gear Design

Hi delimashare

perpendicular means at ninety degrees to the reference plane.
If you draw a line from S1, perpendicular to S1 and make sure it passes through the pivot point of the gear rotation and thats the distance you require for the calculation.

desertfox

RE: Gear Design

(OP)
Hi all,
Thanks desertfox
I have a simple question here.Is the torque constant all through the system?I'm really confused.
delimashare

RE: Gear Design

Hi delimashare,
In answer to your question - no, the torque is not necessarily equal throughout your system. If you can wait another day I'll try and upload something that may help you.

Regards,
desertfox

RE: Gear Design

(OP)
Thanks desertfox,
I really appreciate that.
delimashare

RE: Gear Design

Hi delimashare

I have marked and uploaded your earlier files to show you how to calculate the forces however I need to point out two things:-

1/ I have ignored the angle that S1 makes with the operating shaft on the righthand view of your original pdf post page 1.

2/ Looking at your mechanism righthand view of page 1 at items marked L2 J1 you might find that you have trouble in operating the switch as you will transfer very little torque to the switch with the link L2 in that position.

desertfox

RE: Gear Design

(OP)
Hi desertfox,
I was in a vacation and had no chance to check what you have sent me.Now I'm back to work and will do that soon.
Thank you so much.
delimashare

RE: Gear Design

(OP)
Hi Desertfox,
I followed your instructions to calculate the torque on the operating shaft.Suppose the Torque on the operating shaft was (Z).How do I calculate the force to be applied on the handle?
Regards,
delimashare

RE: Gear Design

Hi delimashare,
If you have now calculated the torque on the operating shaft, finding the force is quite simple. All you have to do is divide the torque on the operating shaft by the length of the handle.
For example, if Z is in Nm and your length of handle is Xm, then force f is equal to Z(Nm)/X(m).
Regards,
desertfox

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources