Wednesday, April 6, 2016

Shrike - HD Camera Mount Design and Testing


What?


I've spent the last few months designing a 3D printed camera mount for my quadcopter. It holds my Foxeer Legend HD camera and SD FPV camera, and protects all the electronics from the inevitable.

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Why?

The Shrike is a super lightweight, minimalist, x-shaped racing quadcopter frame. When built with the right components, it provides a ludicrous 11:1 thrust to weight ratio, and the symmetrical design offers nimble handling and the smallest possible size for 5" propellers. But the design doesn't include much space to mount a HD recording camera. And what's the point of zipping around the sky at 70 mph if I can't share my flights in glorious HD?


How?

Through judicious application of calipers, 3D modeling in Solidworks, and 3D printing at Lehigh's Additive Manufacturing lab.


The Catalyst

Over the winter I had a really nasty crash that resulted in bent standoffs, that put the Shrike out of commission for a few months. All four of aluminum standoffs that attach the frame to the camera and top plate were bent in the crash. Luckily, all of the electronics made it through unscathed; the motor that came apart worked fine with a new c-clip.

Design

As the Shrike was designed, the FPV camera sits in the very center of the frame. This is a design decision that helps keep the quadcopter as small as possible, and by extension very light and fast. Most frames that fit five inch propellers are in the range of 210-250 millimeters, measured diagonally from motor to motor; the Shrike fits the same motors and props but at a sparse 185mm. Needless to say, its size comes at a cost - it's a very tight quad to build and work on. While patience and steady hands are definitely required, this copter is race proven to be one of the fastest frames around.

Because of the flight camera's location, mounting another camera to record HD video is challenging and unwieldy. Most mounts end up looking something like this:

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I started by sketching the profile of the Foxeer camera and Shrike. I wanted to keep all of the components as tightly grouped as possible, for aesthetic purposes as well as to lower the center of gravity. Even after getting rid of the carbon fiber top plate, the Foxeer camera was still raised too high for my liking.

I decided to compress the design by moving the FPV camera forward. This allowed the HD cam to sit nicely, but introduced a new problem - prop interference. The frame's geometry gives only 5mm of clearance between the tips of the props and the center standoffs. I added the propellers to my Solidworks assembly, and made heavy use of the Section View feature to see where things would hit.

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After a lot of trial and error, and a few prototypes printed and scratched, the design was ready for trial. I used the Ultimaker printers in Lehigh's Additive Manufacturing Lab for everything, with PLA as my plastic of choice. It's cheap, stiff, and surprisingly durable, making it a great choice for being driven into the ground at high speeds.

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Initially I designed a latch to keep the camera in place during flight, but the plastic ended up being too stiff to allow the camera to be inserted. Even without the latch, friction holds the camera surprisingly strongly, and there's the option of using a velcro strap if that's not enough.

As this plastic printed part is replacing aluminum and carbon fiber, the question that has been on my mind since the beginning has been - will it hold up in a crash? The walls are all 2mm thick at a minimum, but I want to highlight a key design decision that I think will make this printed part quite resilient. Rather than completely replacing the aluminum standoffs, I designed the mount to slide over two shortened standoffs in the front, and sit over the two bolts in the rear. That way all 4 corners are fixed directly to the frame and supported along their height by metal parts.

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The standoffs I have were cut down by hand, so currently the mount is held down (quite tightly) by friction. But once I pick up some legitimate 25mm standoffs, I'll change the mount so that it is bolted down onto the standoffs for extra security. In the meantime, I plan to crash test it until something breaks, fix the weakness, and repeat.

The Build

Ingredients:

Foxeer Legend 1 HD camera
Foxeer XAT600M / HS1177 CCD  FPV camera
Bonka Power 1300mAH 45C LiPo
8x RGB LED stick (2x) (optional)


These parts are crash-tested by the FPV racing community, and in my are all great choices for the price. Everything is cheap enough that you won't be upset if it breaks, but performs well enough for competitive racing and will deliver plenty of thrills without breaking the bank.

I haven't posted any build information for the Shrike before, so I'll include everything from the ground-up here.

Assembling the frame is fairly straightforward. The bottom plate is 2mm carbon, while the arms are a beefy 4mm. The power distribution board also serves as a top plate, and has two linear voltage regulators (5V and 12V) onboard that we'll use for our FPV gear.

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After desoldering everything but the power wires from the ESCs, cut the motor wires to length and tin them. I decided to mount the ESCs with the pads facing down, so that I wouldn't have to cross the power wires to get to the PDB pads. Remember to add heat shrink before soldering! The ESC signal wires are also soldered to the relevant pins of the flight controller. I also added leads to the FC's onboard 5V regulator and signal pin to drive the 16 RGB programmable LEDs that I decided to use.

Here's a wiring diagram for all of the electronics:

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Here are various photos taken while soldering together the electronics when I first built this quad. The black goop you see is liquid electrical tape, which provides some water protection for the various circuit boards.

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I don't have any great photos of soldering the FPV gear; refer to the wiring diagram to see how it's set up. The trick really is to measure twice and cut once. I always add 25% to the lengths that I measure to add a bit of slack.

With all of the electronics wired, I used double-stick tape to hold them together on top of the flight controller. Here's the complete quad before adding the camera mount:

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With the electronics taken care of, its quite simple to slide the 3D printed part over the standoffs and bolts, slot in the camera, and attach the antenna tubes and video antenna. Here are some glamour shots of the build put together.

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Download


You can download the mount here on thingiverse:
http://www.thingiverse.com/thing:1543406

4 comments:

  1. great work! Very slick well done

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  2. Beautiful! If you ever end up re-printing the camera mount, may I suggest you look at PETG filiment? It is as strong as PLA but less brittle. It can also handle higher heat without deforming, which could be an issue with the heat most VTX produce.

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