Drones - brushless gimbal

1h15min of flight time for Airbotservices'X4 equipped with brushless gimbal & fullHD camera

hugues — Mon, 22 Jun 2015 12:26:34 +0000

1h15min of flight time for Airbotservices'X4 equipped with brushless gimbal & fullHD camera on its 12mm carbon fiber payload rail system.

Video of 1h:15min flight time - Airbotservices X4 /w brushless gimbal & fullHD camera

Attempts have been made reaching more or less 2 hours of flight time on "empty" frames: such crafts carry the absolute bare minimum required to minimize weight, meaning: they do not carry payload(s), and/or do not have extra electronics for autonomous/waypoint capability and/or do not carry optional bi-directional command & monitoring telemetry.

"X4" is an Airbotservices experiment UAV attempting to push the limits of flight autonomy of a "practical" drone : we tried thus something different with a fully equipped drone (BG & full HD camera), in addition having all APM/Arducopter capabilities. It carries the following hardware equipment:

Airbot's payload rail system composed of two parallel 12 mm carbon fiber masts
Airbot's 2-axis brushless gimbal (Airbot's world's lightest at 45g only) stabilized using an Alexmos controller
full HD Mobius Camera
3DRobotics' Pixhawk (APM Arducopter)
3DR Robotics real-time telemetry (bi-directional TX/RX)
GPS (M8N) and second external magnetometer (in addition to internal Pixhawk's magnetometer)
3DR power module powering Pixhawk and used for current and voltage measurements
Airbot's LiIon 23100 mah 4S battery
Power circuit/cabling for the BG

The frame base is built inspired by Forrest Frantz's "CF round tube" constructions techniques.

Some Observations , lessons learned and potential improvements:

Weather status: 50% of time without wind, 50% with ~20km/h breezes
Initial battery state : charged at 4.18V at beginning
Brief Loiter (un)stability hickups. APM version 3.2.1 was used , loiter mode for 95% of the flight. The weather conditions were relatively calm but still with wind bursts once in a while. Even during "no wind" periods of time, "loiter" was having some unexplained, brief (10 seconds or so) strong twitches (or spasms) as if the quad was fighting very strong (but unexistent) winds. I repeated the same experience on Airbotservices X8, totally different craft, same observations.

The three factors that impact loiter's performance (low vibrations, low compass interferences, good GPS performance) were all excellent on X4 & X8:

Vibrations less than +-0,2g;
External Compass with very low offsets and far from EMI;
More than 8 satellites and HDOP<2). M8N on X4, 3DR LEA on X8 (no GPS HW suspicion)

EKF was enabled. P Loiter and rate P Loiter were tested with lower values (0,7 and 0,8 and 0,9) than defaults (=1) with no sensible improvement on loiter's stability. 0,7 value resulted in a bigger unstability versus the default value.

Mechanical vibrations fatigue: As can be observed in the attached video of this blog, Mobius camera detached itself (pitch mount) due to mechanical vibration fatigue. Mobius cam was simply snapped on with a plastic cap. Similarly to loctite to maintain screws tight against vibrations, adhoc glue should have been used to secure the plastic cap "snap on" mechanism (careful, never to use loctite on plastic parts as it make it brittle).
A very positive and conclusive result for "screwless" frames. Airbotservices X4 is built screwless, only using glue between parts, including the 12mm carbon fiber rail system that carries the heavy battery. Although this craft has been flown many hours (each time more than one hour at a time), none of the glued parts have budged nor cracked. Use of glue is key to get a light craft and get such performance (after all, Airbus and Boeing evolved too from rivets to glue in order to lighten their planes). I did not do any structural resistance measurements but I would bet that such frame is way stronger than any screws & bolts alternatives (Forrest might chime here as he 's the expert on the subject).

Final battery status : voltage =3.3V per cell (plugged in, motors stopped) and =3.1V (under charge, motors running). A LiIon cell is fully empty at 2.5V per cell. Stopping at 3.1V, 20% of energy remained in the battery. It is OK to drain a LiIon battery down to 2.75V per cell under charge (=11V for a 4S battery). Extending the flight with a few more minutes was thus possible (better be careful not to damage the battery).

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long endurance flight

quadcopter

fullHD camera

brushless gimbal

World's lightest 2-axis brushless gimbal carrying a fullHD camera

hugues — Sun, 22 Feb 2015 11:08:43 +0000

AirbotServices is proud to announce the world's lightest 2-axis brushless gimbal that carries a fullHD camera.

Here are some build pictures and comments:

Assembly of the cf masts.

First they are cut and sanded to shape, to fit together at a right angle (see above method described by Forrest):

It is tricky to get everything perfectly (or as perfectly as possible) aligned and/or at right angles:

Vuduglu was used (no screws, no brackets) to save weight. this is a toughened methyl methacrylate structural adhesive (like CA but reinforced with fibers, I guess). It is good for this application because it hardens and stays rigid. I would not replace the 3M 2216 glue by this one in a multicopter frame building application though, because you need to keep some vibration resistance and flexibility that you fnid in the 3M 2216 glue nut not as much in this one.

Another advantage of this glue, it start to harden in 10 minutes (while the 3M starts to harden in 90 minutes) and cures in 24h (while the 3M cures in a week).

Then the question is how to fix the two roll/pitch motors on these carbon fiber masts ? Answer : glue and 3D printing.

There are two 3D printed parts , one for the stator, one for the rotor. The stator piece is either glued on if you never need to use the motor for anything else later, or could be even screwed on if you need to get your motor back for antoher application later on.

The stator 3D printed mount is only used on the pitch motor. Indeed the stator of the roll motor will be screwed to the frame hilding the whole brushless gimbal ( a drone's frame for example or a handheld pole).

This piece was custom designed for the particular 1806 motors that are used and fixes itself by three little clips:

The second 3D printed part is what I call the motor cap. It covers the rotor bell of the motor. It holds without glue, nor screws ! Just a precise match, like a glove:

The two holes in the bottom are for ventilation.

Then fitted on the motors:

Now, gluing the pitch motor first on the carbon fiber mast. The position must be precise to balance the CG. I calculated that through a software, Autodesk123D:

Gluing the pitch motor must be done in such a way that the glue point must be precisely on top of the pitch mast, when the roll mast is in a vertical position. I used pens , tape to square everything as needed (yes pens remain useful in the internet age):

Glued pitch motor result after curing time:

You notice on that picture the 3D printed part on the stator of the pitch motor. The two little white marks represent the CG point where the motor center must be glued on.

Next , the full HD camera mount plate for the Mobius camera is glued on the rotor of the pitch motor:

This motor mount was built by Forrest Frantz using a balsa/carbon fiber sandwich. It makes it ultra light and ultra rigid.

Although screw holes were drilled, I did not use them as it is simply glued on the 3D printed cover, capping the motor's bell.

Now the trickiest part of all consists in fixing the roll motor. This is difficult to achieve because you need to be perfectly at right angles and find the right tangent on the round roll mast. You also need to find the center of gravity on the roll mast. So extensive use of squares are required, using gravity for perfect verticals:

The old masonry rope trick is used to find the roll CG.

And the final result:

Weight measurements:

Without the camera:

With the camera:

The weight here includes the motors, the servo cables, the velcro strips to hold the camera on ist mount plate. So it is a real all-in weight

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