[techhelpbb]

Originally Posted by PAR_WIG1350

One idea is to have a potentiometer input to recreate the function of an RC servo, but with whatever motor, transmission, and range of motion you want.

If people are using PWM they wouldn't have any way to inform the microcontroller the maximum value of the potentiometer. So I suppose the value of that potentiometer would have to be fixed? Maybe pick a common value? Also the taper of the potentiometer would need to be fixed, for example linear instead of audio.

Maybe we could outfit the PWM module with a simple serial interface that can be set up once and left that way?

The headers placed on either side of the fan extend all the way down to the power module. They are rather tall, but I envision metal standoffs providing the structural support for the top of the stack so that is not a huge issue in terms of durability. The inputs wires could stick out the sides that are already blocked so they wouldn't affect airflow.

Another concern with the length of the extended headers between the power module and the interface module is that the parallel traces getting longer would be little antenna. Probably not so bad for the PWM signals but it might introduce noise on any current or voltage signals sent in analog from the power section to the interface module.

I suppose instead of really, really tall headers which would be hard to come buy one could use belt cable or PCBs with typical 0.1" headers. However, in either case passing up the sides of the module would block the side intake of airflow leaving access on only 2 sides.

The air gap is where it is so that the intake airflow could pass over the processor, which would likely be mounted on the bottom of its module.

I've got a bunch of ARM processor modules, including chips from Analog Devices, ST Microelectronics, and NXP and I can't say that I feel the need to provide them forced air cooling. Even at their performance level they don't generate a bunch of heat.

However, if you put them physically above the MOSFETs which could disipate 80W-100W of heat under the right circumstances as the heat rises it'll basically cook the chip. In fact in a really bad circumstance I can see how the rising heat might start to reflow the solder paste and since most higher end microcontrollers are surface mount they won't have the mechanical lock that through-hole parts get from the pads their leads pass through.

As for the shield, would a heat-sink be sufficient? the heat-sink could potentially fill the entire air gap as long as the fins would let enough air in to cool the power module sufficiently. This would also improve cooling of the processor.

One downside of a physical heatsink is weight. Also, the tabs on the MOSFETs will require mica insulators to insulate them electrically from the metal heatsink. The tabs are connected to the MOSFET's drains so they are electrically conductive. Worse because of the nature of an H-bridge if you short the high side and low side drains together you'll have short across the supply once the right MOSFETs turn on without electrical insulation to the heat sink.

Obviously mica insulators for these transistor packages are made, it just adds to the base cost of manufacture. Also it's unlikely that we can avoid the fan even with the heatsink. If we put the entire unit in a plastic box we'll need to move the heat out of that enclosure somehow. One solution is put the heatsinks outside the enclosure, but then the transistor leads need to pass through the enclosure walls which makes inspection disassembly more difficult (adding connectors to those wires is possible but just adds more cost and points of failure).

One of the complaints about the Jag is its size, especially its footprint (and its side vents don't help).

True.

The indicator module go on top of the stack using space already occupied by the connectors on the bottom of the input modules. This is an optional module, but I wouldn't be surprised if it would be required should FIRST use the design. FTAs like status indicators.

There's really no doubt that with the skill levels involved we need actually more indicators than are currently present on the Jaguar. Possibly even a small LCD under the right conditions (like the size of your thumb tip or down to the size of watch transreflective LCD).

I believe that the minimum system should be reduced down to the common H-bridge and a basic processor module. if the team then wants to upgrade then they shouldn't need to buy a new processor. Things like high-speed counters (due to cost) and CAN bus interfaces (due to size) should be add-ons. More advanced users could buy more advanced processors to get systems that exceed Jaguar capabilities, but most of what a Jaguar can do should be possible by adding onto the basic processor module and all of what a Victor can do should be possible with out any add-on parts (beyond the minimum system).

To a certain extent the modularity makes sense. Adding a quadrature encoder and the support circuits for it certainly makes sense to make it optional (I am in favor of using support circuits for encoders like that so that we don't swamp the processor interrupts). However, it doesn't really make sense to make I/O modules for one limit switch contact at a time. Cost wise for limits switches it makes more sense to make a module that has 8 ports with pull-up resistors for limit switches and if they want just one limit switch they just have to accept a module that will give them the ability to use 8. The situation might be a little different with I/O modules that are designed to fill the most common FIRST applications. Surely there would be nothing stopping someone from making other modules for applications outside of FIRST.