Excellent its good to have someone on the team who has prior experience particularly with BLDC and FOC as I'm just a newbie with these ;-)I'm quite familiar with motor control applications.
Sure for single motors that's more than adequate, but when dealing with the number of motors I am going to support on this board it becomes a bit more tricky.The Silabs chips come in 25MIPs and 48MIPS. If that isn't fast enough for you to read a 200k sample/sec ADC you are doing something wrong as it only takes 1 instruction to move the ADC register into memory and 1 more to copy it into the SPI bus register.
I am familiar with the FTDI stuff as its very common, but does the Silabs support Linux and Mac as I need both in addition to Windows of course.I've found there are only 2 USB controllers with decent drivers: FTDI (d2xx) and Silabs (usbxpress).
As I mentioned before :Brushless DC motors require 3 H-bridges (1 per coil) so control is not cheap. Hall effect sensors are usually needed for variable torque as you can't deduce the EMF.
Also BEMF can be detected using cross over detection and averaging to reduce noise effects, infact sensoless BLDC control is now quite common, as are low cost sensorless motors. But obviously having sensors helps a lot ;-)The main design is centred around 12 current sensed half bridges and so could theoretically cope with 12 DC motors , 3 bipolar stepper motors, 4 BDLC motors or combinations there of.
Obviously with that kind of encoder the job is a lot easier but I am wondering if the combination of hall effect feedback and BEMF detection along with current sensing can get at least some of the way for the obvious cost benefits.If you want any kind of resolution you /need/ an optical encoder (preferably with 8000 or more lines per rev).
Again when considering multiple motors I think the situation changes, I think that the Xmos solution may well shine in such difficult scenarios vs dedicated hardware based solutions. In fact half of the point of this whole project is that the solution is just software!There is also the issue that the XMOS really isn't that fast when compared to a hardware solution. 60k rpm motors are pretty standard and with 8000 line encoders (x4 for quadrature) you need be processing data between 8mhz to 32mhz which you will have a hard time doing without hardware decoders.
As regards the Stellaris kits, I agree they are very handy with good software support/libraries etc. .I purchased an LM3S3748-B dev board including screen and USB before TI bought luminary, but haven't used it for a while.
On the display and SDRAM front I have a enhanced design version of this project with up to 8MB of SDRAM and an L2, but that's a fairly specialised design. My goal here with this project is to significantly reduce the cost and make it more flexible, approachable and a general control dev board.
Yes cost is the enemy here, which is why I am trying to reduce requirements like the complex encoders etc..I am interested in non-traditional motor solutions with an XMOS design. Brushless DC motors and optical encoders are pretty expensive when compared to stepper motors even if control is easy. I'd be interested if anyone knew of cheap sources of optical encoders. Lowest price I can find is around $20-25. Nema23 Steppers with 166oz torque can easily be bought for $5 in higher volumes.
Commercial servo motors (brushed dc + encoder) run over $100.
regards
Al