Step #2: Cut and drill the booms
Saw 4 square dowel booms to 10"–11" each. Shorter booms will make your quad more agile, and longer booms will make it more stable. Drill two 3mm holes, one 6mm and one
26mm (on-centers) from the end of each boom.
Step #4: Wire the power hub
- Six components will connect to the power hub — the 4 electronic speed controllers (ESCs) , the power module, and the gimbal controller board. First, cut off the male XT60 connector from the APM power module cable. Then strip about ¼" of the insulation from each wire, red and black, on all 6 components, and tin the stripped ends. Saw a ⅜" ring from each end of the copper reducer, and file off any rough edges. Solder each of the 6 red positive leads to the smaller ring, and the corresponding 6 black negative leads to the larger ring. Wrap the smaller ring in ⅜" foam weatherstripping tape and slip the outer ring over it. Finally, paint the entire hub with liquid electrical tape for insulation.
- Wiring the motors and electronic speed controllers together is tedious. Store-bought distribution boards are convenient, but cost space and weight. I prefer this homemade distribution hub made from 2 rings of nested copper pipe to keep things lean and tidy.
Step #9: Build the camera/ battery mount
- The gimbal and battery shelf are assembled from three simple L-shaped brackets. We refer to these as the shelf, roll, and pitch brackets.
- Saw a 36" length of ⅛"×¾" aluminum bar stock into two 18" sections, then saw one of those into two 9" sections, giving 3 pieces total. Make a right-angle bend in each section as indicated on the templates, working over a piece of wood or other scrap with a beveled edge to increase the bend radius to about ⅜". (Too sharp a bend can overstress and weaken the aluminum.) After you’ve made the bends, cut each bracket to final size per the templates.
- Accurately locate, mark, and drill a centered row of three ⅛"-diameter holes on the short leg of the shelf and pitch brackets, and on both legs of the roll bracket. In each case, the outermost hole should be 3mm from the bracket end on-center, and the holes themselves 9.5mm apart on-centers. Finally, step-drill the center hole in each row up to ⅜" to provide clearance for the motor shaft.
- Use two M3×6mm screws to attach the bottom of a gimbal motor to the shelf bracket, and then 2 more to attach the top of the motor to the longer arm of the roll bracket.
- Attach the bottom of the second
motor to the free arm of the roll bracket, and its top to the pitch bracket, in just the same way.
Step #10: Mount the camera and battery
- I designed this quad to balance properly with a 3S 2,200mAh LiPo battery and a GoPro Hero3 White. If you use other equipment be sure you keep the CG (center of gravity) in the middle of your airframe. Here's how to get it balanced.
Though the GoPro is a tough camera, you may want to build a “dummy” version having the same weight, and approximately the same size, to mount during your maiden and subsequent shakedown flights.
- For the gimbal motors to operate smoothly, the camera must be balanced along both axes. Weaken the adhesive on a piece of double-sided tape by sticking it to your shirt and peeling it off. Remove the backing and apply the exposed side to the pitch bracket, then use the weakened side to hold your GoPro in place while you adjust it to find the balance point. Once you’ve got it, use an elastic band or a velcro strap, in addition to the tape, to hold the camera securely in place.
- With the frame upside-down, balance the camera, brackets, and battery across the 2 shock mounts on the underside of the frame. Adjust the position of the whole assembly forward and backward along the frame until the entire quad balances evenly between your fingertips, centered on either side of the body.
- Once you’ve got the CG right, fix the shelf bracket to the shock mounts with 2 sets of crossed zip ties. Apply hook-and-loop tape on top of the shelf bracket and on the underside of the battery, and fix the battery in place. Add a hook-and-loop strap around both bracket and battery as an added precaution.
Step #11: Install the avionics
- Arrange your flight controller, receiver and other modules before attaching them to the airframe. Once you’re happy with the layout, use double-sided tape to secure everything to the frame. Download the wiring diagram for a detailed list of all connections.
- Attach the flight controller. In this build we use 3D
Robotics’ ArduPilot Mega (APM) 2.6, which contains an accelerometer and must be oriented correctly with respect to the frame. Align the arrow on the APM case toward the front of the quad and fix it in place with double-sided tape.
- Add the GPS/compass module, which fits neatly on the rear extension of the bottom frame plate, and also must be aligned with the arrow forward. Tape the module in place and connect the cable to the APM’s “GPS” port.
- Starting from the starboard-front position and proceeding clockwise (viewed from above), connect the ESC signal cables to APM outputs 1, 4, 2, and 3.
- Mount the receiver alongside the APM with double-sided tape, and connect channels 1–5 to the corresponding inputs on the APM.
Step #13: Configure the software
The flight controller, ESCs, and gimbal controller all need to be calibrated and configured before flight. Refer to the bundled or online instructions that came with your equipment. Specific tutorials are linked from the bottom of this page.
- Before you install the propellers, put bits of masking tape on the motor shafts to make it easy to see which way they are spinning. From above, motors 3 and 4 should spin clockwise, and motors 1 and 2 counterclockwise. If a motor is reversed, simply swap any 2 of the 3 leads connecting it to the ESC.
- WARNING:If you need to reverse a motor, be sure to swap the motor control leads only, not the ESC power hub leads. Don’t ever reverse the power connections on an ESC!
- The most important factor for steady flight is balanced props! There are lots of tricks for doing this, but the simplest involves sanding the heavier side of each blade until the prop balances level on a horizontal shaft. (Sand only the flat, not the leading or trailing edges).
- Once the props are balanced, install them on the shafts and tighten the nuts. You’ll use 2 conventional airplane “tractor” props and 2 reverse-pitched “pusher” props. Motors 1 and 2 take tractor props, and motors 3 and 4 take pusher props. (If you’re not using the APM flight controller, your prop configuration may be different.) Once you’ve got it right, mark the number and direction of rota-
tion for each motor on its boom for easy reference.
- Make sure the props are balanced, the parts are securely fastened, and none of the props, gyros, or controls are reversed. Verify that all your radio trim settings are at zero (if you have to trim, do it through the APM, not the radio). Wait for wind-free conditions to actually make the first flight.