C3

project-c3-01
Z frame skeleton with Red bottoms

Unlike my previous build logs, I will make an attempt to keep this a bit more organized…

UPDATE March 18, 2017: I finished resurrecting the C3 as the C5 project (C4 has a negative connotation). The C5 is a lot more solid of a build, but I’m not jumping the gun on it – I have not waterproofed it yet since I want to see how the temp holds up first (and I am not 100% sure what led to the C3’s demise).

Production? Well…

April 5, 2017: Not for this project, but I am making production one of the primary objectives for the next generation of frames. After solving one of my biggest design issues, the next gen frame will be a dramatic improvement over the C series of projects. I will post another project page by the end of the weekend that will outline a few highlights, etc. It is still just a consideration, but it would be fun to be able to see the benefits of all the R&D.

Project VX1

Waterproofing

This is basically a repeat of the C2 project. Making the body out of aluminum has 3 big advantages:

  • The ESC’s (and maybe the VTx) can be mounted against the body and used as a heat sink
  • Material costs went from $111 to $38 (weight stays the same)
  • Since the body can be used as a heat sink, it can be fully enclosed

Bill of Materials (work in progress)

Frame:

  • (1) 2 inch O.D. (outer diameter) x 1.93 inch I.D. (inner diameter) x 106mm long aluminum tubing from McMaster Carr
  • (2) 8mm O.D. x 6mm I.D. x 178mm long carbon fiber tube from Amazon
  • (4) 10mm O.D. x 8mm I.D. x 5mm long carbon fiber tube from Amazon
  • (4) 10mm O.D. x 8mm I.D. x 2mm long carbon fiber tube from Amazon (use leftover from above item)
  • (4) 5mm x 10mm strips of 400 grit sandpaper
  • (4) 2mm x 5mm x 45mm aluminum from McMaster Carr
  • (1-2) plastic Easter eggs from Amazon OR (2) Estes NC-80B nose cones from Amazon (a bit more sturdy than the eggs… a lot of wasted material though)

Electronics: (some things can obviously be substituted as long as they fit)

  • (4) Emax RS2205 2300kv motors from Banggood
  • (4) Emax bullet 20a ESC’s from piroflip
  • Motolabs Tempest flight controller from Extreme RC
  • Ublox M8N GPS from Banggood or Ready to Fly Quads
  • Micro Minimosd from Amazon (also an FTDI adapter for programming it from Amazon)
  • AKK X1 Video transmitter from Amazon
  • Anbee Circular polarized cloverleaf antenna w/ RP-SMA plug from Amazon
  • Crazepony mini FPV cam from Amazon
  • Any standard sized 1300-1400mah 4s lipo

Miscellaneous:

  • Thermal paste from Amazon
  • 400mm x 205mm x 0.5mm silicone thermal pad from Amazon
  • 5 minute epoxy from Amazon
  • Clear silicone sealant from Amazon
  • 6 inch x 6 inch x 0.016 inch copper plate from Amazon
  • (2) antenna tubes with caps
  • Threadlock

I chose the Motolabs Tempest flight controller for the following reasons:

  • Direct lipo input up to 4s without a filter and up to 6s with a filter
  • PDB
  • 3 UART’s none of which share the USB
  • Dedicated Spektrum satellite input
  • SPI bus gyro
project-c3-02
Motolabs Tempest

Motolabs and GPS problem:

As I was setting up the FC in betaflight, I noticed that every time I set the GPS to ublox, it would always return to the default NMEA after rebooting. I found out this is due to the fact that the GPS was not included in the hex build. From what I understand (very limited knowledge on this stuff), it was left out to optimize processing power. GPS is a must for me, so I compiled a hex with the GPS included:

  1. To have the proper compiler (for windows), read and follow the directions in this file: https://github.com/martinbudden/betaflight/blob/master/docs/development/Building in Windows.md
  2. Locate the target file for Motolabs in: /betaflight/src/main/target/motolabs/target.h
  3. Find the line where GPS is commented out (//#define GPS) and remove the //
  4. Recompile the hex file as shown in the file in step 1

The Frame:

  • Drill 8mm holes through each end of the aluminum tube. They should be drilled so the center of the hole is 5mm from the end of the tube. Take the time be sure the arms are parallel and in line with each other. If not, use a file on the aluminum to correct the alignment. Epoxy will take care of any structural integrity that is lost. Also – it’s kind of close to the end and the aluminum may even distort and rip at the edge, but its not a big deal since again the epoxy will save the day.
  • NOTE: read ahead to see where to rough up the inside surfaces (with sandpaper) of the 10mm O.D. rings and the outer surface of the arms where the rings will be placed.
  • Slide 2 of the 10mm O.D. x 2mm long  fiber rings onto each arm (the rings should be on the inside of the body). Once the arms are centered, slide the rings so they are butted up against the body and use super glue to hold them in place.
  • Place the 10mm x 5mm long rings on the ends of the arms and super glue them in place.
  • NOTE: don’t try to epoxy all areas at once – only mix up enough epoxy to do a few places at a time and be sure to rotate the frame to avoid drips until the epoxy sets.
  • Use some 5 minute epoxy to secure the arms in place making sure to use enough for a nice fillet. Do the same for the rings on the ends of the arms.

