Dev Frame Development Part 2

Hardware
1

An update with build video and design files for the proposed dev frame. Still focused on Copter frame but Rover will be coming soon.

This is a continuation of Part 1 over here:

Updated Design Specs

Here’s the short list of feedback from the gitter hardware channel:

  • Need frame size under 2kg and around 450 class
  • Use Air Gear 350 set as base power spec (also similar to DJI Phantom replacement motors)
  • 9-10 inch props on 3 or 4 cells
  • 12mm motor arm tubes since there are off the shelf motor mounts
  • 10mm box tube saves a bit on cost and size and is same as payload mounts for off the shelf gimbals
  • 60mm on center box tube rails also same as off the shelf payload mounts
  • Option for mounting off the shelf crab landing legs since they are cheap and easy to source
  • Option for payload modules to slide and/or clip on/off front of frame
  • Option for battery on rear of frame to balance larger front payloads
  • Option to mount motor tube at different angles to support stretch or hybrid X geometry

To cut down on the blah blah in the post here is an album with the above put into action.

[18 new items added to shared album] Dev Frame D500

Base BOM

Frame (off the shelf)
(4) 10mm x 500mm carbon fiber tube
(2) 12mm x 500mm carbon fiber tube
(4) Tall Landing Gear
(4) 12mm Motor Mount
~$85

Frame (fasteners)
(16) M3 x 30 Cap Screw (button or socket will work)
(16) M3 Threaded Insert
*Add 8 more threaded inserts and fasteners for landing gear mounts
(8) zip ties
~$5

Frame (3D printed)
(8) Box End Clamps
(4) Motor Arm Mounts
(8) Cross Mounts, Zip Tie
~$30 (~6hrs print time at $5 per hour; have not shopped this figure yet)

Frame (misc)
Glue, 2 part PU or epoxy
Double sided tape
Material for platforms
~$10

Power
(1) Air Gear 350 Set
(1) 3 or 4 cell lipo ~ 4-5000MAhr
(1) 4 way PDB w/ 5V reg
~$200

~ $330US for built frame minus autopilot, companion and payload

Build

Goes together just like the older version in this video

Notes

  • Completed a short test flight. Flies fine but needs more testing to see if there are any hidden issues.
  • Carbon fiber tube diameter in my batch of tubes was +0.02/-0.5mm tolerance which is really bad and can require tape shims
  • Still a bunch of design files to tweak. Mostly mounts and various accessory options.
  • Rover will be next. Likely a two wheel skid steer to keep cost and complexity down.

Summary

I’ll attach the design files here in both step and stl. Needs more review and testing. I am sending a few printed kit parts out to alpha testers in the next few weeks. Version 1.0 should be ready after more testing. Likely a few months given the volunteer nature of the dev cycle.

Files and Printing

step and stl files: B4_1060.zip (326.3 KB)

Printing in ABS at 0.3mm layer height, 2 perimeter and 25% infill. No hard requirements set so you can vary as required for your needs.

Update 8/21/17

Files now have version for 12mm motor arms and 16mm motor arms

Pilot hole for M3 threaded inserts is 5mm. Some threaded inserts will not work We may need to reduce that hole size for other inserts to work. I am sourcing mine here:

Update 8/22/17

Changed the title from reference to dev frame as reference frame also refers to spatial coordinate systems like ENU, NED etc.

Update 10/15/17

Version 3 Files B4 1060 v3.zip (378.5 KB)
Change Log

  • Reduced size/weight of Box End Clamps
  • Arm Mounts Clamp (no need for glue)
  • Accessory Holes reduced for M3 screws or M2 inserts
  • Two versions for 4mm and 5mm OD M3 inserts
  • Two versions for 10mm and 16mm arm tubes
  • ESC mounting area with ziptie slot on the Arm Mount
    More details in comments below…
1 Like
2

Looks fantastic! Is it possible to do the 3d prints in black? Is it a limitation of the structure/material that it has to be white? (I know nothing about 3d printing…) It would look awesome in black :slight_smile:

3

Thanks @fnoop! Any color you want. Does not really need to be ABS either. PLA is much easier to print but it’s more brittle and the service temp is a bit on low side. So if you left it in the trunk of your car you might come back to a variable geometry that you did not intend. But for an indoor only bot it should be fine.

