While testing some variants and new versions of the power_dist board, I wanted to be able to simulate the types of loads that it experiences with a fully loaded robot. Some things are easy, like this capacitor attached to an XT30 connector:
I also have giant power resistors in a similar form factor:
However, a dumb load resistor isn’t a particularly representative load. Most likely, the loads that a power_dist will drive are active loads with switching regulators. When the output voltage is lower, the current will be correspondingly higher. That is especially important when validating pre-charge behavior, because it means that the current is much higher during the initial pre-charge window than it would be for a pure resistive load.
Thus, I made a tiny switching regulator to which I can stick a load resistor to the output.
Unfortunately since MacroFab discontinued their prototype tier, it no longer is as convenient to get one offs populated in the US. So this one I did by hand with a stencil, solder paste, a 3D printed frame, and some new tools, a vacuum pick, and a hot plate. I discovered you can get room temperature stable solder paste now — how convenient!
There were a few bugs… I managed to not have 0603 resistors for the voltage sense divider on hand, but had 0402 of the right values so just stuck a blob of solder to connect them. On the same resistors, I also managed to get the PCB labels swapped. Fixing that resulted in a board that does what it is supposed to!
This board has convenient connectorization for powering sub-components of your robot, and also provides a smooth pre-charge sequence so that you can safely connect a large battery to high capacitance loads. I made a short video to show it off.
Another of the tasks I’ve set for myself with regards to future Mech Warfare competitions is redesigning the turret. The previous turret I built had some novel technical features, such as active inertial gimbal stabilization and automatic optical target tracking, however it had some problems too. The biggest one for my purposes now, was that it still used the old RS485 based protocol and not the new CAN-FD based one. Second, the turret had some dynamic stability and rigidity issues. The magazine consisted of an aluminum tube sticking out of the top which made the entire thing very top heavy. The 3d printed fork is the same I one I had made at Shapeways 5 years ago. It is amazingly flexible in the lateral direction, which results in a lot of undesired oscillation if the base platform isn’t perfectly stable. I’ve learned a lot about 3d printing and mechanical design in the meantime (but of course still have a seemingly infinite amount more to learn!) and think I can do better. Finally, cable management between the top and bottom was always challenging. You want to have a large range of motion, but keeping power and data flowing between the two rotating sections was never easy.
My concept with this redesign is twofold, first make the turret be basically an entirely separate robot with no wires connecting it to the main robot and second, try to use as many of the components from the quad A1 as I could to demonstrate their, well, flexibility. Thus, this turret will have a separate battery, power distribution board, raspberry pi, pi3 hat, and a moteus controller for each axis of motion. These are certainly overkill, but hey, the quad A1 can carry a lot of weight.
The unique bits will be a standalone FPV camera, another camera attached to the raspberry PI for target tracking, a targeting laser, and the AEG mechanism, including a new board to manage the firing and loading functions.
Thus I spun a new revision r3, basically just to fix all the blue wires so that I could have some spares without having to worry about the robustness of my hot glue. While I was at it, I updated the logo:
As seems to be the way of things, a few days after I sent this board off to be manufactured, I realized that the CAN port needed to actually be isolated, since when the switches are off, the ground is disconnected from the rest of the system. Sigh. Guess that will wait for r4.