Here is a short build log of how I converted my APM2.5 Quad to a X8 Octo quad.
First I dismounted everything which is always a pain, especially when you have to disconnect these little bastard DF13 connectors. By doing so a few times already (it is my fourth build with same APM...), I had finally to replace the telemetry cable by a new one. Oh well not too bad...
I could scrap the base 3DR power distribution board which was not meant for 8 ESCs and I got instead a vulcanUAV PDB which allows for (way too) many ESCs and 250 amps as seen on this picture.
I soldered also a 3DR power module and connected a Y battery splitter to be able to connect two batteries in parallel.
I prepared the motors. These are 3110-17 (700Kv) tiger motors. I love 'em. As you notice on the picture, I took my lessons from the first builds : every part is now tagged, either with a number, either with a color sticker, in order to know what motors goes on which arm and which cable connects to which ESCs (and so to keep the correct spin direction).
These motor cables are quite long so I decided to braid them, giving an extra EMI improvement and shortening them a bit:
By dismounting the quad, I noticed that the four screws holding the motors to their motor plate came a little bit loose, due to vibrations. I do not want on these parts to use blue loctite because it is a a nightmare to unscrew (for my next fifth build...). I used instead some hot glue as seen there:
(yeah, I know, I had to mix different screws, not pretty but who cares, nobody sees the bottom motor plate anyway...)
Then I laid on the floor the bottom plate, passed the braided motor cables in the arms, connected all the motor cables to the ESCs (thanks to the color stickers), placed the cables as neatly as possible. I shortened the ESCs power cables to the minimum in order to gain a clean placement. I soldered directly the ESCs to the PDB (no risk of bad connectors). By the way, a lesson I've learnt when you solder so much on a board : get a very high power solder iron otherwise the heat latency of the board gets unmanageable (and gets worse for every ESCs that is added).
I decided to keep only one BEC power cable from one of the ESCs. The other are snugged under the PDB (No, I did not cut them, you never know what will be needed in a next build)
Then it was time to work on the APM itself and all of its accesories : receiver, beeper, telemetry, GPS, etc. In order to get vibrations as low as possible, I tried what you see on the picture : APM is mounted on a small plate about 3cm above the center plate, with rubber dampers-white nylon spacer-silicon damper (what you see between the two metal washers).
This carbon fiber plate is thus never in direct contact with the rest of the frame. APM itself is placed on four corners of moongel (I put a balse plate between the carbon plate and APM to raise it a bit so that APM does not touch the metallic washers).
APM is pressed gently on the moongel with two rubber bands. Later on, after I attached the GPS, I also improved a bit the vibrations levels by adding moongel between the GPS on top of APM and the APM case, so that the APM is sandwiched between two layers of moongel.
This is how the Electronics look once finalized and all cabled.
Then I took the beast out for a short maiden flight as seen in the video herebelow:
Comments
@Neil. Thanks I appreciate your feedback, I will add it to my list of builds I want to try.
Sorry Hugues,
I didn't realize the Silver ones were ESCs too, Should work fine.
Nice antivibration mount.
Should have just looked a bit more closely and not paid attention to the following comments so much.
I see a problem at least in your photos.
As commented above you seem to be using only 4 ESCs and by proxy are treating each motor pair as a single motor and if you had the props both going the same direction this would work and permit normal yaw and it would probably work in single motor failure because the other prop could pick up the loss.
But you seem to show your props actually mounted to spin in opposite directions above and below.
Of couse for that you would need 8 ESCs to be able to properly control yaw. and to be running with a X8 setup rather than a quad setup in the firmware.
@Chris
4escs will have roughly the same weight, as they must be capable of handling twice the current, and will likely be considerably more expensive.
As far as I know noone has performed a setup like that for a number of reasons:
firstly if you have 8 motors you might as well build an X8 with counter rotating props, you get more lift and more stability.
If you really wanted to build one without CR props you could, but you would just loose efficiency, stability and yaw authority.
I would say the losses on the bottom motor would be around 60% if the props were not counter rotating - which is to say they will likely only generate 40% of their possible lift.
On the advantages side you may actually find you have slightly more yaw authority with one that does not employ counter rotating props, though this yaw will likely be unstable in comparison to CR setups.
Either way I would like to see one built.
Ok so that's the theory over, now back to my original question. Does using a single ESC to control both motors on each X8 arm have any advantages, beside having 4 less ESC and less weight? Has anyone actually got this set up?
"If you had both props rotating the same direction it would work, but with Counter Rotating setups it would not."
Guess I should learn to read properly, ;)
@lelo
You would be able to yaw fine;
"If you had both props rotating the same direction it would work, but with Counter Rotating setups it would not."
@Neil
I am really confused here. I must be missing something.
I can´t understand why wouldn´t you be able to yaw with that configuration. 2 ccw motors arm1, 2cw motors in arm2, 2 ccw motors arm3, 2cw motors in arm4. Set it as a quad, go fly. As i see it you are still able to yaw.
@Neill - Thanks for the explanation. Even to me it almost make perfect sense.
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