Open-source ESC - is there a potential community?

3689473865?profile=originalGreetings - I have been following this site for some time and I believe that it is time for me to stick my toe in the water.  I am an electrical engineer in my day job and I design the commercial, industrial, and military equivalent of ESC's for various applications.  I have designed the schematics, pbc's, and written the complete firmware (some from application notes, some from scratch) for a number of different applications ranging from 10W applications to 1kW applications (all relatively low-power) and have interfaced with customers using UART, CAN, and I2C.  Most of my experience is with the dsPIC33F series microcontroller.

Though I have adequate experience with the ESC design itself, I lack any real experience with RC or drones besides my own tinkering (I have a Twin Star 2 flying with APM 1 w/ Oilpan).  As a result, I really need feedback for hardware features before ordering any hardware so that I'm not stuck with a first revision that few can use without modification.

I see two potential markets, planes and copters.  The primary requirement of a plane is high-efficiency while the primary requirement of a copter is high current capacity, quick response, and weight.  Correct me if I'm wrong here.  My current interests (and, thus, my development time) lie with the high efficiency mindset.  Most of the hobbyists that I have seen on here equate long flight times with large capacity batteries.  Since the motor consumes a majority of the energy contained in the battery, even modest improvements in efficiency can have drastic effects on flight time.  It would be great if the same board could work well for both applications, so it might be smarter to design for a copter and just use different firmwares, much like ArduPlane and ArduCopter.

A question that many of you are surely asking yourselves is "why not just use ESC32?"  Some time ago, I saw the post regarding ESC32 and noted a couple of things that interested me about the project.  Unfortunately, only the software is open-source, so that gives us - the potential community - little incentive or ability to improve the hardware.  I also noted that the board was 4-layer, which - even if the source is published - most of us don't have a full version of Eagle PCB to edit 4 layers anyway.  ESC32 also has a lack of a couple of features that I really wasn't sure about.  I'm not knocking their design, I think it is great!  In fact, I saw their design and took inspiration from many of their features.  They really did a fantastic job!  The tiny physical size of the ESC32 really suits their project.  I just don't believe that the design is very accessible to the community at this time.

I have taken the liberty of creating a schematic and layout (not quite complete, just need to add I2C hardware).  I made some design decisions, but I am open to changing those if I can be convinced that the community needs them changed.

So, now the proposal, reasons behind some design decisions that I have made, and a request for input (hardware input is most valuable at this point since I'm not working on software just yet):

  • Complete open-source ESC hardware and software using the STM32 platform
    • STM32 physical circuit does not currently conform to ESC32.  I wanted to make these code bases compatible, but ESC32 uses a timer other that TIM1 for the PWM output.  Using TIM1 as the primary FET controllers allows PWM on top-side and bottom side (you can use this to reduce losses), automatic dead-time insertion, and provides other benefits.
    • STM32F103V8 (any STM32F103x8 would have worked)
    • Low-cost development tools, $22 ( vs. the dsPIC's ICD3
    • ARM GCC as the compiler (I like CooCox for the development environment)
    • SWD programming/debugging is a given
  • I2C support
    • Does it need to support both 3.3V and 5V logic or just 5V?
  • Power supply
    • Should the STM32 3.3V requirement be supplied by an on-board voltage regulator or should it have an external supply requirement?
    • Should the ESC supply the typical 5V/2A output common to many ESC's?  This can add considerably to the board space requirement, but having a power supply for your servos that doesn't require an external BEC can be useful.
    • What is a reasonable voltage bus range requirement?  Right now, I'm targeting 6V-18V b/c I believe that this range takes care of 95% of the potential market.  Going beyond that in either direction has the potential to add cost.
  • CAN support
    • This isn't currently in the works b/c it adds to board space, but if there are many applications that demand it, then it should be considered.
  • PWM control
    • As currently designed, will work with a 3.3V or 5V input
  • Current limit
    • Uses a shunt resistor coupled with an op-amp circuit that allows precise real-time current monitoring.  On an I2C bus, this capability could be used to report the real-time current back to the controller (ArduPilot or any other interested party).
  • Clock precision
    • A precise clock requires some type of external oscillator.  The STM32 internal oscillator is rated to be within 1%.  This will affect things like closed-loop actual speeds, pwm frequency precision, and any reported values related to timing (such as reported speed).  It will also have some implications on UART maximum communication speeds.
    • The primary clock speed is limited to 64MHz when using the internal oscillator rather than the 72MHz capability of the part.  This should not be an issue since there is plenty of processing power on-board at 64MHz.
  • UART
    • Full FTDI access to the USART pins, just as the open-source community requires.  I'm sure that a CLI could be implemented using this.
  • Gate resistors on all FETs
    • This probably sounds crazy to some of you, but it gives a precise control of the FET turn-on characteristic.  Turning on the FET slowly (high gate resistance) increases losses on the FET, but drastically reduces the high-frequency noise on the voltage bus.  Turning on the FET quickly reduces FET losses, but drastically increases noise on the voltage bus.  This has a large impact on microcontroller resets, bus capacitor size, and a host of other noise-related design decisions.  Just mind your dead-times, a slow FET can really be a hazard if your dead times are too short.
  • Accessibility
    • 2-layer boards.  It makes the board larger, but much more accessible to the community!
    • Low component counts
    • Ease of programming and configuring the board for an operation on a wide variety of motors, from the simplest RC use to the most complex power-monitoring and reporting.
    • Design that passes batchpcb DFR so that the board is easy to manufacture (cheap)

