How to calculate the force required and design a rack and pinion?

[Govardhanan]

Hello everyone. This is Govardhanan. I am still a student, when mechanics is considered, so please tolerate my simple questions and pls do help me out.

I am trying to dispense some food from the container using a rack and a pinion, but was not successful in that, as the stepper motor I use doesnt give enough torque. So I need to know the torque I am supposed to generate to dispense the food. But I am not sure how to measure the force required to dispense the food. Please help me out in designing this. Thanks a ton in advance.

I have attached the rough explanation drawing and an image of what I have done already.

 

[Tiger15]

Calculating the how the motor torque corresponds to tooth forces and force in the rack is pretty straight forward. There are standard equations for that. (I don't remember them off the top of my head.)

Calculating how much force it takes to push the semi solid food material through the openings is going to be tough because I doubt you'll be able to find the necessary properties of the food material (stiffness, viscosity, etc. Because of that it's might be easier to figure it out through trial and error. You could put a weight on top of the plunger and figure out how many pounds of force you need.

Also instead of redesigning your rack and pinion or replacing the motor, it might be easier to change the openings. More or larger opening should reduce the amount of force needed.