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.

 

Arduino RC servo ramp generator

In testing RC electric drive systems (ESC + BLDC motor), a repeatable scenario was needed to evaluate changes such as changes to commutation advance.

Often these changes have different impact under rapid acceleration or deceleration to slower changes.

This article describes a simple servo signal ramp generator based on Arduino hardware, in this case using an Arduino Nano but most Arduinos or clones could be used or adapted.

Continue reading Arduino RC servo ramp generator

Hobbyking A30 issues

The Hobbyking A30 is an economical power supply for LiPo chargers.

problems were noticed with a Turnigy Accel 8150 charger where the display became corrupted when the case was touched.

HK-A30

It turned out the output terminals of the A30 are isolated from chassis and power supply ground. Above is a scope capture of the voltage to chassis on the -ve output terminal, a common mode voltage of almost 300Vpk. Sure, it will not sustain much current, but it is potentially (pardon the pun) dangerous to any electronic equipment connected to the power supply.

In my case, I dismantled the case and bonded the -ve output terminals  to the mains connector earth terminal with a 2.5mm^2 insulated wire.

Whilst performing that work, I was concerned at the proximity of a large toroidal choke and the top cover with no intervening insulation. I applied some kapton tape to the lid to reduce the risk of problems.

Oh, and the power supply rattled when received. That was an extra case screw loose inside the power supply, and it had fortunately not yet caused apparent damage.

These power supplies are not intended as a general power supply for electronic equipment, and they do make a lot of radio frequency interference (RFI).

SAFETY WARNING: do not remove the covers or attempt such a modification unless you are competent to do so.

Some thoughts on zero crossing detection in sensorless brushless DC motors

A sensorless brushless DC motor senses motor position for the purpose of commutation timing by using the voltage induced in the unused winding at the time. Reliably sensing the motor position for a range of motor constructions and speeds proves a challenge.

ZC

Continue reading Some thoughts on zero crossing detection in sensorless brushless DC motors

COMP_PWM and SimonK ESC firmware

COMP_PWM is an option on SimonK ESC firmware for sensorless brushless DC motors,

SimonK without COMP_PWM

Above is a capture of the waveform during two commutation steps where this FET is low side  modulated. You can see that when the low side FET turns off, voltage rapidly rises to just above battery as the energy stored in the winding inductance drives current through the high side FET body diode (which drops 0.7+V) and the other high side FET that is on.

Continue reading COMP_PWM and SimonK ESC firmware