The following steps were taken to build a light-weight responsive 3-axis gimbal for the GoPro.  I'll cover:

I    Requirements

II   Design

III  Build

IV  Test

V   Performance

Background:  The next duration ship needed to be a video and camera platform. The ship can't be fully designed until the envelope of the gimbal/camera is known.  

This is a photo of the final product.

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Yes, that is one way to do it. I remember seeing a version of this on a video about a new commercial video ship.

Whatever your approach, you need to:

- weigh each part of the ship

- define your camera/gimbal envelope and locate the x & y axis

- then try various ways of placing ship parts around the camera in 3-D

- calculate the ship CG (sum the length from axis x mass of each part) for its x, y, and z axis

- see if you can align the gimbal x & y axis to the ship x and y axis.

For example, another approach would be this, where the CG is centered in the top view and just below the propellers in the back view.

- resulting in a FOV needed for GoPro Video and photography

- can look straight down and even slightly back

- can look straight up

- won't be seeing props even when the propellers are on a 30 degree diagonal to the camera (sharp turn).

the trick in this case is using a spider with a wide front and narrow back so the motor masts cross behind the ship center allowing for the down shot.  then also locating the batteries in z just right to put the CG just below the propellers (naturally stable but low energy to rotate).

Thanks for the quick reply, if one were to design a ship with a front mounted gimbal would you want to line up the center something like this ? it is intended to be a H8 with top motors facing down, i added the ones on top for fun, i doubt there is a benefit to 12 motors ....but it does give you two mounting options on top, are the props better seperated or closer together ?

Really nice drawing.

This is how most ships are made, with the gimbal about 6ish inches from the ship rotational CG (directly to the front or directly below).

                                                ---------------------------Gimbal Axis----------------------------

Ship Rotates                               At CG                 Front of CG            Below CG

   Forward      the camera --->   no change               drops down        moves up/back a bit

   Up             the camera --->    no change               raises up           moves up/fore a bit

   Right          the camera --->   no change               no change          moves up/left a bit

   Left            the camera --->   no change               no change          moves up/right a bit

Also, expect about a 12% to 20% drop in flight time using coax motors.  But if mobility (small size) is the key issue, then the smaller frame can be worth it.  The farther apart the props, the less noise and better efficiency (flight time).

Quads with motors in front and at the bottom can take really great videos as long as the quad is run smoothly. With GoPro level of resolution, some of the displacement effects are minor relative to pixel count. If shooting with a hi-res camera, it can become more of an issue.

A quad like the above drawing would be great (KISS) for a GoPro resolution camera. A lot of pros use it.

would a go pro hero 4 session from factor http://www.cnet.com/products/gopro-hero4-session/ with a weight of 74g improve the shape and allow smaller motors,

and would this camera improve quality with its image stabilzation,

IF i were to mod a Hawkeye Firefly 6S into a similar form factor to GP session ( weight without battery @48g),  where would be the ideal location for HDMI/Power /Control connection ? and in what form ?

would this form factor be better on a 2 axis or 3 axis ?

48g is just 1g or so more than mobius i have seen this 3 axis gimbal using 2804 motors http://www.thingiverse.com/thing:645395

and this one  http://www.ebay.com/itm/Ultra-light-New-v2-CNC-RTF-100g-2-axis-CS-1... uses 1806 18g motors

are the 1806 motors sufficient ?

wow! session rocks in terms of finally centering its lens to it's CG. in order of importance for stability:

1) center the gimbal axis to the CG of the ship

2) center the camera parallax to the axis of the gimbal

then it eliminates a lot of weight and even more important, size, as the moment of inertia (the force it takes to rotate the mass) is a function of the square of the distance of the mass from the axis (double the distance and it takes 4 x the motor).  so not only does the camera shrink, the gimbal motors get about 10 grams lighter and the speed/acceleration (i.e., less tracking error) improves.  This makes possible, the worlds lightest functional high performance gimbal made by Hughes (materials are also important)

https://www.youtube.com/watch?v=21eJ_3_fFls

and yes, for the reduced size of the Seesion, use the GBM 1806. it is large enough for pitch and probably roll (the later would need performance testing). A caution on the 1806 is the axle.  it isn't as strong as the next level up and i don't know how this might affect video on the something as light weight as the Session. Just try it and compare.

Quality? this is a great review that nails Session quality. The session will be great for some but not for those seeking higher video quality.

https://www.youtube.com/watch?v=xxiCVu_SdDw

Image stabilization. This is a method of using pixels to create images with less blur at the cost of pixel count or frame speed. If you have too many pixels or too fast a camera, then this can be effective.  One typically only needs about 8 to 12 megapixels to create a great image for the human eye. So if you have 20 mp, you can waste quite a few pixels to create that stable image.  But if you only have 10 mp as the source, then there is a trade between less blur to the detriment of less resolution or image speed.  For many that just want to document what they did, this can be a good trade.  For those wanting detail, maybe not.

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