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# How to calculate the force required? Design of Rack and Pinion

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## How to calculate the force required? Design of Rack and Pinion

(OP)
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.

https://files.engineering.com/getfile.aspx?folder=...

https://files.engineering.com/getfile.aspx?folder=...

### RE: How to calculate the force required? Design of Rack and Pinion

You might be lucky and find some equation or rule of thumb, but i'd have thought the obvious thing to do would be to stack books on top of the piston until it squeezes all the food out, and then weigh the books.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

### RE: How to calculate the force required? Design of Rack and Pinion

(OP)
Hey Greg,
Thanks for your response man. I will try doing this. Btw, I am trying to design a gear mechanism to dispense this, with a stepper motor of 11.5 kgcm holding torque at the back. Can you help me with power transmissions in gears? As you can see in the attached image, it was a failure when we directly coupled the rack with the motor shaft's pinion.

### RE: How to calculate the force required? Design of Rack and Pinion

Is the rack guided?. A simple LM guide would reduce the frictional forces which needs to be overcome in order to press the food stuff. What is the rated torque of the stepper that you are using?. Looks like a hobby kit to me.

### RE: How to calculate the force required? Design of Rack and Pinion

So, lesson to be learned, if it's not already obvious; figure out the design requirements FIRST. Then, you design and build and test

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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