Building My First Tricopter

Background

After having experimented with quads of varying sizes, I decided it was time to get my teeth stuck into some tricopter building.  Seeing that I would like to use the platform for aerial photography and for experimentation, I was looking for a frame that allowed me both the opportunity of carrying a meaningful payload while enduring as long as possible (with the goal being to keep it under 1,000g AUW while being able to hover for 15+ mins).

After considering a few different options, I decided on the new Turnigy Talon tricopter frame. 

The arms and hubs are made completely of carbon fiber with the mounting blocks for the arms as the motors made from machined aluminum.  Additionally, the arms are made from standard carbon fiber tubes and so can be easily replaced in the case of breakage (arms and propellers tend to be the most commonly broken frame parts on multicopters) .  Once assembled, the frame should weigh in at 350g (accoridng to its instructions) and serves as a good comparison to my DJI 450 quad frame in terms of its overall size, its payload capacity and the space available for mounting equipment.  One salient different is that this tricopter frame has folding arms which allow the frame to be flown three different configurations (including a T-shape) and configured in a fourth for compact storage.  In it's storage configuration it is much smaller than the DJI 450, so much so that it can be easily carried in a small backpack.  Another major difference between a tricopter and quadcopter is that the tricopter requires thrust vectoring of the rear motor/propeller combination in order to control yaw.  For this purpose, a servo is required and a digital servo using metal gears is the preferred way to go.  An ideal servo will have very fast response times, can take a fair amount of abuse and has good centering ability while the amount of torque it can handle is slightly less important. 

Frame Assembly

Assembly was a little tedious as the small parts are not well-suited to my fat fingers.  Additionally, the assembly instructions (which amounted to little more than a breakaway CAD drawing) were basically non-existent.  Would definitely not recommend this build for the beginner.

Steps:

1. Assemble the arm mounts.
   
   
    
   
   
   
   
2. Prepare the hub plates with the appropriate spacers and attachments.
    
   
   
   
   
3. Mount the arms to the hub ensuring that the arms are able to fold properly.
    
   
   
   
   
4. Prepare and attach the motor mounts to the ends of arm.
    
   
   
   
   
5. Voila.  The foldable tricopter frame is compete.  The bare frame tips the scales at 352g.
   
   
   
   
   

Motors and Propeller Sizing

The selection of a motor and propeller for a tricopter is a fairly easy task - much more so than for a quad copter because there is almost no limitation in the size of the propeller one can choose.  While a 450 quadcopter frame can accommodate up to 12-inch propellers (although this even is slightly large due to the proximity of the tips), a similarly sized (and weighted) tricopter frame can accommodate up to 24-inch props (HUGE for a frame of this weight).  In this case we will go with 10 x 4.5 props for now.