# Servo Motor for 180 degrees rotation

I am building a liquid dispensing mechanism and trying to figure out how to use servo motor with arduino. The torque needed isn’t too much, the rod in the figure below is rotated 180 degrees to dispense liquid once, and can be done by rotating between index finger and thumb. I am more interested in a cost effective solution where the components dont cost too much.

What should be the factors to keep in mind when designing servos, as i have seen problems like servo overshoot etc. The main point I have for this question is that which servo would be suitable for this kind of solution? 180 Degree flip every time … It can be one way 180 degrees or it can be clockwise 180 , counter clockwise 180 …

A diagram of what I am trying to achieve is:

Hi! There are a few brands of servos that will rotate 180 degrees. Other people have pointed out some brands are 120-150 degrees.

Are you sure you need 180? if you are operating a ball valve or butterfly valve, a 90 degree rotation is needed to open/close the valve.

If you can move the valve easily with your fingers then a basic servo like a hitec-hs422 would probably do. It does a full 180 degree sweep.

The OP is sure that 180 degrees is needed, that is clear!

The torque needed isn't too much, the rod in the figure below is rotated 180 degrees to dispense liquid once, and can be done by rotating between index finger and thumb.

That indicates about 0.1Nm - but it is always better to measure, not guess, with forces and torques.

Rough guide to torque in human terms:

finger and thumb twisting - 0.1Nm
Screwdriver (using one wrist) - 1Nm
steering wheel (both hands) - 10Nm

So if the valve is brought from 0 degrees to 90 and then down to 0 no liquid will be dispensed?

I am just satisfying my curiosity of what type of dispensing valve this is.

Actually its not a valve per se, its a simplified liquid dispenser. A cap has a rod through it and the rod has grooves on it. The bottle is capped and is placed upside down. now when the rod is rotated, the liquid in the groove is passed to the other side of the cap with a nose and dispensed out.

And yes, its confirmed its a 180 degrees rotation.

Cool, thanks, check out that servo, Its not too expensive and does do a full 180.