These are the fully 3D printed T4 (quadcopter), Mini T4 (quadcopter), and T6 (coaxial hexacopter) designs I've posted on Thingiverse.com (aside: "T" is for Tubular).  The comments section on Thingiverse doesn't provide a great place for discussing designs so I've created this topic here instead.

These designs are based on a tubular arm with a vertical "I" beam running down the centre.  This design seems to be very strong and rigid and all of these designs are very stable in flight.

Other common features include:

  • motor wiring is routed through the arms and down into an enclosed (ventilated) power and ESC tray.
  • batteries are located in the centre of rotation (T6 is designed for dual batteries).
  • bevelled cable "tunnels" provide a way to route cables between the power tray and top plate.
  • Top plate is designed for Pixhawk or APM flight controllers with elevated GPS.
  • Bottom tray has mounting points for a Tarot Gimbal.
  • Optional long and short legs include "springy" feet.  The legs are designed so the 3D printed threads "wrap around" the arms which makes them quite strong for their length.
  • Sketchup files are included so folks can modify both designs to suit their needs. 

I figure I've put hundreds of hours into these designs with prototypes and drawing time.  I'd love to get feedback from anyone who makes one.  Together we can improve these designs for everyone's benefit.

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I finally got around to printing a new version of the T4 myself.  Even though it's only been out there for two weeks we're already up to version 1.04 and I was starting to feel my version 1.00 was so "last week"!

Anyway, here's a few pics of my latest print...

My project for this weekend was to come up with a simple GoPro mount for the front of the T4 quadcopter.  This is intended for folks who want to do some FPV without the extra baggage of carrying a gimbal (which the T4 already supports).  

After a couple of  "mad scientist" designs involving ear plugs and gel pads, I settled on a simple rubber vibration ball based design - although the other design is still in the latest Sketchup file and does actually work.

I think the particular rubber balls I had lying around are a little too soft but here's some video taken with this setup anyway...

Side note: the above video is taken carrying the 6000mah 3S battery - with my 3DR 880kv motors the T4 is almost too lively on lighter 3000mah batteries!  The weight of the 6000mah battery seems to settle it down a little bit ;-)

Brendan,

You've got another convert.  My boy and I downloaded your Thingiverse files and are printing them in anticipation of making a bigger copter than the Blade QX nano we're currently playing with.  I didn't realize you could FPV the GoPro - that seems like a less expensive solution than some I've seen.  Could you point me toward a resource on doing that?
Also, do you use supports when printing the baseplate?  It seems like the autopilot supports are square-bottomed, which would suffer from thread hang-downitis.
Thanks for helping spend my money,
Joe
Joe.  It's great to hear you are making one of these - I'm really enjoying mine.  
For FPV with a GoPro Hero 3 you can use something like a Tarot TL68A10 cable or something similar.  They both plug into the USB port of the side of the camera and provide Ground/Video/Audio wires that you can connect to whatever video transmitter you want to use.  The GoPro just outputs live video from that port whenever it is on - it doesn't event have to be recording.
I didn't use support for any of my prints.  There are some small bridges but nothing challenging.  Perhaps try doing a small bridging calibration test print first to get the best temperature/speed/extrusion rate for your material - but again, the bridges in these parts are very short so shouldn't be a problem.

Quoted from Bret Allen

Joe, just be careful using the Go-Pro as an FPV by itself. Typically, a second flight camera is used for the FPV because it uses the onboard receiver battery to power it. If the battery in the GoPro dies, so does your FPV. I would recommend setting up a switchable system between the 2 cameras if you want to see what the goPro sees. Just some food for thought. :)

You can actually use the TL68A10 cable to power the GoPro too - make sure you only use 5V though (I accidentally put 12v into my Black camera and all the magic smoke came out).  Back in 2012 and early 2013 there were some reports of GoPros locking up - which put a lot of people off using them for FPV flying.  I believe these issues have since been resolved though.

Personally I like using my GoPro for FPV as I can see exactly what I'm recording - especially when you use a gimbal that can tilt via remote control, etc.

Quoted from Bryan

Brendan, does that affect recording framerate or anything?  Recording quality, perhaps?

No issue with selecting any particular frame rate that I'm aware of.  The Go Pro records at full resolution - but you only get "TV" resolution from the video out port for broadcasting back to the ground.

Quoted from Bryan

That's fantastic news, have you done it personally?  Is that the Hero3?  I have a friend who claims that using the video out sacrifices quality, but he's only read on forums rather than tried it himself.

