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.

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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