Friday, April 10, 2015

Q450 Quadcopter servo gimbal setup, Part 1

Digging back into FPV / Aerial Photography with a new camera gimbal
I was inspired by recent articles in Make magazine about FPV racing and the local Minnesota Autonomous Vehicle meetup to do some more quadcopter flying and building.  My main quadcopter is a Hobbyking Q450- which I originally bolted together a year or two ago with a crude FPV camera mount made from a Home Depot low voltage electrical box bandsawed and bent into something usable.  These days there are many, many better options for mounting FPV cameras- ranging from simple servo stabilized mounts through very sophisticated 3-axis brushless gimbals that yield professional video smoothness.

I was looking for a cheap and simple solution, and I ended up buying the "ActionCam Inline Gimbal GOPRO and FPV" kit from Hobbyking. I'm planning on using it to mount and stabilize both a GoPro and my small FPV camera. It uses two standard servos, and the Hobbyking KK2.0 flight controller I have will be able to control the servos without any software updates or hardware.

Kit Assembly
The kit comes with decent hardware, although it doesn't include the screws that join the upper and lower plates together.
Kit Contents

"Instructions"

I used a larger, standard sized analog servo for the roll axis

I originally tried a smaller Hextronik HXT500 5g servo for the pitch axis, but it was a little too small. 

A Turnigy TG9e 9g servo was a good fit for the pitch axis

Unpacked hardware kit. The camera mount pivot is pretty nice, it seems to have some rotary damping

I originally tried pressing the camera tray on to the servo directly. It wasn't quite the correct width- a tad too narrow.

So, I decided to bolt the camera tray on to a servo horn. I drilled the horn in two placed for 2/56 screws. I accidentally cracked the servo horn when I screwed in the outer screw. I didn't have a 2-56 tap so I drilled the holes to size then tapped the holes with a screw- mostly worked. I have since ordered a set of 2-56 taps off of e-bay- next time I'll use the right tool and avoid cracking the servo horn. 

Servo mounted to the camera tray using 2x 2-56 SHCS + 4x washers. I used washers under both the nut and the screw head to allow for maximum clamping of components. 

Second view of mounted pitch servo

Mounting the roll servo. My first try placed the servo horn on the "inside" of the frame, but there wasn't enough clearance for the mounting screws- they hit the servo. So I moved the servo horn on the "outside" of the frame. 

Roll servo showing 2x 2-56 SHCS, washers and nuts


Upper mounting plate attached to servo. (note this is a photo of the first try with the kit's hardware which I ended up ditching) I decided to use my own 2-56 hardware because it seemed to fit better. I also decided to place the roll servo above the vibration damping plates, then attach the vibration damping plate to my Q450 frame. This arrangement seemed to make the most sense for my purposes. 

Roll servo attached to the upper plate- first try with the kit hardware. The threaded ends of the screws extended too far past the upper plate and interfered with the lower plate. 

. Now with the 2-56 screws attaching the servo to the upper plate. Vibration damping balls (blue) installed

Note the head of the screws securing the roll servo are under the upper plate, double-nutted on the top. 

Bolting the lower plate onto the Q450 quadcopter frame


I had to dremmel the slots on the Q450 quad copter frame slightly wider to allow the lower mounting plate to fit. 

Camera gimbal installed. I used 4x 4-40 x 0.75" SHCS to attach the upper mounting plate (with camera gimbal attached) to the lower mounting plate. I didn't have any 4-40 lock nuts, so I used a few drops of blue locktite threadlocker on the threads to keep the nuts from vibrating off during flight. I only used screws on the outside group of damping balls to save weight. 

Ready for plugging in the servos and setting up the KK2.1 flight controller. 

The setup that worked for me for plugging in the camera gimbal servos was the Roll servo in the KK2.1 output #7, and the Pitch servo in KK2.1 output #8.

KK2.1 Setup- first go to "Camera Stab Settings"

The "Gain" settings adjust how much the servo corrects. the "Offset" setting adjusts the neutral location of the gimbal. To check functioning- first take the props off the motors. Then throttle up slightly so the motors are spinning- only then will the gimbal react to motion of the quadcopter. If the gimbal moves the wrong way, change the gain to negative. The gains shown in the photo above is what I'm starting with that appears OK. 
Next steps:

  • Adjust servo arm position on both servos to try and get the offset to zero. This will get a larger range of motion in one direction in both axis. 
  • run servo cables
  • attach both gopro and FPV camera to gimbal
  • fly!

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