There is more, but I'm really trying to keep it hardware-centric at this point.  What I would really like is for some number of people express interest, we create a google group, share eagle files, and really get it going.  It would also be great if we could put some cash together for the first couple of part and board buys so that we aren't sending UPS and digikey wads of cash for 1 and 2 part orders.

Thank you for reading through this looong post.  I will keep an eye on this post and will be responding conversationally.  In about a week, I will re-post any results and - hopefully - we can create a community around this idea!


*EDITED TO ADD google groups page created for this project is located here*


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  • Count me in :)

  • I'm not really sure how $20 for an ESC is overpriced?  I can get a full-featured 100A ESC with data logging for $100 so...  seems pretty good to me?

    Anyway, +1 to Brad as well.  I hope this effort isn't limited to 4S or something.  I need 8S minimum, and would hope for 12S capability.  

    If you restrict it to 5S or something like that, you will limit your market to small multicopters, a market which is saturated already. 

  • Brad's point about higher voltage capabilities is very good. Higher voltage is a much better way to increase power levels instead of  just pushing more amps through everything.

  • rubbish ! - the market is not saturated at all , there are over priced ESC each piece cost about 80 dollar !!!

    no one wants 200 amp , we need good and safe  ESC that would do the job.

    today the only good ESC are over priced !

  • I applaud this effort.  There are just two things I'd like to comment/solicit feedback on relative to the introduction.

    Inductive ringing on the power bus can be a huge problem.  However, I thought adding gate resistance between 5-20 ohms or more was a standard/best practice for a whole litany of reasons.  Perhaps adding an option here would make the product more flexible, as would allowing the user to select off-board ringing mitigation capacitors and even the power MOSFETs themselves.  Which leads me to my second observation...

    Your "target market" is not necessarily the majority of ESC customers, in fact, it is precisely those experimenters for whom "off the shelf" units are unacceptable.  Yes, most hobby R/C applications use 5S LiPoly or lower, but I'd bet that the people in this community who are pushing the envelope, so to speak, are interested in more esoteric results.  Witness the recent "beer lifting" contest entrants as a good example. How about a "brew your own" foundation for an ESC that could do 200A at 10S (42V ~ 34V under load).  The market is saturated with ESCs which are mostly fine for 100A and 5S.  The options are very few (and expensive) for the big ships.

  • wow guys great work..... 

  • Great project Jason, 

    I am a multirotor user, and I have a lot of tips to give u for multirotor use:

    1. make it easy to install ! , most people attach it to a 10X10 mm aluminium square rod, make it easy to install ( also use as heat sink)

    2. make it easy to install ! think that the user should connect 8 of those it a small compartment . put all the connection along one side power and communication ( on the narrow side of the rectangle - not the way you did it) also add two holes to attach it.

    2.5 keep in mind that the users are going to cover it with shrink tape ! we don't like open electronic to dust and water.

    3. add protection against over heat and over current ( don't make it shut down , but reduce output if over heat or over current is sensed )

    4. leave the power supply out if it make it cheaper 

    5.put a protection that if one fails all the other will keep on working (if I2C is used)

  • Nice, please consider designing them so they can easily be stacked on the same power and/or I2C bus.

  • This is such a great idea and had thought the same some months ago .

  • Jason,

    for what its worth, my Olecopter, uses 4 120 amp ESC, and the intention would be to go much higher. I think the future for a heavy lift UAV VTOL would need a minimum of an ESC over 200 Amps, at 37 volts. I think marrying the ESC to an Auxillary Power Unit is probably the next step as the energy density of liquid fuels is much greater than batteries. Whilst having a single PCB is attractive, it would require whole PCB's to be replaced in the field, just for the failure of a single ESC component. At the higher Power outputs heat management does become an issue. As an example, the plettenberg Motors consume such a lot of power, using multiples of these motors, would necessate 400+ amps capacity.

    regards Eddie

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