Concern:

assuming that leader outputs 5V exactly (since it's what does the step down from 12 to 5). This would affect voltage input to the last PSOM.

BPS-PeripheralSOMPCB

The power regulator we use from 5V→5V is a 1769405141. The operating conditions specified in the datasheet are as follows:

As you can see, minimum voltage required for PSOM is 4.5V. If we're not above 4.5V at each peripheral som's input, it will not work since everything runs off the power regulator (everything is isolated through this).

Research:

Length of car:

"Alright here's the results of the calculation with one wire the entire length of the car. This is assuming 20 gauge wire (if we use 24 there will be less resistance technically, and recommended for 5V is 20-24 AWG) and an upper bound of 1W per board (for a total of 4/5A) which realistically won't happen.I'm a little unsure on whether the wire will be longer than this. It's basically from the leaderboard (around the cockpit) to the back left peripheral (back of the car) and then looping back around to the front right peripheral (middle-ish of the car)." - Ishan Deshpande 

But there's also horizontal distance to worry about. Here's a more accurate upper bound from what I think.

Assumptions: Leader is placed 25% of the way through the length of the car.

59/2 = 29.5

Leader to P1 dist: sqrt(44.25^2 + 29.5^2) = 53.1818813 in

P1 to P2 (AKA P3 to P4) dist: 88.5 in

P2 to P3 dist: 59 in

Total wire length is approx.: Leader→P1 + 2(P1→P2) + P2→P3 = 289.181881 inches = 24.0984901 feet

Now with this new upper bound, we plug it in again:

Voltage drop of 0.388V would mean 5V becomes 4.612V at the end of the wire.

Minimum voltage required is 4.5V. With 4.612V we should be fine hopefully, but a change in topology may be good.

In order to cause enough of a drop for voltage to be too close to the minimum of the power regulator, we'd need to run wire ~30ft.

CAN Topology investigation:

Note: we run our power lines with the CAN network, so this would affect both.

Option 1:

A topology like this would fix our length issues by making leader a sort of central node. It would require one extra CAN connector on the leader in order to enable three branches.

Option 2:

A topology like this would also fix our length issues, but it would require development of a power + CAN splitter board that also does some sort of voltage conversion. In terms of CAN topology this means that even if one peripheral node goes down all the other nodes remain active, which is more safety tolerant.

Conclusion:

Option 1 is probably best to avoid having to design a power + CAN splitter board.

We'll still need termination resistors (see https://resources.pcb.cadence.com/blog/2019-termination-resistors-their-function-and-necessity-on-pcbs)

Maximum length with this design can be calced:

Leader to P1/P4 dist: sqrt(44.25^2 + 29.5^2) = 53.1818813 in

P1 to P2 (AKA P3 to P4) dist: 88.5 in

Total: 141.68 in

Voltage @ end nodes becomes ~4.8V which is fine ✅