In summary, it's a hybrid of digital and analog. To the standard quadrature encoder slit counter, we add sensing of the light levels as each slit covers or obscures the phototector. So we get e.g. 200 slits times 8096 light levels inside each slit equals over a million positions. It's so much data that we need an FPGA to process it fast enough. You can breath on the arm and it can sense it.
There is a constant battle between writing for sales/investment and writing for technical disclosure. Sometimes we get some chocolate in the peanut butter. It's certainly not phony, and I'm happy to answer any questions that anyone has about the real technical abilities.
The $2,999 price was for the Dexter 1 which was available at the time the article was written. The current generation is the Dexter HD which is more capable, much easier to build, and (as you noticed) more expensive.
The encoder / motor controller logic is a bit more complex than that. Because the encoders are analog / digital hybrid they generate far more data than standard quadrature encoders. The FPGA is doing huge table lookups, ATAN2, PID, Dithering the motor driver, and all of that at 5 MHz end to end, so we have a 200ns response.
How huge is huge? The rest of the chain sounds pretty straightforward, even at 5MHz. That's not to say that an FPGA is wrong for the application, but nothing in that list screams "must use FPGA" to me.
However, the whole program screams "get to market, then iterate" to me, which is a very effective way to move forward with a product like that.
Note: I've shipped products doing continuous signal processing on DSP, GPU, CPU, SoC, and FPGA. (MCU eventually... Give me time.) I did the mental swag on the described processing chain...
It could probably be handled by the realtime cores on the BeagleBone Black's SoC, or perhaps by an XMOS part, but if someone already knows how to develop for FPGAs there's not much of an incentive to try to shoehorn the task onto a microcontroller.
Anything that involves reading from moderately-to-insanely fast ADCs is a natural FPGA application, especially if multiple channels are involved.
One of the founders wrote a FPGA language. I suspect it's the tool the team knows the best, but may not be the most price optimized. I think that's fine for now, especially since it's still one of the most affordable arms available.
1. The encoders on the Dexter arm are at the joints because that gives us the ability to compensate for backlash in the drive system.
2. The motor dance issue happens because the feedback loop on most control systems isn't fast enough. With the FPGA, our control loop is 5 MHz / 200nS so we can correct before an oscillation has time to happen.
3. Our encoders give more than 1 million CPR (clicks per revolution) so we can sense an error before it has time to become an issue that might lead to oscillation.
(2 and 3) are the real magic of the arms design
4. Yes, Harmonic drives are hell. And they are not actually free of backlash, it's just "soft" e.g. they bend slightly. At this point, they are the best solutions, but we have prototypes of a cycloidal drive that costs less (in quantity) and gives us better performance. There are issues to work out, especially related to smoothness and wear, but we are making progress on it.
In summary, it's a hybrid of digital and analog. To the standard quadrature encoder slit counter, we add sensing of the light levels as each slit covers or obscures the phototector. So we get e.g. 200 slits times 8096 light levels inside each slit equals over a million positions. It's so much data that we need an FPGA to process it fast enough. You can breath on the arm and it can sense it.
There is a constant battle between writing for sales/investment and writing for technical disclosure. Sometimes we get some chocolate in the peanut butter. It's certainly not phony, and I'm happy to answer any questions that anyone has about the real technical abilities.
The $2,999 price was for the Dexter 1 which was available at the time the article was written. The current generation is the Dexter HD which is more capable, much easier to build, and (as you noticed) more expensive.