Yep, works fine for me.  I was using a Hero3 Black until I accidentally stuck 12v into the USB port (bad).  I know use a Hero3+ Silver and that works fine too.  All of my flight videos are recorded with one of these.

Quoted from Joe Williams:

Brendan - are you willing to post some more details about the motors/ESC/battery needed for this platform?  I'm struggling to understand what the ecalc website is telling me.  (http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en)  It looks like 800kv motors with 20A ESC would be sufficient, and reasonably paired with a 6000 mA-hr 3S1P battery.  Got any guidance?  I'd like to buy gear that could be used in a variety of platforms rather than just optimized for this one.

We're making good progress on the prints, although I've had a couple of problems.  The 'spring-leg' legs don't spring - I think I'm overextruding a bit so the moving parts became one.  Also, I had one corner of the base lift slightly so now the propeller arm doesn't slide in.  I'll make some measurements to see if sanding will make it work but, if not, it's another 8 hour print.  Precious little free time to get these things done!
Hi Joe,  Yes I use to spend quite a bit of time frowning at ecalc myself.  I got a little frustrated with some of my first (badly) chosen combinations and decided to try an stick to what was proven.  
For example 3DRobotics use pretty much the same combination of Motor/ESC/Propeller on all of their vehicles (quad, hex, octo, Y6, X8) and I've been using their 850kv (or 880kv) motors with 10x4.7 APC props and 20amp ESCs for the last 6 months with great results.  All of these run fine on any 3S battery (or even 4S battery).  I'm not so particular about ESCs and have used many different ones with good results - including the 4-in-1 QBrain pictured on the T4 quadcopter page.
Regarding batteries it really is all about weight.  For the T4 alone I like using the 6000mah nano-tech because it is almost overpowered with the 880kv motors and a lighter battery.  However when I add a gimal under it the weight starts to creep up and it flies better with a bit smaller battery (e.g. 3,500mah) - although still okay with the 6000.
I hope that helps?
 

Regarding the prints, with one springy leg I had to run a blade along the plunger slot to help break it free (and then give it a reasonably hard push down onto the bench). Once moving you can try lubricating with a bit of olive oil or similar.

If it helps, with PLA I use budget hairspray on the glass with the heated base plate set to 55 deg C. For me higher baseplate temps increase the chance of warping. With this combination I haven't had any issues and normally have to put the prints in the freezer for a couple of minutes to get them to pop off the glass (after they're down to room temp).

Quoted from Jin Choi

Okay, as an exercise, I have pulled together all the equipment you have mentioned in this forum and on thingiverse, and here's what I've ended up with. Selecting the cheapest options for everything except FPV, I get ~$490. Going up to the Pixhawk to add autopilot is $740, and FPV goes to $1170. Have I missed anything?

I have some questions.
That Q Brain 4x ESC is slightly more than the cost of one 3DR ESC?
The KK2 is $31, the APM and Pixhawk are like 9x more. Is that for GPS/autopilot, etc.?
My assumption is that I need one motor, propeller and (non-Q Brain) ESC per arm, is that right?
You haven't mentioned a model for your controller, the thing you hold with the sticks. Any recommendations?
Body
T4
http://www.thingiverse.com/thing:261145
 
Motors
3DRobotics 850Kv
 
3DRobotics 880Kv
 
Propellers
3DRobotics APC 10x47
 
ESC
3DRobotics 20A
 
Q Brain 4x20A ESC
 
 
Flight Controller
Pixhawk (with autopilot)
 
APM
+wireless data $100
+GPS $80
 
KK2
 
 
 
FPV
FatShark Attitude SD goggles
 
ImmersionRC 5.8Ghz 600mW transmitter

Thanks Jin. I hate adding up costs like that :-)

If you were starting from nothing I think you could sneak in at about $300 with the following recipe:
- KK2 flight controller
- QBrain 4-in-1 ESC
- 3DR 850KV motors
- 2 sets of 10x4.7 propellers
- a 3000mah 3S battery
- a basic Lipo battery charger
- a basic transmitter like the Turnigy 9X with 8 channel receiver
- a few plugs and cables (eg male-to-male servo cables to connect KK2 to the radio receiver, XT60 or Deans connectors for connecting QBrain to battery)

If you use separate ESCs then you'll need some way to distribute power from the single battery connector to each of them (either homemade or 3DR and Hobby-king sell boards). The QBrain really makes it easier AND cheaper!

