Small Tricopter for acro training : Update Mk2

by bluefishnz | December 22, 2013 | (0) Posted in Just Fun

I am now getting to the point with my skill level that I would like to try and start doing flips. However I sure as hell dont want to use any of my main quads to start learning as I know I will be crashing alot.

So I wanted an easy to make / repair and cheap frame learn on.

I decided on a T frame tricopter. The reason been I like tricopters, a T copter only has two frame parts and I had the material to make the frame.

Main materials:

  • 12mm square pine rod
  • 14mm OD Ushaped alloy
  • Parts for a David W yaw system
  • ESCs 30amp Rctimer
  • Motors SK3 1275kv
  • Servo : HK 939MG

The main backbone of the TCopter is 2 lenghts of 12mm square pine glued using gorilla glue. This makes for a very strong and light weight main frame. I then cut a 100mm length of 14mmOD U-shaped alloy tube which was bolted at 90 degrees to the main back bone. I also used glue on this joint. The allows me to bolt in the front frame arm, and easily replace if / when it gets broken.

I offset the mount to be about 15mm from the end of the backbone so that when i crash there is some buffer and the strong back bone would take most of the crash force not the T joint.

The front frame arm is bolted inplace with 2 3mm bolts that go through the alloy tube and the wooden frame. I want to change this in the next version and eliminate the requirement of the bolts.  I also made the front arm longer than required so that on ground impacts it will provide some protection for the motors.

Next I mounted the motors. the motors are about 400mm center to center. They are held inplace with doublesided tape and zipties.

 With the motors mounted I was then able to find the CG. I then mounted one of my trusty platic containers to hold the KK2 and the receiver. I like having them inside a protective container.


The container was ziptied to the backbone with some foam in the middle. In this version I drilled through the frame. In version two I will go around the ouside of the frame like you do with the motor mount zipties.


Next up was the making the yaw system. I wont repeat here as its a David W design and I got the parts from hobbyking. The only thing I did different was to drill two hole in the top plate that allowed me to screw the motor directly on.


For this frame I am using a cheap HK 939MG servo. I am testing it to see how long it works for. So far after 10flights it seems to be still 100%

I cut the bottom tab off so it could be mounted flat in the vertical position. To make everything line up I had to glue a popsical stick underneath the servo to match the yaw system.


Here it is all mounted and ready to go. As you can see I also left quite a bit of frame hanging out the rear. This was done for two reason.

  1. Just encase I found the 400mm motor to motor size two small I could easily adjust to make it bigger (450-500mm)
  2. In the event of a tail in crash the yaw sytem and motor are protected.

Here is the little sucker all finished. A few other things I did to help with easy repair

  1. Front ESC are mounted to the main frame, not the from arm, makes replacing the front arm easier if it get broken.
  2. Extra length on frame and arm to protect the motors in crashes
  3. Wood easily found in hardware stroes in my location. 




I have taken it out for a few flights now and like how it flies. I have not jumped into acro yet as still testing and getting basic tuning done.

Next steps will be to find a big open field, up the Expo and stick scaling and give flips ago.... wish me luck. I will update on progress, crash damage and what needs to be changed for version 2.

Update 1:

Ok so I was out flying and expolring new DR/Expo/Stick scaling combos and I had a couple of crashes, then on one crash this happened..

The complete bell housing came off. Somehow during one of my crashes the shaft had snapped at the c-clip groove. I put the bell housing back and it snapped back in and was held by the magnetic forces and it flew fine. The other damage was to mount of the front arm to the backbone. The bolts and glue were not strong enough to stop the crashes causing movement in the joint. I will address in version 2. 


 UPDATE ... on to MK2

After a big nose in lawn dart.... on tarmac I was face with a rebuild so decided to make the front arms folding to help prevent crash damage.

I used the fibre glass sheet I had made and recycled some plates that I was no longer using. I had ond that would work for the top plate. So started with that.

First tet fit and testing the arm positions.


I then cut a bottom plate, I used a box cutter and hacksaw.


After the first fit with the top plate. I decided to make it much smaller as it didnt need to be so big.


New small sized plates for the foldable front arms and secured on the double width body.


The finished frame, new main body, folding arms using fibre glass plates.


The first flight, it flew great... then I decided to try some acro ... I can confirm that it crashed well and the folding arms did the trick, just broken zipties.

very happy with my little t-copter MK2. It flew great. however I had a nasty crash and I think I have broken the servo as its not behaving. So waiting for a new servo to arrive to get this bird back crashing.




Widkin on January 20, 2014
Nice log. One thing, though: you really should not fly with the motor bell just held on by the magnets. It could rip out while spinning up quickly and then veer off and hit someone in the eye or something. Please be careful.
Log In to reply
bluefishnz on January 22, 2014
Indeed you are very correct, but the matter is resolved as the next "flight" resulted in another big crash, and that motor is now deceased.
Log In to reply

You need to log-in to comment on articles.

Small Tricopter for acro training : Update Mk2