ORIGINAL: Volfy
If you just want to drop the output voltage of a 7.2V 6-cell pack down to around 6V, why not just wire up a 1A diode inline with the battery pack? Any of the 1N4001, 4002, etc. will have a forward voltage drop of about 1.0V.
Fully charged NiMh can hold 1.5V per cell (for a very short period) that means you may start with much higher voltage than you wanted.
ORIGINAL: Volfy
Voltage regulators have their uses obviously, but I don't buy all that hoopla about expensive LiPo packs and shiny regulator heatsinks. People buy 'em because they look sexy inside a 40% Yak and because the Pros use them. For me, direct cconnections and heavy-duty switch/connector is the best policy.
I use home-made 7805 based voltage regulators for my engines and I'm very happy with that. They cost and weight nothing, and with 2 cells lipo they don't need a heat sink. I do this for weight - 2 lipos are almost twice lighter than 4 NiMh. While making my own regulators (7805 + 2 capacitors) I include small piezo buzzer (like this [link=http://www.kingstate.com.tw/product/kpe-242/kpe-242.gif]KPE-242[/link]) that costs and weights almost nothing. Thanks to that I can hear when ignition is 'hot'. Buzzer is on the 5V side so I know that battery, switch and regulator are working fine when I flip the switch. And after landing and killing the engine the beeping reminds me to tun the ignition off.
RS is really expensive, but I got my parts from local electronic store (5-pack of 7805 for 2 dollars). The most expensive is a power switch itself
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RysiuM