Flight controllers like the KK2 are great value if you just want basic stabilisation. The APM and newer Pixhawk add the option for GPS and programming flight missions using a PC or tablet, return to launch if RC link fails, auto land if battery gets low, etc... The current Ardupilot software will probably be the last for the APM hardware as the developers have now reached the limit of what it can handle. Development will continue rapidly with the Pixhawk.

For RC gear I started out with the Turnigy 9X mentioned about and then moved to a Spektrum DX8 and have just received a new Taranis.

Quoted from Terry McCafferty:

Brendan,
Sorry to bug you with the newbee questions, but you are so good at answering them....
Received my package from 3D today!  I went with the full Pixhawk approach.  Still waiting on Q Brain quad ESC  from hobbyking.  I've never done this before so didn't know if I need connectors,...  When I get the ESC, I should be able to figure it out.

I am debating on ordering the gimbal, but don't have the video figured out completely.  They sell a controller board for the T-2D.  Do I need that or does the Pixhawk take care of the interface?  I can't decide on goggles or tablet so may just wait on video and get it I the air and more familiar with the options.

I ran out of steam the other night when ordering stuff and didn't get the batteries ordered.  It seemed like the ones I wanted were all back ordered.  What source do you get batteries from?  Also, I want a good charger that is fast, safe, and preferably will handle more than one battery at a time.  Do these exist?  I saw high amperage, but they didn't mention whether they do multiple batteries.

And finally, I need the radio gear.  I don't want intro stuff.  You mention the Taranis.  Do you think that is the ticket for quads?

Thanks again for your help.

Hi Terry.  Great to hear you are working on one of these.  

Regarding connectors you'll need a hefty connector to connect the battery to the ESC (eg XT60 or Deans).  The ESC and the motors should just plug together (3.5mm bullet connectors) but you'll probably have WAY too much cable (3DR motors and QBrain all have really long leads) so you'll probably want to to shorten them.  Did you get a 3DR power module? - if so that just goes in between the battery and ESC (also a longer 6-wire DF13 cable can be handy to reach from the power module in the power tray to the Pixhawk).  It's worth getting a couple of spare 6-wire and 4-wire DF13 cables from 3DR (the standard GPS to Pixhawk cable is okay but could be longer).

The T-2D controller board should just be listed as a spare part.  If you've ordered the full T-2D gimbal then you should get everything you need the arms, motors, controller board, and even USB cable for connecting to your computer.  The only connection you may want to make between the gimbal and the Pixhawk would be to pass through a signal from your RC transmitter (eg one of the knobs) so you can control the tilt of the gimbal from the ground.  For FPV you'll need to add a camera, video transmitter and a cable to connect the two - plus receiver and googles (or monitor) on the ground.

I got most of my batteries from HobbyKing (I'm in New Zealand) or my local hobby shop.  Yes you can buy all sort of battery chargers (2 dock and 4 dock).  Be aware that many of them require a pretty grunty power supply in addition to the charger.  A 6000mah battery requires about 6 amps (@12 volts) if you want to recharge it in one hour.  Twice that (12 amps) to do it in half an hour.

I haven't played with my new Taranis yet but that would be the one I would buy right now if starting out.  Stocks are still pretty limited though I believe.

Good luck with the build.  Please let me know how it goes and/or post photos!

Quoted from Jin:

I'm trying to put together a BOM for everything needed to fly a T4. I don't want to leave anything out, and I don't want to pick something wrong. I am completely new to this. I've taken my list and turned it into a Google Spreadsheet, could you take a look?

https://docs.google.com/spreadsheet/ccc?key=0AonItoYoQDSmdGlZZ3lsd3...

I have some questions.

Propellers: two sets or four?

Batteries: what is the difference between 2S, 3S, 4S... What about C ratings? I listed several battery options, but I'm not sure what is appropriate/inappropriate.

Charger: is the one I listed appropriate?

Transmitter: what does the Taranis give you that the Turnigy lacks? mode 1 or mode 2?

Flight controllers: what GPS modules can the Pixhawk take? What do you use?

Connectors: I'm probably missing some. XT60: male/female?

You mentioned a "3DR power module", does that need to go on the list?

For your simple GoPro mount, source for vibration balls?

Thanks,

-Jin

Thanks for your questions Jin.

3DR seem to sell their propellers in pairs so you'll need 2 push/pull pairs (4 propellers) - but I'd recommend getting spares anyway (you will probably need them).

