So here's the scenario: we have a golf cart with 48V total battery power, made up of 8 6V batteries. We want to take one of the 6V's and use it to power the on board electronics.
If you mean using a 6V tap on the 48V battery pile, I'll advice against it, as that will create an unbalanced drain that, even if small, over time may develop into a chain with a weak link, which will matter for the entire pile.
Much better to go with a separate battery (or switching down from the entire pile, but going 48V to 6V, you need every percentage of efficiency that you can get).
In theory, the voltage will spike like hell, since the batteries are driving a big old DC motor.
Theory is good, but nothing replaces a 'scope on the working motor under somewhat average conditions.
Getting specifics on both voltage, current. rise- and fall times and max spike time is crucial to calculate your needed filter.
Will the motor go on the total pile of 48V?
If so, you have both the division rate of 8 and the low impedance of the battery to help, but just in case you want to go with a tap... Always attack noise where it emanates, not at the other end of the wire.
Imagine a rope that two persons hold between them and one start shaking it up and down to create oscillations. Where do you think it will take the least amount of strength from you, grabbing the rope to kill the oscillations? (Poking the eye of one of them, while probably quite efficient, doesn't count here
We will, I assume, need a capacitor or something to filter it a bit. But I'm not sure how people arrive at the values for their filter caps.
Is there an easy way to figure that out, or do I just toss a 10uF onto it and see what happens? :-P
Don't underestimate the value (and speed) of empirical selection.
In your case, I'd first concentrate on the motor and dampen the spikes it generates with caps and a transil/tranzorb/VDR of a suitable size. This could easily get the spikes to less than 60V and even if
the battery didn't kill any of it, your circuit would only see 60/8=7.5V max at the bottom 6V battery, hardly a challenge for an LDO, or a Pi (CLC) filter or even a simple RC filter followed by a zener.