Bell crank linkage problem

[TyVan07]

Hi,
I have what I thought would be a routine design problem that has turned into a head scratcher. I want to control a ring of 145" diameter by moving it approximately 20 degrees around its centre, it does not move axially. I need to do this with a smaller diameter crank which enables me to push on one side of the large wheel, and pull on the other side. The problem is I cannot find any geometry which allows me to do this. Either the links want to extend, or the hole centres change. Is there a magic ratio that allows this geometry to work?

I've attached a sketch with dimensions to illustrate this. Any ideas?

Regards,
Tyler

 

[Compositepro]

Only one to one will work. Or use a chain drive.

 

[Philrock]

I agree with Compositepro, as far as solving your problem with simple pivot ended rigid links.

Is there any reason a chain drive as Compositepro suggested would not work?

A rather inelegant solution would be to make both wheels into gears, and replace the links with racks. It would be difficult to get good load sharing between the two racks - great precision would be required.

 

[TyVan07]

Thanks for the replies, two reasons a chain drive will not work, it only applies a pull force and not a push and the application I'm using it in is underwater and sees lots of debris = bad for chains.

 

[TyVan07]

Curious, what is the reason or theory that proves this is not possible?

 

[mfgenggear]

synthetic rubber timing belt

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[chicopee]

TyVan,this problem was a head scratcher for me too, until I saw the sketch. The descritpion of the event that you want to occur is different than what the sketch is showing. It is a honorable task to solve this type of problem, however, your terminolgy in your description has much to be desired. You should improve your writing skill.
Looking at your sketch, I would explore two solid links both of which would have pinned connections on these wheels. The pinned connection would travel within circular grooves (machined in one or both wheels) of certain lengths allowing the pinned connection to travel freely a small amount. Upon reaching the ends of these grooves the pinned connections would rotate the driven wheel thru the desired angle.