3D printed T4 and T6

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.

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!

Replies

Brendan22 April 19, 2014 at 10:45pm

Announcing a new arrival - the T4 Mini Quadcopter ...isn't it cute!
- K Taylor > Brendan22 April 25, 2014 at 5:11pm
  
  Which 3d printer to you use?
  - Brendan22 > K Taylor April 25, 2014 at 5:16pm
    
    Makergear M2.
Brendan22 April 5, 2014 at 9:43pm

Here's a little teaser ...some prototypes from a T4 quadcopter related project I'm working on at the moment...
- Joe Williams > Brendan22 April 18, 2014 at 10:24am
  
  Hi Brendan,
  
  Looks like you've really got some momentum going with this project! I have to admire your modeling skills, particularly since you're using SketchUp. Very impressive.
  
  I have a quick question about mounting the motors. I've got my printer back in action after a gearbox problem and successfully printed the quad parts, but the mounting holes in the T4 arms don't match up with those in the 3DR 850kv motors. The motors have two pairs of holes, each pair a different distance from center. Your arm has four equidistant holes. Do you just use two fasteners (not my favorite) or do I somehow have an oddball set of motors?
  
  Thanks for doing this!
  - Brendan22 > Joe Williams April 18, 2014 at 3:04pm
    
    Hi Joe and thanks for your comments. From the bottom of the T4 instructions page...
    
    This sized motor typically has a 16x19mm mounting pattern but unfortunately the wires on different models exit the motors from different corners so the only way to work with all motors was to provide a 19x19mm hole pattern and mount the motors using only 2 bolts (with Locktite). Experience has proven this is not a problem and, in fact, seems to be common practice - for example all 3D Robotics off-the-shelf vehicles only use 2 bolts to mount their motors.
    - Joe Williams > Brendan22 April 18, 2014 at 5:13pm
      
      Rats, I was afraid it was obvious and I was just missing something. Since you opened this thread I hadn't been back to the Thingiverse site so missed that bit of goodness.
      
      Thanks much!
Jin Choi March 31, 2014 at 2:22pm

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.
- Brendan22 > Jin Choi March 31, 2014 at 2:45pm
  
  Excellent Jin. That's a great resource for anyone looking to source components.
  
  A couple of observations:
  
  - The Pixhawk and APM products you linked to both include GPS and power modules in the price you quoted.
  
  - The Taranis you linked to is Mode 1 (easy to change - see YouTube) and wasn't the "kit" version so you'd need to buy a separate receiver like this X8R.
  
  - The Attitude goggles you linked to already includes a transmitter and receiver that could get you started. If you did want to upgrade to the ImmersionRC 600mw transmitter then I'd also recommend a pair of their Spironet Antenna.
Brendan22 March 29, 2014 at 1:31pm

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!

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