A quick search showed lots of tutorials/discussions/videos about Lipo batteries (eg. here, here, and here). But I'll try to summarise:

The "S" number relates to the voltage:
2S = 8.4v (fully charged) down to 7v (about as low as you'd want to drain it before landing)
3S = 12.6v down to 10.5v
4S = 16.8v down to 14v

...so you need a battery that is suitable to power the other bits in your vehicle. I stick mostly stick with 3S because it works with these ESCs and motors and a lot if FPV gear can handle 12v power supply so you can power directly from the battery without any other converters.

The C rating tells you how much current (amps) you can pull out of the battery in any moment (without cooking it). 1C would mean you could only pull the same number of amps as the batteries capacity - eg a 6000mah (6 amp/hour) battery could only supply you with 6 amps of current at any moment. the T4 will need about 16 amps (4 amps per motor) to hover - so 6 amps wouldn't be enough. Fortunately batteries come with higher than a 1C rating. The 6000mah nan-tech battery can handle 25C continuously (25 x 6amps = 150 amps) and up to 50C for a short period (50 x 6 amps = 300 amps!) - we don't need that much :-)

Regarding battery life, if you were only drawing 1C out of a battery it would last for about 1 hour. 2C would give you 0.5 hours and 4C about 0.25 of an hour.

Now charging. It is recommended to charge a battery at up to 1C (which would take 1 hour to charge) - so for your 6000mah battery that would be 6 amps. The charger you linked to was only capable of up to 2 amps so expect about a 3 hour charge time. Also it did not include a power supply so you'll need one of those to power the charger (that can also handle 2+amps and 12 volts).

The Turnigy 9X is a good basic transmitter that would be fine with the KK2 controller but it has a couple of limitations. Background - different RC receivers have different ways to get the RC signals from the receiver to the flight controller. The "old" way is to use a 3-wire (PWM) cable for each RC channel (throttle, roll, pitch, yaw, and often a mode switch +others up to 8 channels/cables) - this is what the 9X supports. Other manufacturers came up with other standards to send all of those same signals over a single cable - PPM, SBUS and Spektrum has their own one too. Now the trick is that not all flight controllers can handle all of the different types of RC receiver signals. A relevant example is the Pixhawk which doesn't support the "old" PWM 8-cable option - so you have to add another small PPM encoder box to take those "up to" 8-cables and encode them into a single cable that you can plug in to the Pixhawk.

The other major limitation of the 9X receiver is it doesn't have a failsafe mode which means...if you loose RC signal it will either a) keep going in the direction it was or b) fall out of the sky. I dont recall which applies for the 9X receiver. With more advanced receivers you can set a special failsafe option that the flight controller can detect to do something clever. The KK2 can't do much with that info but more advanced flight controllers can, for example, fly your vehicle back to you using GPS, or perhaps just land where it is.

Mode 1 versus mode 2 is simply about which stick is the throttle, yaw, etc. For quadcopters I believe Mode 2 is the most common (throttle and yaw on left stick, roll and pitch on the right stick).

If you go with the Pixhawk then get the 3DR GPS/compass module to go with it.

For the combination (KK2 and QBrain) you're looking at you won't need a separate power module. The QBrain provides a 5V power out connection with connects to the KK2 to power it and the attached RC receiver. It really makes everything simple. For Pixhawk and APM flight controllers the 3DR power module provides the extra function of reading the voltage and current being used which can then be sent back to you on the ground via telemetry.

You'll need some 10cm male-to-male servo cables (at least 5) to connect the KK2 to the RC receiver.

As far as other bits and pieces you'll needs bolts, double-sided foam tape and other similar stuff mentioned on the T4 instructions page. Also some vibration gel to put under your flight controller (and a rubber band). Also some heat shrink (and soldering gear) to shorten the motor/ESC cables.

For dampers you could try these or these ...but I'll put up another (simpler) GoPro mounting option that uses the same Gel pads as the flight controller sometime soon.

There's probably more stuff but that's all I can think of right now ...the options are endless and I learn more every day!

I've updated the BOM with some more suitable batteries and chargers, added a power supply, some bits and bobs...
Is the APM power module the same for the Pixhawk?
The entire new Compatibility section is nebulous, I don't understand all the parts. I've decided when the time comes I'm going to get a Taranis, so I am not as interested in all that any more. I don't like the idea of having some range I can't go beyond without an automatic crash waiting at the boundary.

Please, if you have a moment, let me know where my spreadsheet is incorrect or incomplete.

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