HS 81 Servo Rotor Capture

Attaching to a Rotor

Servos are small electric motors which use gearing to provide a relatively large amount of torque, for a small amount of electric power. They are often used as actuators, to convert electrical energy to mechanical energy. A typical example is the HiTec HS 81 shown below



They typically operate from 6 volts, and have three leads positive (RED), Negative (BLACK), and Signal (YELLOW). The rotor (the white plastic attachment) is driven left or right depending on the nature and timing of the voltage on the Signal lead.

These servo's are quite sensitive, and can be driven from low current/low voltage devices directly (E.g Arduino). Whilst we are using are Arduino for many our our projects, how we do that will that will be covered in other articles

Usually the mechanical attachment takes the form of a spring, or an actuator wire to create mechanical movement

The rotors are quite small typically 20- 23mm across, and have very small holes, <1mm. Per the picture below

The challenge we have here at NoYoo is that we need to attach something much larger, a wooden arm which whilst quite light, is physically much larger than the rotor.

The way is which we resolved this challenge was to fabricate a piece of plastic which encapsulated the rotor, and provided a bolt-able platform to attach to our fixture.

Putting the two together you can see how we now have the base of a platform for attaching other devices to the rotor



Now attaching the actuator arm becomes a simple task of bolting it up, and enclosing the rotor, which is still attached the the servo in the normal manner meshing the two gears, secured with a small self- tapper



And from the other side



In close up , you can see the rotor is enclosed between the capture and the fixture



This approach works well, and avoids the sort of once only problems if you had glued the two parts together. It is very strong and easily dismantled

Machining the Rotor Capture

The 'capture' was milled from a 25mm Delrin rod on a Bilby 3040 CNC machine.

It was first drawn in Design Spark Mechanical, in 2D, then transformed into 3D. Saved in AutoCAD file format .dxf, and posted to CAM software

As per the screen capture below





The AutoCAD file was then processed in SheetCAM to assign tools and tool-paths to route each of the features on the CNC. When complete SheeCAM processed the file into GCode control the CNC machine. The picture below shows the tool-paths

The GCode was then loaded to Mach3 to control the CNC machine to route the part . Mach 3 is configured to the actual CNC machine and translates the GCode instructions to the CNC X,Y and Z axes to drive the tool-bit.

Download the drawing and GCode here

And from the file links below you can download the .dxf 3D drawings, and the SheetCAM produced GCode.

Design Spark Drawing file

Servo Rotor GCode



If you have any questions, would like to leave a comment, please do, your feedback will make all the difference ...thanks for dropping by 

Peter