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Old Jan 15, 2004, 09:24 AM
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mmormota's Avatar
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Quote:
Originally posted by whanderson
[B]Free, open, and registration free schematics, source code, and design info is at:
http://www.microchip.com/1010/suppdo...n857/index.htm
It is at most a good starting point to a new design, but not a working firmware.
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Old Jan 15, 2004, 09:34 AM
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DIY controller

Hi,
Is there any application for model electric aircraft BLDC at microchip?? I know there is one very good for brushed motors....
Regards
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Old Jan 15, 2004, 09:37 AM
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Quote:
Originally posted by mmormota
It is at most a good starting point to a new design, but not a working firmware.
It is working firmware as presented. It does need some adaptation for use with RC systems. Should not be a problem for any PIC wonk. Is it your desire to have others do all the grunt work for you?
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Old Jan 15, 2004, 09:40 AM
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Re: DIY controller

Quote:
Originally posted by hadihf
Hi,
Is there any application for model electric aircraft BLDC at microchip?? I know there is one very good for brushed motors....
Regards
This will get you started:
http://www.microchip.com/1010/suppdo...n857/index.htm
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Old Jan 15, 2004, 09:43 AM
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DIY Controller

Hi,
We are talking about teamwork here..right..
Regards
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Old Jan 15, 2004, 10:06 AM
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Re: DIY Controller

Quote:
Originally posted by hadihf
Hi,
We are talking about teamwork here..right..
Regards
I helped get the ball down field. The Microchip app notes get you to 90% of your goal. What more does the team want coach?
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Old Jan 15, 2004, 12:16 PM
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Israel
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Hello everyone , I'm new here

I wonder if there is an ability to use the original CD-ROM controller ( with the sensors ) to drive the improuved CD-Rom motor.
Is the original CD-ROM controller able to vary speed , if not how much rpm is x50 ?
As i undestand all we need is to:
1. Rewind , remagnet the motor ( and gently return it back to its place ).
2. Replace power elements in the controller.
3. Make some ( simple ?? ) interface between Rx to CD-ROM controller input.

Thanks , Dany

third thread posting this in , am i totaly talking rubbish ?
i know that original controller is weak thats why i purosed to add power elements ( FETs )
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Old Jan 15, 2004, 05:25 PM
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From what I have learned, we really need to sense more than one phase. A triple op-amp setup would be better.

There is just not enough control of the motor with only one sensing position, and it is not reliable enought to reliably run the motor under a varying load such as an airplane propeller.

Know that I am not absolutely sure about anything I just said, but it is what I have heard in the past and it really makes sense to me.
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Old Jan 15, 2004, 06:21 PM
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Quote:
Originally posted by zagisrule!
From what I have learned, we really need to sense more than one phase. A triple op-amp setup would be better.

There is just not enough control of the motor with only one sensing position, and it is not reliable enought to reliably run the motor under a varying load such as an airplane propeller.

Know that I am not absolutely sure about anything I just said, but it is what I have heard in the past and it really makes sense to me.
read this: http://www.microchip.com/1010/suppdo...n857/index.htm
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Old Jan 15, 2004, 10:28 PM
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Ok, I have seen and read that document, but I think that the method of sensing only one point off the motor is not going to be precise enough to allow the motor to run correctly under the varying load conditions on a model airplane prop. In a dive, prop speeds up, if the controller misses a beat the motor will have to loose 2 more positions in order for the controller to regain proper control. With a input to the MCU for each of three phases, the MCU just waits for phase X to go high, then turns on phase Y. MCU waits for Y to go hihg, then turns on phase Z. Repeats over and over. Not that simple in real life of course, but it is the concept that counts here.

The Microchip controller might loose sync with the motor is my point. There is a good chance I am wrong, I am no EE, but if the RC filter works as well as you all hope, why are there no commercial controls that use that method? ESC companies would rapidly adopt that technique if it worked well enough to sell. It would eliminate at least 20 parts on average and you could make the PCB alot smaller. I can assure you that the companies have seen the AN857 document too, where do you think most of them get their brushed ideas from? Microchip App notes of course.

I think that despite the added complexity, a more accurate method of rotor position sensing should be used. I didn't think that a few months ago when I was trying to sort all this out, but it makes so much more sense to me now that a 3-phase sensing system be employed.
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Old Jan 16, 2004, 12:45 AM
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Hello all,

Check out the reference design. Looks like it is only specified to/capable of 8000 RPM. That is pretty poor with a 20MHz part. Surely someone can do better.

