Sensored Brushless Motors: How do they work

[losikid]

I'm trying to do a little R&D work for a Motor In Wheel crawler i'm going to attempt to build while i'm in a machining class this winter. So theres the some background info.

As of now i'm just trying to get everything worked out, so far i've got a basic idea of everything. Now i'm trying to work out details like the stall in between each wheel which will act like open diffs. Not very good for crawlers.

So after a little research i found that a sensored brushless motors could be a good candidate to eliminate the stall. I've read that the sensors in a sensored brushless motor actually will sensor speed that the output shaft is spinning.

So for you motor gurus could you please explain to me how the esc determines the power going to the motor and if it goes off the speed of the motor or is it another variable that determines. If it is another variable could it be used to eliminate the stall?

Also any other ideas to get rid of it?

[benoj]

i always thought the sensor was to tell where the rotors position was to the esc to prevent low rpm cogging

[losikid]

Yea, but is there a way to use that technology to make all the motors spin at the exact same speed or rpms, if one side has more traction than the other or a stress load

[Harley]

Originally Posted by losikid

So after a little research i found that a sensored brushless motors could be a good candidate to eliminate the stall. I've read that the sensors in a sensored brushless motor actually will sensor speed that the output shaft is spinning.

So for you motor gurus could you please explain to me how the esc determines the power going to the motor and if it goes off the speed of the motor or is it another variable that determines. If it is another variable could it be used to eliminate the stall?

Also any other ideas to get rid of it?

You must be reading on a different type of sensored motor, not the kind most typically used in RC.

[Harley]

Originally Posted by losikid

Yea, but is there a way to use that technology to make all the motors spin at the exact same speed or rpms, if one side has more traction than the other or a stress load

Not affordably, but anything is possible.

[losikid]

Originally Posted by Harley0706

You must be reading on a different type of sensored motor, not the kind most typically used in RC.

Its sensored brushless motors for sure. Nothing precisely toward rc motors except on here http://www.team3sixrc.com/rcelectronics101.htm and just about everywhere i go it seems that it mentions a sensor on sensored brushless motor that senses speed to make the motor more efficient, so theres gotta be something the esc does to use that info. I've never ran or programmed a brushless setup so i'm not exactly sure what is available in programming it. Although it seems there is a way to relate the speed of the motor to the throttle position on my radio. I know on a brushed unit that its just pumping more amps into the motor to get it to go, but a brushless you have sensors that are detecting the position of the rotor and how much power to give to a certain spot to make it spin. What i can't find out is what the esc uses in order to control where that power goes and how much power to use. I'm hoping there is a direct relationship to the position of my throttle on my radio and the speed of the motor. So lets say 25% throttle gives me 25% of the speed the motor is capable of, even under a load.

[Harley]

Originally Posted by losikid

So lets say 25% throttle gives me 25% of the speed the motor is capable of, even under a load.

No it's not a direct relationship, that's just not really possible due to load. The sensor is really only functional at low speed for startup.

[losikid]

how difficult would it be to make it a direct relation ship sense the sensor is already there

[EddieO]

I would suggest going over to maybe rcgroups.com (which is mostly a plane website).....they have been using brushless much longer than us and they have tons of info over there on how the motors work and such....might be worth just using the search feature to see what threads it brings up...you will probably find lots of different size motors too, which will probably suit your project a lot better than what we currently have over in the rc car arena.

I've been thinking of the same type of crawler for a while now.....I even sketched out some of my ideas for it. The only problem I came up with is that it would be nearly impossible to drive efficiently and complete most courses in the alloted time......just massively complicates things.

Later EddieO

[losikid]

Originally Posted by EddieO

I would suggest going over to maybe rcgroups.com (which is mostly a plane website).....they have been using brushless much longer than us and they have tons of info over there on how the motors work and such....might be worth just using the search feature to see what threads it brings up...you will probably find lots of different size motors too, which will probably suit your project a lot better than what we currently have over in the rc car arena.

I've been thinking of the same type of crawler for a while now.....I even sketched out some of my ideas for it. The only problem I came up with is that it would be nearly impossible to drive efficiently and complete most courses in the alloted time......just massively complicates things.

Later EddieO

Yea i've got everything down except the electronics with the open diff reaction. But theres so many options available by doing this.

[JohnRobHolmes]

RC esc's are voltage based, so they feed as much current as needed to keep the motor spinning as fast as the load will allow at the given timing advance and RMS voltage. They are about the "dumbest" motor controllers you can build. Input set voltage, pass as much current as the back EMF allows. To keep the wheels turning the same speed you will either need a velocity feedback loop that will adjust the throttle of each controller (relatively simple), or you will need controllers that talk with each other to adjust the motor speed to the lowest in the bunch (fully custom controllers).

Are you familiar with arduino products? Can you program?

[losikid]

No i'm not familiar with arduino products and i don't know how to program but i learn fast and i like playing with circuit boards and such as funds let me, right now i have a custom radio i made that works great on the pc sim but i can't get it to bind (i think bad rx but i'm not paying to ship a new one in from china (hobbyking) I also had some one tell me that a double loop double PI regulator (speed and current) can keep the speed costant to the reference speed until the power requested (speed*torque) is bigger than the power the motor can supply which i'm guessing is what you just said.

