Rescue Hexacopter Project


Design - Arms

Each arm of the hexacopter will consist of several components: the boom, bottom motor mount, top motor mount, and two ESC to Motor connection plugs (one male and one female). The arms will be removable to allow for easy storage. They will connect to the main frame by the use of two wing-tip screws.

Arm Assembly

The boom

The booms we designed from 22 mm carbon fiber tubes. These will be purchased online and will be cut and drilled as necessary by our Metals class. Each boom will have a motor mount on one end and a male ESC to Motor connection plug on the other end. The booms should be 383 mm long with holes for the motor mounts on one end and two holes perpendicular to the motor mount holes located about 90 mm from the opposite end. These holes will be used to lock the tube in place against the frame of the body.

Top and Bottom motor mounts

The bottom motor mount we designed to attach to the boom by four bolts providing clamping pressure with the top motor mount and with one bolt to prevent rotational movement. The top motor mount is designed to provide a clamping surface while still allowing the motor to freely rotate. We will need six of each of them for the project.

Top and Bottom motor mount

Top and Bottom U7 Motor Mounts

To design the top motor mount, we took the diameter of the U7 motor which is 60.7 mm and added four millimeters to provide a 2 mm clearance. The outer ring we set at a diameter of 72 mm. The bottom of the plate was placed 3.5 inches from the center of the circle to allow room to wire the motor. The bottom plate has 3 mm mounting holes to attach the U7 motor.


The motor mounts will attach to the booms using (5) 4 mm x 35 mm bolts and (5) 4 mm nuts. The bolts will be coated with Loc-Tite to prevent the nuts from working off due to vibration. In addition, two screws will be used on the top and bottom to lock the wiring plug in place within the boom.

The installed motor mount should look like this:

Installed Motor Mount

Installed Motor Mount

Arm Plug

Since we want the arms to be easily removed for storage, we designed an arm plug to be fabricated locally out of rubber or printed in plastic on our 3D printer. Each motor has 3 wires which connects the motor to the Electronic Speed Controller or ESC. We needed to devise a system which would only allow the correct arm to be installed in each arm location. The arm plug was the result of our efforts. The plug will be a cylinder of rubber or plastic 28 mm tall with a diameter of 20 mm. On one face we placed 3 holes 4 mm in diameter with a depth of 12 mm. The holes were placed 10 mm from the center and 120 degrees from each other. On the reverse side, 2 millimeter holes were made in the same locations. The concept is to solder wires to 3.5 bullet connectors which are then epoxied into the 4 mm holes in the arm plug with the wires extending through the 2 mm holes on the back of the plug.

By using female connectors on the motor side of the boom and male connectors on the body side of the boom, we can simply plug in the arms into female arm plugs secured to the body of the craft.

The prototype of the Arm Plug looks like this:

Arm Plug


To complete the build, we will need (12) ESC to Motor Connectors - Female and (6) ESC to Motor Connectors - Male. The following shows both the female and male ESC to Motor Connectors:

ESC to Motor Connectors

ESC to Motor Connectors

We will use the orientation of the holes to determine which arm can be plugged in. For example, the arms which have motors running clockwise will have connectors that have a single hole at top, those with motors running counter clockwise will have connectors which have two holes on the top of the connector. Therefore if the wrong arm is plugged in, it will be readily noticeable as the motor and prop will be upside down.

ESC to Motor Orientation

Clockwise orientation (left) and counter clockwise orientation (right)


Arm Component Drawings
Part/Assembly PDF STEP
3.5 mm Bullet Connector - Female 3.5 Bullet Female.pdf 3.5 Bullet Female.stp
3.5 mm Bullet Connector - Male 3.5 Bullet Male.pdf 3.5 Bullet Male.stp
4 x 10 mm Hex Screw 4x10 mm Hex Screw.pdf 4x10 mm Hex Screw.stp
4 x 35 mm Hex Screw 4 x 35 mm Hex Screw.pdf 4 x 35 mm Hex Screw.stp
4 mm Hex Nut 4 mm Hex Nut.pdf 4 mm Hex Nut.stp
383 x 22 mm CF Tube 383x22 mm CF Tube.pdf 383x22 mm CF Tube.stp
Arm Plug Arm Plug.pdf Arm Plug.stp
Bottom U7 Motor Mount U7 Bottom.pdf U7 Bottom.stp
ESC to Motor Connector - Female ESC to Motor female.pdf ESC to Motor female.stp
ESC to Motor Connector - Male ESC to Motor male.pdf ESC to Motor male.stp
Top U7 Motor Mount U7 Top.pdf U7 Top.stp
Arm Assembly - Complete Arm Assembly.pdf Arm Assembly.stp