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Help building single revolution motor/servo/stepper circuit

llphil67

New Member
I am trying to design a system that will trigger a motor/servo/stepper to rotate one full revolution only. This is not the project, but is an example: a coin rolls over a microswitch which triggers a motor to make exactly one revolution and stop, ready for another coin drop to repeat process. I am very new to this so I will need to know specifically what I need to obtain and how to build the system. Thank You in advance.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
The simplest setup would be a geared DC motor with a cam attached to the output shaft, as well as whatever it drives.
(Gearing reduces the speed and gives things time to happen, plus vastly increasing the motor torque).

The cam needs to operate a microswitch at the "zero" position of the shaft rotation. The switch breaks the circuit and stops the motor.

The trigger switch just connects across the stop switch to make the motor run past the stop position, so the stop switch releases and keeps power on to the motor.

That's how simple mechanical car windscreen wipers stop in the "parked" position - a contact or switch that keeps power on until they get to the right point.

You could also use the stop switch to operate a relay that controls power to the motor. Having that connect a low value resistor across the motor when it releases would give a more accurate fast stop rather than the motor coasting on a bit.

Example geared motors; the type you need depends on how fast it must and how much power the output shaft needs:



If it's something that must operate fast. eg. less than a second for a turn, you are probably going to need a more sophisticated and much more complex system.
 

danadak

Active Member
The simple method described above excellent. But if there is a coin jam,
wrong size coin, another countries coin sized different, you could stall
the motor.

Using a micro and a RC 360 degree servo motor you could detect motor current
and manage a stall, even reverse motor to possibly unfreeze jam.

Regards, Dana.
 

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