How to start BLDC motor only 1 turn with max torque and power - Page 1
Forum section: electronics / projects

author: cmcraeslo
author_rank: Regular Contributor
timestamp: July 28, 2020, 06:33:51 pm
content: Hey guys.I have a BLDC motor that I want to turn 360 degrees (only one rotation).I'm looking for the most efficient way (fast/powerful) to drive it directly while loaded.What would be the best strategy to make that happen? There are no hall sensors installed, but I can probably fit them somehow if that is needed.Motor is rated at 2kW and will be running at 48V.Gearbox and reduction is not possible.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2020, 06:47:30 pm
content: BLDC motor control is worth complete books. It's been written about widely. A lot of freely available appnotes and tutorials.Start by Googling and when in doubt, feel free to ask any specific question.Sensing the absolute rotor angle directly (hall sensors or otherwise) makes things much easier by removing sensorless estimation logic requirement so if you can add the sensors, do it. With sensors, there is absolutely no difference between "starting" or running at higher speed, it's all fairly simple.

author: Benta
author_rank: Super Contributor
timestamp: July 28, 2020, 07:01:46 pm
content: You have the completely wrong motor for this applicationA BLDC motor without commutation feedback is difficult to start already, and very, very, very difficult (read: impossible) to start under load.And even if you add Hall-sensors, angle precision will be miserable, position stability as well.Look for a stepper motor instead, this will do what you want.

author: thm_w
author_rank: Super Contributor
timestamp: July 28, 2020, 10:59:42 pm
content: Quote from: Benta on July 28, 2020, 07:01:46 pm2kW stepper motor?This is the biggest one I found:https://www.omc-stepperonline.com/nema-42-stepper-motor/dual-shaft-nema-42-cnc-stepper-motor-30nm-4248oz-in-8a-110x201mm-4-wires.htmlAnyway, need more info from OP, why is a gearbox reduction not possible? RPM/torque?

author: cmcraeslo
author_rank: Regular Contributor
timestamp: July 29, 2020, 06:17:17 am
content: Hello guys.To be completely honest, the title is a little misleading.I actually have round linear motor that has 3 coils on the outside + N/S magnet pairs in series on the rod.This is what i'm trying to move.

author: Benta
author_rank: Super Contributor
timestamp: July 29, 2020, 07:53:06 pm
content: Quote from: cmcraeslo on July 29, 2020, 06:17:17 amDon't mushroom us when asking questions. It decreases your popularity to far below zero.

author: dcarr
author_rank: Regular Contributor
timestamp: July 29, 2020, 08:00:10 pm
content: I think you need a high resolution encoder on the shaft. With that you should be able to do well.

author: jbb
author_rank: Super Contributor
timestamp: July 29, 2020, 10:27:47 pm
content: Yeah, it makes no sense to deliberately ask about the wrong thing.I’m sure there’s research on that kind of motor. Maybe it’s a Linear Permanent Magnet motor? Looks like the kind of thing that might be used for machinery - are special things like accurate positioning and low vibration needed?

author: langwadt
author_rank: Super Contributor
timestamp: July 29, 2020, 10:46:40 pm
content: Quote from: thm_w on July 28, 2020, 10:59:42 pmrating a stepper motor on power doesn't make much sense it is all about low speed torque

author: duak
author_rank: Super Contributor
timestamp: July 30, 2020, 12:33:54 am
content: The drawing has the term TPMLL which leads to a paper on Tubular Permanent Magnet Linear Launchers and the magnetic modeling thereof.I would say these things are also known as Linear Brushless DC motors. They operate very much like rotary BLDC motors except that the motion is linear instead of rotary. Both need a three phase drive of some sort. The currents' magnitudes and polarity have to match the position of the windings relative to the magnets to develop a force efficiently. This is called commutaion. Without having worked with LPDCMs I would expect that 3 hall effect sensors in proximity to the magnets could be used to determine the relative position of the windings to the magnets and switch the winding currents like those in a 6 step rotary BLDC. In essence, it will become a linear 3 winding stepper motor. seehttps://www.infineon.com/dgdl/an-1187.pdf?fileId=5546d462533600a40153559af4db1155To make the movement more smooth, the Hall effect sensor outputs could be interpreted as analog levels and more sinusoidal currents applied to the windings. For smoother operation, a linear encoder of some sort could be used to determine the position and thus the winding currents. I suppose the ultimate is to use a laser interferometer to determine the position. Here's a link to sinusoidal control:https://www.st.com/resource/en/application_note/cd00110782-low-cost-sinusoidal-control-of-bldc-motors-with-hall-sensors-using-st7fmc-stmicroelectronics.pdfIf the point is to accelerate as quickly as possible with the simplest driver and smoothness is not important, it might be possible to adapt a Sensorless BLDC driver that reads the Back EMF voltage off the windings as they pass over the magnets. Here's some of many links available:https://www.nxp.com/docs/en/brochure/BBCNTRLBLDCART.pdfhttps://www.st.com/resource/en/application_note/dm00072008-sensorless-sixstep-bldc-commutation-stmicroelectronics.pdf

author: mgwalker95
author_rank: Contributor
timestamp: July 30, 2020, 04:25:16 am
content: The most efficient way to drive a linear motor like this is going to be a control algorithm that will measure the position of the shaft and use sinusoidal control, But you can use Trap control if you want it easier to control and dont care about noise. the position of the shaft shouldn't be hard to measure because all you need is 3 hall sensors like a regular BLDC motor or you can use one hall sensor that reads the magnetic field as a analog value.Here is a good beginners guide from digikey:https://www.digikey.com/en/articles/how-to-power-and-control-brushless-dc-motorsOne big difference between a regular BLDC motor and a "BLDC motor" like this is that this motor can reach an end where the motor must stop, so your control algorithm must take this into account.

author: cmcraeslo
author_rank: Regular Contributor
timestamp: July 30, 2020, 04:58:18 am
content: Quote from: Benta on July 29, 2020, 07:53:06 pmIt was not my intention to mislead. It was just the fact that this is indeed a BLDC motor, just laid out differently. I was merely explaining what the setup and the reason behind the "1 turn" motor be.

author: cmcraeslo
author_rank: Regular Contributor
timestamp: July 30, 2020, 05:03:41 am
content: Quote from: duak on July 30, 2020, 12:33:54 amPoint is to accelerate as fast as possible, position and smoothness is not important as it will be stopped mechanically (and obviously controlled by the electronics). It is to replace pneumatic actuator.There's no Back EMF voltage when motor is stalled so I'm worried i'll get unwanted forward/backward moves when starting the commutation.

author: cmcraeslo
author_rank: Regular Contributor
timestamp: July 30, 2020, 05:05:43 am
content: Quote from: jbb on July 29, 2020, 10:27:47 pmI'm trying to replace pneumatic actuator (on/off), so no, position and and smoothness is not important. Only speed and power. It will be stopped mechanically. End switch will be available to stop it in the software.

author: Berni
author_rank: Super Contributor
timestamp: July 30, 2020, 05:30:34 am
content: Quote from: cmcraeslo on July 30, 2020, 04:58:18 amAsking an incomplete cut down question on forums is the best way of getting answers that go in the complete wrong direction. Quite often the person asking the question then finds out 3 pages of discussion later that what he is trying to do is the wrong solution for the problem to begin with.If this is some super secret project where nobody must know what you are doing then figure it out yourself. If you ask people for free engineering advice at least put in the work to describe the whole problem accurately. People here are friendly and happy to help, but not asking the question correctly just wastes everyones time.