Nunya asked in Science & MathematicsEngineering · 7 years ago

# 360 rotation Servo question?

Do full rotation servos also have the ability to stop at any of the 360 degrees like a regular half rotation servo? Is there a special name for this? I am having trobule googling it. Thanks!

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• 7 years ago

So long as it isn't listed as a continuous rotation servo, yes... it is a fully positional servo with 0 360 degree limits. (0 and 360 are coincident)

Source(s): 30years engineering
• MarkG
Lv 7
7 years ago

Your typical cheap RC servo has about a 180 degree range of mechanical travel. However most radio transmitter systems do not provide enough pulse width to drive them more than 90 degrees or so. There are electronic and mechanical devices that enable a radio control system to effectively operate at is near full 180 degrees of travel. This is done electronically with a pulse stretcher to double the pulse with from the receiver that is sent to the servo OR bu a mechanical advantage system like a 2:1 gear train or linkage.

Both ways of doubling the travel to 180 come at the expense of lowering resolution. Mechanical systems add size ,weight and loss of torque In simple terms the same small control input you perform by moving the stick on the radio transmitter that yields a small movement on a 90 degree servo will result in a movement twice the size on a 180 degree servo. You get twice the range of movement but loose the fine control.

The servo is limited in its trave because of mechanical stops AND limitations in the turning ability of a potentiometer shaft used for feedback.

THe travel to a distinct angle is done by adjusting a variable resistance as the shaft turns. The resistance is used to determine if the shaft is in teh desired position and if it isn't an electric motor is powered in one direction or the other to move the shaft in position. When the resistance matches the desired position the power to the motor is cut.

Regular servos are capable of of being modified for 360 rotation. THe mode involves removing mechanical stops and mechanically disconnecting the variable resistor from the shaft.

The potentiometers have a limited amount of travel and in most cases probably won't let you turn their shafts more than 180 degrees. To get full 360 positional control (non rotation) you need a feedback potentiometer that has the capability of having its shaft turned 360 or more without the wiper arm crossing over to a low side resistance as it nears 360 degrees. This would be a difficult modification to do if you want the feedback resistance to be contained within the servo housing. however if you have the room and mechanical appititude you can us a multiturn pot mounted outside of the housing as the feedback pot. You would just need a 1:1 gear train the connects the servo and potentiometer shafts and pass the wires back into the servo case and connect them to the controller.