I use natural ABS because I have tuned my process for it. Color dyes can change print temps and it’s just not worth it for me in most cases. I am thinking about using red for my production color. I also want to test nGen and/or other Amphora based filaments for this project. ABS stinks and air really needs to be filtered when you are running a bunch of printers.

Other consideration is ABS acetone welds really well but that is so far not requirement for this design. You also have to consider how well glue adheres.

4

Great! My favourite colour is purple :slight_smile:

Printing notes for different materials and the pros/cons of each material will be really important for people to print well from local services. My local 3d printer only has a couple of different materials and when I had a case (for the Joule) printed they took quite a while to interpret the 3d files and decide which materials would work best and altered a few things to make it stronger. If the community can build up a bit of knowledge around what works well, as well as your expertise, it should make the printed parts more robust as time goes on.

5

Cool!
What is the weight of the system including the 5000mAh battery (without any additional payload)?

6

It’s about 35oz or 992g without battery. 4S 5000 Battery is about 16oz or 454g. No payload or companion.

7

Uploaded step and stl files (see bottom of main post). Also forgot to mention my GPS Mount. Like the rest, nothing fancy. Uses 10mm tube for mast; make it as tall as you like. It is glued in place this time. Removable mount very doable. Did require me to solder two cables together to get the length to reach. This frame can get long in the body so not all stock cable length assumptions work out.

IMG_20170820_210138.jpg512×512 46.2 KB

8

So just to be clear for the hard of thinking around here (ie. me), what exactly do I need to ask to be printed? What is the difference between step and stl files? How many of each bit do I need? You’ve said in the BOM:
(8) Box End Clamps
(4) Motor Arm Mounts
(8) Cross Mounts, Zip Tie

There are two types of motor arm mounts in the STL files - which ones do I need?

8 cross mount zip ties, that will give me 4 mounting points? I can print as many of these as I want/need?

I need one landing gear mount for each corner, so 4 in total?

Can I print another 4 box end clamp halfs and 2 motor mounts to put in the middle for a hex?

9

Could the top of the box end clamps be used to mount flat board/CF plates?
Could the box end motor arm mounts incorporate a simple damper (just like a rubber ring), which the tube would sit in?
(These are just ideas for future improvements/options)

10

This is cool, retracts that will fit on the bottom box tubes:

And there are lots of fixed landing legs that will fit on the tubes as well, eg:

11

File Types:

  • step will be good for those who want to hack on design
  • stl is used to slice for printing.

Motor arm mounts have two variants:

  • straight is original design and supports an H (you need 4 for H)
  • multi supports both a straight H and a 30 arm angle for X (you need 4 for variable geometry)

Cross mounts:

  • 8 has been plenty for me
  • I used 4 top and 4 bottom with 1/16 ply across them from front to back
  • With a deck on both layers from front to back it’s the most room I have ever had to place gear on a frame this size
  • Print as many as you want need

Landing gear mounts:

  • Yep, one for each corner. a few backups won’t hurt.
  • I designed all pilot holes for 3mm inserts
  • I used M3 x 10ish to mount the gear (the gear usually comes with cheap M2.5 which I threw away as I hate junk fasteners)

For hex mod:

  • You could put box end clamp in middle to make hex
  • You might need longer box tubes and/or shorter props
  • Never tried it
  • Would love to see it

Other

  • You could skip the cross mounts and mount your plates to top of box ends if your plate was stiff enough
  • I am not a fan of dampening the motors a bunch as I think it has too much potential to interfere with proper tuning
  • Some of our designs use 1/32 silicone sheet under the motor with a washer under the motor mount that also has a silicone sheet. Forms a sandwich: motor, silicone, motor mount, silicone, washer, fastener
  • In general, I would prefer the frame stay as stiff as we can get it as the autopilot is already sitting on gyro tape on a platform that is mounted on double sided tape; if you have vibe issues with this setup it’s likely something big enough that should not be hidden with dampeners in the power system.
12

Thanks to @fnoop and others in gitter for the testing and feedback. V3 files have been posted up in the main post.