How hard would it be to do the velocity feedback loop you speak of,

[losikid]

BUMP

Next I've done some research on double loop pi regulator and i think that it will actually work i found a diagram which shows what i've been looking for, but this is off a simulator software not an actual esc, i have yet to find a esc that has one, probably out there but not very popular with google. Here's the link go to the last page, i plan on reading this whole thing when i have some free time, it showed some diagrams of the controller it is using so i might be able to make my own. Here's the link http://www.powersimtech.com/manual/T...p%20Design.pdf

Also JRH could you discuss a little more about what your ideas are,

[losikid]

bump

[ThunderVP]

So far there are no R/C ESCs that "link" together to run multiple motors in perfect sync. This would be a great addition for the dual motor monster trucks and crawlers alike.

Another option to get the feedback you are looking for, would be to add an encoder on each wheel. This would give exact rotational data. Although you would need to run the encoders into a programable controller of some kind. This could then link between the Rx and ESCs and alter the control to each ESC to keep them running in sync.

If you build a 4 motor in wheel setup, I would try it just running the motor drives all together and see if the change in individual wheel speed even effects performance that much.
It may not even need more than some creative mixing from a programable 6 channel radio. Good luck with the build.

[losikid]

Originally Posted by ThunderVP

So far there are no R/C ESCs that "link" together to run multiple motors in perfect sync. This would be a great addition for the dual motor monster trucks and crawlers alike.

Another option to get the feedback you are looking for, would be to add an encoder on each wheel. This would give exact rotational data. Although you would need to run the encoders into a programable controller of some kind. This could then link between the Rx and ESCs and alter the control to each ESC to keep them running in sync.

If you build a 4 motor in wheel setup, I would try it just running the motor drives all together and see if the change in individual wheel speed even effects performance that much.
It may not even need more than some creative mixing from a programable 6 channel radio. Good luck with the build.

I've had jrh and a guy on rcgroups tell me similar things but i haven't got a response on how to build it. I see having the double loop idea would be ideal for any application of crawler 1 motor, 2 motor, or my idea 4 motors. This is because from what i have read if i tell the esc to do 25% of the max sped of the motor it will make that motor do 25% as long as the power is there to support it. So with a shaft driven 1 motor you will always have the speed you tell the motor to do. This comes in handy when your crawler gets in a big bind, you give full throttle to get out of the stall but once traction is loss you have full wheelspeed for a amount of time depending on your reaction. But this new esc will instantly cut power bringing it down to the desired speed in a second or less. Same goes for multi motor crawlers, it will also keep the motors in sync so no more stall between axles or in my case wheels, just imagine a moa with no stall, now there'd be no reason for a shafty. It makes you wonder why no one has made one, yet i think its because sensored motors in the hobbyworld is just now becoming popular

[Dquill78]

I know this is an old post, but it comes up on search results about reading the sensors on a sensored brushless motor.

You can do what OP is asking, and it's actually a really cool project. It's just going to take a bit more than a few pieces of wire and off the shelf parts. What you'll need to do is use a microcontroller(MC) to read a sample of the signal from the sensor wires. I say sample because the sensors still need to be connected to the ESCs so that the ESC still knows the motor position for proper phasing of the commutation phase. You probably only need to sample one of the sensors on each motor, at least to start.

Additionally, and this part was being missed, is the radio RX unit cannot be connected to the ESC's (other than just to get power). The signal pins on the rx unit for the channels for the motors need to only connect to the MC. The signal wires for the ESC's also need to connect to different pins on the MC. You can't have the ESC's get a signal directly from the rx unit because you won't be able to override that signal. You need to program the MC to read the pulses it gets in from the rx unit so that it knows what the user wants the crawler to do. You also have to program the MC to produce the pwm pulses to send out to the ESCs. Additionally you'll program the MC to read the pulses it gets from the sensor wires so that it knows how fast a motor is spinning. Now that all user input is having to go through your code in the MC before any outputs are affected, you can program the MC to do anything you want. Throttle position can become speed control by programming in a simple control loop where the MC reads the pulses in to know what speed the user wants, and modulates the output PWMs that go to the ESCs to based on that desired speed and the feedback it gets from the motor sensors to measure if it's below, at, or above that speed. A well written and tuned control loop will handle changing load just fine, and keep the speed quite stable within the load limits of the motor. Just to clarify, this control loop is in firmware you've written.

As for traction control when you have individual wheel motors, yes. That's nearly the same. It's just the speed control described above with a modification to your code. You'll still read in the pulses from the rx unit that would normally mean throttle position, and consider those a desired/target speed. The modification is that you'll read the sensors from all motors and keep them all at that speed. Ideally you'll allow some slippage from one side to the other to make turning easier and so you don't force a tire to break traction in order to turn. So maybe you'd want to have the average of the measures motor speed match that speed, and also modulate the individual motors so that their individual measured speeds are within 10-15% of each other.

This is a lot of coding. A real microcontroller will be better and simpler than something like a raspberry Pi for this. The learning curve is high because you have to first learn C/C++ programming, learn about control loops or control systems and about the signals used (mostly servo PWM). Arduino is the likely choice for a newbie because there's a ton of learning materials out there as well as some libraries that reduce the amount of code you need to write. I really like this individual wheel motor with traction control idea though. It would be really cool to pull it off. It's just going to take a lot of work.

[JohnRobHolmes]

It is a lot of coding. I ended up working with another engineering group on basically this sort of project, where they took our ESCs and motors and used an IC to control the entire thing. Some fancy pants robot, with fancy pants prices to support the fancy pants engineering time. I had nothing to do with the control IC, just supplied the motors and ESCs. They estimated about 100 hours to get the coding right when I asked how much labor was involved.

[jtthebiggafigga]

You might want to look up the heli speed controllers. They are not sensored but they have a governer mode.