Regulators are used in a variety of ways. Most servos should be run on 6v. 2-cell Li-Ion batteries start at 8.4v and the "don't fly" voltage is 6.9v which is well above the recommended voltage for most servos. JR type connectors and 22 ga wire have some power loss (see the servo extension page for test data), so an adjustable regulator can be useful so that you can set the voltage to 6.5v or so to accommodate the voltage drop through all the connections to the servos. All regulators have a heat sink for heavy duty operation. Most planes can simply use a 6V inline (not adjustable) regulator. If you use an isolator so that the receiver is run off of an independent battery pack from the servos, then you can use the 5.4v regulator for the receiver. You must use the 6v regulator for DA and C&H ignition systems, while the new 3W and ZDZ ignitions should not use regulators with LiIon batteries. Do not use the MPI 5.4V regulator for ignitions, either use the MPI 6V regulator or the Smart-Fly 5.2V ignition regulator.

Regulators should be used on any type of battery pack which can put out more than 6V. All servos can take 6V, but they can't take much more voltage than that. Also, many receivers don't like more voltage than that. Servos can start to jitter if the voltage is too high. You must use a 6V (5 cell) NiCad or NiMh pack or a 7.2V Li Ion pack to provide 6V to your servos. The regulator ensures that excessive voltage doesn't get to the servos. The advantage of the regulators is how they fail. Almost always the regulator will fail from excessive heat, so don't wrap the regulator in foam!! If you have a 40%+ plane and do lots of hard 3D flying, get the adjustable regulators with the large heat sinks and large output capacitors made by MPI, Fromeco or Smart-Fly and use a standard switch or use the Smart-Fly combo. These regulators also have adjustable voltages over 6V so you can get even more power and speed from your servos. There are a few ways regulators fail. One is that they continue to regulate properly during the flight, and then when power is turned off, they will not power up again once the power is turned on again. So when you turn your switch on for the next flight, you will notice that a pack is not working. Simply replace the regulator and you are flying again. I have never had a regulator stop the flow of current to a Rx during flight, and with the heat sink version there is little chance of a regulator failure. Another failure mode is another fail safe method in that if too much power goes through the reg, that the reg fails and goes to 8.4v rather than going to zero volts. This way you will at least have power to your receiver or ignition, and while this is not recommended, it is better than no current. A third failure is that the leads going into the reg can simply fail from vibration, and then there is no current output, so it is necessary to strap down the wires exiting the regs so they don't flop around and break.

Plugs: The typical JR/universal type plugs are fine for 2-cell batteries on planes 100cc and smaller. Use Deans plugs for 150cc planes using 4-cell batteries.

** Recommendations for 150cc planes
Adjustable Regs - the only Rx regs which are not adjustable are the MPI 5.4v and 6v regulators, so this includes the SuperReg, TurboReg, Fromeco adjustable regulator, MPI adjustable regulator, etc.
1) TBM's #1 suggestion for 150cc planes is the Smart Fly SuperReg with any of the Smart Fly Power Expanders using the Smart Fly slider fail safe switch.
2) A single Fromeco Wolverine switch (which connects to two batteries and draws the batteries down equally), into any of the adjustable regulators.
3) Two Smart Fly Super Switch HD's into any adjustable regulator.
4) Smart Fly adjustable voltage Regulator HD