Beholder Lite Arm
I chose the Beholder Lite for my Gimbal'd quad 'cause it was dirt cheap at $170, easily converted to firewall mounting, and it had a really slick way of bolting on the GoPro. I just have one problem with it, the aluminum arm between the two motors.
The arm is a bit flimsy and springy, and I can't help but wonder if it's the cause of some occasional vibes in my video. It also bends on impact really easily (even hard landings can make it sag), which might actually be a benefit as it's acting as a crumple zone and saving other components. However, it never bends back exactly, so alignment and CG are off and the gimbal's performance suffers.
My Gimbal'd quad is so dialed now that it almost never has a mechanical problem, and aerial photography flying is so tame I can be reasonably sure I won't crash. So I drew up a replacement arm for 3mm and 1.6mm carbon.
It's held together top/bottom with a 10mm M3 standoff and two bolts.
The two arms are bolted together with a M3 nut and bolt. I stole this from the QAV540g's gimbal, it's a cute way to join CNC'd sheets at 90 degrees. There's two sets of mounting holes for the roll motor to account for the GoPro4's slightly different CG.
I wanted to make the gusset flush with the tops of the arms so it would look really slick, but that would put a stress riser in the arm right where the reinforcement ends. So it will have to stay ugly. It should be much more rigid than the original arm, and would probably snap on impact.
This is my first part with relief cuts, with 1.5mm tabs and countersunk holes for the bolt heads. One of the arms has reliefs cut on both sides, so I guess Nick had to flip the part and re-align it to whittle down the other side. He did a great job, with everything slotting together perfectly. This really opens up a whole world of possibilities.
We're in the midst of a terrible winter right now, so it'll be a while before this gets tested. It's also the least sexy item I have lined up to test once the weather warms up. Aerial photography just can't compete with racing and combat.
Update: I couldn't leave well enough alone. I saw some flaws in the first version and had to fix them. First, I made the roll motor holes slots so there would be infinite adjustment for balance. I also shortened the arm to increase stiffness.
Finally, I was worried that the arm was too strong and would destroy the frame in a frontal impact, so I gave it a weak point to snap. With trusses above and below the arm should be just as resistant to sagging from the camera's weight, but it should snap easily in the event of a good bash from the front.