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Following on the work described in an earlier post, we wanted to build an inexpensive quadcopter that could be controlled by an onboard ODROID U-3 single-board computer.

We were happy with the Naze32 / Baseflight / Multiwii Serial Protocol, but were delighted to discover the new Flip32 flight controller from Ready To Fly Quads. At $16, the Flip32 is even more absurdly inexpensive than the $25 Naze32! But the real advantage we saw in the Flip32 was its soldering holes for not only UART (like the Naze32), but also I²C (for sensor input) and SWD (for firmware debugging). 

Based on our success with the inexpensive ZMR250 frame from Multirotor Superstore,
we decided to go with the same basic setup, swapping in the Flip32 for the Naze32. (This excellent video has a side-by-side comparison for anyone interested, and this video series helped us get started with the build.)

Two other requirements were: (1) a secure mount for the Flip32 and ODROID U-3 and (2) a cleaner power distribution, to avoid the messiness shown below from the homebrew squid distro we did on our previous build:

For the secure mount, we decided to take the plunge into 3D printing, with the goal of having our first print job be a simple rectangular slab that would support both the Flip32 and the ODROID. For the power distro, we opted for the inexpensive Quadcopter Power Distribution Board from HobbyKing – a little big for this vehicle, perhaps, but featuring pre-soldered 3mm bullet connectors, a vibration-isolating foam pad on the bottom, and widely-spaced holes that proved helpful for mounting the Flip32 and ODROID.

Here are the basic parts and their costs rounded up to whole dollars, excluding the 3D printing, zip-ties,
jumpers, heat-shrink tubing, E6000 adhesive, and other stuff we already had in the shop. Naturally you'll
want to order extra ESCs, motors, and props, but this gives you a basic idea of the cost:

• Multirotor Superstore:
  • ZMR250 Carbon Fiber Mini Quadcopter frame 1 @ $40
  • MS 12amp ESC (SimonK RapidESC) 4 @ $16
  • Airbot Titan 2204 2300kv Brushless Motor 4 @ $20
  • 3S 1300MAH 35C LIPO BATTERY 1 @ $16
  • 3x40 Right Angle Pin Header Set 1 @ $3
  • 2x40 Right Angle Pin Header Set 1 @ $2

• ReadyToFlyQuads:
  • Flip32 Flight Controller 1 @ $16

• HobbyKing:
  • FrSky VD5M Receiver 1 @ $12
  • Quadcopter Power Distribution Board 1 @ $4
  • Micro Server Connectors (5 per bag) 1 @ 2
  • Gemfan 5030 Multirotor ABS Propellers (pair) 2 @ $2

• McMaster-Carr:
  • 10mm M3 male-female nylon hex standoffs 4 @ $2
  • 6mm M3 male-female nylon hex standoffs 4 @ $2
  • M3 nylon hex nuts, 100 pack 1 @ $11
  • M3 nylon pan-head machine screws, 1 pack 1 @ $8

• Lowes:
  • 7/32" six-point socket head 1 @ $3

• TOTAL $281

Here's a quick pictorial run-through of the build:

The ZMR25 frame, minus top plate, FPV plates, legs, and other stuff we didn't use

Adding the Velcro one-wrap for the battery, before sandwiching the plates together

The power distro,with 10mm standoffs

This inexpensive 7/32" socket-wrench head from Lowes was the right size for holding the locknuts in place while we bolted together the frame.  We prefer metric, but none of the metric sizes they had was right for deez nuts!

The power distro, glued to the frame with E6000 (a.k.a. Goop)

Power distro battery cables passed through to the bottom of the frame, then EC-3 connector soldered on

Motors mounted and ESCs Velcroed on the frame and connected to the distro, wires secured by cable tie

Our 3D-printed mount for attaching the flight controller to the power distro. We put our school's logo
(the Trident) on top for fun. STL available here.  Our next version will be longer and have additional holes for mounting the ODROID U-3.

We designed and 3D-printed legs  for extra clearance and stability

The Flip32 with headers soldered on for ESCs, receiver, and UART / I²C

The Flip32 on our 3D-printed mount

Neoprene tubing on power distro standoffs, for additional vibration isolation

All wiring completed, including FrSky VD5M receiver

Closeup side view

When the students return on Monday we'll have the maiden flight with this vehicle, in “Dronehenge”, our tiny aerodrome in the Washington and Lee Science Center. Those standup desks make a nice safety barrier! If we're successful, there will be a Part II to this post, showing how to mount the ODROID.

Dronehenge!