The boards are from OSH Park (formerly DorkbotPDX PCB Order, you might be able to tell by the color scheme). It's a terrific deal for small boards: $5/in^2 for three boards. For example, this board was 3in^2, so I got six for $30. The total time from order to delivery was a bit under three weeks.
These boards have exactly the same logic section as v1.1, but an entirely redesigned, smaller power section. Instead of massive D2Pak-7 FETs, it uses Super SO-8s. These are extremely popular in RC ESCs because of their low cost, relatively high power density, and thin package (more compact and easier to heat sink). I'll be trying two different FETs: the Infineon BSC016N04LS G (40V, 1.6mΩ) and BSC028N06LS3 G (60V, 2.8mΩ).
One difficulty with using Super SO-8 FETs is that, although it's possible to solder them from the sides, good thermal performance will probably only be possible if the drain pad under the chip is reflowed. The DRV8301 magic chip needs its ground pad reflowed anyway, so this doesn't add any extra steps for me.
|It's just one trip to the bagel toaster.|
Even though v1.2s is only reduced to 2/3 of the area footprint of v1.1, there's also a significant reduction in height thanks to the low-profile FETs:
The left-most board is a v1.1 without any wires or external capacitors. The middle board is v1.2s with XBee headers fitted. The right-most board is v1.2s with no XBee headers. In the smallest configuration, it's 7mm in thickness. The tallest components are now the three pushbuttons, and even those are lower profile versions of the ones in v1.1.
Here's what it looks like wired up:
The total weight with 16AWG wire and connectors is 35g, compared to 66g for FFv1.1 with 14AWG wire. Most of the weight is in the wire and connectors. The FETs are nowhere near as beefy as the D2Pak-7s, but I think the 40V/1.6mΩ version might still be able to handle 20A continuous and 40A peak current. (Compared to ~40A continuous and 75A peak for v1.1.)
The first assembled board survived power-up without exploding, so therefore it was flightworthy.
Poor Talon quad - it really has become a test bed for just about every piece of hardware. It has so much stuff attached to it now in such a disorganized and heavy way. I put a single FFv1.2s on, loaded with identical firmware as the other three v1.1's. Since they're running closed-loop RPM control now, the slight mismatch shouldn't matter much. Here it is ready for its first test flight with the Chair of Safety still in place:
After a few successful indoor test flights, I also took it outside a few times with the data collection running. The data is from the v1.2s, which was fitted with the XBee. The other three v1.1's are running blind. Here are a couple data segments showing climbs and fast maneuvers:
RPM tracking looks good and the average current is around 5A, peak 10A. The FETs are room temperature and I suspect I won't be able to even get them warm until I try it out on the CineStar...
One more motor controller done. Time to start a new one. Here's the teaser: