Tricopter – Revision III


New videos coming soon! See bottom of page for more.

With the Revision I Quadcopter being more of a learning curve for me in both 3D design and RC piloting, I give you this! Stemmed from years of experience, this 3D printed tricopter frame can compete with some of the top performers out there. The bare 660mm motor-to-motor frame (sans electronics) weighs only 220 grams with pine wood arms!

The design files are free for you to use! You can download them here from Thingiverse. Or by zip archive here.

It folds up too!

I modified Thingiverse user ennui2342′s tricopter body, based off of David Windestål’s RCExplorer tricopter, to support the stronger, more common (in the US) 1/2inch wood dowels. Other modifications were made as well.  I also loosely based my landing gear/motor mounts off of jphillips’ designs. The vibration dampening bottom plates among other features are unique to this tricopter.

When you build this frame, you can choose to go as big or as small as you want. You can even go down to the 250-300 class racers. Nothing else has to change!

DSC_0918wp

As you will see in the instructions below, I’ll prefer the large-ish 660mm frame for its relative docileness in the air.

Prototype pictures:


 Build it yourself!


Essential hardware you will need for the frame includes (available at your local hardware store):

Note: A list of RC hardware (motors, props and such) that I found works well with this frame is included near the bottom of this page. You should however be able to use any hardware you desire or happen have on hand.

  • For yaw mechanism:
    • (1) 35mm M4 socket cap screw
    • (1) M4 Nylock nut
    • (1) BMS-385DMAX Digtal Servo (or equivalent)
  • For general purpose frame assembly
    • (13) 25mm M3 socket cap screws
    • (13) M3 Nylock nuts
    • (2) 350mm lengths of 1/2″ (12.7mm) square wooden dowel
    • (1) 320mm length of 1/2″ (12.7mm) square wooden dowel
    • 3M VHB tape (aka. Scotch Permanent or Extreme Mounting Tape)
    • (16) 8mm M3 socket cap screws (to mount motors to mounts)

As stated above, even though the frame can support a wide array of hardware, a guide for choosing your electronics is included near the bottom.

 

Printing


For rigidity and durability, I recommend printing everything with 30% infill, and 4 perimeters/shells all around (top and bottom as well). That’s pretty simple isn’t it?

A recent update (“optional-plate_larger_motor_mounts_kit.stl”) adds larger motor mounts that support motors with 18.9/25mm through 25/25mm (M3) mounting hole spacing. This is oppose to the more common 16/19mm hole spacing option. These larger motors shouldn’t be necessary for most builds, but nonetheless are included for your experimentation.

In another recent update, (“optional-plate_larger-longer_motor_mounts_kit.stl” and “optional-plate_standard-longer_motor_mounts_kit.stl”) the landing struts were extended 22mm (100mm total height; watch for small printers). Unless desired for user preference, these should only be necessary for a particularly low-hanging battery tray due to the use of extra-large rubber dampeners and/or extra-large batteries.

Other minor updates are described on this tricopter’s Thingiverse page.

platepic
Note: Some optional features shown. Larger and longer motor mount kits not shown.
DSC_0066
Everything (sans-vitamins) you’ll need for a basic frame with vibration dampened GoPro/FPV mount.

You may need to bore out some holes and polish some edges, but don’t worry about that right now. Just get handy some sandpaper and a 1/8inch and 5/32inch drill bit if you don’t have any metric ones laying around. These would be for M3 and M4 holes respectively.

 

Assembly


Building the frame is pretty self-explanatory if you follow the pictures. You can even use any size arms/booms you want; it’s pretty universal for all size classes. For a perfect equilateral design though, just make sure you cut the rear wood dowel 30mm shorter then the other two.

For a large 660mm frame, begin by cutting two 350mm lengths of 1/2″ (12.7mm) square wooden dowel and one 320mm length of the same. If you are not picky or just lazy, three 350mm lengths will work just as fine as well.

Alternatively, If you only want to buy/use a single 3 foot piece of 1/2 inch dowel from the hardware store, you can cut two 310mm pieces (front arms) and a single 280mm piece (rear tail) to make full use of a single dowel.

Once you get the arms cut, you will need to drill one 1/8inch or 3mm hole 15mm away from each of the ends of every arm. Make sure you center these holes as well. The final frame will measure roughly 660mm between each motor shaft.

