Tricopter build – 20140123

My first tricopter build is based on a frame from Hobbyking. they say:

Designed from the ground-up by our own engineering team, the X900 Tricopter is a culmination of months of design, testing and material sourcing to provide you with the perfect mix of quality, performance and value.

Oh well, with hype like that, the reality can only fall short!

The size is 820mm diagonal between motor shafts (not 900mm as the type suggests).

Key elements of the configuration are:

  • Hobbyking X900 tricopter frame;
  • Turnigy D3530-14 1000kv Brushless Motor;
  • Hobbywing Skywalker 4S 40A ESC, loaded with BLHeli v11.0;
  • HK 11×4.5 SF two blade propellers;
  • Hextronic MultiWii 328P Flight Controller w/FTDI & DSM2 Port;
  • FRSKY V8FR-II HV receiver;
  • Battery monitor;
  • Turnigy Discovery Beeper
  • Zippy 3000mAh 3S 30C LiPo battery;
  • Turnigy 9XR/OpenTx transmitter.

The frame has had its problems.

spring

 

The springs used for the “shock absorbing landing legs” are low grade and straighten out when stretched by the legs, see above. Fundamentally, the leg design is flawed, the spring fouls the recommended tail servo and it fouls the mounting screws at the end of the tricopter arms.

TriFoot

The replaced plated steel springs were placed under the inboard arm mounting nut and washer and onto one of the pins in the leg assembly, see above. They don’t found anything in this configuration. The shock absorbing leg folds up so that the servo bracket etc take the bump when the tricopter lands… the most delicate part of the whole craft is unprotected. A temporary measure is some foam zip tied to the legs, but the whole shock absorbing leg is proving to be a bit of a worthless gimmick.

The kit lacked appropriate screws to fix the servo to its bracket and the servo crank to the ball link crank, in my case some 2mm hex head screws and nuts were used.

The one part of the frame that seems well done is the tail servo bearing and motor support. The system is free of backlash, and control is stable.

The ESCs were unwrapped, cables and JST-1.0mm attached to the C2 pads as permanent programming cables and longer motor wires fitted, re-wrapped and loaded with BLHeli Multi v11.0. The ESC was given a bench test on some challenging motors at 4S, and it was very responsive with no hint of sync problems.

The FC was loaded with Mutliwii 2.3 configured for a tricopter.

Initial flights have been good, the craft has plenty of power on a flat battery, is quite responsive for such long arms, and quite stable though tuning work continues. Expectation is that a 4S battery will allow carrying camera payload should that transpire.

More when it is tuned!

SimonK ESC FW – test of commit 8873df24…

The above source was built with COMP_PWM for an Afro30 ESC and bench tested on three motors that have had sync issues in some previous FW versions:

  • Hobbyking DT-750;
  • Turnigy 4822-690kV; and
  • Turnigy 2730-1500.

On 4S and using a servo tester, the motors were tested for sync loss as indicated by the red LED on the Afro30.No attempts were made to tune timing, default advance was used.

Continue reading SimonK ESC FW – test of commit 8873df24…

Wire current rating for single FEP (Teflon) or Silicone insulated (200°) conductor in free air (30°).

AWGCond dia (mm)CSA (mm^2)R/km (Ω)Imax
26.533.60.513241
35.826.70.647209
45.221.20.815180
54.616.81.03156
64.113.31.30135
73.710.51.63117
83.38.372.06101
92.96.632.6087.4
102.65.263.2875.6
112.34.174.1365.4
122.13.315.2156.6
131.82.626.5748.9
141.62.088.2942.3
151.51.6510.536.6
161.31.3113.231.7
171.21.0416.627.4
181.00.82321.023.7
190.910.65326.420.5
200.810.51833.317.7
210.720.41042.015.3
220.640.32653.013.3
230.570.25866.811.5
240.510.20584.29.93
250.460.1621068.59
260.410.1291347.43
270.360.1021696.43
280.320.0812135.56
290.290.0642694.81
300.260.0513394.16

Derived in part from data published by Wiremax.

 

Speaker cable as RF transmission line

Speaker cable and similar Figure-8 twin in various sizes is popular as RF transmission line, particularly with QRP operators, especially those operating portable in the field (eg SOTA activators). Indeed, SOTA seems to have triggered a revival in the use of these cables. With the large number of online recommendations, one could be forgiven for thinking that a dipole and feed line formed entirely from #24 speaker wire is the antenna of choice.

With that in mind, this article looks at the performance of Jaycar WB1702 speaker cable, 14×0.14mm conductors (#24) with PVC insulation, cost $0.50/m.

Continue reading Speaker cable as RF transmission line

Measuring matched line loss

Matched Line Loss (MLL) is the loss or attenuation of a transmission line terminated in its actual characteristic impedance, and usually give for some length, eg dB/100′, dB/100m, dB/m.

One method that occurs in ham radio articles is to measure the input resistance of a resonant s/c or o/c stub, and to calculate MLL as 8.686*Rin/Zo/length dB/unitlength. (This is not the only method, or even a good one, but it is commonly used.)

Continue reading Measuring matched line loss