-John
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Old Jan 16, 2004, 08:37 AM
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Quote:
Originally posted by zagisrule!
Ok, I have seen and read that document, but I think that the method of sensing only one point off the motor is not going to be precise enough to allow the motor to run correctly under the varying load conditions on a model airplane prop. In a dive, prop speeds up, if the controller misses a beat the motor will have to loose 2 more positions in order for the controller to regain proper control. With a input to the MCU for each of three phases, the MCU just waits for phase X to go high, then turns on phase Y. MCU waits for Y to go hihg, then turns on phase Z. Repeats over and over. Not that simple in real life of course, but it is the concept that counts here.

The Microchip controller might loose sync with the motor is my point. There is a good chance I am wrong, I am no EE, but if the RC filter works as well as you all hope, why are there no commercial controls that use that method? ESC companies would rapidly adopt that technique if it worked well enough to sell. It would eliminate at least 20 parts on average and you could make the PCB alot smaller. I can assure you that the companies have seen the AN857 document too, where do you think most of them get their brushed ideas from? Microchip App notes of course.

I think that despite the added complexity, a more accurate method of rotor position sensing should be used. I didn't think that a few months ago when I was trying to sort all this out, but it makes so much more sense to me now that a 3-phase sensing system be employed.
AN857 says the following:
;************************************************* *********************
; *
; Notes: Sensorless brushless motor control *
; *
; Closed loop 3 phase brushless DC motor control. *
; Two potentiometers control operation. One potentiometer (A0) *
; controls PWM (voltage) and RPM (from table). The other *
; potentiometer (A1) provides a PWM offset to the PWM derived *
; from A0. Phase A motor terminal is connected via voltage *
; divider to A3. This is read while the drive is on during *
; phase 4. The result is the peak applied voltage (Vsupply). *
; A3 is also read while the drive is on at two times during *
; phase 5. The result is the BEMF voltage. The BEMF voltage is *
; read at the quarter (t1) and mid (t2) points of the phase 5 *
; period. BEMF is compared to VSupply/2. If BEMF is above *
; VSupply/2 at t1 and below VSupply/2w at t2 then no speed *
; adjustment is made. If BEMF is high at both t1 and t2 then *
; the speed is reduced. If BEMF is low at t1 and t2 then the *
; speed is increased. *
; *
;************************************************* *********************

BEMF is read 2 different times per rotation. If you want more accuracy, go for it.
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Old Jan 16, 2004, 08:39 AM
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Quote:
Originally posted by JohnnyS
Hello all,

Check out the reference design. Looks like it is only specified to/capable of 8000 RPM. That is pretty poor with a 20MHz part. Surely someone can do better.

-John
If 8000 RPM is not high enough, change the CCP module setup.
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Old Jan 16, 2004, 10:20 AM
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Ugh...




Ok, Because I think that the 3-phase sensing is better than Microchips method, I will work on it this way and you can do it your way Whanderson. Since you seem to know everything there is to know about this, perhaps you could build the demo circuit and tell us all how it works for the model motors. Also note that timing is going to probably need changed around because our motors tend to not be the high-wind, low current servo motors that they tested that code on. But you already knew that didn't you? It would be a real help if someone would build this and tell if/how it works. If it does work, I was off base with my comments, if not, we can get to work on a different design. My bottom line is...someone needs to build it. If no one else does it, I will do it. Only then will we know if the single RC filter is sufficient.


I have toyed with the idea of 3 RC filters, one at each phase. Perhaps this would discard the need for a triple op-amp and add simplicity.


I built Takao's old design, and I could not get it to arm. Even with a VERY low input, the controller would just go beep...beep...beep Yes, I adjusted my radio ALL the way down, both in all the EPA settings and trim. Anyway, I think that if there was a software fix for this portion of the code, it might run well as it is. Does anyone code AVR's here? I have a programmer and software to do it, I just don't know what and how to change it. The only thing that I am starting to understand is PBP, but that of course, is for PIC's, and this is not a PIC. All we need to do for now is push up the lower arming limit so I can get it to arm. If someone can do that, I will test the control and see if we can get this thing running. How is that for teamwork?





-Matt


Attached is a low-quality pic of the breadboarded Takao Shimizu design.
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Old Jan 16, 2004, 12:21 PM
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Quote:
Originally posted by zagisrule!
Ugh...
I built Takao's old design, and I could not get it to arm. Even with a VERY low input, the controller would just go beep...beep...beep Yes, I adjusted my radio ALL the way down, both in all the EPA settings and trim. Anyway, I think that if there was a software fix for this portion of the code, it might run well as it is. Does anyone code AVR's here? I have a programmer and software to do it, I just don't know what and how to change it. The only thing that I am starting to understand is PBP, but that of course, is for PIC's, and this is not a PIC. All we need to do for now is push up the lower arming limit so I can get it to arm. If someone can do that, I will test the control and see if we can get this thing running. How is that for teamwork?
I am willing to overlook your comments about me and offer to help with your arming problem. I do Atmel as well as PIC. Supply the source code you are using and I will take a whack at it.
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