Here’s what we learned…

  • Sanding holes to size and gluing tubes in the arm mounts sucked
  • The box end clamps were still a bit bigger than they needed to be
  • 4 x 10mm tubes at 60mm center makes for a nice stiff box with lots of room
  • 10mm arm tubes might be stiff enough for smaller builds
  • 16mm tubes will work for bigger builds
  • 12mm arm tubes just makes things confusing for little gain
  • Some other stuff I am probably forgetting

Here’s what is in the works…

  • A small frame built from just 10mm tubes
  • More testing

B4 Box End 1060-4-16 v1.png800×600 96.7 KB
B4 Box End 1060-4-16 Back.png800×600 71.9 KB

I am working on the all 10mm tube frame. I have spent a bunch of time looking at this design and really want something as an ultra simple base. Hybrid X seems to be the best compromise geometry. Using all 10mm tubes means I can take 4 x 500mm tubes and cut ~200mm from each tube for the motor arms; that leaves me with ~300mm for the box. Still lots of room and it appears to be stiff enough for smaller build running up to ~9in props. Using 10mm tubes also allows me to print simple clamping motor mounts. Overall, it just feels right.

1 Like
13

All 10mm D500 in Stretch X. Air Gear 350 with stock 9in props. About 180mm long box frame. Plenty of room for payload in front and back. Battery or payload could be underslung. So far just hover checks. Flies fine. Vibes all check good and it hovers at about 11 amps with a 4S 4400 at gross weight of ~1300g. Autotune will be next. Then a payload sled for an FPV camera.

New photo by Coby Leuschke New photo by Coby Leuschke
14

Had access to a really big gym so completed an auto-tune in all axis. Went really well. I also under-slung the battery for the test flight in anticipation of leaving room for a companion computer up top.

Logs, pics and more design file tweaks coming in the the next week or so. So far the all 10mm tube D500 is looking very promising for builds 2kg or less. Once I get done testing the air gear 350 on 9in I am going to change out for my preferred KDE motors on 10in APC self tightening props. https://www.kdedirect.com/collections/uas-multi-rotor-brushless-motors/products/kde2315xf-885

15

This is still WIP. Hoping to have something for March release.

1 Like
16

Latest progress…

Got rid of the insert requirement. Believe someone commented earlier about just using screws into plastic. I was skeptical but it does seem to work OK. At least up to the 500mm class frame we will support with this design. Multiple screw insert/retract cycles could be an issue but I am willing to bet most frames won’t last that long. Plus it’s easy just to print a new part if you strip a hole.

Also removing support for 16mm tubes. We need to keep this easy and simple – 16mm tubes just opens us up to heavy lifting and use cases outside of intended vision for the Dev Frame.

300mm frame with 6in props as the new basic frame (digital FPV use case):

  • (2) 10mm OD x 500mm tubes and cut into quarters. <20 bucks in CF tube.
  • #6 screws used for frame are bigger than needed but cheap and easy to find
  • #4 screws for sensor mounting
  • Added roll cage with sensor mount area
  • Added little landing gear to protect battery and or sensors on bottom.

To Do…

  • RPi Cam Mount for front
  • GPS mount
  • Test flights/crashes
  • AutoTune and PIDS
  • Test Maverick and Drone Link with Raspi0 for digital video
  • More test flights/crashes
  • Refine any weak points
  • Document the build and post to GoodRobots github repo

And then…Repeat for a D500 size frame.

10 new photos · Album by Coby Leuschke
5 Likes
17

Awesome work @Coby, it’s looking good. Are you releasing design files to allow us to test during development?

1 Like
18

Thanks! Sure. Here’s the link: https://github.com/goodrobots/DevFrame

I am printing in all ABS. 2 Perimeters with 50% infill is plenty except motor mounts and landing gear which I am doing at 100% infill. Using 3 perimeters for the arm tube clamps to make sure the threads have more plastic in that area. You could likely use 3 perimeters and 50% on the entire thing. Needs testing/crashing to know for sure. Weak point is the new landing gear – Had to include a through hole for screw driver exactly where it should not go. Might need to make those a seperate part later. Otherwise these parts should all print with no support required and no big overhangs.

Edit: Box End Clamp A/B are pairs; you need four pairs total. You can omit basic Clamp A for Roll Cage on top. Totally up to how you want to build it. Four arm tube clamps and eight motor mount halves will finish. # 6 x 1in for box end clamps and # 6 x 3/4in for tube clamps. Eight M3x18 for motor mounts, which are 19mm spacing. Then you just need as many ZipTie Cross Mounts as you think you need.

My two layers will look like this…

pixhawk
– CF tube –
Power distro

Raspi0
– CF tube –
Battery

Enjoy!

1 Like
19

Great thanks. Will print this when I get a chance and test.

2 Likes
20

I am starting to track the releases using a more git proper approach

3 Likes