Can the EasySky 6A Brushless ESC operate in reverse? - Page 1
Forum section: electronics / beginners

author: CoilKid
author_rank: Contributor
timestamp: December 26, 2014, 05:26:30 am
content: I am building a physics project with a brushless motor, and I found the EasySky 6A Brushless ESC for Cessna 182/Dolphin Glider/Piper JC Airplanes (it seemed cheap). Before I buy it though, can anyone tell me if it can operate in reverse? (the motor will need to make sudden changes in the direction of applied torque).Intuitively, it seems like it should; ESCs are controlled by servo signals, and you can easily reverse a servo. However, it has been suggested to me that being an ESC made for model airplanes (which do not usually have a motor reverse button) it may not have that ability designed into it.Several minutes of Google searches for the data sheets for this, yielded nothing but Chinese web stores and incomprehensible URLs.I don't know if this sort of question is appropriate here, but any help would be appreciated.

author: Circlotron
author_rank: Super Contributor
timestamp: December 26, 2014, 07:13:21 am
content: You may want to look at an ESC that is meant for a model car perhaps. That would likely have the facility to go both directions. In your application, watch out that you do not try to pull the motor speed down too rapidly. If you run it down faster than it would coast down naturally, the motor will be working as a generator (ok, an alternator...) and the kinetec energy of the rotating mass needs to go somewhere. It will pump up the DC buss of the ESC. May be okay if there is a direct battery connection too all three sources and drains of the mosfets in the ESC but if using a power supply the voltage will go up high and maybe pop something. You would need to have some kind of zener + power transistor voltage limiting clamp cct across the buss.I work on sliding doors and this is an issue with the ones that use a PMSM like your model motor.

author: CoilKid
author_rank: Contributor
timestamp: December 26, 2014, 06:31:43 pm
content: I can't let the flywheel run down like that. For my purposes, it can safely be assumed that the object the motor is attached to is free-floating. (The flywheel turns one way, and the object turns the other.) Letting it run down would be too time consuming.In other words, if the motor slows the rotation of the flywheel, and the motor is fixed, the kinetic energy of the flywheel has to be absorbed by the motor. However, if the motor slows the rotation of the flywheel, and the motor is free, the kinetic energy of the flywheelshouldrotate the free-floating motor, and not have to be absorbed by the motor.I took a look at the model car ESCs, and they seem to run in the $40-50 each. For my physics project, I will need a minimum of three. I would prefer to keep my costs low, which is why I was looking at model airplane ESCs ($10-30).I need to work on doing more calculations to confirm that the kinetic energy would not be absorbed, but if I'm correct, would a model airplane ESC work?

author: zapta
author_rank: Super Contributor
timestamp: December 26, 2014, 08:46:32 pm
content: Few weeks a ago I saw a high end quadcopter that can fly upside down by quickly reversing the rotors (that is, not by batting the blades tilt). Don't have the name with me but you can try searching for it.Edit: If you just want the reverse direction, swap two of the three wires.

author: CoilKid
author_rank: Contributor
timestamp: December 26, 2014, 09:08:02 pm
content: Well, it would be an in-flight reversal. I don't think that switching the wires will work for me. Thanks for the suggestion though.

author: zapta
author_rank: Super Contributor
timestamp: December 26, 2014, 09:44:25 pm
content: Google search forreversible escprovides many hits.

author: CoilKid
author_rank: Contributor
timestamp: December 26, 2014, 11:23:06 pm
content: Could anESC like thiswork for my application? I think I could just get it, but I can't seem to find any spec sheets for it.

author: mikerj
author_rank: Super Contributor
timestamp: December 27, 2014, 07:44:55 am
content: Quote from: CoilKid on December 26, 2014, 06:31:43 pmThe reason model aircraft ESCs are cheaper is that they don't need the numerous power MOSFETs required to implement an H bridge since they don't need to be reversible.

author: Circlotron
author_rank: Super Contributor
timestamp: December 27, 2014, 08:55:36 am
content: The sliding doors I work on use six mosfets. The motor reverses because the switching sequence of the mosfets reverse. You might find a three MOSFET inverter in a small brushless fan motor, but a unit of decent power like we are talking about here will have 6 mosfets.

author: CoilKid
author_rank: Contributor
timestamp: December 27, 2014, 04:09:34 pm
content: I don't believe it has to be powerful. I will be using it to power a harddrive spindle motor, not a model airplane motor.