project-c3-03

  • Using super glue, glue a strip of sandpaper on each of the rings on the ends of the arms (this gives a better bite for the arm clamps to grab on to).

project-c3-07

  • Using a 1/8 inch drill, drill holes into the pylon arms as shown below. Make 2 of each pylon arm to make sure the motor wires are oriented correctly. NOTE: The diameters on the holes should be 3.2mm, not 3.29mm…
dimensions-arms-16mm-a
Arm with 16mm spacing
dimensions-arms-19mm-a
Arm with 19mm spacing
  • Using threadlock, loosely attach the pylon arms to the arm clamps and clamp them onto the body arms.
  • Using a dremel tool, cut out an opening for the battery in the bottom of the aluminum frame Using the pattern below.

dimensions-battery-cutout

  • Using a dremel tool, cut a slot in the arms wide enough to run wire down them for the motors.
  • Cut ands sand down either the Easter eggs or nose cones until they match up with the aluminum body diameter.
  • Carefully drill a hole through the front nose cone for the FPV camera lens.
  • Don’t attach the front/back cones on yet. The frame is done for now.

Update February 14, 2017:

project-c3-15b

Project C3 is finished, but in a rush to get it finished in time for vacation, I was unable to keep a rolling build log. I hope to work on the build details while relaxing on vacation. Most of all, I hope to get a little bit of flying in with some video footage.

Test Flight:

I did an extremely brief test flight just to be sure it was air worthy (basically did a 5 second hover, quick 100 foot climb, then landed). The real test should come this week in some 80-82°F weather to see how well everything stays cool.

The TSA:

A word of advice from the TSA: don’t wrap your lipos in electrical tape – they don’t like the way they look. I had to explain how the batteries had to be modified to fit in the drone before they let me take the lipos along with me…

Update February 17, 2017:

Where Do I Start???

Things started off well on the C3’s official maiden flight. I was a wimp though and mainly flew in angle mode. I strapped a GoPro knock off onto it and got a little sunset footage – nothing exciting and the camera wasn’t very secure so it was shaky. The C3 was a bit warm due to the enclosed electronics.

2017-02-17-23-35-46

The next day was a trip to a remote island with no amenities. I did an initial 4 minute flight with no issues – except for the satellite count which I didn’t care to wait for since I just wanted video of the scenery.

screenshot_2017-02-17-16-55-57

Mistakes Happen:

It took me a little thinking to figure out what happened, but here it is:

  • I finally decided it was time to have some fun with the C3
  • After taking off, I gunned it, dropped throttle, then did a full throw invert
  • The “not very secured” GoPro knockoff whiplashed itself loose enough to hit the left front prop
  • If you notice in the pics, the left front motor is a clockwise motor where it should have been a ccw… I knew about this building mistake but as you know, the nut won’t come loose very easily and is the reason many motor manufacturers make only ccw motors
  • Since this was a cw motor, it had a ccw threaded nut – but since it was rotating ccw, all it took was a quick jolt (like the prop hitting something) to get the nut to loosen up. Once loose, it only took a split second to fly off

Reasons for this conclusion:

  • The quad started spinning immediately after inverting and centering the stick
  • Switching to angle mode did not level out the quad
  • No prop or nut was on the front left motor

Did It Survive?

No. I wish I could say it simply fell to the ground or, better yet, simply splash land in the ocean (to test out the waterproof body). Unfortunately, the quad was spinning rather fast and slammed into the charter boat awning bar completely destroying all hopes of it being waterproof. Not that I need  say this, but electronics do not like salt water – especially electronics that have a 4s battery connected to them (besides a dent, the battery is fine).

2017-02-17-22-58-06

2017-02-17-22-55-21
Point of impact
2017_0217_20545700
Salt water and ESC’s don’t mix

The Motor Mounts:

However, there is always a bright side. The motor mounts worked the way they were intended to in a crash – they bent and absorbed the impact which saved the arm mounts from bending and the carbon fiber arms from breaking.

2017_0217_20564800
Very peculiar how they all bent the same direction and roughly the same amount…

IF I had crashed on land or straight into the water (granted the waterproof body worked), I would have been able to replace the bent motor arms that I had pre-cut and drilled in case of such a mishap. A 3 foot piece of the aluminum for these arms is only $0.80 which is easy to cut with clipping pliers and enough to make 18 arms.

Where to go from here?

I think I will basically do a rebuild, but use a smarter choice in color (black really absorbed the sun) and leave as much of the aluminum exposed as possible to help cool it even better since it did get quite warm and I didn’t even push it very hard.

Yes it is kind of a heartbreaker to have it destroyed, but that’s really part of the fun – it’s an adventure trying something new and I enjoy salvaging and rebuilding just as much as flying.

 

 

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