SimonK commit 8873df24: (20140119) with COMP_PWM was loaded on the F-30A ESCs on this X450 quad with APM FC, 3S, Hobbyking D3530-14 motors and 11×4.5 SF propellers.
Performed rapid acceleration under WOT, motor idle, recovery, maneuvers and no issues, no hint of sync problems, works fine.
Eric Nichols, KL7AJ, published a manifesto entitled “SWR Meters Make You Stupid” announced on eHam in March 2010. Eric is clearly a disciple of Walt Maxwell (W2DU SK), his first announcement states
By popular demand, my complete treatise on transmission lines. Approved by Walt Maxwell, W2DU as if Walt’s blessing was an imprimatur from the ham radio church.
Continue reading Do SWR meters make you stupid
Tests on the tricopter using a data logger to capture motor speed, current and pack voltage gives an insight into platform operation.
Above, data capture from the tricopter on 3S. The datalogger adds 50g mass.
The plot shows the device hovering at about 5000rpm and 10.8A at 11V. Two WOT ascents were made to check acceleration and motor recovery during closed throttle descents. From idle, it takes about 500ms to accelerate to hover rpm. This test was repeated and the motor reliably restarted every time and the tumbling craft stabilised quickly. A set of 12×4.7SF props has been ordered to try at 3S to more fully load the motors.
Similar tests were conducted also on 4S, and peak current on WOT was 80A on 15.5V for 8500rpm. Operation on 4S would provide sufficient lift to carry a camera payload, but WOT operation exceeds the motor’s continuous current rating.
The tricopter project lumbers on, delayed by faulty parts.
The recommended tail servo, a Hobbyking HK 922 Metal Gear Digital Servo, failed. It had a rough spot at about 70% of its range from new and which became worse quite quickly until the motor had insufficient torque to overcome it.
Continue reading Tricopter build – 20140131
From time to time, correspondents have asked how the Cobwebb antenna works, and particularly how the impedance matching scheme works.
Firstly, what is the Cobwebb?
It is an innovative antenna for small spaces, quite compact and as I recall originally intended to cover five amateur bands from 20-10m.
Continue reading Cobwebb antenna impedance matching scheme
An antenna feed line is intended to convey energy from the transmitter to the antenna, and usually without giving rise to radiation itself.
The term “common mode” comes from consideration of the currents on an open two wire line, and it refers to the net or unbalance current, ie the current that would give rise to external fields, to radiation.
This article looks at the equivalent common mode current in a coaxial transmission line.
Continue reading Common mode current and coaxial feed lines
There are frequent recommendations of RG174 for portable stations (eg SOTA), usually running QRP, principally because it is light and easy to wind up into a small package to fit into a pack. RG174 commonly uses silver coated steel (SCS) centre conductor, sometimes copper clad steel (CCS), sometimes copper.
Continue reading RG174 for portable HF operation
There is a risk of damage when flashing ESCs. It accrues from the fact that ESCs have a three legged H bridge and if a high and low FET are turned on simultaneously, damaging currents may flow. In fact, this can be an issue if the FETs are on together for just microseconds on each PWM cycle. Loading the wrong hex module is a recipe for disaster, it may turn on FETs in an unexpected way.
Continue reading An inexpensive current limiter for flashing and initial testing of ESCs – Mk I
On 10 December 2013, the ACMA issued a notice as a result of a single complaint from a member of the public, the notice essentially requiring that I obtain a new call sign.
Continue reading New ham licence, finally!