The Problem
It seems as though everybody who builds a quadcopter uses 4 individual PWM ESC's (that are often zip-tied to the rotor arms).
http://ng.uavp.ch/moin/UserCopters
http://quadcopter.wordpress.com/
http://scsuquadcopter2010.blogspot.com/
http://t413.com/news/category/quadcopter
http://vrhome.net/vassilis/2009/01/q...bly-completed/
etc...
Overall it's a bit messy and there are wires and small PCB's everywhere. Some people also convert their ESC's to receive I2C commands instead of PWM since it's faster and easier to pair with their flight controller.
The Solution
This is a 4 channel motor controller based on Atmel AVR's that can be controlled using serial, I2C, or even a standard PWM input. This is a single circuit board with 4 sets of 3-phase motor outputs. Each of the four segments on the board can power up to a 30A motor (so 120A max for the entire board). Each of the four segments is controlled INDIVIDUALLY (required for quadcopters).
In addition, the board can act as a master power management board for any other boards you hook into it. Your battery will plug into this controller (think Dean's connectors), and there will be regulated 3.3v and 5v outputs that can be used to power your flight controller or other circuit boards on your aircraft.
Possible Uses
Quadcopters! That's what this is designed for. That being said, this would work on practically any model that uses more than one brushless motor (4 motor electric planes maybe?).
Form Factor (roughly 4" square)
The board is designed to be a part of a low-height modular stacking system that I'm using for my quadcopter. I'm also developing an AVR-based flight controller (with full IMU) that can stack on top of this, as well as other add-on boards. There is a common communication bus between all boards stacked together. I can share more about this if anyone is interested (in either the modular form factor or the AVR-based flight controller board). The size of the board was made to fit the custom centerplates I'm having cut for my quadcopter.
Features
- 4 individual brushless motor controller channels on a single circuit board.
- Very fast update rate (using 20Mhz AVRs so there's a lot of room to spare!)
- Up to 30A per motor.
- Uses Atmel AVR's, so you can reprogram it as much as you like.
- Current limiting/feedback per motor (automatically reduces throttle if a particular motor exceeds the maximum current you've set - doesn't just shut the motor off like other ESC's).
- All surface mount components.
- Open source!
- Low-profile board (most likely less than 7mm thick).
- Serial/I2C digital communication/control.
Availability
I am only gauging interest at this point in order to determine if I should make extra boards to sell. If there is interest, I'll have extra PCB's made and assembled for anybody that wants one. I'm expecting to be able to sell them for around $120.00.
Are any of you interested?
Comments
My particular quad is going to be roughly 28" in diameter. With a quad of this size I don't think a rotor mounted ESC vs. a central ESC will make any difference at all. After all, each ESC and the wiring weighs almost nothing relative to the frame, motors and batteries.
I like the cleanliness of routed motor wires all meeting on a central board that can be controlled through a common data interface. I also like how the stacking design completely eliminates all wires from the flight controller to the ESC - everything is available through the stacking connector.
Another advantage to this design is the lack of data conversion. More specifically, there's no need to generate PWM on your flight controller, and there is no need for the ESC to decode the PWM coming in. This also adds more accuracy and resolution when controlling motor speed since these variables can be sent to the ESC as data bytes rather than relying on the ESC to decode the difference between a 1ms pulse and a 2ms pulse. This fine-grain control could be really advantages to a quadcopters stabilization routine.
Although stock Mikrokopter frames don't seem to exploit this obvious advantage of discrete ESCs - they do this instead.
I guess a multi-channel ESC would be advantageous on small from factor quads where the added weight of heavy-gauge drive wires would still be lower than the weight of 4 discrete ESCs. Right?
Because 1 burned esc better than 1 burned controller with esc :)
It reduces replacement costs when fails.
And long motor wires possible but not right solution
It looks like a lot of people are mounting their ESC's on the centermost part of their rotor arms, so the wires wouldn't have more than 2" added to them at most to reach the edge of a centrally located ESC.
Great point though!
Also, the longer motor wires act as baby antennas and radiate the motor clocking signals.
Regards,
TCIII
MikroKopter probably went with discrete ESC's to minimize the length of the 3 phase motor wires. It's lighter to have 2 longer battery wires than 3 longer motor wires.
Sounds interesting. I would consider purchasing your board.
Regards,
TCIII
I would definitely be interested if they come up for sale.
Cheers,
Sam
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