Now for the motor mounts. These may have been difficult to print due to the 13mm bridge your printer may have had to construct. If you notice any slop inside these pieces, clean it out with a hobby-knife, and/or small abrasive files.

DSC_0058

Generally, 1/2 inch wood dowel is manufactured a little over sized. You may need to pass the last 25mm or so of each end over some sandpaper. Continue to do that until you have a snug fit where the holes line up; this shouldn’t take much effort. If it becomes too loose, add painters tape. You’ll want a snug fit to avoid any vibrations. The rear motor mount should go on the shorter, 320mm dowel you cut.

DSC_0053

Make sure the 25mm M3 socket cap screws will fit in the respective holes. You may tighten all three of these down right now, but we will have to work on the rear yaw hinge later.

DSC_0052

At this time you are going to want to decide which of the two plate options you want, if any. I recommend the FPV plate since it can fit either a 9-gram pan/tilt servo (like the one FatShark sells) or a GoPro by using the easy-to-swap GoPro mounting bracket.

This is probably the most tedious part of the build. Use the pictures to your advantage. You’ll need to determine the rubber pieces you are going to use for vibration damping. I chose soft rubber bumpons, but Sugru blocks and rubber tubing are other fair (if not better) alternatives. Visit here to learn more about the ideal vibration dampening materiel to suit your needs (Hint: foam rolls). You’ll probably just need some glue to keep them from sliding around. Observe the pictures to determine where they go.

DSC_0037

First find the battery plate, optional FPV plate, and bottom frame piece. Line up the rectangular holes on all three (or two) of these pieces and insert three zip-ties from the inside of the bottom frame piece. You are also going to want to add some VHB double-sided tape between the battery and FPV plates (if applicable). Thread the zip-ties through their respective holes before sticking any pieces together. You should not tighten these zip-ties very tight at all. They  are mainly there to support the weight of everything below.


Now again find the shorter, 320mm dowel you cut. It wasn’t exactly necessary to drill a hole on one end of it. Pick the side that you want to have go inside the center frame assembly (the side without the motor mount). You may need to lightly sand down the two edges of this end of this piece of wood in order to make it fit the slot in back of printed center frame pieces. This should be a snug fit without screws clamping the halves down. If it is too loose, add some painters tape where necessary. The two ribs in each of these rear slots will grip the dowel once you tighten all the bolts.

DSC_0035

Once all that is complete, insert some screws from the top printed frame into the bottom printed frame and loosely tighten a Nylock nut on each of the protruding ends. Align the holes on the two side-arms with the respective ones inside the printed frame assembly. Insert more socket cap screws and tighten firmly. Return to each of the previous screws and tighten them down firmly as well. Careful not to over-tighten any of these or you might break something. You’ll want the arms to swing forward and back with a moderate friction involved, but you don’t want them to swing freely in flight (that would be bad).

DSC_0033

For constructing the yaw mechanism you’ll want that one 35mm M4 socket cap screw and M4 Nylock nut. Begin by making sure the two budding faces of the printed parts are fairly flush with one-another on all degrees of rotation.

DSC_0030

Remove the tail piece from the wood arm you put it on earlier if it is still there. It is best to ensure the M4 screw rotates freely in the hole on this end, rather then the motor mount’s end. Depending on your printer this might be a tight fit. Use a  4mm or 5/32inch drill bit to bore out this hole if necessary.

Now insert the socket cap screw from the side where the wood enters. There will be a little recess where the head of this screw goes within the mount.

DSC_0028

From there, feed the (smaller) motor mount piece onto the protruding screw. Tighten this firmly with the M4 Nylock nut and rotate the two pieces around a few times. Now loosen this nut just enough so a minimal force is required to move the hinge. Ensure that there is no play in the gap. It is okay if the hinge does not “pinwheel” freely when spun. Your servo should still be able to move it.

If you still observe excess ‘play’ in the gap between these two pieces, take it apart and polish/clean the two faces again. You can also use white lithium grease or similar for lubrication.

DSC_0025

 

Electronics, wiring, and propellers


By now you have a pretty universal frame that can support a fairly wide range of hardware. If you’ve been in the hobby for a while, you might already have most of what you need.

