Factors of Four

Just as I predicted last week, I’m too busy with work to go flying, but it would have been difficult anyway with the strong Easterly wind that’s blowing this morning.

I’ve been soldering rather a lot of small quadcopters for an event that we’re running next week:


Four almost complete HubSans (top row), with the fifth left unmodified. The flight controllers and motors are in the next row, with the white 3D printed frames next and the four sets of flight controller wires at the bottom. The left most white frame (ghost) contains the HubSan prototype making up the first of the 5 custom conversions. The butterfly second from the left is using my own HubSan kit which was the initial proof of concept.

What we’ve done is to take the electronics out of the HubSan X4 H107C (camera version) and add plugs and sockets to allow the motors to be removed. Then we’ve put the HubSan flight controller into a custom 3D printed frame. The HubSan X4 H107C only cost £32 each on Amazon as we got the 0.3 megapixel version which has recently been superseded by the 2 mega pixel version.

The picture shows the current progress before the sockets have been added to the flight controllers and before the plugs have been added to the motors. We actually have 6 HubSans, with the prototype already modified and not in the picture, the four HubSans here are part way through modification, and the sixth one on the right of the picture we are going to leave unmodified. If you count up the number of soldering operations required to do this, then you can see why I’ve been at it all day. Also, in the later pictures showing the completed work, it’s obvious that it’s got dark while I’ve been working and the picture is in artificial light.


Four modified HubSans with all the connectors attached. The picture is yellow because it’s quite dark by this point and my lighting is not very good.

So that’s 5 quadcopters modified as follows:

  1. Disassemble HubSan, remove rubber feet, props and de-solder camera.
  2. Remove 8 LED connections to flight controller.
  3. Remove 8 motor connections to flight controller.
  4. Remove 4 motors and flight controller.
  5. Solder 8 sockets onto 4.5cm wires (red+blue, black+white) and solder 8 wires with sockets onto the flight controller. Apply 2cm of heat shrink to each socket.
  6. Solder 8 plugs onto the two wires from each of the four motors. Apply 1.5cm of heat shrink to each plug.

Counting up, that’s 5×16=80 wires to de-solder, 5x(8+8+8)=120 solder connections to make. All divisible by four. Thank goodness I didn’t have the stupid idea of making hexcopters instead.

Anyway, it’s all done now, so I just need to check that all the electronics still works. I’ve checked the motors using a 4 cell NiMH pack to verify that all 20 run. The only real way of testing the flight controllers is to put them into a frame and connect the motors, so I’ll do that over the next few days.

One thing worth mentioning is my use of salvaged connectors for the motors and flight controllers. I had initially been using square DuPont connectors (Futaba servo plugs) with standard square metal header pins. At this size, they are a bit fiddly to connect, with the two pins connected to the motors not being as mechanically secure as I would like. My solution was to buy a 25 way D plug and socket from Maplin and remove the metal pins.


How to make 1mm bullet connectors – open up a 25 way D connector and salvage the pins.

I’ll do a follow up post on how to do this, but the pins and sockets make really good connectors for small models if you solder wires to them and then cover with heat shrink. It’s like a micro version of a bullet connector and, being round, they’re really easy to push together.

That’s all for this week as I need to get back to work making some more frame designs for us to 3D print. I’ve taken lots of images of the process though, so I’ll post more once I’ve had time to do the video editing.

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