author: mzzj
author_rank: Super Contributor
timestamp: December 28, 2014, 07:54:30 am
content: Quote from: mikerj on December 27, 2014, 07:44:55 amNowadays most aircraft motors are bldc type motors that need 3 half-bridges anyways. Running on reverse is just a matter of software limitations.OP should also beware of the limitations in these sensor less bldc controllers if you need any finesse in the control or require low speeds.

author: rob77
author_rank: Super Contributor
timestamp: December 28, 2014, 10:11:19 am
content: Don't do it ! any brushless DC motor controller intended to propel a model airplane can't SUDDENLY change direction ! and the most important part, those can't go to low RPM while maintaining torque !to maintain torque @ low rpm you need a hall-sensor feedback to the controller - i'm sure you'll NOT find a BLDC motor with hall sensors and controller capable of handling hall sensors among the stuff for model airplanes.those model airplane ESCs you mentioning are starting the BLDC motor as stepper motor (unusable torque at startup and kind of jerky start) and once the rotor is moving somehow - and the ESC have a induced feedback (sensing the 3rd wire) it starts to commutate as it should.

author: Circlotron
author_rank: Super Contributor
timestamp: December 29, 2014, 01:07:56 pm
content: Just being pedantic but those plane motors are not actually brushless DC (BLDC) motors, they are 3-phase permanent magnet synchronous motors (PMSM). A BLDC motor has all the electronics inside the motor and only two wires for DC power coming out, like a computer fan motor for instance. A PMSM motor has 3 wires for AC power coming out. The electronics are external.

author: CM800
author_rank: Frequent Contributor
timestamp: December 29, 2014, 01:20:42 pm
content: Quote from: Circlotron on December 29, 2014, 01:07:56 pmComing from a person who actually works for a company in the Motion control industry, BLDCs don't always have the electronics inside the motor, in fact most do not.the most common BLDC motor without integrated drive electronics are Servo motors (the proper ones, not the crappy little RC ones)

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2014, 02:04:49 pm
content: Quote from: Circlotron on December 29, 2014, 01:07:56 pmI agree. If one connects a so-called BLDC motor which doesn't have any built in drive electronics directly to a battery, they get lots of smoke. The term brushless DC is a bit of a misnomer and should really be reserved for motors with built in drive electronics.

author: rob77
author_rank: Super Contributor
timestamp: December 29, 2014, 02:31:52 pm
content: Quote from: Hero999 on December 29, 2014, 02:04:49 pmlet me slightly disagreethe term brush-less DC motor is pretty accurate for the motor without electronics...DC motor => permanent magnet motor with mechanical commutator also known as the "brush"brushless DC motor => same as above but missing the "brush", therefore an incomplete device => you have to add your electronic "brush".

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2014, 03:00:43 pm
content: Quote from: rob77 on December 29, 2014, 02:31:52 pmA permanent magnet brushed DC motor normally has a wound armature and a permanent magnet stator.A so-called brushless DC motor doesn't have an armature though does it? It has a wound stator and a permanent magnet stator? How does it differ from a permanent magnet synchronous AC motor?

author: rob77
author_rank: Super Contributor
timestamp: December 29, 2014, 03:31:17 pm
content: Quote from: Hero999 on December 29, 2014, 03:00:43 pmwon't fight youyou are right Sir and the whole world should change the established naming conventioni promise i will repeat the mantra "PMSM permanent-magnet synchronous motor" at least 100 times a day to get used to itand i hope the rest of the world will do the same !

author: mzzj
author_rank: Super Contributor
timestamp: December 29, 2014, 08:04:30 pm
content: Quote from: Circlotron on December 29, 2014, 01:07:56 pmSometimes BLDC motor means pmsm motor optimized for trapezoidal waveform instead the usual sine.Once customs caught my rc-parts package from china and you would not belive the stubbornness of the old cow insisting that " these are electric motors, not rc toy parts"Next problem was that there was no tariff code for a 50 watt pmsm and her other suqqestions were not much better than "toy parts"Permanent magnet synchronous motors of over 2MW? Not really..Universal voltage motors of less than 100w? Well...not reallyAfter 30 minutes of arm-wrestling about correct tariff codes I told her that I would not care less even if she declared them as a "induction motor, 3-phase, over 500 kW"

author: Circlotron
author_rank: Super Contributor
timestamp: December 30, 2014, 12:08:51 pm
content: ^^ PMSM = PMSL

author: netdudeuk
author_rank: Frequent Contributor
timestamp: December 30, 2014, 07:17:20 pm
content: When people with model aircraft have the prop turning in the wrong direction, it's just a matter of swapping any two of the motor wires to the ESC. I'm not sure if this is of any help and what the practical / electronic implications might be but you could potentially use a DPDT relay to produce this effect ...