If there is one proprietary piece, it is the tail servo. I recommend the BMS-385DMAX Digital Servo. Otherwise I’m sure you can make any other sub-20g servo work as long as it fits in the slot on the tail (~27mm long by ~13mm wide).

Beyond that, for the servo linkage use either proper servo clips and push rods or bend some 1mm music wire. I suggest you duplicate the linkages on both sides for redundancy and pretensioning.
Also, you should make sure your servo is centered before mounting the horn. Depending on the size of your linkages, you may also have to adjust your min or max values in your configuration GUI as well as the servo direction.

DSC_0367

The ESC clips are best suited for ESCs with an approximately 25mm width. This includes Turnigy Plush 18A, 25A, and probably the 30A ESCs. If your choice of ESC differs in this sense, you can either physically modify the clips by removing the tabs or print three of the optional auxiliary clips. If you use the auxiliary clips, you will also need a zip tie or two accompanying each one.


When attaching your motors to the mounts, you will need to use four 8mm M3 socket cap screws for each motor. These are most likely the only screws to ever come loose on this copter. Chech their tightness often and/or apply a thread locker that won’t damage the plastic you are using.

DSC_0524-web

You are going to want to make (or purchase) I wire harness to distribute power to your ESCs. I made mine to incorporate the small lengths of wire already attached to my ESCs for convenience. Do whatever looks best for you.  I used 14AWG wire (16AWG is also fair), 3.5mm bullet connectors, and a XT60 connector. Again, do what is best for you.

DSC_0022

DSC_0023

To secure the battery, I use a single Scorpion brand “Extra Large” (~410mm) Velcro battery strap. It is looped twice between the bottom plate-stack and the bottom frame piece. It crosses once over the battery.


To safely utilize the top of the frame pieces for mounting flight controllers and receivers among other things, print out the “optional_countersink_plate.stl”. Use double-sided VHB tape to secure it to the top of the tricopter. This will give you a flush surface to mount everything on. If you have extra-thick double sided tape, you can use that in place of this part.


If you want your tricopter to fly really fast, you’ll need to put on at least three propellers. Two normal props plus one pusher prop would preform best, but you can use three of the same if that’s all you have.

It is crucial that you balance your props! It will save you a lot of time, hassle, and money in the future. Look it up on the Internet, just do it!

Only after you program (see below) and test everything should you put your props on. Also, make sure the motors match the directions your props are designed for (swap two of the three phases to change a motor’s direction).

 

Additional notes


Note: Review previous images for proper use of the printed cable and ESC clips. These are pretty self-explanatory nonetheless. They clip on any part of the wooden arms and wires can be fitted into the exposed loop at one end. Otherwise, use zip-ties.

Note: You must program your ESCs before flight, otherwise your tricopter may will plummet back to earth unexpectedly. Observe the following image and use your ESC programming card and its manual to duplicate these settings on all three of your ESCs.

DSC_0532b-web

Note: If you are using the MultiWii flight controller like me, open up the MultiWii.ino file through the Arduino IDE and click on the config.h tab. You will need to change the lines stated below. This is only applicable to the hardware used and the specific version of software available at the time of this writeup. Search around the net for instructions and tutorials that match your specific setup.

  • First, uncomment (remove the “//”) the line for the “TRI” type of multicopter,
    #define TRI
  • Then adjust the minthrottle line like so. This may differ for you, basically it is the minimum value needed to keep your motors spinning. Think of it like a combustion engine’s idle speed per se. You can use the MultiWii Config GUI to help you. (1)
    #define MINTHROTTLE 1032
  • Likewise, maxthrottle can be adjusted as so, (1)
    #define MAXTHROTTLE 2000
  • Below that, you will need to change the line for mincommand like so. Again, this may differ for you, basically it is what the ESCs think is 0% throttle if talking to a traditional RC transmitter. (1)
    #define MINCOMMAND 900
  • Swap the “//” on these two lines so they read:
    //#define I2C_SPEED 100000L   
    #define I2C_SPEED 400000L  
    
