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Old Dec 15, 2009, 03:15 PM
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IDEA: DIY Brushless ESC w/ I2C & PWM support (for quadrocopter)

Hi Guys -

I have been doing MUCH research and analysis of various setups. etc. The goal is to eventually build my own custom quadrocopter.

It seems that the high-end quads out there are using I2C ESCs. I know that some have modified TowerPros, and Rusty has created an I2C->PWM converter, but I am seeking something more elegant...

There are TONS of free schematics out there, but oddly I can't seem to find one for a brushless speed controller. It can't be that difficult, right? I'd imagine it is just 3 channels of FETs and a microcontroller - anyone have knowledge of this?

Once we have a solid circuit, we can then make our own ESCs. I am thinking to use ATMega328 w/ arduino bootloader for easy programming, but of course this is debatable.

Some of the advantages of having our own schematic:

-Can group buy and have true I2C ESCs cheaply.
-Can design the PCB in various form-factors, including a single board with multiple ESCs on it (think a single board with 4 seperate channels for quadrocopters
-Can experiment with various other aspects (feedback, rpm sensing, etc etc etc).

Comments, Questions, all welcome!

Thanks,

-Jamie
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Old Dec 15, 2009, 04:06 PM
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I would add dynamic braking so as obtain some deceleration control of larger inertia props so that quad stability is not compromised when using them. Secondly, to dump the back-EMF regeneratively back into the battery.

BTW, have you check in the DIY or power sections of RC Groups? I seem to remember brushless esc schematics being in either place.

Dan
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Old Dec 15, 2009, 04:46 PM
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Look for Sensorless BLDC App Notes

Pick your flavor of micro and then go to their web site and search their application notes for: Sensorless BLDC

Here's a link to one for an atmel.

http://www.atmel.com/dyn/resources/p...ts/doc8012.pdf
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Old Feb 02, 2010, 07:16 AM
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Hi !
i have studied a little bit about bldc motors and their control.
but i am having problem with understanding the starting phase of bldc motor , i have read we have to bring the rotor to a known position , what is the known position ?? and how to bring it and by what technique the controller comes to know that now its the desired ??
please help me !!!!
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Old Feb 11, 2010, 01:25 PM
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sensors or trial and error

I believe that you either need sensors to "sense" the true position, which could be done through halls, encoders, etc or you run through a sequence and try and bump the motor by trial and error. Then when/if the motor moves you can measure the back-emf and figure out where the motor is. This is most likely why typically ESC might appear jumpy at low speeds or when just starting.
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Old Feb 11, 2010, 03:44 PM
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I like arduinos.

why i2c thou? are you going for an autonomous craft or something that you control?

if you want to control it, it may make more sense to use serial so you could use something like a xbee transceiver.
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Old Feb 11, 2010, 04:00 PM
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I question the need for I2C. You can get great results with cheap PWM ESC, there are so many examples of these around. I mean, I2C is great but at 4x the cost it's not worth it.
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Old Feb 11, 2010, 07:48 PM
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Quote:
Originally Posted by dcaspi View Post
I question the need for I2C. You can get great results with cheap PWM ESC, there are so many examples of these around. I mean, I2C is great but at 4x the cost it's not worth it.
While decent stability is achievable with standard i2c ESCs, there must be a reason that so many multicopters are going with i2c ESCs:

-Mikrokopter
-X3D BL
-Shrediquette
.. and others

i2c allows a faster update rate than PWM ESCs. This has been proven.

Not to mention that the microcontroller is then relieved of the strain of generating PWM pulses.

Also, with the great work of quad and Arthur P (and others), you can now modify Turnigy/TowerPro ESCs to work with i2c, so the 4x cost point is no longer valid:

http://www.rcgroups.com/forums/showt...766589&page=45


-Jamie
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Old Feb 12, 2010, 12:36 AM
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Kiryat Yam, Israel
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Quote:
Originally Posted by asifjahmed View Post
While decent stability is achievable with standard i2c ESCs, there must be a reason that so many multicopters are going with i2c ESCs:

-Mikrokopter
-X3D BL
-Shrediquette
.. and others

i2c allows a faster update rate than PWM ESCs. This has been proven.
You can update at ~500Hz with many PWM ESCs. I update @ 100Hz and I think it's an overkill. Why do you need more than that?
Quote:
Not to mention that the microcontroller is then relieved of the strain of generating PWM pulses.
At least with AVR (e.g., Arduino) it's done in h/w, no strain.
Quote:
Also, with the great work of quad and Arthur P (and others), you can now modify Turnigy/TowerPro ESCs to work with i2c, so the 4x cost point is no longer valid:

http://www.rcgroups.com/forums/showt...766589&page=45


-Jamie
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