  • Now scroll down a few lines and uncomment the following line. This of course is if you use the applicable Crius SE line of flight controllers.
    #define CRIUS_SE
  • Since arming via a traditional yaw input may make your rear prop strike the ground, swap these two lines so they read:
    //#define ALLOW_ARM_DISARM_VIA_TX_YAW
    #define ALLOW_ARM_DISARM_VIA_TX_ROLL
  • Finally, scroll down a ways and uncomment the line reading the following. This will let you use an additional channel on your receiver (total of 6 now) for mode switching, which you can define in the MultiWiiConf GUI.
    #define RCAUXPIN8

(1) – Special note for the MINCOMMAND and MIN/MAXTHROTTLE (again, this varies for some ESC brands): I strongly suggest you first program your ESCs and tell them what your transmitter’s min and max throttles are. To do this (on Turnigy ESCs at least) boot up each ESC, one at a time, while it’s plugged into the throttle channel on your radio receiver and with transmitter at full throttle. Wait for two beeps then drop the throttle to zero. Otherwise, if you neglect to do this you might get a tricopter with poor response times or perhaps even take off immediately upon arming.

Once you are done editing the code, you are now free to upload the sketch to the flight board via an FTDI cable. Make sure the FTDI cable is set for +3.3V logic level and +5v VCC output voltages with DTR enabled. This may differ from your AIO board. Check the manual!

Note:  PID calibration. Finding these often unique variables is a general procedure many DIY multicopter enthusiasts have to go through. The defaults should work fairly well, but aditional tuning may be required to get the most out of your hardware. Using the MultiWiiConf program you can also define exactly what your auxiliary channels do and reverse your servo direction if necessary.

Note: There are a few ways to mount a GoPro here. The best option is to print the ‘optional_gopro_mount_for_fpv_plate.stl”. This uses four small zip-ties that will fit in the four identical holes seen on both this piece, and the front of the vibration dampened FPV plate.
Otherwise, if you used the plain ‘auxiliary plate’, use a flat GoPro sticky mount in it.
Alternatively, if you want to put in an FPV board camera with pan/tilt servos (like the ones FatShark sells), just drop the required servo into the slot on the FPV plate and secure it with screws or two zip ties like so.


Note: For the curious, the hardware I currently use for this tricopter is listed below. It is not at all necessary to follow these exact specifications; you can use whatever you want.

Note: Finally, go fly and have fun!

 

Additional media


The first full length ‘promo’ video for this tricopter using a slightly under powered power setup (something akin to a mini quad).

If you didn’t catch it above, here is this tricopter’s first crash (includes pictures):

 

The first real test flight of this tricopter:

 

 

7 thoughts on “Tricopter – Revision III”

  1. is there anyway i can pay you for the printed plates?? if so please let me know this is a awsome build id like to build one…is it crash tested??

    1. Unfortunately, I am not selling any printed parts at this time. I suggest you try places like 3D Hubs or your local hackerspace for cheap 3D prints. And yes, thanks to its foldable arms, the tricopter handles crashes very well.

  2. I’ve got one of the Kickstarter Pocket Drones from AirDroids. I’ve also got a 3D printer. Are you familiar with the Pocket Drone? I’m wondering if I could use the components of that tricopter on this frame.

    1. Maybe. I doubt those motors, props, and ESCs together will give you decent performance given the relative size of my tricopter. You could try shortening the arms a bit on mine though and see if that works. Honestly though, I’d rather just spend $170-$220 and get ALL the new parts from HobbyKing (including transmitter and Flight Controller). I have a list to start you off near the bottom of this page.
      You might be able to salvage some things from the Pocket Drone (TX/RX, FC, charger?), then again, two tricopters is better then one. 😉

  3. I am almost done building mine but I feel the front arms will bend back in flight. How much should they resist? And will 900g motors do the trick?

    1. The front arms should be able to hold up their own weight if you hold the tricopter upright by its tail. You’ll want all your screws to be tight, but not so tight where the plastic begins to fail. If you need to, take apart the main frame and sand/file down the tops of the semicircular endstop bits on the central hub pieces (These are the nibs that the arms touch under full extension). This will allow the frame to come in closer contact with the wood arms; providing a tighter grip that resists in-flight folding.
      Also, 900g thrust motors will work, however keep in mind there is a little of room for improvement there.

Leave a Reply

Your email address will not be published. Required fields are marked *